diff --git a/CMakeLists.txt b/CMakeLists.txt
index 20d19fa167..0e4d5cfb43 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -426,7 +426,7 @@ set(ZIG_STAGE2_SOURCES
     "${CMAKE_SOURCE_DIR}/lib/std/os.zig"
     "${CMAKE_SOURCE_DIR}/lib/std/os/bits.zig"
     "${CMAKE_SOURCE_DIR}/lib/std/os/bits/linux.zig"
-    "${CMAKE_SOURCE_DIR}/lib/std/os/bits/linux/errno-generic.zig"
+    "${CMAKE_SOURCE_DIR}/lib/std/os/bits/linux/errno/generic.zig"
     "${CMAKE_SOURCE_DIR}/lib/std/os/bits/linux/netlink.zig"
     "${CMAKE_SOURCE_DIR}/lib/std/os/bits/linux/prctl.zig"
     "${CMAKE_SOURCE_DIR}/lib/std/os/bits/linux/securebits.zig"
diff --git a/lib/std/Thread.zig b/lib/std/Thread.zig
index cd742cc955..9d3b0cb1fc 100644
--- a/lib/std/Thread.zig
+++ b/lib/std/Thread.zig
@@ -9,9 +9,10 @@
 //! both evented I/O and async I/O, see the respective names in the top level std namespace.
 
 const std = @import("std.zig");
+const builtin = @import("builtin");
 const os = std.os;
 const assert = std.debug.assert;
-const target = std.Target.current;
+const target = builtin.target;
 const Atomic = std.atomic.Atomic;
 
 pub const AutoResetEvent = @import("Thread/AutoResetEvent.zig");
@@ -24,7 +25,8 @@ pub const Condition = @import("Thread/Condition.zig");
 
 pub const spinLoopHint = @compileError("deprecated: use std.atomic.spinLoopHint");
 
-pub const use_pthreads = target.os.tag != .windows and std.Target.current.os.tag != .wasi and std.builtin.link_libc;
+pub const use_pthreads = target.os.tag != .windows and target.os.tag != .wasi and builtin.link_libc;
+const is_gnu = target.abi.isGnu();
 
 const Thread = @This();
 const Impl = if (target.os.tag == .windows)
@@ -38,7 +40,7 @@ else
 
 impl: Impl,
 
-pub const max_name_len = switch (std.Target.current.os.tag) {
+pub const max_name_len = switch (target.os.tag) {
     .linux => 15,
     .windows => 31,
     .macos, .ios, .watchos, .tvos => 63,
@@ -64,20 +66,21 @@ pub fn setName(self: Thread, name: []const u8) SetNameError!void {
         break :blk name_buf[0..name.len :0];
     };
 
-    switch (std.Target.current.os.tag) {
+    switch (target.os.tag) {
         .linux => if (use_pthreads) {
             const err = std.c.pthread_setname_np(self.getHandle(), name_with_terminator.ptr);
-            return switch (err) {
-                0 => {},
-                os.ERANGE => unreachable,
-                else => return os.unexpectedErrno(err),
-            };
+            switch (err) {
+                .SUCCESS => return,
+                .RANGE => unreachable,
+                else => |e| return os.unexpectedErrno(e),
+            }
         } else if (use_pthreads and self.getHandle() == std.c.pthread_self()) {
+            // TODO: this is dead code. what did the author of this code intend to happen here?
             const err = try os.prctl(.SET_NAME, .{@ptrToInt(name_with_terminator.ptr)});
-            return switch (err) {
-                0 => {},
-                else => return os.unexpectedErrno(err),
-            };
+            switch (@intToEnum(os.E, err)) {
+                .SUCCESS => return,
+                else => |e| return os.unexpectedErrno(e),
+            }
         } else {
             var buf: [32]u8 = undefined;
             const path = try std.fmt.bufPrint(&buf, "/proc/self/task/{d}/comm", .{self.getHandle()});
@@ -87,7 +90,7 @@ pub fn setName(self: Thread, name: []const u8) SetNameError!void {
 
             try file.writer().writeAll(name);
         },
-        .windows => if (std.Target.current.os.isAtLeast(.windows, .win10_rs1)) |res| {
+        .windows => if (target.os.isAtLeast(.windows, .win10_rs1)) |res| {
             // SetThreadDescription is only available since version 1607, which is 10.0.14393.795
             // See https://en.wikipedia.org/wiki/Microsoft_Windows_SDK
             if (!res) {
@@ -110,24 +113,25 @@ pub fn setName(self: Thread, name: []const u8) SetNameError!void {
             if (self.getHandle() != std.c.pthread_self()) return error.Unsupported;
 
             const err = std.c.pthread_setname_np(name_with_terminator.ptr);
-            return switch (err) {
-                0 => {},
-                else => return os.unexpectedErrno(err),
-            };
+            switch (err) {
+                .SUCCESS => return,
+                else => |e| return os.unexpectedErrno(e),
+            }
         },
         .netbsd => if (use_pthreads) {
             const err = std.c.pthread_setname_np(self.getHandle(), name_with_terminator.ptr, null);
-            return switch (err) {
-                0 => {},
-                os.EINVAL => unreachable,
-                os.ESRCH => unreachable,
-                os.ENOMEM => unreachable,
-                else => return os.unexpectedErrno(err),
-            };
+            switch (err) {
+                .SUCCESS => return,
+                .INVAL => unreachable,
+                .SRCH => unreachable,
+                .NOMEM => unreachable,
+                else => |e| return os.unexpectedErrno(e),
+            }
         },
         .freebsd, .openbsd => if (use_pthreads) {
             // Use pthread_set_name_np for FreeBSD because pthread_setname_np is FreeBSD 12.2+ only.
-            // TODO maybe revisit this if depending on FreeBSD 12.2+ is acceptable because pthread_setname_np can return an error.
+            // TODO maybe revisit this if depending on FreeBSD 12.2+ is acceptable because
+            // pthread_setname_np can return an error.
 
             std.c.pthread_set_name_np(self.getHandle(), name_with_terminator.ptr);
         },
@@ -151,20 +155,20 @@ pub fn getName(self: Thread, buffer_ptr: *[max_name_len:0]u8) GetNameError!?[]co
     buffer_ptr[max_name_len] = 0;
     var buffer = std.mem.span(buffer_ptr);
 
-    switch (std.Target.current.os.tag) {
-        .linux => if (use_pthreads and comptime std.Target.current.abi.isGnu()) {
+    switch (target.os.tag) {
+        .linux => if (use_pthreads and is_gnu) {
             const err = std.c.pthread_getname_np(self.getHandle(), buffer.ptr, max_name_len + 1);
-            return switch (err) {
-                0 => std.mem.sliceTo(buffer, 0),
-                os.ERANGE => unreachable,
-                else => return os.unexpectedErrno(err),
-            };
+            switch (err) {
+                .SUCCESS => return std.mem.sliceTo(buffer, 0),
+                .RANGE => unreachable,
+                else => |e| return os.unexpectedErrno(e),
+            }
         } else if (use_pthreads and self.getHandle() == std.c.pthread_self()) {
             const err = try os.prctl(.GET_NAME, .{@ptrToInt(buffer.ptr)});
-            return switch (err) {
-                0 => std.mem.sliceTo(buffer, 0),
-                else => return os.unexpectedErrno(err),
-            };
+            switch (@intToEnum(os.E, err)) {
+                .SUCCESS => return std.mem.sliceTo(buffer, 0),
+                else => |e| return os.unexpectedErrno(e),
+            }
         } else if (!use_pthreads) {
             var buf: [32]u8 = undefined;
             const path = try std.fmt.bufPrint(&buf, "/proc/self/task/{d}/comm", .{self.getHandle()});
@@ -179,7 +183,7 @@ pub fn getName(self: Thread, buffer_ptr: *[max_name_len:0]u8) GetNameError!?[]co
             // musl doesn't provide pthread_getname_np and there's no way to retrieve the thread id of an arbitrary thread.
             return error.Unsupported;
         },
-        .windows => if (std.Target.current.os.isAtLeast(.windows, .win10_rs1)) |res| {
+        .windows => if (target.os.isAtLeast(.windows, .win10_rs1)) |res| {
             // GetThreadDescription is only available since version 1607, which is 10.0.14393.795
             // See https://en.wikipedia.org/wiki/Microsoft_Windows_SDK
             if (!res) {
@@ -198,20 +202,20 @@ pub fn getName(self: Thread, buffer_ptr: *[max_name_len:0]u8) GetNameError!?[]co
         },
         .macos, .ios, .watchos, .tvos => if (use_pthreads) {
             const err = std.c.pthread_getname_np(self.getHandle(), buffer.ptr, max_name_len + 1);
-            return switch (err) {
-                0 => std.mem.sliceTo(buffer, 0),
-                os.ESRCH => unreachable,
-                else => return os.unexpectedErrno(err),
-            };
+            switch (err) {
+                .SUCCESS => return std.mem.sliceTo(buffer, 0),
+                .SRCH => unreachable,
+                else => |e| return os.unexpectedErrno(e),
+            }
         },
         .netbsd => if (use_pthreads) {
             const err = std.c.pthread_getname_np(self.getHandle(), buffer.ptr, max_name_len + 1);
-            return switch (err) {
-                0 => std.mem.sliceTo(buffer, 0),
-                os.EINVAL => unreachable,
-                os.ESRCH => unreachable,
-                else => return os.unexpectedErrno(err),
-            };
+            switch (err) {
+                .SUCCESS => return std.mem.sliceTo(buffer, 0),
+                .INVAL => unreachable,
+                .SRCH => unreachable,
+                else => |e| return os.unexpectedErrno(e),
+            }
         },
         .freebsd, .openbsd => if (use_pthreads) {
             // Use pthread_get_name_np for FreeBSD because pthread_getname_np is FreeBSD 12.2+ only.
@@ -288,7 +292,7 @@ pub const SpawnError = error{
 /// The caller must eventually either call `join()` to wait for the thread to finish and free its resources
 /// or call `detach()` to excuse the caller from calling `join()` and have the thread clean up its resources on completion`.
 pub fn spawn(config: SpawnConfig, comptime function: anytype, args: anytype) SpawnError!Thread {
-    if (std.builtin.single_threaded) {
+    if (builtin.single_threaded) {
         @compileError("Cannot spawn thread when building in single-threaded mode");
     }
 
@@ -611,13 +615,13 @@ const PosixThreadImpl = struct {
         errdefer allocator.destroy(args_ptr);
 
         var attr: c.pthread_attr_t = undefined;
-        if (c.pthread_attr_init(&attr) != 0) return error.SystemResources;
-        defer assert(c.pthread_attr_destroy(&attr) == 0);
+        if (c.pthread_attr_init(&attr) != .SUCCESS) return error.SystemResources;
+        defer assert(c.pthread_attr_destroy(&attr) == .SUCCESS);
 
         // Use the same set of parameters used by the libc-less impl.
         const stack_size = std.math.max(config.stack_size, 16 * 1024);
-        assert(c.pthread_attr_setstacksize(&attr, stack_size) == 0);
-        assert(c.pthread_attr_setguardsize(&attr, std.mem.page_size) == 0);
+        assert(c.pthread_attr_setstacksize(&attr, stack_size) == .SUCCESS);
+        assert(c.pthread_attr_setguardsize(&attr, std.mem.page_size) == .SUCCESS);
 
         var handle: c.pthread_t = undefined;
         switch (c.pthread_create(
@@ -626,10 +630,10 @@ const PosixThreadImpl = struct {
             Instance.entryFn,
             if (@sizeOf(Args) > 1) @ptrCast(*c_void, args_ptr) else undefined,
         )) {
-            0 => return Impl{ .handle = handle },
-            os.EAGAIN => return error.SystemResources,
-            os.EPERM => unreachable,
-            os.EINVAL => unreachable,
+            .SUCCESS => return Impl{ .handle = handle },
+            .AGAIN => return error.SystemResources,
+            .PERM => unreachable,
+            .INVAL => unreachable,
             else => |err| return os.unexpectedErrno(err),
         }
     }
@@ -640,19 +644,19 @@ const PosixThreadImpl = struct {
 
     fn detach(self: Impl) void {
         switch (c.pthread_detach(self.handle)) {
-            0 => {},
-            os.EINVAL => unreachable, // thread handle is not joinable
-            os.ESRCH => unreachable, // thread handle is invalid
+            .SUCCESS => {},
+            .INVAL => unreachable, // thread handle is not joinable
+            .SRCH => unreachable, // thread handle is invalid
             else => unreachable,
         }
     }
 
     fn join(self: Impl) void {
         switch (c.pthread_join(self.handle, null)) {
-            0 => {},
-            os.EINVAL => unreachable, // thread handle is not joinable (or another thread is already joining in)
-            os.ESRCH => unreachable, // thread handle is invalid
-            os.EDEADLK => unreachable, // two threads tried to join each other
+            .SUCCESS => {},
+            .INVAL => unreachable, // thread handle is not joinable (or another thread is already joining in)
+            .SRCH => unreachable, // thread handle is invalid
+            .DEADLK => unreachable, // two threads tried to join each other
             else => unreachable,
         }
     }
@@ -937,13 +941,13 @@ const LinuxThreadImpl = struct {
             tls_ptr,
             &instance.thread.child_tid.value,
         ))) {
-            0 => return Impl{ .thread = &instance.thread },
-            os.EAGAIN => return error.ThreadQuotaExceeded,
-            os.EINVAL => unreachable,
-            os.ENOMEM => return error.SystemResources,
-            os.ENOSPC => unreachable,
-            os.EPERM => unreachable,
-            os.EUSERS => unreachable,
+            .SUCCESS => return Impl{ .thread = &instance.thread },
+            .AGAIN => return error.ThreadQuotaExceeded,
+            .INVAL => unreachable,
+            .NOMEM => return error.SystemResources,
+            .NOSPC => unreachable,
+            .PERM => unreachable,
+            .USERS => unreachable,
             else => |err| return os.unexpectedErrno(err),
         }
     }
@@ -982,9 +986,9 @@ const LinuxThreadImpl = struct {
                 tid,
                 null,
             ))) {
-                0 => continue,
-                os.EINTR => continue,
-                os.EAGAIN => continue,
+                .SUCCESS => continue,
+                .INTR => continue,
+                .AGAIN => continue,
                 else => unreachable,
             }
         }
@@ -1011,7 +1015,7 @@ fn testThreadName(thread: *Thread) !void {
 }
 
 test "setName, getName" {
-    if (std.builtin.single_threaded) return error.SkipZigTest;
+    if (builtin.single_threaded) return error.SkipZigTest;
 
     const Context = struct {
         start_wait_event: ResetEvent = undefined,
@@ -1029,7 +1033,7 @@ test "setName, getName" {
             // Wait for the main thread to have set the thread field in the context.
             ctx.start_wait_event.wait();
 
-            switch (std.Target.current.os.tag) {
+            switch (target.os.tag) {
                 .windows => testThreadName(&ctx.thread) catch |err| switch (err) {
                     error.Unsupported => return error.SkipZigTest,
                     else => return err,
@@ -1054,7 +1058,7 @@ test "setName, getName" {
     context.start_wait_event.set();
     context.test_done_event.wait();
 
-    switch (std.Target.current.os.tag) {
+    switch (target.os.tag) {
         .macos, .ios, .watchos, .tvos => {
             const res = thread.setName("foobar");
             try std.testing.expectError(error.Unsupported, res);
@@ -1063,7 +1067,7 @@ test "setName, getName" {
             error.Unsupported => return error.SkipZigTest,
             else => return err,
         },
-        else => |tag| if (tag == .linux and use_pthreads and comptime std.Target.current.abi.isMusl()) {
+        else => |tag| if (tag == .linux and use_pthreads and comptime target.abi.isMusl()) {
             try thread.setName("foobar");
 
             var name_buffer: [max_name_len:0]u8 = undefined;
@@ -1096,7 +1100,7 @@ fn testIncrementNotify(value: *usize, event: *ResetEvent) void {
 }
 
 test "Thread.join" {
-    if (std.builtin.single_threaded) return error.SkipZigTest;
+    if (builtin.single_threaded) return error.SkipZigTest;
 
     var value: usize = 0;
     var event: ResetEvent = undefined;
@@ -1110,7 +1114,7 @@ test "Thread.join" {
 }
 
 test "Thread.detach" {
-    if (std.builtin.single_threaded) return error.SkipZigTest;
+    if (builtin.single_threaded) return error.SkipZigTest;
 
     var value: usize = 0;
     var event: ResetEvent = undefined;
diff --git a/lib/std/Thread/Condition.zig b/lib/std/Thread/Condition.zig
index 8485f84aa4..9513e794ed 100644
--- a/lib/std/Thread/Condition.zig
+++ b/lib/std/Thread/Condition.zig
@@ -81,17 +81,17 @@ pub const PthreadCondition = struct {
 
     pub fn wait(cond: *PthreadCondition, mutex: *Mutex) void {
         const rc = std.c.pthread_cond_wait(&cond.cond, &mutex.impl.pthread_mutex);
-        assert(rc == 0);
+        assert(rc == .SUCCESS);
     }
 
     pub fn signal(cond: *PthreadCondition) void {
         const rc = std.c.pthread_cond_signal(&cond.cond);
-        assert(rc == 0);
+        assert(rc == .SUCCESS);
     }
 
     pub fn broadcast(cond: *PthreadCondition) void {
         const rc = std.c.pthread_cond_broadcast(&cond.cond);
-        assert(rc == 0);
+        assert(rc == .SUCCESS);
     }
 };
 
@@ -115,9 +115,9 @@ pub const AtomicCondition = struct {
                             0,
                             null,
                         ))) {
-                            0 => {},
-                            std.os.EINTR => {},
-                            std.os.EAGAIN => {},
+                            .SUCCESS => {},
+                            .INTR => {},
+                            .AGAIN => {},
                             else => unreachable,
                         }
                     },
@@ -136,8 +136,8 @@ pub const AtomicCondition = struct {
                         linux.FUTEX_PRIVATE_FLAG | linux.FUTEX_WAKE,
                         1,
                     ))) {
-                        0 => {},
-                        std.os.EFAULT => {},
+                        .SUCCESS => {},
+                        .FAULT => {},
                         else => unreachable,
                     }
                 },
diff --git a/lib/std/Thread/Futex.zig b/lib/std/Thread/Futex.zig
index 81dba07996..a896942d6e 100644
--- a/lib/std/Thread/Futex.zig
+++ b/lib/std/Thread/Futex.zig
@@ -152,12 +152,12 @@ const LinuxFutex = struct {
             @bitCast(i32, expect),
             ts_ptr,
         ))) {
-            0 => {}, // notified by `wake()`
-            std.os.EINTR => {}, // spurious wakeup
-            std.os.EAGAIN => {}, // ptr.* != expect
-            std.os.ETIMEDOUT => return error.TimedOut,
-            std.os.EINVAL => {}, // possibly timeout overflow
-            std.os.EFAULT => unreachable,
+            .SUCCESS => {}, // notified by `wake()`
+            .INTR => {}, // spurious wakeup
+            .AGAIN => {}, // ptr.* != expect
+            .TIMEDOUT => return error.TimedOut,
+            .INVAL => {}, // possibly timeout overflow
+            .FAULT => unreachable,
             else => unreachable,
         }
     }
@@ -168,9 +168,9 @@ const LinuxFutex = struct {
             linux.FUTEX_PRIVATE_FLAG | linux.FUTEX_WAKE,
             std.math.cast(i32, num_waiters) catch std.math.maxInt(i32),
         ))) {
-            0 => {}, // successful wake up
-            std.os.EINVAL => {}, // invalid futex_wait() on ptr done elsewhere
-            std.os.EFAULT => {}, // pointer became invalid while doing the wake
+            .SUCCESS => {}, // successful wake up
+            .INVAL => {}, // invalid futex_wait() on ptr done elsewhere
+            .FAULT => {}, // pointer became invalid while doing the wake
             else => unreachable,
         }
     }
@@ -215,13 +215,13 @@ const DarwinFutex = struct {
         };
 
         if (status >= 0) return;
-        switch (-status) {
-            darwin.EINTR => {},
+        switch (@intToEnum(std.os.E, -status)) {
+            .INTR => {},
             // Address of the futex is paged out. This is unlikely, but possible in theory, and
             // pthread/libdispatch on darwin bother to handle it. In this case we'll return
             // without waiting, but the caller should retry anyway.
-            darwin.EFAULT => {},
-            darwin.ETIMEDOUT => if (!timeout_overflowed) return error.TimedOut,
+            .FAULT => {},
+            .TIMEDOUT => if (!timeout_overflowed) return error.TimedOut,
             else => unreachable,
         }
     }
@@ -237,11 +237,11 @@ const DarwinFutex = struct {
             const status = darwin.__ulock_wake(flags, addr, 0);
 
             if (status >= 0) return;
-            switch (-status) {
-                darwin.EINTR => continue, // spurious wake()
-                darwin.EFAULT => continue, // address of the lock was paged out
-                darwin.ENOENT => return, // nothing was woken up
-                darwin.EALREADY => unreachable, // only for ULF_WAKE_THREAD
+            switch (@intToEnum(std.os.E, -status)) {
+                .INTR => continue, // spurious wake()
+                .FAULT => continue, // address of the lock was paged out
+                .NOENT => return, // nothing was woken up
+                .ALREADY => unreachable, // only for ULF_WAKE_THREAD
                 else => unreachable,
             }
         }
@@ -255,8 +255,8 @@ const PosixFutex = struct {
         var waiter: List.Node = undefined;
 
         {
-            assert(std.c.pthread_mutex_lock(&bucket.mutex) == 0);
-            defer assert(std.c.pthread_mutex_unlock(&bucket.mutex) == 0);
+            assert(std.c.pthread_mutex_lock(&bucket.mutex) == .SUCCESS);
+            defer assert(std.c.pthread_mutex_unlock(&bucket.mutex) == .SUCCESS);
 
             if (ptr.load(.SeqCst) != expect) {
                 return;
@@ -272,8 +272,8 @@ const PosixFutex = struct {
                 waiter.data.wait(null) catch unreachable;
             };
 
-            assert(std.c.pthread_mutex_lock(&bucket.mutex) == 0);
-            defer assert(std.c.pthread_mutex_unlock(&bucket.mutex) == 0);
+            assert(std.c.pthread_mutex_lock(&bucket.mutex) == .SUCCESS);
+            defer assert(std.c.pthread_mutex_unlock(&bucket.mutex) == .SUCCESS);
 
             if (waiter.data.address == address) {
                 timed_out = true;
@@ -297,8 +297,8 @@ const PosixFutex = struct {
             waiter.data.notify();
         };
 
-        assert(std.c.pthread_mutex_lock(&bucket.mutex) == 0);
-        defer assert(std.c.pthread_mutex_unlock(&bucket.mutex) == 0);
+        assert(std.c.pthread_mutex_lock(&bucket.mutex) == .SUCCESS);
+        defer assert(std.c.pthread_mutex_unlock(&bucket.mutex) == .SUCCESS);
 
         var waiters = bucket.list.first;
         while (waiters) |waiter| {
@@ -340,16 +340,13 @@ const PosixFutex = struct {
         };
 
         fn deinit(self: *Self) void {
-            const rc = std.c.pthread_cond_destroy(&self.cond);
-            assert(rc == 0 or rc == std.os.EINVAL);
-
-            const rm = std.c.pthread_mutex_destroy(&self.mutex);
-            assert(rm == 0 or rm == std.os.EINVAL);
+            _ = std.c.pthread_cond_destroy(&self.cond);
+            _ = std.c.pthread_mutex_destroy(&self.mutex);
         }
 
         fn wait(self: *Self, timeout: ?u64) error{TimedOut}!void {
-            assert(std.c.pthread_mutex_lock(&self.mutex) == 0);
-            defer assert(std.c.pthread_mutex_unlock(&self.mutex) == 0);
+            assert(std.c.pthread_mutex_lock(&self.mutex) == .SUCCESS);
+            defer assert(std.c.pthread_mutex_unlock(&self.mutex) == .SUCCESS);
 
             switch (self.state) {
                 .empty => self.state = .waiting,
@@ -378,28 +375,31 @@ const PosixFutex = struct {
                 }
 
                 const ts_ref = ts_ptr orelse {
-                    assert(std.c.pthread_cond_wait(&self.cond, &self.mutex) == 0);
+                    assert(std.c.pthread_cond_wait(&self.cond, &self.mutex) == .SUCCESS);
                     continue;
                 };
 
                 const rc = std.c.pthread_cond_timedwait(&self.cond, &self.mutex, ts_ref);
-                assert(rc == 0 or rc == std.os.ETIMEDOUT);
-                if (rc == std.os.ETIMEDOUT) {
-                    self.state = .empty;
-                    return error.TimedOut;
+                switch (rc) {
+                    .SUCCESS => {},
+                    .TIMEDOUT => {
+                        self.state = .empty;
+                        return error.TimedOut;
+                    },
+                    else => unreachable,
                 }
             }
         }
 
         fn notify(self: *Self) void {
-            assert(std.c.pthread_mutex_lock(&self.mutex) == 0);
-            defer assert(std.c.pthread_mutex_unlock(&self.mutex) == 0);
+            assert(std.c.pthread_mutex_lock(&self.mutex) == .SUCCESS);
+            defer assert(std.c.pthread_mutex_unlock(&self.mutex) == .SUCCESS);
 
             switch (self.state) {
                 .empty => self.state = .notified,
                 .waiting => {
                     self.state = .notified;
-                    assert(std.c.pthread_cond_signal(&self.cond) == 0);
+                    assert(std.c.pthread_cond_signal(&self.cond) == .SUCCESS);
                 },
                 .notified => unreachable,
             }
diff --git a/lib/std/Thread/Mutex.zig b/lib/std/Thread/Mutex.zig
index 35095b2a3c..522d1fe418 100644
--- a/lib/std/Thread/Mutex.zig
+++ b/lib/std/Thread/Mutex.zig
@@ -143,9 +143,9 @@ pub const AtomicMutex = struct {
                         @enumToInt(new_state),
                         null,
                     ))) {
-                        0 => {},
-                        std.os.EINTR => {},
-                        std.os.EAGAIN => {},
+                        .SUCCESS => {},
+                        .INTR => {},
+                        .AGAIN => {},
                         else => unreachable,
                     }
                 },
@@ -164,8 +164,8 @@ pub const AtomicMutex = struct {
                     linux.FUTEX_PRIVATE_FLAG | linux.FUTEX_WAKE,
                     1,
                 ))) {
-                    0 => {},
-                    std.os.EFAULT => {},
+                    .SUCCESS => {},
+                    .FAULT => unreachable, // invalid pointer passed to futex_wake
                     else => unreachable,
                 }
             },
@@ -182,10 +182,10 @@ pub const PthreadMutex = struct {
 
         pub fn release(held: Held) void {
             switch (std.c.pthread_mutex_unlock(&held.mutex.pthread_mutex)) {
-                0 => return,
-                std.c.EINVAL => unreachable,
-                std.c.EAGAIN => unreachable,
-                std.c.EPERM => unreachable,
+                .SUCCESS => return,
+                .INVAL => unreachable,
+                .AGAIN => unreachable,
+                .PERM => unreachable,
                 else => unreachable,
             }
         }
@@ -195,7 +195,7 @@ pub const PthreadMutex = struct {
     /// the mutex is unavailable. Otherwise returns Held. Call
     /// release on Held.
     pub fn tryAcquire(m: *PthreadMutex) ?Held {
-        if (std.c.pthread_mutex_trylock(&m.pthread_mutex) == 0) {
+        if (std.c.pthread_mutex_trylock(&m.pthread_mutex) == .SUCCESS) {
             return Held{ .mutex = m };
         } else {
             return null;
@@ -206,12 +206,12 @@ pub const PthreadMutex = struct {
     /// held by the calling thread.
     pub fn acquire(m: *PthreadMutex) Held {
         switch (std.c.pthread_mutex_lock(&m.pthread_mutex)) {
-            0 => return Held{ .mutex = m },
-            std.c.EINVAL => unreachable,
-            std.c.EBUSY => unreachable,
-            std.c.EAGAIN => unreachable,
-            std.c.EDEADLK => unreachable,
-            std.c.EPERM => unreachable,
+            .SUCCESS => return Held{ .mutex = m },
+            .INVAL => unreachable,
+            .BUSY => unreachable,
+            .AGAIN => unreachable,
+            .DEADLK => unreachable,
+            .PERM => unreachable,
             else => unreachable,
         }
     }
diff --git a/lib/std/Thread/ResetEvent.zig b/lib/std/Thread/ResetEvent.zig
index 356b8eb78d..bbf9e7263a 100644
--- a/lib/std/Thread/ResetEvent.zig
+++ b/lib/std/Thread/ResetEvent.zig
@@ -130,7 +130,7 @@ pub const PosixEvent = struct {
 
     pub fn init(ev: *PosixEvent) !void {
         switch (c.getErrno(c.sem_init(&ev.sem, 0, 0))) {
-            0 => return,
+            .SUCCESS => return,
             else => return error.SystemResources,
         }
     }
@@ -147,9 +147,9 @@ pub const PosixEvent = struct {
     pub fn wait(ev: *PosixEvent) void {
         while (true) {
             switch (c.getErrno(c.sem_wait(&ev.sem))) {
-                0 => return,
-                c.EINTR => continue,
-                c.EINVAL => unreachable,
+                .SUCCESS => return,
+                .INTR => continue,
+                .INVAL => unreachable,
                 else => unreachable,
             }
         }
@@ -165,10 +165,10 @@ pub const PosixEvent = struct {
         ts.tv_nsec = @intCast(@TypeOf(ts.tv_nsec), @mod(timeout_abs, time.ns_per_s));
         while (true) {
             switch (c.getErrno(c.sem_timedwait(&ev.sem, &ts))) {
-                0 => return .event_set,
-                c.EINTR => continue,
-                c.EINVAL => unreachable,
-                c.ETIMEDOUT => return .timed_out,
+                .SUCCESS => return .event_set,
+                .INTR => continue,
+                .INVAL => unreachable,
+                .TIMEDOUT => return .timed_out,
                 else => unreachable,
             }
         }
@@ -177,10 +177,10 @@ pub const PosixEvent = struct {
     pub fn reset(ev: *PosixEvent) void {
         while (true) {
             switch (c.getErrno(c.sem_trywait(&ev.sem))) {
-                0 => continue, // Need to make it go to zero.
-                c.EINTR => continue,
-                c.EINVAL => unreachable,
-                c.EAGAIN => return, // The semaphore currently has the value zero.
+                .SUCCESS => continue, // Need to make it go to zero.
+                .INTR => continue,
+                .INVAL => unreachable,
+                .AGAIN => return, // The semaphore currently has the value zero.
                 else => unreachable,
             }
         }
diff --git a/lib/std/Thread/RwLock.zig b/lib/std/Thread/RwLock.zig
index 1d606a9cf1..0721aad3f7 100644
--- a/lib/std/Thread/RwLock.zig
+++ b/lib/std/Thread/RwLock.zig
@@ -13,7 +13,7 @@ impl: Impl,
 
 const RwLock = @This();
 const std = @import("../std.zig");
-const builtin = std.builtin;
+const builtin = @import("builtin");
 const assert = std.debug.assert;
 const Mutex = std.Thread.Mutex;
 const Semaphore = std.Semaphore;
@@ -165,43 +165,41 @@ pub const PthreadRwLock = struct {
     }
 
     pub fn deinit(rwl: *PthreadRwLock) void {
-        const safe_rc = switch (std.builtin.os.tag) {
-            .dragonfly, .netbsd => std.os.EAGAIN,
-            else => 0,
+        const safe_rc: std.os.E = switch (builtin.os.tag) {
+            .dragonfly, .netbsd => .AGAIN,
+            else => .SUCCESS,
         };
-
         const rc = std.c.pthread_rwlock_destroy(&rwl.rwlock);
-        assert(rc == 0 or rc == safe_rc);
-
+        assert(rc == .SUCCESS or rc == safe_rc);
         rwl.* = undefined;
     }
 
     pub fn tryLock(rwl: *PthreadRwLock) bool {
-        return pthread_rwlock_trywrlock(&rwl.rwlock) == 0;
+        return pthread_rwlock_trywrlock(&rwl.rwlock) == .SUCCESS;
     }
 
     pub fn lock(rwl: *PthreadRwLock) void {
         const rc = pthread_rwlock_wrlock(&rwl.rwlock);
-        assert(rc == 0);
+        assert(rc == .SUCCESS);
     }
 
     pub fn unlock(rwl: *PthreadRwLock) void {
         const rc = pthread_rwlock_unlock(&rwl.rwlock);
-        assert(rc == 0);
+        assert(rc == .SUCCESS);
     }
 
     pub fn tryLockShared(rwl: *PthreadRwLock) bool {
-        return pthread_rwlock_tryrdlock(&rwl.rwlock) == 0;
+        return pthread_rwlock_tryrdlock(&rwl.rwlock) == .SUCCESS;
     }
 
     pub fn lockShared(rwl: *PthreadRwLock) void {
         const rc = pthread_rwlock_rdlock(&rwl.rwlock);
-        assert(rc == 0);
+        assert(rc == .SUCCESS);
     }
 
     pub fn unlockShared(rwl: *PthreadRwLock) void {
         const rc = pthread_rwlock_unlock(&rwl.rwlock);
-        assert(rc == 0);
+        assert(rc == .SUCCESS);
     }
 };
 
diff --git a/lib/std/Thread/StaticResetEvent.zig b/lib/std/Thread/StaticResetEvent.zig
index 40974938d0..e15a6a0a54 100644
--- a/lib/std/Thread/StaticResetEvent.zig
+++ b/lib/std/Thread/StaticResetEvent.zig
@@ -201,7 +201,7 @@ pub const AtomicEvent = struct {
             const waiting = std.math.maxInt(i32); // wake_count
             const ptr = @ptrCast(*const i32, waiters);
             const rc = linux.futex_wake(ptr, linux.FUTEX_WAKE | linux.FUTEX_PRIVATE_FLAG, waiting);
-            assert(linux.getErrno(rc) == 0);
+            assert(linux.getErrno(rc) == .SUCCESS);
         }
 
         fn wait(waiters: *u32, timeout: ?u64) !void {
@@ -221,10 +221,10 @@ pub const AtomicEvent = struct {
                 const ptr = @ptrCast(*const i32, waiters);
                 const rc = linux.futex_wait(ptr, linux.FUTEX_WAIT | linux.FUTEX_PRIVATE_FLAG, expected, ts_ptr);
                 switch (linux.getErrno(rc)) {
-                    0 => continue,
-                    os.ETIMEDOUT => return error.TimedOut,
-                    os.EINTR => continue,
-                    os.EAGAIN => return,
+                    .SUCCESS => continue,
+                    .TIMEDOUT => return error.TimedOut,
+                    .INTR => continue,
+                    .AGAIN => return,
                     else => unreachable,
                 }
             }
diff --git a/lib/std/c.zig b/lib/std/c.zig
index c8b3020dc7..700a1dc250 100644
--- a/lib/std/c.zig
+++ b/lib/std/c.zig
@@ -35,11 +35,11 @@ pub usingnamespace switch (std.Target.current.os.tag) {
     else => struct {},
 };
 
-pub fn getErrno(rc: anytype) c_int {
+pub fn getErrno(rc: anytype) E {
     if (rc == -1) {
-        return _errno().*;
+        return @intToEnum(E, _errno().*);
     } else {
-        return 0;
+        return .SUCCESS;
     }
 }
 
@@ -270,22 +270,22 @@ pub extern "c" fn utimes(path: [*:0]const u8, times: *[2]timeval) c_int;
 pub extern "c" fn utimensat(dirfd: fd_t, pathname: [*:0]const u8, times: *[2]timespec, flags: u32) c_int;
 pub extern "c" fn futimens(fd: fd_t, times: *const [2]timespec) c_int;
 
-pub extern "c" fn pthread_create(noalias newthread: *pthread_t, noalias attr: ?*const pthread_attr_t, start_routine: fn (?*c_void) callconv(.C) ?*c_void, noalias arg: ?*c_void) c_int;
-pub extern "c" fn pthread_attr_init(attr: *pthread_attr_t) c_int;
-pub extern "c" fn pthread_attr_setstack(attr: *pthread_attr_t, stackaddr: *c_void, stacksize: usize) c_int;
-pub extern "c" fn pthread_attr_setstacksize(attr: *pthread_attr_t, stacksize: usize) c_int;
-pub extern "c" fn pthread_attr_setguardsize(attr: *pthread_attr_t, guardsize: usize) c_int;
-pub extern "c" fn pthread_attr_destroy(attr: *pthread_attr_t) c_int;
+pub extern "c" fn pthread_create(noalias newthread: *pthread_t, noalias attr: ?*const pthread_attr_t, start_routine: fn (?*c_void) callconv(.C) ?*c_void, noalias arg: ?*c_void) E;
+pub extern "c" fn pthread_attr_init(attr: *pthread_attr_t) E;
+pub extern "c" fn pthread_attr_setstack(attr: *pthread_attr_t, stackaddr: *c_void, stacksize: usize) E;
+pub extern "c" fn pthread_attr_setstacksize(attr: *pthread_attr_t, stacksize: usize) E;
+pub extern "c" fn pthread_attr_setguardsize(attr: *pthread_attr_t, guardsize: usize) E;
+pub extern "c" fn pthread_attr_destroy(attr: *pthread_attr_t) E;
 pub extern "c" fn pthread_self() pthread_t;
-pub extern "c" fn pthread_join(thread: pthread_t, arg_return: ?*?*c_void) c_int;
-pub extern "c" fn pthread_detach(thread: pthread_t) c_int;
+pub extern "c" fn pthread_join(thread: pthread_t, arg_return: ?*?*c_void) E;
+pub extern "c" fn pthread_detach(thread: pthread_t) E;
 pub extern "c" fn pthread_atfork(
     prepare: ?fn () callconv(.C) void,
     parent: ?fn () callconv(.C) void,
     child: ?fn () callconv(.C) void,
 ) c_int;
-pub extern "c" fn pthread_key_create(key: *pthread_key_t, destructor: ?fn (value: *c_void) callconv(.C) void) c_int;
-pub extern "c" fn pthread_key_delete(key: pthread_key_t) c_int;
+pub extern "c" fn pthread_key_create(key: *pthread_key_t, destructor: ?fn (value: *c_void) callconv(.C) void) E;
+pub extern "c" fn pthread_key_delete(key: pthread_key_t) E;
 pub extern "c" fn pthread_getspecific(key: pthread_key_t) ?*c_void;
 pub extern "c" fn pthread_setspecific(key: pthread_key_t, value: ?*c_void) c_int;
 pub extern "c" fn sem_init(sem: *sem_t, pshared: c_int, value: c_uint) c_int;
@@ -339,24 +339,24 @@ pub extern "c" fn dn_expand(
 ) c_int;
 
 pub const PTHREAD_MUTEX_INITIALIZER = pthread_mutex_t{};
-pub extern "c" fn pthread_mutex_lock(mutex: *pthread_mutex_t) c_int;
-pub extern "c" fn pthread_mutex_unlock(mutex: *pthread_mutex_t) c_int;
-pub extern "c" fn pthread_mutex_trylock(mutex: *pthread_mutex_t) c_int;
-pub extern "c" fn pthread_mutex_destroy(mutex: *pthread_mutex_t) c_int;
+pub extern "c" fn pthread_mutex_lock(mutex: *pthread_mutex_t) E;
+pub extern "c" fn pthread_mutex_unlock(mutex: *pthread_mutex_t) E;
+pub extern "c" fn pthread_mutex_trylock(mutex: *pthread_mutex_t) E;
+pub extern "c" fn pthread_mutex_destroy(mutex: *pthread_mutex_t) E;
 
 pub const PTHREAD_COND_INITIALIZER = pthread_cond_t{};
-pub extern "c" fn pthread_cond_wait(noalias cond: *pthread_cond_t, noalias mutex: *pthread_mutex_t) c_int;
-pub extern "c" fn pthread_cond_timedwait(noalias cond: *pthread_cond_t, noalias mutex: *pthread_mutex_t, noalias abstime: *const timespec) c_int;
-pub extern "c" fn pthread_cond_signal(cond: *pthread_cond_t) c_int;
-pub extern "c" fn pthread_cond_broadcast(cond: *pthread_cond_t) c_int;
-pub extern "c" fn pthread_cond_destroy(cond: *pthread_cond_t) c_int;
+pub extern "c" fn pthread_cond_wait(noalias cond: *pthread_cond_t, noalias mutex: *pthread_mutex_t) E;
+pub extern "c" fn pthread_cond_timedwait(noalias cond: *pthread_cond_t, noalias mutex: *pthread_mutex_t, noalias abstime: *const timespec) E;
+pub extern "c" fn pthread_cond_signal(cond: *pthread_cond_t) E;
+pub extern "c" fn pthread_cond_broadcast(cond: *pthread_cond_t) E;
+pub extern "c" fn pthread_cond_destroy(cond: *pthread_cond_t) E;
 
-pub extern "c" fn pthread_rwlock_destroy(rwl: *pthread_rwlock_t) callconv(.C) c_int;
-pub extern "c" fn pthread_rwlock_rdlock(rwl: *pthread_rwlock_t) callconv(.C) c_int;
-pub extern "c" fn pthread_rwlock_wrlock(rwl: *pthread_rwlock_t) callconv(.C) c_int;
-pub extern "c" fn pthread_rwlock_tryrdlock(rwl: *pthread_rwlock_t) callconv(.C) c_int;
-pub extern "c" fn pthread_rwlock_trywrlock(rwl: *pthread_rwlock_t) callconv(.C) c_int;
-pub extern "c" fn pthread_rwlock_unlock(rwl: *pthread_rwlock_t) callconv(.C) c_int;
+pub extern "c" fn pthread_rwlock_destroy(rwl: *pthread_rwlock_t) callconv(.C) E;
+pub extern "c" fn pthread_rwlock_rdlock(rwl: *pthread_rwlock_t) callconv(.C) E;
+pub extern "c" fn pthread_rwlock_wrlock(rwl: *pthread_rwlock_t) callconv(.C) E;
+pub extern "c" fn pthread_rwlock_tryrdlock(rwl: *pthread_rwlock_t) callconv(.C) E;
+pub extern "c" fn pthread_rwlock_trywrlock(rwl: *pthread_rwlock_t) callconv(.C) E;
+pub extern "c" fn pthread_rwlock_unlock(rwl: *pthread_rwlock_t) callconv(.C) E;
 
 pub const pthread_t = *opaque {};
 pub const FILE = opaque {};
diff --git a/lib/std/c/darwin.zig b/lib/std/c/darwin.zig
index 22473a3899..117172fc7b 100644
--- a/lib/std/c/darwin.zig
+++ b/lib/std/c/darwin.zig
@@ -193,8 +193,8 @@ pub const pthread_attr_t = extern struct {
 
 const pthread_t = std.c.pthread_t;
 pub extern "c" fn pthread_threadid_np(thread: ?pthread_t, thread_id: *u64) c_int;
-pub extern "c" fn pthread_setname_np(name: [*:0]const u8) c_int;
-pub extern "c" fn pthread_getname_np(thread: std.c.pthread_t, name: [*:0]u8, len: usize) c_int;
+pub extern "c" fn pthread_setname_np(name: [*:0]const u8) E;
+pub extern "c" fn pthread_getname_np(thread: std.c.pthread_t, name: [*:0]u8, len: usize) E;
 
 pub extern "c" fn arc4random_buf(buf: [*]u8, len: usize) void;
 
diff --git a/lib/std/c/linux.zig b/lib/std/c/linux.zig
index 694af28904..2ce98e2246 100644
--- a/lib/std/c/linux.zig
+++ b/lib/std/c/linux.zig
@@ -186,8 +186,8 @@ const __SIZEOF_PTHREAD_MUTEX_T = if (os_tag == .fuchsia) 40 else switch (abi) {
 };
 const __SIZEOF_SEM_T = 4 * @sizeOf(usize);
 
-pub extern "c" fn pthread_setname_np(thread: std.c.pthread_t, name: [*:0]const u8) c_int;
-pub extern "c" fn pthread_getname_np(thread: std.c.pthread_t, name: [*:0]u8, len: usize) c_int;
+pub extern "c" fn pthread_setname_np(thread: std.c.pthread_t, name: [*:0]const u8) E;
+pub extern "c" fn pthread_getname_np(thread: std.c.pthread_t, name: [*:0]u8, len: usize) E;
 
 pub const RTLD_LAZY = 1;
 pub const RTLD_NOW = 2;
diff --git a/lib/std/c/netbsd.zig b/lib/std/c/netbsd.zig
index 32b7cc69e3..07af1dc689 100644
--- a/lib/std/c/netbsd.zig
+++ b/lib/std/c/netbsd.zig
@@ -95,5 +95,5 @@ pub const pthread_attr_t = extern struct {
 
 pub const sem_t = ?*opaque {};
 
-pub extern "c" fn pthread_setname_np(thread: std.c.pthread_t, name: [*:0]const u8, arg: ?*c_void) c_int;
-pub extern "c" fn pthread_getname_np(thread: std.c.pthread_t, name: [*:0]u8, len: usize) c_int;
+pub extern "c" fn pthread_setname_np(thread: std.c.pthread_t, name: [*:0]const u8, arg: ?*c_void) E;
+pub extern "c" fn pthread_getname_np(thread: std.c.pthread_t, name: [*:0]u8, len: usize) E;
diff --git a/lib/std/fs.zig b/lib/std/fs.zig
index 494d871974..cb33464dd2 100644
--- a/lib/std/fs.zig
+++ b/lib/std/fs.zig
@@ -339,10 +339,10 @@ pub const Dir = struct {
                         if (rc == 0) return null;
                         if (rc < 0) {
                             switch (os.errno(rc)) {
-                                os.EBADF => unreachable, // Dir is invalid or was opened without iteration ability
-                                os.EFAULT => unreachable,
-                                os.ENOTDIR => unreachable,
-                                os.EINVAL => unreachable,
+                                .BADF => unreachable, // Dir is invalid or was opened without iteration ability
+                                .FAULT => unreachable,
+                                .NOTDIR => unreachable,
+                                .INVAL => unreachable,
                                 else => |err| return os.unexpectedErrno(err),
                             }
                         }
@@ -385,11 +385,11 @@ pub const Dir = struct {
                         else
                             os.system.getdents(self.dir.fd, &self.buf, self.buf.len);
                         switch (os.errno(rc)) {
-                            0 => {},
-                            os.EBADF => unreachable, // Dir is invalid or was opened without iteration ability
-                            os.EFAULT => unreachable,
-                            os.ENOTDIR => unreachable,
-                            os.EINVAL => unreachable,
+                            .SUCCESS => {},
+                            .BADF => unreachable, // Dir is invalid or was opened without iteration ability
+                            .FAULT => unreachable,
+                            .NOTDIR => unreachable,
+                            .INVAL => unreachable,
                             else => |err| return os.unexpectedErrno(err),
                         }
                         if (rc == 0) return null;
@@ -457,10 +457,10 @@ pub const Dir = struct {
                         if (rc == 0) return null;
                         if (rc < 0) {
                             switch (os.errno(rc)) {
-                                os.EBADF => unreachable, // Dir is invalid or was opened without iteration ability
-                                os.EFAULT => unreachable,
-                                os.ENOTDIR => unreachable,
-                                os.EINVAL => unreachable,
+                                .BADF => unreachable, // Dir is invalid or was opened without iteration ability
+                                .FAULT => unreachable,
+                                .NOTDIR => unreachable,
+                                .INVAL => unreachable,
                                 else => |err| return os.unexpectedErrno(err),
                             }
                         }
@@ -522,11 +522,11 @@ pub const Dir = struct {
                     if (self.index >= self.end_index) {
                         const rc = os.linux.getdents64(self.dir.fd, &self.buf, self.buf.len);
                         switch (os.linux.getErrno(rc)) {
-                            0 => {},
-                            os.EBADF => unreachable, // Dir is invalid or was opened without iteration ability
-                            os.EFAULT => unreachable,
-                            os.ENOTDIR => unreachable,
-                            os.EINVAL => unreachable,
+                            .SUCCESS => {},
+                            .BADF => unreachable, // Dir is invalid or was opened without iteration ability
+                            .FAULT => unreachable,
+                            .NOTDIR => unreachable,
+                            .INVAL => unreachable,
                             else => |err| return os.unexpectedErrno(err),
                         }
                         if (rc == 0) return null;
@@ -655,12 +655,12 @@ pub const Dir = struct {
                     if (self.index >= self.end_index) {
                         var bufused: usize = undefined;
                         switch (w.fd_readdir(self.dir.fd, &self.buf, self.buf.len, self.cookie, &bufused)) {
-                            w.ESUCCESS => {},
-                            w.EBADF => unreachable, // Dir is invalid or was opened without iteration ability
-                            w.EFAULT => unreachable,
-                            w.ENOTDIR => unreachable,
-                            w.EINVAL => unreachable,
-                            w.ENOTCAPABLE => return error.AccessDenied,
+                            .SUCCESS => {},
+                            .BADF => unreachable, // Dir is invalid or was opened without iteration ability
+                            .FAULT => unreachable,
+                            .NOTDIR => unreachable,
+                            .INVAL => unreachable,
+                            .NOTCAPABLE => return error.AccessDenied,
                             else => |err| return os.unexpectedErrno(err),
                         }
                         if (bufused == 0) return null;
@@ -2557,12 +2557,12 @@ fn copy_file(fd_in: os.fd_t, fd_out: os.fd_t) CopyFileError!void {
     if (comptime std.Target.current.isDarwin()) {
         const rc = os.system.fcopyfile(fd_in, fd_out, null, os.system.COPYFILE_DATA);
         switch (os.errno(rc)) {
-            0 => return,
-            os.EINVAL => unreachable,
-            os.ENOMEM => return error.SystemResources,
+            .SUCCESS => return,
+            .INVAL => unreachable,
+            .NOMEM => return error.SystemResources,
             // The source file is not a directory, symbolic link, or regular file.
             // Try with the fallback path before giving up.
-            os.ENOTSUP => {},
+            .OPNOTSUPP => {},
             else => |err| return os.unexpectedErrno(err),
         }
     }
diff --git a/lib/std/fs/wasi.zig b/lib/std/fs/wasi.zig
index 378e4a7bac..2bfc384773 100644
--- a/lib/std/fs/wasi.zig
+++ b/lib/std/fs/wasi.zig
@@ -121,13 +121,13 @@ pub const PreopenList = struct {
         while (true) {
             var buf: prestat_t = undefined;
             switch (fd_prestat_get(fd, &buf)) {
-                ESUCCESS => {},
-                ENOTSUP => {
+                .SUCCESS => {},
+                .OPNOTSUPP => {
                     // not a preopen, so keep going
                     fd = try math.add(fd_t, fd, 1);
                     continue;
                 },
-                EBADF => {
+                .BADF => {
                     // OK, no more fds available
                     break;
                 },
@@ -137,7 +137,7 @@ pub const PreopenList = struct {
             const path_buf = try self.buffer.allocator.alloc(u8, preopen_len);
             mem.set(u8, path_buf, 0);
             switch (fd_prestat_dir_name(fd, path_buf.ptr, preopen_len)) {
-                ESUCCESS => {},
+                .SUCCESS => {},
                 else => |err| return os.unexpectedErrno(err),
             }
             const preopen = Preopen.new(fd, PreopenType{ .Dir = path_buf });
diff --git a/lib/std/io/c_writer.zig b/lib/std/io/c_writer.zig
index 9f551b08fc..bbb7f1daf3 100644
--- a/lib/std/io/c_writer.zig
+++ b/lib/std/io/c_writer.zig
@@ -17,19 +17,19 @@ pub fn cWriter(c_file: *std.c.FILE) CWriter {
 fn cWriterWrite(c_file: *std.c.FILE, bytes: []const u8) std.fs.File.WriteError!usize {
     const amt_written = std.c.fwrite(bytes.ptr, 1, bytes.len, c_file);
     if (amt_written >= 0) return amt_written;
-    switch (std.c._errno().*) {
-        0 => unreachable,
-        os.EINVAL => unreachable,
-        os.EFAULT => unreachable,
-        os.EAGAIN => unreachable, // this is a blocking API
-        os.EBADF => unreachable, // always a race condition
-        os.EDESTADDRREQ => unreachable, // connect was never called
-        os.EDQUOT => return error.DiskQuota,
-        os.EFBIG => return error.FileTooBig,
-        os.EIO => return error.InputOutput,
-        os.ENOSPC => return error.NoSpaceLeft,
-        os.EPERM => return error.AccessDenied,
-        os.EPIPE => return error.BrokenPipe,
+    switch (@intToEnum(os.E, std.c._errno().*)) {
+        .SUCCESS => unreachable,
+        .INVAL => unreachable,
+        .FAULT => unreachable,
+        .AGAIN => unreachable, // this is a blocking API
+        .BADF => unreachable, // always a race condition
+        .DESTADDRREQ => unreachable, // connect was never called
+        .DQUOT => return error.DiskQuota,
+        .FBIG => return error.FileTooBig,
+        .IO => return error.InputOutput,
+        .NOSPC => return error.NoSpaceLeft,
+        .PERM => return error.AccessDenied,
+        .PIPE => return error.BrokenPipe,
         else => |err| return os.unexpectedErrno(err),
     }
 }
diff --git a/lib/std/os.zig b/lib/std/os.zig
index e85a6fe42f..7781233a49 100644
--- a/lib/std/os.zig
+++ b/lib/std/os.zig
@@ -116,13 +116,13 @@ pub fn close(fd: fd_t) void {
     if (comptime std.Target.current.isDarwin()) {
         // This avoids the EINTR problem.
         switch (darwin.getErrno(darwin.@"close$NOCANCEL"(fd))) {
-            EBADF => unreachable, // Always a race condition.
+            .BADF => unreachable, // Always a race condition.
             else => return,
         }
     }
     switch (errno(system.close(fd))) {
-        EBADF => unreachable, // Always a race condition.
-        EINTR => return, // This is still a success. See https://github.com/ziglang/zig/issues/2425
+        .BADF => unreachable, // Always a race condition.
+        .INTR => return, // This is still a success. See https://github.com/ziglang/zig/issues/2425
         else => return,
     }
 }
@@ -159,11 +159,11 @@ pub fn getrandom(buffer: []u8) GetRandomError!void {
             };
 
             switch (res.err) {
-                0 => buf = buf[res.num_read..],
-                EINVAL => unreachable,
-                EFAULT => unreachable,
-                EINTR => continue,
-                ENOSYS => return getRandomBytesDevURandom(buf),
+                .SUCCESS => buf = buf[res.num_read..],
+                .INVAL => unreachable,
+                .FAULT => unreachable,
+                .INTR => continue,
+                .NOSYS => return getRandomBytesDevURandom(buf),
                 else => return unexpectedErrno(res.err),
             }
         }
@@ -175,7 +175,7 @@ pub fn getrandom(buffer: []u8) GetRandomError!void {
             return;
         },
         .wasi => switch (wasi.random_get(buffer.ptr, buffer.len)) {
-            0 => return,
+            .SUCCESS => return,
             else => |err| return unexpectedErrno(err),
         },
         else => return getRandomBytesDevURandom(buffer),
@@ -238,7 +238,7 @@ pub const RaiseError = UnexpectedError;
 pub fn raise(sig: u8) RaiseError!void {
     if (builtin.link_libc) {
         switch (errno(system.raise(sig))) {
-            0 => return,
+            .SUCCESS => return,
             else => |err| return unexpectedErrno(err),
         }
     }
@@ -255,7 +255,7 @@ pub fn raise(sig: u8) RaiseError!void {
         _ = linux.sigprocmask(SIG_SETMASK, &set, null);
 
         switch (errno(rc)) {
-            0 => return,
+            .SUCCESS => return,
             else => |err| return unexpectedErrno(err),
         }
     }
@@ -267,10 +267,10 @@ pub const KillError = error{PermissionDenied} || UnexpectedError;
 
 pub fn kill(pid: pid_t, sig: u8) KillError!void {
     switch (errno(system.kill(pid, sig))) {
-        0 => return,
-        EINVAL => unreachable, // invalid signal
-        EPERM => return error.PermissionDenied,
-        ESRCH => unreachable, // always a race condition
+        .SUCCESS => return,
+        .INVAL => unreachable, // invalid signal
+        .PERM => return error.PermissionDenied,
+        .SRCH => unreachable, // always a race condition
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -342,19 +342,19 @@ pub fn read(fd: fd_t, buf: []u8) ReadError!usize {
 
         var nread: usize = undefined;
         switch (wasi.fd_read(fd, &iovs, iovs.len, &nread)) {
-            wasi.ESUCCESS => return nread,
-            wasi.EINTR => unreachable,
-            wasi.EINVAL => unreachable,
-            wasi.EFAULT => unreachable,
-            wasi.EAGAIN => unreachable,
-            wasi.EBADF => return error.NotOpenForReading, // Can be a race condition.
-            wasi.EIO => return error.InputOutput,
-            wasi.EISDIR => return error.IsDir,
-            wasi.ENOBUFS => return error.SystemResources,
-            wasi.ENOMEM => return error.SystemResources,
-            wasi.ECONNRESET => return error.ConnectionResetByPeer,
-            wasi.ETIMEDOUT => return error.ConnectionTimedOut,
-            wasi.ENOTCAPABLE => return error.AccessDenied,
+            .SUCCESS => return nread,
+            .INTR => unreachable,
+            .INVAL => unreachable,
+            .FAULT => unreachable,
+            .AGAIN => unreachable,
+            .BADF => return error.NotOpenForReading, // Can be a race condition.
+            .IO => return error.InputOutput,
+            .ISDIR => return error.IsDir,
+            .NOBUFS => return error.SystemResources,
+            .NOMEM => return error.SystemResources,
+            .CONNRESET => return error.ConnectionResetByPeer,
+            .TIMEDOUT => return error.ConnectionTimedOut,
+            .NOTCAPABLE => return error.AccessDenied,
             else => |err| return unexpectedErrno(err),
         }
     }
@@ -370,18 +370,18 @@ pub fn read(fd: fd_t, buf: []u8) ReadError!usize {
     while (true) {
         const rc = system.read(fd, buf.ptr, adjusted_len);
         switch (errno(rc)) {
-            0 => return @intCast(usize, rc),
-            EINTR => continue,
-            EINVAL => unreachable,
-            EFAULT => unreachable,
-            EAGAIN => return error.WouldBlock,
-            EBADF => return error.NotOpenForReading, // Can be a race condition.
-            EIO => return error.InputOutput,
-            EISDIR => return error.IsDir,
-            ENOBUFS => return error.SystemResources,
-            ENOMEM => return error.SystemResources,
-            ECONNRESET => return error.ConnectionResetByPeer,
-            ETIMEDOUT => return error.ConnectionTimedOut,
+            .SUCCESS => return @intCast(usize, rc),
+            .INTR => continue,
+            .INVAL => unreachable,
+            .FAULT => unreachable,
+            .AGAIN => return error.WouldBlock,
+            .BADF => return error.NotOpenForReading, // Can be a race condition.
+            .IO => return error.InputOutput,
+            .ISDIR => return error.IsDir,
+            .NOBUFS => return error.SystemResources,
+            .NOMEM => return error.SystemResources,
+            .CONNRESET => return error.ConnectionResetByPeer,
+            .TIMEDOUT => return error.ConnectionTimedOut,
             else => |err| return unexpectedErrno(err),
         }
     }
@@ -407,17 +407,17 @@ pub fn readv(fd: fd_t, iov: []const iovec) ReadError!usize {
     if (builtin.os.tag == .wasi and !builtin.link_libc) {
         var nread: usize = undefined;
         switch (wasi.fd_read(fd, iov.ptr, iov.len, &nread)) {
-            wasi.ESUCCESS => return nread,
-            wasi.EINTR => unreachable,
-            wasi.EINVAL => unreachable,
-            wasi.EFAULT => unreachable,
-            wasi.EAGAIN => unreachable, // currently not support in WASI
-            wasi.EBADF => return error.NotOpenForReading, // can be a race condition
-            wasi.EIO => return error.InputOutput,
-            wasi.EISDIR => return error.IsDir,
-            wasi.ENOBUFS => return error.SystemResources,
-            wasi.ENOMEM => return error.SystemResources,
-            wasi.ENOTCAPABLE => return error.AccessDenied,
+            .SUCCESS => return nread,
+            .INTR => unreachable,
+            .INVAL => unreachable,
+            .FAULT => unreachable,
+            .AGAIN => unreachable, // currently not support in WASI
+            .BADF => return error.NotOpenForReading, // can be a race condition
+            .IO => return error.InputOutput,
+            .ISDIR => return error.IsDir,
+            .NOBUFS => return error.SystemResources,
+            .NOMEM => return error.SystemResources,
+            .NOTCAPABLE => return error.AccessDenied,
             else => |err| return unexpectedErrno(err),
         }
     }
@@ -426,16 +426,16 @@ pub fn readv(fd: fd_t, iov: []const iovec) ReadError!usize {
         // TODO handle the case when iov_len is too large and get rid of this @intCast
         const rc = system.readv(fd, iov.ptr, iov_count);
         switch (errno(rc)) {
-            0 => return @intCast(usize, rc),
-            EINTR => continue,
-            EINVAL => unreachable,
-            EFAULT => unreachable,
-            EAGAIN => return error.WouldBlock,
-            EBADF => return error.NotOpenForReading, // can be a race condition
-            EIO => return error.InputOutput,
-            EISDIR => return error.IsDir,
-            ENOBUFS => return error.SystemResources,
-            ENOMEM => return error.SystemResources,
+            .SUCCESS => return @intCast(usize, rc),
+            .INTR => continue,
+            .INVAL => unreachable,
+            .FAULT => unreachable,
+            .AGAIN => return error.WouldBlock,
+            .BADF => return error.NotOpenForReading, // can be a race condition
+            .IO => return error.InputOutput,
+            .ISDIR => return error.IsDir,
+            .NOBUFS => return error.SystemResources,
+            .NOMEM => return error.SystemResources,
             else => |err| return unexpectedErrno(err),
         }
     }
@@ -469,21 +469,21 @@ pub fn pread(fd: fd_t, buf: []u8, offset: u64) PReadError!usize {
 
         var nread: usize = undefined;
         switch (wasi.fd_pread(fd, &iovs, iovs.len, offset, &nread)) {
-            wasi.ESUCCESS => return nread,
-            wasi.EINTR => unreachable,
-            wasi.EINVAL => unreachable,
-            wasi.EFAULT => unreachable,
-            wasi.EAGAIN => unreachable,
-            wasi.EBADF => return error.NotOpenForReading, // Can be a race condition.
-            wasi.EIO => return error.InputOutput,
-            wasi.EISDIR => return error.IsDir,
-            wasi.ENOBUFS => return error.SystemResources,
-            wasi.ENOMEM => return error.SystemResources,
-            wasi.ECONNRESET => return error.ConnectionResetByPeer,
-            wasi.ENXIO => return error.Unseekable,
-            wasi.ESPIPE => return error.Unseekable,
-            wasi.EOVERFLOW => return error.Unseekable,
-            wasi.ENOTCAPABLE => return error.AccessDenied,
+            .SUCCESS => return nread,
+            .INTR => unreachable,
+            .INVAL => unreachable,
+            .FAULT => unreachable,
+            .AGAIN => unreachable,
+            .BADF => return error.NotOpenForReading, // Can be a race condition.
+            .IO => return error.InputOutput,
+            .ISDIR => return error.IsDir,
+            .NOBUFS => return error.SystemResources,
+            .NOMEM => return error.SystemResources,
+            .CONNRESET => return error.ConnectionResetByPeer,
+            .NXIO => return error.Unseekable,
+            .SPIPE => return error.Unseekable,
+            .OVERFLOW => return error.Unseekable,
+            .NOTCAPABLE => return error.AccessDenied,
             else => |err| return unexpectedErrno(err),
         }
     }
@@ -505,20 +505,20 @@ pub fn pread(fd: fd_t, buf: []u8, offset: u64) PReadError!usize {
     while (true) {
         const rc = pread_sym(fd, buf.ptr, adjusted_len, ioffset);
         switch (errno(rc)) {
-            0 => return @intCast(usize, rc),
-            EINTR => continue,
-            EINVAL => unreachable,
-            EFAULT => unreachable,
-            EAGAIN => return error.WouldBlock,
-            EBADF => return error.NotOpenForReading, // Can be a race condition.
-            EIO => return error.InputOutput,
-            EISDIR => return error.IsDir,
-            ENOBUFS => return error.SystemResources,
-            ENOMEM => return error.SystemResources,
-            ECONNRESET => return error.ConnectionResetByPeer,
-            ENXIO => return error.Unseekable,
-            ESPIPE => return error.Unseekable,
-            EOVERFLOW => return error.Unseekable,
+            .SUCCESS => return @intCast(usize, rc),
+            .INTR => continue,
+            .INVAL => unreachable,
+            .FAULT => unreachable,
+            .AGAIN => return error.WouldBlock,
+            .BADF => return error.NotOpenForReading, // Can be a race condition.
+            .IO => return error.InputOutput,
+            .ISDIR => return error.IsDir,
+            .NOBUFS => return error.SystemResources,
+            .NOMEM => return error.SystemResources,
+            .CONNRESET => return error.ConnectionResetByPeer,
+            .NXIO => return error.Unseekable,
+            .SPIPE => return error.Unseekable,
+            .OVERFLOW => return error.Unseekable,
             else => |err| return unexpectedErrno(err),
         }
     }
@@ -558,15 +558,15 @@ pub fn ftruncate(fd: fd_t, length: u64) TruncateError!void {
     }
     if (std.Target.current.os.tag == .wasi and !builtin.link_libc) {
         switch (wasi.fd_filestat_set_size(fd, length)) {
-            wasi.ESUCCESS => return,
-            wasi.EINTR => unreachable,
-            wasi.EFBIG => return error.FileTooBig,
-            wasi.EIO => return error.InputOutput,
-            wasi.EPERM => return error.AccessDenied,
-            wasi.ETXTBSY => return error.FileBusy,
-            wasi.EBADF => unreachable, // Handle not open for writing
-            wasi.EINVAL => unreachable, // Handle not open for writing
-            wasi.ENOTCAPABLE => return error.AccessDenied,
+            .SUCCESS => return,
+            .INTR => unreachable,
+            .FBIG => return error.FileTooBig,
+            .IO => return error.InputOutput,
+            .PERM => return error.AccessDenied,
+            .TXTBSY => return error.FileBusy,
+            .BADF => unreachable, // Handle not open for writing
+            .INVAL => unreachable, // Handle not open for writing
+            .NOTCAPABLE => return error.AccessDenied,
             else => |err| return unexpectedErrno(err),
         }
     }
@@ -579,14 +579,14 @@ pub fn ftruncate(fd: fd_t, length: u64) TruncateError!void {
 
         const ilen = @bitCast(i64, length); // the OS treats this as unsigned
         switch (errno(ftruncate_sym(fd, ilen))) {
-            0 => return,
-            EINTR => continue,
-            EFBIG => return error.FileTooBig,
-            EIO => return error.InputOutput,
-            EPERM => return error.AccessDenied,
-            ETXTBSY => return error.FileBusy,
-            EBADF => unreachable, // Handle not open for writing
-            EINVAL => unreachable, // Handle not open for writing
+            .SUCCESS => return,
+            .INTR => continue,
+            .FBIG => return error.FileTooBig,
+            .IO => return error.InputOutput,
+            .PERM => return error.AccessDenied,
+            .TXTBSY => return error.FileBusy,
+            .BADF => unreachable, // Handle not open for writing
+            .INVAL => unreachable, // Handle not open for writing
             else => |err| return unexpectedErrno(err),
         }
     }
@@ -620,20 +620,20 @@ pub fn preadv(fd: fd_t, iov: []const iovec, offset: u64) PReadError!usize {
     if (builtin.os.tag == .wasi and !builtin.link_libc) {
         var nread: usize = undefined;
         switch (wasi.fd_pread(fd, iov.ptr, iov.len, offset, &nread)) {
-            wasi.ESUCCESS => return nread,
-            wasi.EINTR => unreachable,
-            wasi.EINVAL => unreachable,
-            wasi.EFAULT => unreachable,
-            wasi.EAGAIN => unreachable,
-            wasi.EBADF => return error.NotOpenForReading, // can be a race condition
-            wasi.EIO => return error.InputOutput,
-            wasi.EISDIR => return error.IsDir,
-            wasi.ENOBUFS => return error.SystemResources,
-            wasi.ENOMEM => return error.SystemResources,
-            wasi.ENXIO => return error.Unseekable,
-            wasi.ESPIPE => return error.Unseekable,
-            wasi.EOVERFLOW => return error.Unseekable,
-            wasi.ENOTCAPABLE => return error.AccessDenied,
+            .SUCCESS => return nread,
+            .INTR => unreachable,
+            .INVAL => unreachable,
+            .FAULT => unreachable,
+            .AGAIN => unreachable,
+            .BADF => return error.NotOpenForReading, // can be a race condition
+            .IO => return error.InputOutput,
+            .ISDIR => return error.IsDir,
+            .NOBUFS => return error.SystemResources,
+            .NOMEM => return error.SystemResources,
+            .NXIO => return error.Unseekable,
+            .SPIPE => return error.Unseekable,
+            .OVERFLOW => return error.Unseekable,
+            .NOTCAPABLE => return error.AccessDenied,
             else => |err| return unexpectedErrno(err),
         }
     }
@@ -649,19 +649,19 @@ pub fn preadv(fd: fd_t, iov: []const iovec, offset: u64) PReadError!usize {
     while (true) {
         const rc = preadv_sym(fd, iov.ptr, iov_count, ioffset);
         switch (errno(rc)) {
-            0 => return @bitCast(usize, rc),
-            EINTR => continue,
-            EINVAL => unreachable,
-            EFAULT => unreachable,
-            EAGAIN => return error.WouldBlock,
-            EBADF => return error.NotOpenForReading, // can be a race condition
-            EIO => return error.InputOutput,
-            EISDIR => return error.IsDir,
-            ENOBUFS => return error.SystemResources,
-            ENOMEM => return error.SystemResources,
-            ENXIO => return error.Unseekable,
-            ESPIPE => return error.Unseekable,
-            EOVERFLOW => return error.Unseekable,
+            .SUCCESS => return @bitCast(usize, rc),
+            .INTR => continue,
+            .INVAL => unreachable,
+            .FAULT => unreachable,
+            .AGAIN => return error.WouldBlock,
+            .BADF => return error.NotOpenForReading, // can be a race condition
+            .IO => return error.InputOutput,
+            .ISDIR => return error.IsDir,
+            .NOBUFS => return error.SystemResources,
+            .NOMEM => return error.SystemResources,
+            .NXIO => return error.Unseekable,
+            .SPIPE => return error.Unseekable,
+            .OVERFLOW => return error.Unseekable,
             else => |err| return unexpectedErrno(err),
         }
     }
@@ -723,20 +723,20 @@ pub fn write(fd: fd_t, bytes: []const u8) WriteError!usize {
         }};
         var nwritten: usize = undefined;
         switch (wasi.fd_write(fd, &ciovs, ciovs.len, &nwritten)) {
-            wasi.ESUCCESS => return nwritten,
-            wasi.EINTR => unreachable,
-            wasi.EINVAL => unreachable,
-            wasi.EFAULT => unreachable,
-            wasi.EAGAIN => unreachable,
-            wasi.EBADF => return error.NotOpenForWriting, // can be a race condition.
-            wasi.EDESTADDRREQ => unreachable, // `connect` was never called.
-            wasi.EDQUOT => return error.DiskQuota,
-            wasi.EFBIG => return error.FileTooBig,
-            wasi.EIO => return error.InputOutput,
-            wasi.ENOSPC => return error.NoSpaceLeft,
-            wasi.EPERM => return error.AccessDenied,
-            wasi.EPIPE => return error.BrokenPipe,
-            wasi.ENOTCAPABLE => return error.AccessDenied,
+            .SUCCESS => return nwritten,
+            .INTR => unreachable,
+            .INVAL => unreachable,
+            .FAULT => unreachable,
+            .AGAIN => unreachable,
+            .BADF => return error.NotOpenForWriting, // can be a race condition.
+            .DESTADDRREQ => unreachable, // `connect` was never called.
+            .DQUOT => return error.DiskQuota,
+            .FBIG => return error.FileTooBig,
+            .IO => return error.InputOutput,
+            .NOSPC => return error.NoSpaceLeft,
+            .PERM => return error.AccessDenied,
+            .PIPE => return error.BrokenPipe,
+            .NOTCAPABLE => return error.AccessDenied,
             else => |err| return unexpectedErrno(err),
         }
     }
@@ -751,20 +751,20 @@ pub fn write(fd: fd_t, bytes: []const u8) WriteError!usize {
     while (true) {
         const rc = system.write(fd, bytes.ptr, adjusted_len);
         switch (errno(rc)) {
-            0 => return @intCast(usize, rc),
-            EINTR => continue,
-            EINVAL => unreachable,
-            EFAULT => unreachable,
-            EAGAIN => return error.WouldBlock,
-            EBADF => return error.NotOpenForWriting, // can be a race condition.
-            EDESTADDRREQ => unreachable, // `connect` was never called.
-            EDQUOT => return error.DiskQuota,
-            EFBIG => return error.FileTooBig,
-            EIO => return error.InputOutput,
-            ENOSPC => return error.NoSpaceLeft,
-            EPERM => return error.AccessDenied,
-            EPIPE => return error.BrokenPipe,
-            ECONNRESET => return error.ConnectionResetByPeer,
+            .SUCCESS => return @intCast(usize, rc),
+            .INTR => continue,
+            .INVAL => unreachable,
+            .FAULT => unreachable,
+            .AGAIN => return error.WouldBlock,
+            .BADF => return error.NotOpenForWriting, // can be a race condition.
+            .DESTADDRREQ => unreachable, // `connect` was never called.
+            .DQUOT => return error.DiskQuota,
+            .FBIG => return error.FileTooBig,
+            .IO => return error.InputOutput,
+            .NOSPC => return error.NoSpaceLeft,
+            .PERM => return error.AccessDenied,
+            .PIPE => return error.BrokenPipe,
+            .CONNRESET => return error.ConnectionResetByPeer,
             else => |err| return unexpectedErrno(err),
         }
     }
@@ -798,20 +798,20 @@ pub fn writev(fd: fd_t, iov: []const iovec_const) WriteError!usize {
     if (builtin.os.tag == .wasi and !builtin.link_libc) {
         var nwritten: usize = undefined;
         switch (wasi.fd_write(fd, iov.ptr, iov.len, &nwritten)) {
-            wasi.ESUCCESS => return nwritten,
-            wasi.EINTR => unreachable,
-            wasi.EINVAL => unreachable,
-            wasi.EFAULT => unreachable,
-            wasi.EAGAIN => unreachable,
-            wasi.EBADF => return error.NotOpenForWriting, // can be a race condition.
-            wasi.EDESTADDRREQ => unreachable, // `connect` was never called.
-            wasi.EDQUOT => return error.DiskQuota,
-            wasi.EFBIG => return error.FileTooBig,
-            wasi.EIO => return error.InputOutput,
-            wasi.ENOSPC => return error.NoSpaceLeft,
-            wasi.EPERM => return error.AccessDenied,
-            wasi.EPIPE => return error.BrokenPipe,
-            wasi.ENOTCAPABLE => return error.AccessDenied,
+            .SUCCESS => return nwritten,
+            .INTR => unreachable,
+            .INVAL => unreachable,
+            .FAULT => unreachable,
+            .AGAIN => unreachable,
+            .BADF => return error.NotOpenForWriting, // can be a race condition.
+            .DESTADDRREQ => unreachable, // `connect` was never called.
+            .DQUOT => return error.DiskQuota,
+            .FBIG => return error.FileTooBig,
+            .IO => return error.InputOutput,
+            .NOSPC => return error.NoSpaceLeft,
+            .PERM => return error.AccessDenied,
+            .PIPE => return error.BrokenPipe,
+            .NOTCAPABLE => return error.AccessDenied,
             else => |err| return unexpectedErrno(err),
         }
     }
@@ -820,20 +820,20 @@ pub fn writev(fd: fd_t, iov: []const iovec_const) WriteError!usize {
     while (true) {
         const rc = system.writev(fd, iov.ptr, iov_count);
         switch (errno(rc)) {
-            0 => return @intCast(usize, rc),
-            EINTR => continue,
-            EINVAL => unreachable,
-            EFAULT => unreachable,
-            EAGAIN => return error.WouldBlock,
-            EBADF => return error.NotOpenForWriting, // Can be a race condition.
-            EDESTADDRREQ => unreachable, // `connect` was never called.
-            EDQUOT => return error.DiskQuota,
-            EFBIG => return error.FileTooBig,
-            EIO => return error.InputOutput,
-            ENOSPC => return error.NoSpaceLeft,
-            EPERM => return error.AccessDenied,
-            EPIPE => return error.BrokenPipe,
-            ECONNRESET => return error.ConnectionResetByPeer,
+            .SUCCESS => return @intCast(usize, rc),
+            .INTR => continue,
+            .INVAL => unreachable,
+            .FAULT => unreachable,
+            .AGAIN => return error.WouldBlock,
+            .BADF => return error.NotOpenForWriting, // Can be a race condition.
+            .DESTADDRREQ => unreachable, // `connect` was never called.
+            .DQUOT => return error.DiskQuota,
+            .FBIG => return error.FileTooBig,
+            .IO => return error.InputOutput,
+            .NOSPC => return error.NoSpaceLeft,
+            .PERM => return error.AccessDenied,
+            .PIPE => return error.BrokenPipe,
+            .CONNRESET => return error.ConnectionResetByPeer,
             else => |err| return unexpectedErrno(err),
         }
     }
@@ -875,23 +875,23 @@ pub fn pwrite(fd: fd_t, bytes: []const u8, offset: u64) PWriteError!usize {
 
         var nwritten: usize = undefined;
         switch (wasi.fd_pwrite(fd, &ciovs, ciovs.len, offset, &nwritten)) {
-            wasi.ESUCCESS => return nwritten,
-            wasi.EINTR => unreachable,
-            wasi.EINVAL => unreachable,
-            wasi.EFAULT => unreachable,
-            wasi.EAGAIN => unreachable,
-            wasi.EBADF => return error.NotOpenForWriting, // can be a race condition.
-            wasi.EDESTADDRREQ => unreachable, // `connect` was never called.
-            wasi.EDQUOT => return error.DiskQuota,
-            wasi.EFBIG => return error.FileTooBig,
-            wasi.EIO => return error.InputOutput,
-            wasi.ENOSPC => return error.NoSpaceLeft,
-            wasi.EPERM => return error.AccessDenied,
-            wasi.EPIPE => return error.BrokenPipe,
-            wasi.ENXIO => return error.Unseekable,
-            wasi.ESPIPE => return error.Unseekable,
-            wasi.EOVERFLOW => return error.Unseekable,
-            wasi.ENOTCAPABLE => return error.AccessDenied,
+            .SUCCESS => return nwritten,
+            .INTR => unreachable,
+            .INVAL => unreachable,
+            .FAULT => unreachable,
+            .AGAIN => unreachable,
+            .BADF => return error.NotOpenForWriting, // can be a race condition.
+            .DESTADDRREQ => unreachable, // `connect` was never called.
+            .DQUOT => return error.DiskQuota,
+            .FBIG => return error.FileTooBig,
+            .IO => return error.InputOutput,
+            .NOSPC => return error.NoSpaceLeft,
+            .PERM => return error.AccessDenied,
+            .PIPE => return error.BrokenPipe,
+            .NXIO => return error.Unseekable,
+            .SPIPE => return error.Unseekable,
+            .OVERFLOW => return error.Unseekable,
+            .NOTCAPABLE => return error.AccessDenied,
             else => |err| return unexpectedErrno(err),
         }
     }
@@ -913,22 +913,22 @@ pub fn pwrite(fd: fd_t, bytes: []const u8, offset: u64) PWriteError!usize {
     while (true) {
         const rc = pwrite_sym(fd, bytes.ptr, adjusted_len, ioffset);
         switch (errno(rc)) {
-            0 => return @intCast(usize, rc),
-            EINTR => continue,
-            EINVAL => unreachable,
-            EFAULT => unreachable,
-            EAGAIN => return error.WouldBlock,
-            EBADF => return error.NotOpenForWriting, // Can be a race condition.
-            EDESTADDRREQ => unreachable, // `connect` was never called.
-            EDQUOT => return error.DiskQuota,
-            EFBIG => return error.FileTooBig,
-            EIO => return error.InputOutput,
-            ENOSPC => return error.NoSpaceLeft,
-            EPERM => return error.AccessDenied,
-            EPIPE => return error.BrokenPipe,
-            ENXIO => return error.Unseekable,
-            ESPIPE => return error.Unseekable,
-            EOVERFLOW => return error.Unseekable,
+            .SUCCESS => return @intCast(usize, rc),
+            .INTR => continue,
+            .INVAL => unreachable,
+            .FAULT => unreachable,
+            .AGAIN => return error.WouldBlock,
+            .BADF => return error.NotOpenForWriting, // Can be a race condition.
+            .DESTADDRREQ => unreachable, // `connect` was never called.
+            .DQUOT => return error.DiskQuota,
+            .FBIG => return error.FileTooBig,
+            .IO => return error.InputOutput,
+            .NOSPC => return error.NoSpaceLeft,
+            .PERM => return error.AccessDenied,
+            .PIPE => return error.BrokenPipe,
+            .NXIO => return error.Unseekable,
+            .SPIPE => return error.Unseekable,
+            .OVERFLOW => return error.Unseekable,
             else => |err| return unexpectedErrno(err),
         }
     }
@@ -971,23 +971,23 @@ pub fn pwritev(fd: fd_t, iov: []const iovec_const, offset: u64) PWriteError!usiz
     if (builtin.os.tag == .wasi and !builtin.link_libc) {
         var nwritten: usize = undefined;
         switch (wasi.fd_pwrite(fd, iov.ptr, iov.len, offset, &nwritten)) {
-            wasi.ESUCCESS => return nwritten,
-            wasi.EINTR => unreachable,
-            wasi.EINVAL => unreachable,
-            wasi.EFAULT => unreachable,
-            wasi.EAGAIN => unreachable,
-            wasi.EBADF => return error.NotOpenForWriting, // Can be a race condition.
-            wasi.EDESTADDRREQ => unreachable, // `connect` was never called.
-            wasi.EDQUOT => return error.DiskQuota,
-            wasi.EFBIG => return error.FileTooBig,
-            wasi.EIO => return error.InputOutput,
-            wasi.ENOSPC => return error.NoSpaceLeft,
-            wasi.EPERM => return error.AccessDenied,
-            wasi.EPIPE => return error.BrokenPipe,
-            wasi.ENXIO => return error.Unseekable,
-            wasi.ESPIPE => return error.Unseekable,
-            wasi.EOVERFLOW => return error.Unseekable,
-            wasi.ENOTCAPABLE => return error.AccessDenied,
+            .SUCCESS => return nwritten,
+            .INTR => unreachable,
+            .INVAL => unreachable,
+            .FAULT => unreachable,
+            .AGAIN => unreachable,
+            .BADF => return error.NotOpenForWriting, // Can be a race condition.
+            .DESTADDRREQ => unreachable, // `connect` was never called.
+            .DQUOT => return error.DiskQuota,
+            .FBIG => return error.FileTooBig,
+            .IO => return error.InputOutput,
+            .NOSPC => return error.NoSpaceLeft,
+            .PERM => return error.AccessDenied,
+            .PIPE => return error.BrokenPipe,
+            .NXIO => return error.Unseekable,
+            .SPIPE => return error.Unseekable,
+            .OVERFLOW => return error.Unseekable,
+            .NOTCAPABLE => return error.AccessDenied,
             else => |err| return unexpectedErrno(err),
         }
     }
@@ -1002,22 +1002,22 @@ pub fn pwritev(fd: fd_t, iov: []const iovec_const, offset: u64) PWriteError!usiz
     while (true) {
         const rc = pwritev_sym(fd, iov.ptr, iov_count, ioffset);
         switch (errno(rc)) {
-            0 => return @intCast(usize, rc),
-            EINTR => continue,
-            EINVAL => unreachable,
-            EFAULT => unreachable,
-            EAGAIN => return error.WouldBlock,
-            EBADF => return error.NotOpenForWriting, // Can be a race condition.
-            EDESTADDRREQ => unreachable, // `connect` was never called.
-            EDQUOT => return error.DiskQuota,
-            EFBIG => return error.FileTooBig,
-            EIO => return error.InputOutput,
-            ENOSPC => return error.NoSpaceLeft,
-            EPERM => return error.AccessDenied,
-            EPIPE => return error.BrokenPipe,
-            ENXIO => return error.Unseekable,
-            ESPIPE => return error.Unseekable,
-            EOVERFLOW => return error.Unseekable,
+            .SUCCESS => return @intCast(usize, rc),
+            .INTR => continue,
+            .INVAL => unreachable,
+            .FAULT => unreachable,
+            .AGAIN => return error.WouldBlock,
+            .BADF => return error.NotOpenForWriting, // Can be a race condition.
+            .DESTADDRREQ => unreachable, // `connect` was never called.
+            .DQUOT => return error.DiskQuota,
+            .FBIG => return error.FileTooBig,
+            .IO => return error.InputOutput,
+            .NOSPC => return error.NoSpaceLeft,
+            .PERM => return error.AccessDenied,
+            .PIPE => return error.BrokenPipe,
+            .NXIO => return error.Unseekable,
+            .SPIPE => return error.Unseekable,
+            .OVERFLOW => return error.Unseekable,
             else => |err| return unexpectedErrno(err),
         }
     }
@@ -1098,27 +1098,27 @@ pub fn openZ(file_path: [*:0]const u8, flags: u32, perm: mode_t) OpenError!fd_t
     while (true) {
         const rc = open_sym(file_path, flags, perm);
         switch (errno(rc)) {
-            0 => return @intCast(fd_t, rc),
-            EINTR => continue,
+            .SUCCESS => return @intCast(fd_t, rc),
+            .INTR => continue,
 
-            EFAULT => unreachable,
-            EINVAL => unreachable,
-            EACCES => return error.AccessDenied,
-            EFBIG => return error.FileTooBig,
-            EOVERFLOW => return error.FileTooBig,
-            EISDIR => return error.IsDir,
-            ELOOP => return error.SymLinkLoop,
-            EMFILE => return error.ProcessFdQuotaExceeded,
-            ENAMETOOLONG => return error.NameTooLong,
-            ENFILE => return error.SystemFdQuotaExceeded,
-            ENODEV => return error.NoDevice,
-            ENOENT => return error.FileNotFound,
-            ENOMEM => return error.SystemResources,
-            ENOSPC => return error.NoSpaceLeft,
-            ENOTDIR => return error.NotDir,
-            EPERM => return error.AccessDenied,
-            EEXIST => return error.PathAlreadyExists,
-            EBUSY => return error.DeviceBusy,
+            .FAULT => unreachable,
+            .INVAL => unreachable,
+            .ACCES => return error.AccessDenied,
+            .FBIG => return error.FileTooBig,
+            .OVERFLOW => return error.FileTooBig,
+            .ISDIR => return error.IsDir,
+            .LOOP => return error.SymLinkLoop,
+            .MFILE => return error.ProcessFdQuotaExceeded,
+            .NAMETOOLONG => return error.NameTooLong,
+            .NFILE => return error.SystemFdQuotaExceeded,
+            .NODEV => return error.NoDevice,
+            .NOENT => return error.FileNotFound,
+            .NOMEM => return error.SystemResources,
+            .NOSPC => return error.NoSpaceLeft,
+            .NOTDIR => return error.NotDir,
+            .PERM => return error.AccessDenied,
+            .EXIST => return error.PathAlreadyExists,
+            .BUSY => return error.DeviceBusy,
             else => |err| return unexpectedErrno(err),
         }
     }
@@ -1193,28 +1193,28 @@ pub fn openatWasi(dir_fd: fd_t, file_path: []const u8, lookup_flags: lookupflags
     while (true) {
         var fd: fd_t = undefined;
         switch (wasi.path_open(dir_fd, lookup_flags, file_path.ptr, file_path.len, oflags, base, inheriting, fdflags, &fd)) {
-            wasi.ESUCCESS => return fd,
-            wasi.EINTR => continue,
+            .SUCCESS => return fd,
+            .INTR => continue,
 
-            wasi.EFAULT => unreachable,
-            wasi.EINVAL => unreachable,
-            wasi.EACCES => return error.AccessDenied,
-            wasi.EFBIG => return error.FileTooBig,
-            wasi.EOVERFLOW => return error.FileTooBig,
-            wasi.EISDIR => return error.IsDir,
-            wasi.ELOOP => return error.SymLinkLoop,
-            wasi.EMFILE => return error.ProcessFdQuotaExceeded,
-            wasi.ENAMETOOLONG => return error.NameTooLong,
-            wasi.ENFILE => return error.SystemFdQuotaExceeded,
-            wasi.ENODEV => return error.NoDevice,
-            wasi.ENOENT => return error.FileNotFound,
-            wasi.ENOMEM => return error.SystemResources,
-            wasi.ENOSPC => return error.NoSpaceLeft,
-            wasi.ENOTDIR => return error.NotDir,
-            wasi.EPERM => return error.AccessDenied,
-            wasi.EEXIST => return error.PathAlreadyExists,
-            wasi.EBUSY => return error.DeviceBusy,
-            wasi.ENOTCAPABLE => return error.AccessDenied,
+            .FAULT => unreachable,
+            .INVAL => unreachable,
+            .ACCES => return error.AccessDenied,
+            .FBIG => return error.FileTooBig,
+            .OVERFLOW => return error.FileTooBig,
+            .ISDIR => return error.IsDir,
+            .LOOP => return error.SymLinkLoop,
+            .MFILE => return error.ProcessFdQuotaExceeded,
+            .NAMETOOLONG => return error.NameTooLong,
+            .NFILE => return error.SystemFdQuotaExceeded,
+            .NODEV => return error.NoDevice,
+            .NOENT => return error.FileNotFound,
+            .NOMEM => return error.SystemResources,
+            .NOSPC => return error.NoSpaceLeft,
+            .NOTDIR => return error.NotDir,
+            .PERM => return error.AccessDenied,
+            .EXIST => return error.PathAlreadyExists,
+            .BUSY => return error.DeviceBusy,
+            .NOTCAPABLE => return error.AccessDenied,
             else => |err| return unexpectedErrno(err),
         }
     }
@@ -1239,30 +1239,30 @@ pub fn openatZ(dir_fd: fd_t, file_path: [*:0]const u8, flags: u32, mode: mode_t)
     while (true) {
         const rc = openat_sym(dir_fd, file_path, flags, mode);
         switch (errno(rc)) {
-            0 => return @intCast(fd_t, rc),
-            EINTR => continue,
+            .SUCCESS => return @intCast(fd_t, rc),
+            .INTR => continue,
 
-            EFAULT => unreachable,
-            EINVAL => unreachable,
-            EBADF => unreachable,
-            EACCES => return error.AccessDenied,
-            EFBIG => return error.FileTooBig,
-            EOVERFLOW => return error.FileTooBig,
-            EISDIR => return error.IsDir,
-            ELOOP => return error.SymLinkLoop,
-            EMFILE => return error.ProcessFdQuotaExceeded,
-            ENAMETOOLONG => return error.NameTooLong,
-            ENFILE => return error.SystemFdQuotaExceeded,
-            ENODEV => return error.NoDevice,
-            ENOENT => return error.FileNotFound,
-            ENOMEM => return error.SystemResources,
-            ENOSPC => return error.NoSpaceLeft,
-            ENOTDIR => return error.NotDir,
-            EPERM => return error.AccessDenied,
-            EEXIST => return error.PathAlreadyExists,
-            EBUSY => return error.DeviceBusy,
-            EOPNOTSUPP => return error.FileLocksNotSupported,
-            EWOULDBLOCK => return error.WouldBlock,
+            .FAULT => unreachable,
+            .INVAL => unreachable,
+            .BADF => unreachable,
+            .ACCES => return error.AccessDenied,
+            .FBIG => return error.FileTooBig,
+            .OVERFLOW => return error.FileTooBig,
+            .ISDIR => return error.IsDir,
+            .LOOP => return error.SymLinkLoop,
+            .MFILE => return error.ProcessFdQuotaExceeded,
+            .NAMETOOLONG => return error.NameTooLong,
+            .NFILE => return error.SystemFdQuotaExceeded,
+            .NODEV => return error.NoDevice,
+            .NOENT => return error.FileNotFound,
+            .NOMEM => return error.SystemResources,
+            .NOSPC => return error.NoSpaceLeft,
+            .NOTDIR => return error.NotDir,
+            .PERM => return error.AccessDenied,
+            .EXIST => return error.PathAlreadyExists,
+            .BUSY => return error.DeviceBusy,
+            .OPNOTSUPP => return error.FileLocksNotSupported,
+            .AGAIN => return error.WouldBlock,
             else => |err| return unexpectedErrno(err),
         }
     }
@@ -1286,9 +1286,9 @@ pub fn openatW(dir_fd: fd_t, file_path_w: []const u16, flags: u32, mode: mode_t)
 pub fn dup(old_fd: fd_t) !fd_t {
     const rc = system.dup(old_fd);
     return switch (errno(rc)) {
-        0 => return @intCast(fd_t, rc),
-        EMFILE => error.ProcessFdQuotaExceeded,
-        EBADF => unreachable, // invalid file descriptor
+        .SUCCESS => return @intCast(fd_t, rc),
+        .MFILE => error.ProcessFdQuotaExceeded,
+        .BADF => unreachable, // invalid file descriptor
         else => |err| return unexpectedErrno(err),
     };
 }
@@ -1296,11 +1296,11 @@ pub fn dup(old_fd: fd_t) !fd_t {
 pub fn dup2(old_fd: fd_t, new_fd: fd_t) !void {
     while (true) {
         switch (errno(system.dup2(old_fd, new_fd))) {
-            0 => return,
-            EBUSY, EINTR => continue,
-            EMFILE => return error.ProcessFdQuotaExceeded,
-            EINVAL => unreachable, // invalid parameters passed to dup2
-            EBADF => unreachable, // invalid file descriptor
+            .SUCCESS => return,
+            .BUSY, .INTR => continue,
+            .MFILE => return error.ProcessFdQuotaExceeded,
+            .INVAL => unreachable, // invalid parameters passed to dup2
+            .BADF => unreachable, // invalid file descriptor
             else => |err| return unexpectedErrno(err),
         }
     }
@@ -1331,23 +1331,23 @@ pub fn execveZ(
     envp: [*:null]const ?[*:0]const u8,
 ) ExecveError {
     switch (errno(system.execve(path, child_argv, envp))) {
-        0 => unreachable,
-        EFAULT => unreachable,
-        E2BIG => return error.SystemResources,
-        EMFILE => return error.ProcessFdQuotaExceeded,
-        ENAMETOOLONG => return error.NameTooLong,
-        ENFILE => return error.SystemFdQuotaExceeded,
-        ENOMEM => return error.SystemResources,
-        EACCES => return error.AccessDenied,
-        EPERM => return error.AccessDenied,
-        EINVAL => return error.InvalidExe,
-        ENOEXEC => return error.InvalidExe,
-        EIO => return error.FileSystem,
-        ELOOP => return error.FileSystem,
-        EISDIR => return error.IsDir,
-        ENOENT => return error.FileNotFound,
-        ENOTDIR => return error.NotDir,
-        ETXTBSY => return error.FileBusy,
+        .SUCCESS => unreachable,
+        .FAULT => unreachable,
+        .@"2BIG" => return error.SystemResources,
+        .MFILE => return error.ProcessFdQuotaExceeded,
+        .NAMETOOLONG => return error.NameTooLong,
+        .NFILE => return error.SystemFdQuotaExceeded,
+        .NOMEM => return error.SystemResources,
+        .ACCES => return error.AccessDenied,
+        .PERM => return error.AccessDenied,
+        .INVAL => return error.InvalidExe,
+        .NOEXEC => return error.InvalidExe,
+        .IO => return error.FileSystem,
+        .LOOP => return error.FileSystem,
+        .ISDIR => return error.IsDir,
+        .NOENT => return error.FileNotFound,
+        .NOTDIR => return error.NotDir,
+        .TXTBSY => return error.FileBusy,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -1543,16 +1543,17 @@ pub fn getcwd(out_buffer: []u8) GetCwdError![]u8 {
     }
 
     const err = if (builtin.link_libc) blk: {
-        break :blk if (std.c.getcwd(out_buffer.ptr, out_buffer.len)) |_| 0 else std.c._errno().*;
+        const c_err = if (std.c.getcwd(out_buffer.ptr, out_buffer.len)) |_| 0 else std.c._errno().*;
+        break :blk @intToEnum(E, c_err);
     } else blk: {
         break :blk errno(system.getcwd(out_buffer.ptr, out_buffer.len));
     };
     switch (err) {
-        0 => return mem.spanZ(std.meta.assumeSentinel(out_buffer.ptr, 0)),
-        EFAULT => unreachable,
-        EINVAL => unreachable,
-        ENOENT => return error.CurrentWorkingDirectoryUnlinked,
-        ERANGE => return error.NameTooLong,
+        .SUCCESS => return mem.spanZ(std.meta.assumeSentinel(out_buffer.ptr, 0)),
+        .FAULT => unreachable,
+        .INVAL => unreachable,
+        .NOENT => return error.CurrentWorkingDirectoryUnlinked,
+        .RANGE => return error.NameTooLong,
         else => return unexpectedErrno(err),
     }
 }
@@ -1601,21 +1602,21 @@ pub fn symlinkZ(target_path: [*:0]const u8, sym_link_path: [*:0]const u8) SymLin
         @compileError("symlink is not supported on Windows; use std.os.windows.CreateSymbolicLink instead");
     }
     switch (errno(system.symlink(target_path, sym_link_path))) {
-        0 => return,
-        EFAULT => unreachable,
-        EINVAL => unreachable,
-        EACCES => return error.AccessDenied,
-        EPERM => return error.AccessDenied,
-        EDQUOT => return error.DiskQuota,
-        EEXIST => return error.PathAlreadyExists,
-        EIO => return error.FileSystem,
-        ELOOP => return error.SymLinkLoop,
-        ENAMETOOLONG => return error.NameTooLong,
-        ENOENT => return error.FileNotFound,
-        ENOTDIR => return error.NotDir,
-        ENOMEM => return error.SystemResources,
-        ENOSPC => return error.NoSpaceLeft,
-        EROFS => return error.ReadOnlyFileSystem,
+        .SUCCESS => return,
+        .FAULT => unreachable,
+        .INVAL => unreachable,
+        .ACCES => return error.AccessDenied,
+        .PERM => return error.AccessDenied,
+        .DQUOT => return error.DiskQuota,
+        .EXIST => return error.PathAlreadyExists,
+        .IO => return error.FileSystem,
+        .LOOP => return error.SymLinkLoop,
+        .NAMETOOLONG => return error.NameTooLong,
+        .NOENT => return error.FileNotFound,
+        .NOTDIR => return error.NotDir,
+        .NOMEM => return error.SystemResources,
+        .NOSPC => return error.NoSpaceLeft,
+        .ROFS => return error.ReadOnlyFileSystem,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -1644,22 +1645,22 @@ pub const symlinkatC = @compileError("deprecated: renamed to symlinkatZ");
 /// See also `symlinkat`.
 pub fn symlinkatWasi(target_path: []const u8, newdirfd: fd_t, sym_link_path: []const u8) SymLinkError!void {
     switch (wasi.path_symlink(target_path.ptr, target_path.len, newdirfd, sym_link_path.ptr, sym_link_path.len)) {
-        wasi.ESUCCESS => {},
-        wasi.EFAULT => unreachable,
-        wasi.EINVAL => unreachable,
-        wasi.EACCES => return error.AccessDenied,
-        wasi.EPERM => return error.AccessDenied,
-        wasi.EDQUOT => return error.DiskQuota,
-        wasi.EEXIST => return error.PathAlreadyExists,
-        wasi.EIO => return error.FileSystem,
-        wasi.ELOOP => return error.SymLinkLoop,
-        wasi.ENAMETOOLONG => return error.NameTooLong,
-        wasi.ENOENT => return error.FileNotFound,
-        wasi.ENOTDIR => return error.NotDir,
-        wasi.ENOMEM => return error.SystemResources,
-        wasi.ENOSPC => return error.NoSpaceLeft,
-        wasi.EROFS => return error.ReadOnlyFileSystem,
-        wasi.ENOTCAPABLE => return error.AccessDenied,
+        .SUCCESS => {},
+        .FAULT => unreachable,
+        .INVAL => unreachable,
+        .ACCES => return error.AccessDenied,
+        .PERM => return error.AccessDenied,
+        .DQUOT => return error.DiskQuota,
+        .EXIST => return error.PathAlreadyExists,
+        .IO => return error.FileSystem,
+        .LOOP => return error.SymLinkLoop,
+        .NAMETOOLONG => return error.NameTooLong,
+        .NOENT => return error.FileNotFound,
+        .NOTDIR => return error.NotDir,
+        .NOMEM => return error.SystemResources,
+        .NOSPC => return error.NoSpaceLeft,
+        .ROFS => return error.ReadOnlyFileSystem,
+        .NOTCAPABLE => return error.AccessDenied,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -1671,21 +1672,21 @@ pub fn symlinkatZ(target_path: [*:0]const u8, newdirfd: fd_t, sym_link_path: [*:
         @compileError("symlinkat is not supported on Windows; use std.os.windows.CreateSymbolicLink instead");
     }
     switch (errno(system.symlinkat(target_path, newdirfd, sym_link_path))) {
-        0 => return,
-        EFAULT => unreachable,
-        EINVAL => unreachable,
-        EACCES => return error.AccessDenied,
-        EPERM => return error.AccessDenied,
-        EDQUOT => return error.DiskQuota,
-        EEXIST => return error.PathAlreadyExists,
-        EIO => return error.FileSystem,
-        ELOOP => return error.SymLinkLoop,
-        ENAMETOOLONG => return error.NameTooLong,
-        ENOENT => return error.FileNotFound,
-        ENOTDIR => return error.NotDir,
-        ENOMEM => return error.SystemResources,
-        ENOSPC => return error.NoSpaceLeft,
-        EROFS => return error.ReadOnlyFileSystem,
+        .SUCCESS => return,
+        .FAULT => unreachable,
+        .INVAL => unreachable,
+        .ACCES => return error.AccessDenied,
+        .PERM => return error.AccessDenied,
+        .DQUOT => return error.DiskQuota,
+        .EXIST => return error.PathAlreadyExists,
+        .IO => return error.FileSystem,
+        .LOOP => return error.SymLinkLoop,
+        .NAMETOOLONG => return error.NameTooLong,
+        .NOENT => return error.FileNotFound,
+        .NOTDIR => return error.NotDir,
+        .NOMEM => return error.SystemResources,
+        .NOSPC => return error.NoSpaceLeft,
+        .ROFS => return error.ReadOnlyFileSystem,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -1707,22 +1708,22 @@ pub const LinkError = UnexpectedError || error{
 
 pub fn linkZ(oldpath: [*:0]const u8, newpath: [*:0]const u8, flags: i32) LinkError!void {
     switch (errno(system.link(oldpath, newpath, flags))) {
-        0 => return,
-        EACCES => return error.AccessDenied,
-        EDQUOT => return error.DiskQuota,
-        EEXIST => return error.PathAlreadyExists,
-        EFAULT => unreachable,
-        EIO => return error.FileSystem,
-        ELOOP => return error.SymLinkLoop,
-        EMLINK => return error.LinkQuotaExceeded,
-        ENAMETOOLONG => return error.NameTooLong,
-        ENOENT => return error.FileNotFound,
-        ENOMEM => return error.SystemResources,
-        ENOSPC => return error.NoSpaceLeft,
-        EPERM => return error.AccessDenied,
-        EROFS => return error.ReadOnlyFileSystem,
-        EXDEV => return error.NotSameFileSystem,
-        EINVAL => unreachable,
+        .SUCCESS => return,
+        .ACCES => return error.AccessDenied,
+        .DQUOT => return error.DiskQuota,
+        .EXIST => return error.PathAlreadyExists,
+        .FAULT => unreachable,
+        .IO => return error.FileSystem,
+        .LOOP => return error.SymLinkLoop,
+        .MLINK => return error.LinkQuotaExceeded,
+        .NAMETOOLONG => return error.NameTooLong,
+        .NOENT => return error.FileNotFound,
+        .NOMEM => return error.SystemResources,
+        .NOSPC => return error.NoSpaceLeft,
+        .PERM => return error.AccessDenied,
+        .ROFS => return error.ReadOnlyFileSystem,
+        .XDEV => return error.NotSameFileSystem,
+        .INVAL => unreachable,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -1743,23 +1744,23 @@ pub fn linkatZ(
     flags: i32,
 ) LinkatError!void {
     switch (errno(system.linkat(olddir, oldpath, newdir, newpath, flags))) {
-        0 => return,
-        EACCES => return error.AccessDenied,
-        EDQUOT => return error.DiskQuota,
-        EEXIST => return error.PathAlreadyExists,
-        EFAULT => unreachable,
-        EIO => return error.FileSystem,
-        ELOOP => return error.SymLinkLoop,
-        EMLINK => return error.LinkQuotaExceeded,
-        ENAMETOOLONG => return error.NameTooLong,
-        ENOENT => return error.FileNotFound,
-        ENOMEM => return error.SystemResources,
-        ENOSPC => return error.NoSpaceLeft,
-        ENOTDIR => return error.NotDir,
-        EPERM => return error.AccessDenied,
-        EROFS => return error.ReadOnlyFileSystem,
-        EXDEV => return error.NotSameFileSystem,
-        EINVAL => unreachable,
+        .SUCCESS => return,
+        .ACCES => return error.AccessDenied,
+        .DQUOT => return error.DiskQuota,
+        .EXIST => return error.PathAlreadyExists,
+        .FAULT => unreachable,
+        .IO => return error.FileSystem,
+        .LOOP => return error.SymLinkLoop,
+        .MLINK => return error.LinkQuotaExceeded,
+        .NAMETOOLONG => return error.NameTooLong,
+        .NOENT => return error.FileNotFound,
+        .NOMEM => return error.SystemResources,
+        .NOSPC => return error.NoSpaceLeft,
+        .NOTDIR => return error.NotDir,
+        .PERM => return error.AccessDenied,
+        .ROFS => return error.ReadOnlyFileSystem,
+        .XDEV => return error.NotSameFileSystem,
+        .INVAL => unreachable,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -1822,20 +1823,20 @@ pub fn unlinkZ(file_path: [*:0]const u8) UnlinkError!void {
         return unlinkW(file_path_w.span());
     }
     switch (errno(system.unlink(file_path))) {
-        0 => return,
-        EACCES => return error.AccessDenied,
-        EPERM => return error.AccessDenied,
-        EBUSY => return error.FileBusy,
-        EFAULT => unreachable,
-        EINVAL => unreachable,
-        EIO => return error.FileSystem,
-        EISDIR => return error.IsDir,
-        ELOOP => return error.SymLinkLoop,
-        ENAMETOOLONG => return error.NameTooLong,
-        ENOENT => return error.FileNotFound,
-        ENOTDIR => return error.NotDir,
-        ENOMEM => return error.SystemResources,
-        EROFS => return error.ReadOnlyFileSystem,
+        .SUCCESS => return,
+        .ACCES => return error.AccessDenied,
+        .PERM => return error.AccessDenied,
+        .BUSY => return error.FileBusy,
+        .FAULT => unreachable,
+        .INVAL => unreachable,
+        .IO => return error.FileSystem,
+        .ISDIR => return error.IsDir,
+        .LOOP => return error.SymLinkLoop,
+        .NAMETOOLONG => return error.NameTooLong,
+        .NOENT => return error.FileNotFound,
+        .NOTDIR => return error.NotDir,
+        .NOMEM => return error.SystemResources,
+        .ROFS => return error.ReadOnlyFileSystem,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -1875,24 +1876,24 @@ pub fn unlinkatWasi(dirfd: fd_t, file_path: []const u8, flags: u32) UnlinkatErro
     else
         wasi.path_unlink_file(dirfd, file_path.ptr, file_path.len);
     switch (res) {
-        wasi.ESUCCESS => return,
-        wasi.EACCES => return error.AccessDenied,
-        wasi.EPERM => return error.AccessDenied,
-        wasi.EBUSY => return error.FileBusy,
-        wasi.EFAULT => unreachable,
-        wasi.EIO => return error.FileSystem,
-        wasi.EISDIR => return error.IsDir,
-        wasi.ELOOP => return error.SymLinkLoop,
-        wasi.ENAMETOOLONG => return error.NameTooLong,
-        wasi.ENOENT => return error.FileNotFound,
-        wasi.ENOTDIR => return error.NotDir,
-        wasi.ENOMEM => return error.SystemResources,
-        wasi.EROFS => return error.ReadOnlyFileSystem,
-        wasi.ENOTEMPTY => return error.DirNotEmpty,
-        wasi.ENOTCAPABLE => return error.AccessDenied,
+        .SUCCESS => return,
+        .ACCES => return error.AccessDenied,
+        .PERM => return error.AccessDenied,
+        .BUSY => return error.FileBusy,
+        .FAULT => unreachable,
+        .IO => return error.FileSystem,
+        .ISDIR => return error.IsDir,
+        .LOOP => return error.SymLinkLoop,
+        .NAMETOOLONG => return error.NameTooLong,
+        .NOENT => return error.FileNotFound,
+        .NOTDIR => return error.NotDir,
+        .NOMEM => return error.SystemResources,
+        .ROFS => return error.ReadOnlyFileSystem,
+        .NOTEMPTY => return error.DirNotEmpty,
+        .NOTCAPABLE => return error.AccessDenied,
 
-        wasi.EINVAL => unreachable, // invalid flags, or pathname has . as last component
-        wasi.EBADF => unreachable, // always a race condition
+        .INVAL => unreachable, // invalid flags, or pathname has . as last component
+        .BADF => unreachable, // always a race condition
 
         else => |err| return unexpectedErrno(err),
     }
@@ -1905,23 +1906,23 @@ pub fn unlinkatZ(dirfd: fd_t, file_path_c: [*:0]const u8, flags: u32) UnlinkatEr
         return unlinkatW(dirfd, file_path_w.span(), flags);
     }
     switch (errno(system.unlinkat(dirfd, file_path_c, flags))) {
-        0 => return,
-        EACCES => return error.AccessDenied,
-        EPERM => return error.AccessDenied,
-        EBUSY => return error.FileBusy,
-        EFAULT => unreachable,
-        EIO => return error.FileSystem,
-        EISDIR => return error.IsDir,
-        ELOOP => return error.SymLinkLoop,
-        ENAMETOOLONG => return error.NameTooLong,
-        ENOENT => return error.FileNotFound,
-        ENOTDIR => return error.NotDir,
-        ENOMEM => return error.SystemResources,
-        EROFS => return error.ReadOnlyFileSystem,
-        ENOTEMPTY => return error.DirNotEmpty,
+        .SUCCESS => return,
+        .ACCES => return error.AccessDenied,
+        .PERM => return error.AccessDenied,
+        .BUSY => return error.FileBusy,
+        .FAULT => unreachable,
+        .IO => return error.FileSystem,
+        .ISDIR => return error.IsDir,
+        .LOOP => return error.SymLinkLoop,
+        .NAMETOOLONG => return error.NameTooLong,
+        .NOENT => return error.FileNotFound,
+        .NOTDIR => return error.NotDir,
+        .NOMEM => return error.SystemResources,
+        .ROFS => return error.ReadOnlyFileSystem,
+        .NOTEMPTY => return error.DirNotEmpty,
 
-        EINVAL => unreachable, // invalid flags, or pathname has . as last component
-        EBADF => unreachable, // always a race condition
+        .INVAL => unreachable, // invalid flags, or pathname has . as last component
+        .BADF => unreachable, // always a race condition
 
         else => |err| return unexpectedErrno(err),
     }
@@ -1982,25 +1983,25 @@ pub fn renameZ(old_path: [*:0]const u8, new_path: [*:0]const u8) RenameError!voi
         return renameW(old_path_w.span().ptr, new_path_w.span().ptr);
     }
     switch (errno(system.rename(old_path, new_path))) {
-        0 => return,
-        EACCES => return error.AccessDenied,
-        EPERM => return error.AccessDenied,
-        EBUSY => return error.FileBusy,
-        EDQUOT => return error.DiskQuota,
-        EFAULT => unreachable,
-        EINVAL => unreachable,
-        EISDIR => return error.IsDir,
-        ELOOP => return error.SymLinkLoop,
-        EMLINK => return error.LinkQuotaExceeded,
-        ENAMETOOLONG => return error.NameTooLong,
-        ENOENT => return error.FileNotFound,
-        ENOTDIR => return error.NotDir,
-        ENOMEM => return error.SystemResources,
-        ENOSPC => return error.NoSpaceLeft,
-        EEXIST => return error.PathAlreadyExists,
-        ENOTEMPTY => return error.PathAlreadyExists,
-        EROFS => return error.ReadOnlyFileSystem,
-        EXDEV => return error.RenameAcrossMountPoints,
+        .SUCCESS => return,
+        .ACCES => return error.AccessDenied,
+        .PERM => return error.AccessDenied,
+        .BUSY => return error.FileBusy,
+        .DQUOT => return error.DiskQuota,
+        .FAULT => unreachable,
+        .INVAL => unreachable,
+        .ISDIR => return error.IsDir,
+        .LOOP => return error.SymLinkLoop,
+        .MLINK => return error.LinkQuotaExceeded,
+        .NAMETOOLONG => return error.NameTooLong,
+        .NOENT => return error.FileNotFound,
+        .NOTDIR => return error.NotDir,
+        .NOMEM => return error.SystemResources,
+        .NOSPC => return error.NoSpaceLeft,
+        .EXIST => return error.PathAlreadyExists,
+        .NOTEMPTY => return error.PathAlreadyExists,
+        .ROFS => return error.ReadOnlyFileSystem,
+        .XDEV => return error.RenameAcrossMountPoints,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -2036,26 +2037,26 @@ pub fn renameat(
 /// See also `renameat`.
 pub fn renameatWasi(old_dir_fd: fd_t, old_path: []const u8, new_dir_fd: fd_t, new_path: []const u8) RenameError!void {
     switch (wasi.path_rename(old_dir_fd, old_path.ptr, old_path.len, new_dir_fd, new_path.ptr, new_path.len)) {
-        wasi.ESUCCESS => return,
-        wasi.EACCES => return error.AccessDenied,
-        wasi.EPERM => return error.AccessDenied,
-        wasi.EBUSY => return error.FileBusy,
-        wasi.EDQUOT => return error.DiskQuota,
-        wasi.EFAULT => unreachable,
-        wasi.EINVAL => unreachable,
-        wasi.EISDIR => return error.IsDir,
-        wasi.ELOOP => return error.SymLinkLoop,
-        wasi.EMLINK => return error.LinkQuotaExceeded,
-        wasi.ENAMETOOLONG => return error.NameTooLong,
-        wasi.ENOENT => return error.FileNotFound,
-        wasi.ENOTDIR => return error.NotDir,
-        wasi.ENOMEM => return error.SystemResources,
-        wasi.ENOSPC => return error.NoSpaceLeft,
-        wasi.EEXIST => return error.PathAlreadyExists,
-        wasi.ENOTEMPTY => return error.PathAlreadyExists,
-        wasi.EROFS => return error.ReadOnlyFileSystem,
-        wasi.EXDEV => return error.RenameAcrossMountPoints,
-        wasi.ENOTCAPABLE => return error.AccessDenied,
+        .SUCCESS => return,
+        .ACCES => return error.AccessDenied,
+        .PERM => return error.AccessDenied,
+        .BUSY => return error.FileBusy,
+        .DQUOT => return error.DiskQuota,
+        .FAULT => unreachable,
+        .INVAL => unreachable,
+        .ISDIR => return error.IsDir,
+        .LOOP => return error.SymLinkLoop,
+        .MLINK => return error.LinkQuotaExceeded,
+        .NAMETOOLONG => return error.NameTooLong,
+        .NOENT => return error.FileNotFound,
+        .NOTDIR => return error.NotDir,
+        .NOMEM => return error.SystemResources,
+        .NOSPC => return error.NoSpaceLeft,
+        .EXIST => return error.PathAlreadyExists,
+        .NOTEMPTY => return error.PathAlreadyExists,
+        .ROFS => return error.ReadOnlyFileSystem,
+        .XDEV => return error.RenameAcrossMountPoints,
+        .NOTCAPABLE => return error.AccessDenied,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -2074,25 +2075,25 @@ pub fn renameatZ(
     }
 
     switch (errno(system.renameat(old_dir_fd, old_path, new_dir_fd, new_path))) {
-        0 => return,
-        EACCES => return error.AccessDenied,
-        EPERM => return error.AccessDenied,
-        EBUSY => return error.FileBusy,
-        EDQUOT => return error.DiskQuota,
-        EFAULT => unreachable,
-        EINVAL => unreachable,
-        EISDIR => return error.IsDir,
-        ELOOP => return error.SymLinkLoop,
-        EMLINK => return error.LinkQuotaExceeded,
-        ENAMETOOLONG => return error.NameTooLong,
-        ENOENT => return error.FileNotFound,
-        ENOTDIR => return error.NotDir,
-        ENOMEM => return error.SystemResources,
-        ENOSPC => return error.NoSpaceLeft,
-        EEXIST => return error.PathAlreadyExists,
-        ENOTEMPTY => return error.PathAlreadyExists,
-        EROFS => return error.ReadOnlyFileSystem,
-        EXDEV => return error.RenameAcrossMountPoints,
+        .SUCCESS => return,
+        .ACCES => return error.AccessDenied,
+        .PERM => return error.AccessDenied,
+        .BUSY => return error.FileBusy,
+        .DQUOT => return error.DiskQuota,
+        .FAULT => unreachable,
+        .INVAL => unreachable,
+        .ISDIR => return error.IsDir,
+        .LOOP => return error.SymLinkLoop,
+        .MLINK => return error.LinkQuotaExceeded,
+        .NAMETOOLONG => return error.NameTooLong,
+        .NOENT => return error.FileNotFound,
+        .NOTDIR => return error.NotDir,
+        .NOMEM => return error.SystemResources,
+        .NOSPC => return error.NoSpaceLeft,
+        .EXIST => return error.PathAlreadyExists,
+        .NOTEMPTY => return error.PathAlreadyExists,
+        .ROFS => return error.ReadOnlyFileSystem,
+        .XDEV => return error.RenameAcrossMountPoints,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -2172,22 +2173,22 @@ pub const mkdiratC = @compileError("deprecated: renamed to mkdiratZ");
 pub fn mkdiratWasi(dir_fd: fd_t, sub_dir_path: []const u8, mode: u32) MakeDirError!void {
     _ = mode;
     switch (wasi.path_create_directory(dir_fd, sub_dir_path.ptr, sub_dir_path.len)) {
-        wasi.ESUCCESS => return,
-        wasi.EACCES => return error.AccessDenied,
-        wasi.EBADF => unreachable,
-        wasi.EPERM => return error.AccessDenied,
-        wasi.EDQUOT => return error.DiskQuota,
-        wasi.EEXIST => return error.PathAlreadyExists,
-        wasi.EFAULT => unreachable,
-        wasi.ELOOP => return error.SymLinkLoop,
-        wasi.EMLINK => return error.LinkQuotaExceeded,
-        wasi.ENAMETOOLONG => return error.NameTooLong,
-        wasi.ENOENT => return error.FileNotFound,
-        wasi.ENOMEM => return error.SystemResources,
-        wasi.ENOSPC => return error.NoSpaceLeft,
-        wasi.ENOTDIR => return error.NotDir,
-        wasi.EROFS => return error.ReadOnlyFileSystem,
-        wasi.ENOTCAPABLE => return error.AccessDenied,
+        .SUCCESS => return,
+        .ACCES => return error.AccessDenied,
+        .BADF => unreachable,
+        .PERM => return error.AccessDenied,
+        .DQUOT => return error.DiskQuota,
+        .EXIST => return error.PathAlreadyExists,
+        .FAULT => unreachable,
+        .LOOP => return error.SymLinkLoop,
+        .MLINK => return error.LinkQuotaExceeded,
+        .NAMETOOLONG => return error.NameTooLong,
+        .NOENT => return error.FileNotFound,
+        .NOMEM => return error.SystemResources,
+        .NOSPC => return error.NoSpaceLeft,
+        .NOTDIR => return error.NotDir,
+        .ROFS => return error.ReadOnlyFileSystem,
+        .NOTCAPABLE => return error.AccessDenied,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -2198,21 +2199,21 @@ pub fn mkdiratZ(dir_fd: fd_t, sub_dir_path: [*:0]const u8, mode: u32) MakeDirErr
         return mkdiratW(dir_fd, sub_dir_path_w.span().ptr, mode);
     }
     switch (errno(system.mkdirat(dir_fd, sub_dir_path, mode))) {
-        0 => return,
-        EACCES => return error.AccessDenied,
-        EBADF => unreachable,
-        EPERM => return error.AccessDenied,
-        EDQUOT => return error.DiskQuota,
-        EEXIST => return error.PathAlreadyExists,
-        EFAULT => unreachable,
-        ELOOP => return error.SymLinkLoop,
-        EMLINK => return error.LinkQuotaExceeded,
-        ENAMETOOLONG => return error.NameTooLong,
-        ENOENT => return error.FileNotFound,
-        ENOMEM => return error.SystemResources,
-        ENOSPC => return error.NoSpaceLeft,
-        ENOTDIR => return error.NotDir,
-        EROFS => return error.ReadOnlyFileSystem,
+        .SUCCESS => return,
+        .ACCES => return error.AccessDenied,
+        .BADF => unreachable,
+        .PERM => return error.AccessDenied,
+        .DQUOT => return error.DiskQuota,
+        .EXIST => return error.PathAlreadyExists,
+        .FAULT => unreachable,
+        .LOOP => return error.SymLinkLoop,
+        .MLINK => return error.LinkQuotaExceeded,
+        .NAMETOOLONG => return error.NameTooLong,
+        .NOENT => return error.FileNotFound,
+        .NOMEM => return error.SystemResources,
+        .NOSPC => return error.NoSpaceLeft,
+        .NOTDIR => return error.NotDir,
+        .ROFS => return error.ReadOnlyFileSystem,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -2274,20 +2275,20 @@ pub fn mkdirZ(dir_path: [*:0]const u8, mode: u32) MakeDirError!void {
         return mkdirW(dir_path_w.span(), mode);
     }
     switch (errno(system.mkdir(dir_path, mode))) {
-        0 => return,
-        EACCES => return error.AccessDenied,
-        EPERM => return error.AccessDenied,
-        EDQUOT => return error.DiskQuota,
-        EEXIST => return error.PathAlreadyExists,
-        EFAULT => unreachable,
-        ELOOP => return error.SymLinkLoop,
-        EMLINK => return error.LinkQuotaExceeded,
-        ENAMETOOLONG => return error.NameTooLong,
-        ENOENT => return error.FileNotFound,
-        ENOMEM => return error.SystemResources,
-        ENOSPC => return error.NoSpaceLeft,
-        ENOTDIR => return error.NotDir,
-        EROFS => return error.ReadOnlyFileSystem,
+        .SUCCESS => return,
+        .ACCES => return error.AccessDenied,
+        .PERM => return error.AccessDenied,
+        .DQUOT => return error.DiskQuota,
+        .EXIST => return error.PathAlreadyExists,
+        .FAULT => unreachable,
+        .LOOP => return error.SymLinkLoop,
+        .MLINK => return error.LinkQuotaExceeded,
+        .NAMETOOLONG => return error.NameTooLong,
+        .NOENT => return error.FileNotFound,
+        .NOMEM => return error.SystemResources,
+        .NOSPC => return error.NoSpaceLeft,
+        .NOTDIR => return error.NotDir,
+        .ROFS => return error.ReadOnlyFileSystem,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -2346,20 +2347,20 @@ pub fn rmdirZ(dir_path: [*:0]const u8) DeleteDirError!void {
         return rmdirW(dir_path_w.span());
     }
     switch (errno(system.rmdir(dir_path))) {
-        0 => return,
-        EACCES => return error.AccessDenied,
-        EPERM => return error.AccessDenied,
-        EBUSY => return error.FileBusy,
-        EFAULT => unreachable,
-        EINVAL => unreachable,
-        ELOOP => return error.SymLinkLoop,
-        ENAMETOOLONG => return error.NameTooLong,
-        ENOENT => return error.FileNotFound,
-        ENOMEM => return error.SystemResources,
-        ENOTDIR => return error.NotDir,
-        EEXIST => return error.DirNotEmpty,
-        ENOTEMPTY => return error.DirNotEmpty,
-        EROFS => return error.ReadOnlyFileSystem,
+        .SUCCESS => return,
+        .ACCES => return error.AccessDenied,
+        .PERM => return error.AccessDenied,
+        .BUSY => return error.FileBusy,
+        .FAULT => unreachable,
+        .INVAL => unreachable,
+        .LOOP => return error.SymLinkLoop,
+        .NAMETOOLONG => return error.NameTooLong,
+        .NOENT => return error.FileNotFound,
+        .NOMEM => return error.SystemResources,
+        .NOTDIR => return error.NotDir,
+        .EXIST => return error.DirNotEmpty,
+        .NOTEMPTY => return error.DirNotEmpty,
+        .ROFS => return error.ReadOnlyFileSystem,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -2413,15 +2414,15 @@ pub fn chdirZ(dir_path: [*:0]const u8) ChangeCurDirError!void {
         return chdirW(utf16_dir_path[0..len]);
     }
     switch (errno(system.chdir(dir_path))) {
-        0 => return,
-        EACCES => return error.AccessDenied,
-        EFAULT => unreachable,
-        EIO => return error.FileSystem,
-        ELOOP => return error.SymLinkLoop,
-        ENAMETOOLONG => return error.NameTooLong,
-        ENOENT => return error.FileNotFound,
-        ENOMEM => return error.SystemResources,
-        ENOTDIR => return error.NotDir,
+        .SUCCESS => return,
+        .ACCES => return error.AccessDenied,
+        .FAULT => unreachable,
+        .IO => return error.FileSystem,
+        .LOOP => return error.SymLinkLoop,
+        .NAMETOOLONG => return error.NameTooLong,
+        .NOENT => return error.FileNotFound,
+        .NOMEM => return error.SystemResources,
+        .NOTDIR => return error.NotDir,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -2443,12 +2444,12 @@ pub const FchdirError = error{
 pub fn fchdir(dirfd: fd_t) FchdirError!void {
     while (true) {
         switch (errno(system.fchdir(dirfd))) {
-            0 => return,
-            EACCES => return error.AccessDenied,
-            EBADF => unreachable,
-            ENOTDIR => return error.NotDir,
-            EINTR => continue,
-            EIO => return error.FileSystem,
+            .SUCCESS => return,
+            .ACCES => return error.AccessDenied,
+            .BADF => unreachable,
+            .NOTDIR => return error.NotDir,
+            .INTR => continue,
+            .IO => return error.FileSystem,
             else => |err| return unexpectedErrno(err),
         }
     }
@@ -2501,16 +2502,16 @@ pub fn readlinkZ(file_path: [*:0]const u8, out_buffer: []u8) ReadLinkError![]u8
     }
     const rc = system.readlink(file_path, out_buffer.ptr, out_buffer.len);
     switch (errno(rc)) {
-        0 => return out_buffer[0..@bitCast(usize, rc)],
-        EACCES => return error.AccessDenied,
-        EFAULT => unreachable,
-        EINVAL => unreachable,
-        EIO => return error.FileSystem,
-        ELOOP => return error.SymLinkLoop,
-        ENAMETOOLONG => return error.NameTooLong,
-        ENOENT => return error.FileNotFound,
-        ENOMEM => return error.SystemResources,
-        ENOTDIR => return error.NotDir,
+        .SUCCESS => return out_buffer[0..@bitCast(usize, rc)],
+        .ACCES => return error.AccessDenied,
+        .FAULT => unreachable,
+        .INVAL => unreachable,
+        .IO => return error.FileSystem,
+        .LOOP => return error.SymLinkLoop,
+        .NAMETOOLONG => return error.NameTooLong,
+        .NOENT => return error.FileNotFound,
+        .NOMEM => return error.SystemResources,
+        .NOTDIR => return error.NotDir,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -2537,17 +2538,17 @@ pub const readlinkatC = @compileError("deprecated: renamed to readlinkatZ");
 pub fn readlinkatWasi(dirfd: fd_t, file_path: []const u8, out_buffer: []u8) ReadLinkError![]u8 {
     var bufused: usize = undefined;
     switch (wasi.path_readlink(dirfd, file_path.ptr, file_path.len, out_buffer.ptr, out_buffer.len, &bufused)) {
-        wasi.ESUCCESS => return out_buffer[0..bufused],
-        wasi.EACCES => return error.AccessDenied,
-        wasi.EFAULT => unreachable,
-        wasi.EINVAL => unreachable,
-        wasi.EIO => return error.FileSystem,
-        wasi.ELOOP => return error.SymLinkLoop,
-        wasi.ENAMETOOLONG => return error.NameTooLong,
-        wasi.ENOENT => return error.FileNotFound,
-        wasi.ENOMEM => return error.SystemResources,
-        wasi.ENOTDIR => return error.NotDir,
-        wasi.ENOTCAPABLE => return error.AccessDenied,
+        .SUCCESS => return out_buffer[0..bufused],
+        .ACCES => return error.AccessDenied,
+        .FAULT => unreachable,
+        .INVAL => unreachable,
+        .IO => return error.FileSystem,
+        .LOOP => return error.SymLinkLoop,
+        .NAMETOOLONG => return error.NameTooLong,
+        .NOENT => return error.FileNotFound,
+        .NOMEM => return error.SystemResources,
+        .NOTDIR => return error.NotDir,
+        .NOTCAPABLE => return error.AccessDenied,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -2567,16 +2568,16 @@ pub fn readlinkatZ(dirfd: fd_t, file_path: [*:0]const u8, out_buffer: []u8) Read
     }
     const rc = system.readlinkat(dirfd, file_path, out_buffer.ptr, out_buffer.len);
     switch (errno(rc)) {
-        0 => return out_buffer[0..@bitCast(usize, rc)],
-        EACCES => return error.AccessDenied,
-        EFAULT => unreachable,
-        EINVAL => unreachable,
-        EIO => return error.FileSystem,
-        ELOOP => return error.SymLinkLoop,
-        ENAMETOOLONG => return error.NameTooLong,
-        ENOENT => return error.FileNotFound,
-        ENOMEM => return error.SystemResources,
-        ENOTDIR => return error.NotDir,
+        .SUCCESS => return out_buffer[0..@bitCast(usize, rc)],
+        .ACCES => return error.AccessDenied,
+        .FAULT => unreachable,
+        .INVAL => unreachable,
+        .IO => return error.FileSystem,
+        .LOOP => return error.SymLinkLoop,
+        .NAMETOOLONG => return error.NameTooLong,
+        .NOENT => return error.FileNotFound,
+        .NOMEM => return error.SystemResources,
+        .NOTDIR => return error.NotDir,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -2590,58 +2591,58 @@ pub const SetIdError = error{ResourceLimitReached} || SetEidError;
 
 pub fn setuid(uid: uid_t) SetIdError!void {
     switch (errno(system.setuid(uid))) {
-        0 => return,
-        EAGAIN => return error.ResourceLimitReached,
-        EINVAL => return error.InvalidUserId,
-        EPERM => return error.PermissionDenied,
+        .SUCCESS => return,
+        .AGAIN => return error.ResourceLimitReached,
+        .INVAL => return error.InvalidUserId,
+        .PERM => return error.PermissionDenied,
         else => |err| return unexpectedErrno(err),
     }
 }
 
 pub fn seteuid(uid: uid_t) SetEidError!void {
     switch (errno(system.seteuid(uid))) {
-        0 => return,
-        EINVAL => return error.InvalidUserId,
-        EPERM => return error.PermissionDenied,
+        .SUCCESS => return,
+        .INVAL => return error.InvalidUserId,
+        .PERM => return error.PermissionDenied,
         else => |err| return unexpectedErrno(err),
     }
 }
 
 pub fn setreuid(ruid: uid_t, euid: uid_t) SetIdError!void {
     switch (errno(system.setreuid(ruid, euid))) {
-        0 => return,
-        EAGAIN => return error.ResourceLimitReached,
-        EINVAL => return error.InvalidUserId,
-        EPERM => return error.PermissionDenied,
+        .SUCCESS => return,
+        .AGAIN => return error.ResourceLimitReached,
+        .INVAL => return error.InvalidUserId,
+        .PERM => return error.PermissionDenied,
         else => |err| return unexpectedErrno(err),
     }
 }
 
 pub fn setgid(gid: gid_t) SetIdError!void {
     switch (errno(system.setgid(gid))) {
-        0 => return,
-        EAGAIN => return error.ResourceLimitReached,
-        EINVAL => return error.InvalidUserId,
-        EPERM => return error.PermissionDenied,
+        .SUCCESS => return,
+        .AGAIN => return error.ResourceLimitReached,
+        .INVAL => return error.InvalidUserId,
+        .PERM => return error.PermissionDenied,
         else => |err| return unexpectedErrno(err),
     }
 }
 
 pub fn setegid(uid: uid_t) SetEidError!void {
     switch (errno(system.setegid(uid))) {
-        0 => return,
-        EINVAL => return error.InvalidUserId,
-        EPERM => return error.PermissionDenied,
+        .SUCCESS => return,
+        .INVAL => return error.InvalidUserId,
+        .PERM => return error.PermissionDenied,
         else => |err| return unexpectedErrno(err),
     }
 }
 
 pub fn setregid(rgid: gid_t, egid: gid_t) SetIdError!void {
     switch (errno(system.setregid(rgid, egid))) {
-        0 => return,
-        EAGAIN => return error.ResourceLimitReached,
-        EINVAL => return error.InvalidUserId,
-        EPERM => return error.PermissionDenied,
+        .SUCCESS => return,
+        .AGAIN => return error.ResourceLimitReached,
+        .INVAL => return error.InvalidUserId,
+        .PERM => return error.PermissionDenied,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -2680,9 +2681,10 @@ pub fn isatty(handle: fd_t) bool {
         while (true) {
             var wsz: linux.winsize = undefined;
             const fd = @bitCast(usize, @as(isize, handle));
-            switch (linux.syscall3(.ioctl, fd, linux.TIOCGWINSZ, @ptrToInt(&wsz))) {
-                0 => return true,
-                EINTR => continue,
+            const rc = linux.syscall3(.ioctl, fd, linux.TIOCGWINSZ, @ptrToInt(&wsz));
+            switch (linux.getErrno(rc)) {
+                .SUCCESS => return true,
+                .INTR => continue,
                 else => return false,
             }
         }
@@ -2777,22 +2779,22 @@ pub fn socket(domain: u32, socket_type: u32, protocol: u32) SocketError!socket_t
         socket_type;
     const rc = system.socket(domain, filtered_sock_type, protocol);
     switch (errno(rc)) {
-        0 => {
+        .SUCCESS => {
             const fd = @intCast(fd_t, rc);
             if (!have_sock_flags) {
                 try setSockFlags(fd, socket_type);
             }
             return fd;
         },
-        EACCES => return error.PermissionDenied,
-        EAFNOSUPPORT => return error.AddressFamilyNotSupported,
-        EINVAL => return error.ProtocolFamilyNotAvailable,
-        EMFILE => return error.ProcessFdQuotaExceeded,
-        ENFILE => return error.SystemFdQuotaExceeded,
-        ENOBUFS => return error.SystemResources,
-        ENOMEM => return error.SystemResources,
-        EPROTONOSUPPORT => return error.ProtocolNotSupported,
-        EPROTOTYPE => return error.SocketTypeNotSupported,
+        .ACCES => return error.PermissionDenied,
+        .AFNOSUPPORT => return error.AddressFamilyNotSupported,
+        .INVAL => return error.ProtocolFamilyNotAvailable,
+        .MFILE => return error.ProcessFdQuotaExceeded,
+        .NFILE => return error.SystemFdQuotaExceeded,
+        .NOBUFS => return error.SystemResources,
+        .NOMEM => return error.SystemResources,
+        .PROTONOSUPPORT => return error.ProtocolNotSupported,
+        .PROTOTYPE => return error.SocketTypeNotSupported,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -2840,12 +2842,12 @@ pub fn shutdown(sock: socket_t, how: ShutdownHow) ShutdownError!void {
             .both => SHUT_RDWR,
         });
         switch (errno(rc)) {
-            0 => return,
-            EBADF => unreachable,
-            EINVAL => unreachable,
-            ENOTCONN => return error.SocketNotConnected,
-            ENOTSOCK => unreachable,
-            ENOBUFS => return error.SystemResources,
+            .SUCCESS => return,
+            .BADF => unreachable,
+            .INVAL => unreachable,
+            .NOTCONN => return error.SocketNotConnected,
+            .NOTSOCK => unreachable,
+            .NOBUFS => return error.SystemResources,
             else => |err| return unexpectedErrno(err),
         }
     }
@@ -2924,20 +2926,20 @@ pub fn bind(sock: socket_t, addr: *const sockaddr, len: socklen_t) BindError!voi
     } else {
         const rc = system.bind(sock, addr, len);
         switch (errno(rc)) {
-            0 => return,
-            EACCES => return error.AccessDenied,
-            EADDRINUSE => return error.AddressInUse,
-            EBADF => unreachable, // always a race condition if this error is returned
-            EINVAL => unreachable, // invalid parameters
-            ENOTSOCK => unreachable, // invalid `sockfd`
-            EADDRNOTAVAIL => return error.AddressNotAvailable,
-            EFAULT => unreachable, // invalid `addr` pointer
-            ELOOP => return error.SymLinkLoop,
-            ENAMETOOLONG => return error.NameTooLong,
-            ENOENT => return error.FileNotFound,
-            ENOMEM => return error.SystemResources,
-            ENOTDIR => return error.NotDir,
-            EROFS => return error.ReadOnlyFileSystem,
+            .SUCCESS => return,
+            .ACCES => return error.AccessDenied,
+            .ADDRINUSE => return error.AddressInUse,
+            .BADF => unreachable, // always a race condition if this error is returned
+            .INVAL => unreachable, // invalid parameters
+            .NOTSOCK => unreachable, // invalid `sockfd`
+            .ADDRNOTAVAIL => return error.AddressNotAvailable,
+            .FAULT => unreachable, // invalid `addr` pointer
+            .LOOP => return error.SymLinkLoop,
+            .NAMETOOLONG => return error.NameTooLong,
+            .NOENT => return error.FileNotFound,
+            .NOMEM => return error.SystemResources,
+            .NOTDIR => return error.NotDir,
+            .ROFS => return error.ReadOnlyFileSystem,
             else => |err| return unexpectedErrno(err),
         }
     }
@@ -2993,11 +2995,11 @@ pub fn listen(sock: socket_t, backlog: u31) ListenError!void {
     } else {
         const rc = system.listen(sock, backlog);
         switch (errno(rc)) {
-            0 => return,
-            EADDRINUSE => return error.AddressInUse,
-            EBADF => unreachable,
-            ENOTSOCK => return error.FileDescriptorNotASocket,
-            EOPNOTSUPP => return error.OperationNotSupported,
+            .SUCCESS => return,
+            .ADDRINUSE => return error.AddressInUse,
+            .BADF => unreachable,
+            .NOTSOCK => return error.FileDescriptorNotASocket,
+            .OPNOTSUPP => return error.OperationNotSupported,
             else => |err| return unexpectedErrno(err),
         }
     }
@@ -3099,23 +3101,23 @@ pub fn accept(
             }
         } else {
             switch (errno(rc)) {
-                0 => {
+                .SUCCESS => {
                     break @intCast(socket_t, rc);
                 },
-                EINTR => continue,
-                EAGAIN => return error.WouldBlock,
-                EBADF => unreachable, // always a race condition
-                ECONNABORTED => return error.ConnectionAborted,
-                EFAULT => unreachable,
-                EINVAL => return error.SocketNotListening,
-                ENOTSOCK => unreachable,
-                EMFILE => return error.ProcessFdQuotaExceeded,
-                ENFILE => return error.SystemFdQuotaExceeded,
-                ENOBUFS => return error.SystemResources,
-                ENOMEM => return error.SystemResources,
-                EOPNOTSUPP => unreachable,
-                EPROTO => return error.ProtocolFailure,
-                EPERM => return error.BlockedByFirewall,
+                .INTR => continue,
+                .AGAIN => return error.WouldBlock,
+                .BADF => unreachable, // always a race condition
+                .CONNABORTED => return error.ConnectionAborted,
+                .FAULT => unreachable,
+                .INVAL => return error.SocketNotListening,
+                .NOTSOCK => unreachable,
+                .MFILE => return error.ProcessFdQuotaExceeded,
+                .NFILE => return error.SystemFdQuotaExceeded,
+                .NOBUFS => return error.SystemResources,
+                .NOMEM => return error.SystemResources,
+                .OPNOTSUPP => unreachable,
+                .PROTO => return error.ProtocolFailure,
+                .PERM => return error.BlockedByFirewall,
                 else => |err| return unexpectedErrno(err),
             }
         }
@@ -3144,13 +3146,13 @@ pub const EpollCreateError = error{
 pub fn epoll_create1(flags: u32) EpollCreateError!i32 {
     const rc = system.epoll_create1(flags);
     switch (errno(rc)) {
-        0 => return @intCast(i32, rc),
+        .SUCCESS => return @intCast(i32, rc),
         else => |err| return unexpectedErrno(err),
 
-        EINVAL => unreachable,
-        EMFILE => return error.ProcessFdQuotaExceeded,
-        ENFILE => return error.SystemFdQuotaExceeded,
-        ENOMEM => return error.SystemResources,
+        .INVAL => unreachable,
+        .MFILE => return error.ProcessFdQuotaExceeded,
+        .NFILE => return error.SystemFdQuotaExceeded,
+        .NOMEM => return error.SystemResources,
     }
 }
 
@@ -3183,17 +3185,17 @@ pub const EpollCtlError = error{
 pub fn epoll_ctl(epfd: i32, op: u32, fd: i32, event: ?*epoll_event) EpollCtlError!void {
     const rc = system.epoll_ctl(epfd, op, fd, event);
     switch (errno(rc)) {
-        0 => return,
+        .SUCCESS => return,
         else => |err| return unexpectedErrno(err),
 
-        EBADF => unreachable, // always a race condition if this happens
-        EEXIST => return error.FileDescriptorAlreadyPresentInSet,
-        EINVAL => unreachable,
-        ELOOP => return error.OperationCausesCircularLoop,
-        ENOENT => return error.FileDescriptorNotRegistered,
-        ENOMEM => return error.SystemResources,
-        ENOSPC => return error.UserResourceLimitReached,
-        EPERM => return error.FileDescriptorIncompatibleWithEpoll,
+        .BADF => unreachable, // always a race condition if this happens
+        .EXIST => return error.FileDescriptorAlreadyPresentInSet,
+        .INVAL => unreachable,
+        .LOOP => return error.OperationCausesCircularLoop,
+        .NOENT => return error.FileDescriptorNotRegistered,
+        .NOMEM => return error.SystemResources,
+        .NOSPC => return error.UserResourceLimitReached,
+        .PERM => return error.FileDescriptorIncompatibleWithEpoll,
     }
 }
 
@@ -3205,11 +3207,11 @@ pub fn epoll_wait(epfd: i32, events: []epoll_event, timeout: i32) usize {
         // TODO get rid of the @intCast
         const rc = system.epoll_wait(epfd, events.ptr, @intCast(u32, events.len), timeout);
         switch (errno(rc)) {
-            0 => return @intCast(usize, rc),
-            EINTR => continue,
-            EBADF => unreachable,
-            EFAULT => unreachable,
-            EINVAL => unreachable,
+            .SUCCESS => return @intCast(usize, rc),
+            .INTR => continue,
+            .BADF => unreachable,
+            .FAULT => unreachable,
+            .INVAL => unreachable,
             else => unreachable,
         }
     }
@@ -3224,14 +3226,14 @@ pub const EventFdError = error{
 pub fn eventfd(initval: u32, flags: u32) EventFdError!i32 {
     const rc = system.eventfd(initval, flags);
     switch (errno(rc)) {
-        0 => return @intCast(i32, rc),
+        .SUCCESS => return @intCast(i32, rc),
         else => |err| return unexpectedErrno(err),
 
-        EINVAL => unreachable, // invalid parameters
-        EMFILE => return error.ProcessFdQuotaExceeded,
-        ENFILE => return error.SystemFdQuotaExceeded,
-        ENODEV => return error.SystemResources,
-        ENOMEM => return error.SystemResources,
+        .INVAL => unreachable, // invalid parameters
+        .MFILE => return error.ProcessFdQuotaExceeded,
+        .NFILE => return error.SystemFdQuotaExceeded,
+        .NODEV => return error.SystemResources,
+        .NOMEM => return error.SystemResources,
     }
 }
 
@@ -3265,14 +3267,14 @@ pub fn getsockname(sock: socket_t, addr: *sockaddr, addrlen: *socklen_t) GetSock
     } else {
         const rc = system.getsockname(sock, addr, addrlen);
         switch (errno(rc)) {
-            0 => return,
+            .SUCCESS => return,
             else => |err| return unexpectedErrno(err),
 
-            EBADF => unreachable, // always a race condition
-            EFAULT => unreachable,
-            EINVAL => unreachable, // invalid parameters
-            ENOTSOCK => return error.FileDescriptorNotASocket,
-            ENOBUFS => return error.SystemResources,
+            .BADF => unreachable, // always a race condition
+            .FAULT => unreachable,
+            .INVAL => unreachable, // invalid parameters
+            .NOTSOCK => return error.FileDescriptorNotASocket,
+            .NOBUFS => return error.SystemResources,
         }
     }
 }
@@ -3294,14 +3296,14 @@ pub fn getpeername(sock: socket_t, addr: *sockaddr, addrlen: *socklen_t) GetSock
     } else {
         const rc = system.getpeername(sock, addr, addrlen);
         switch (errno(rc)) {
-            0 => return,
+            .SUCCESS => return,
             else => |err| return unexpectedErrno(err),
 
-            EBADF => unreachable, // always a race condition
-            EFAULT => unreachable,
-            EINVAL => unreachable, // invalid parameters
-            ENOTSOCK => return error.FileDescriptorNotASocket,
-            ENOBUFS => return error.SystemResources,
+            .BADF => unreachable, // always a race condition
+            .FAULT => unreachable,
+            .INVAL => unreachable, // invalid parameters
+            .NOTSOCK => return error.FileDescriptorNotASocket,
+            .NOBUFS => return error.SystemResources,
         }
     }
 }
@@ -3384,61 +3386,61 @@ pub fn connect(sock: socket_t, sock_addr: *const sockaddr, len: socklen_t) Conne
 
     while (true) {
         switch (errno(system.connect(sock, sock_addr, len))) {
-            0 => return,
-            EACCES => return error.PermissionDenied,
-            EPERM => return error.PermissionDenied,
-            EADDRINUSE => return error.AddressInUse,
-            EADDRNOTAVAIL => return error.AddressNotAvailable,
-            EAFNOSUPPORT => return error.AddressFamilyNotSupported,
-            EAGAIN, EINPROGRESS => return error.WouldBlock,
-            EALREADY => return error.ConnectionPending,
-            EBADF => unreachable, // sockfd is not a valid open file descriptor.
-            ECONNREFUSED => return error.ConnectionRefused,
-            ECONNRESET => return error.ConnectionResetByPeer,
-            EFAULT => unreachable, // The socket structure address is outside the user's address space.
-            EINTR => continue,
-            EISCONN => unreachable, // The socket is already connected.
-            ENETUNREACH => return error.NetworkUnreachable,
-            ENOTSOCK => unreachable, // The file descriptor sockfd does not refer to a socket.
-            EPROTOTYPE => unreachable, // The socket type does not support the requested communications protocol.
-            ETIMEDOUT => return error.ConnectionTimedOut,
-            ENOENT => return error.FileNotFound, // Returned when socket is AF_UNIX and the given path does not exist.
+            .SUCCESS => return,
+            .ACCES => return error.PermissionDenied,
+            .PERM => return error.PermissionDenied,
+            .ADDRINUSE => return error.AddressInUse,
+            .ADDRNOTAVAIL => return error.AddressNotAvailable,
+            .AFNOSUPPORT => return error.AddressFamilyNotSupported,
+            .AGAIN, .INPROGRESS => return error.WouldBlock,
+            .ALREADY => return error.ConnectionPending,
+            .BADF => unreachable, // sockfd is not a valid open file descriptor.
+            .CONNREFUSED => return error.ConnectionRefused,
+            .CONNRESET => return error.ConnectionResetByPeer,
+            .FAULT => unreachable, // The socket structure address is outside the user's address space.
+            .INTR => continue,
+            .ISCONN => unreachable, // The socket is already connected.
+            .NETUNREACH => return error.NetworkUnreachable,
+            .NOTSOCK => unreachable, // The file descriptor sockfd does not refer to a socket.
+            .PROTOTYPE => unreachable, // The socket type does not support the requested communications protocol.
+            .TIMEDOUT => return error.ConnectionTimedOut,
+            .NOENT => return error.FileNotFound, // Returned when socket is AF_UNIX and the given path does not exist.
             else => |err| return unexpectedErrno(err),
         }
     }
 }
 
 pub fn getsockoptError(sockfd: fd_t) ConnectError!void {
-    var err_code: u32 = undefined;
+    var err_code: i32 = undefined;
     var size: u32 = @sizeOf(u32);
     const rc = system.getsockopt(sockfd, SOL_SOCKET, SO_ERROR, @ptrCast([*]u8, &err_code), &size);
     assert(size == 4);
     switch (errno(rc)) {
-        0 => switch (err_code) {
-            0 => return,
-            EACCES => return error.PermissionDenied,
-            EPERM => return error.PermissionDenied,
-            EADDRINUSE => return error.AddressInUse,
-            EADDRNOTAVAIL => return error.AddressNotAvailable,
-            EAFNOSUPPORT => return error.AddressFamilyNotSupported,
-            EAGAIN => return error.SystemResources,
-            EALREADY => return error.ConnectionPending,
-            EBADF => unreachable, // sockfd is not a valid open file descriptor.
-            ECONNREFUSED => return error.ConnectionRefused,
-            EFAULT => unreachable, // The socket structure address is outside the user's address space.
-            EISCONN => unreachable, // The socket is already connected.
-            ENETUNREACH => return error.NetworkUnreachable,
-            ENOTSOCK => unreachable, // The file descriptor sockfd does not refer to a socket.
-            EPROTOTYPE => unreachable, // The socket type does not support the requested communications protocol.
-            ETIMEDOUT => return error.ConnectionTimedOut,
-            ECONNRESET => return error.ConnectionResetByPeer,
+        .SUCCESS => switch (@intToEnum(E, err_code)) {
+            .SUCCESS => return,
+            .ACCES => return error.PermissionDenied,
+            .PERM => return error.PermissionDenied,
+            .ADDRINUSE => return error.AddressInUse,
+            .ADDRNOTAVAIL => return error.AddressNotAvailable,
+            .AFNOSUPPORT => return error.AddressFamilyNotSupported,
+            .AGAIN => return error.SystemResources,
+            .ALREADY => return error.ConnectionPending,
+            .BADF => unreachable, // sockfd is not a valid open file descriptor.
+            .CONNREFUSED => return error.ConnectionRefused,
+            .FAULT => unreachable, // The socket structure address is outside the user's address space.
+            .ISCONN => unreachable, // The socket is already connected.
+            .NETUNREACH => return error.NetworkUnreachable,
+            .NOTSOCK => unreachable, // The file descriptor sockfd does not refer to a socket.
+            .PROTOTYPE => unreachable, // The socket type does not support the requested communications protocol.
+            .TIMEDOUT => return error.ConnectionTimedOut,
+            .CONNRESET => return error.ConnectionResetByPeer,
             else => |err| return unexpectedErrno(err),
         },
-        EBADF => unreachable, // The argument sockfd is not a valid file descriptor.
-        EFAULT => unreachable, // The address pointed to by optval or optlen is not in a valid part of the process address space.
-        EINVAL => unreachable,
-        ENOPROTOOPT => unreachable, // The option is unknown at the level indicated.
-        ENOTSOCK => unreachable, // The file descriptor sockfd does not refer to a socket.
+        .BADF => unreachable, // The argument sockfd is not a valid file descriptor.
+        .FAULT => unreachable, // The address pointed to by optval or optlen is not in a valid part of the process address space.
+        .INVAL => unreachable,
+        .NOPROTOOPT => unreachable, // The option is unknown at the level indicated.
+        .NOTSOCK => unreachable, // The file descriptor sockfd does not refer to a socket.
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -3454,13 +3456,13 @@ pub fn waitpid(pid: pid_t, flags: u32) WaitPidResult {
     while (true) {
         const rc = system.waitpid(pid, &status, if (builtin.link_libc) @intCast(c_int, flags) else flags);
         switch (errno(rc)) {
-            0 => return .{
+            .SUCCESS => return .{
                 .pid = @intCast(pid_t, rc),
                 .status = @bitCast(u32, status),
             },
-            EINTR => continue,
-            ECHILD => unreachable, // The process specified does not exist. It would be a race condition to handle this error.
-            EINVAL => unreachable, // Invalid flags.
+            .INTR => continue,
+            .CHILD => unreachable, // The process specified does not exist. It would be a race condition to handle this error.
+            .INVAL => unreachable, // Invalid flags.
             else => unreachable,
         }
     }
@@ -3484,12 +3486,12 @@ pub fn fstat(fd: fd_t) FStatError!Stat {
     if (builtin.os.tag == .wasi and !builtin.link_libc) {
         var stat: wasi.filestat_t = undefined;
         switch (wasi.fd_filestat_get(fd, &stat)) {
-            wasi.ESUCCESS => return Stat.fromFilestat(stat),
-            wasi.EINVAL => unreachable,
-            wasi.EBADF => unreachable, // Always a race condition.
-            wasi.ENOMEM => return error.SystemResources,
-            wasi.EACCES => return error.AccessDenied,
-            wasi.ENOTCAPABLE => return error.AccessDenied,
+            .SUCCESS => return Stat.fromFilestat(stat),
+            .INVAL => unreachable,
+            .BADF => unreachable, // Always a race condition.
+            .NOMEM => return error.SystemResources,
+            .ACCES => return error.AccessDenied,
+            .NOTCAPABLE => return error.AccessDenied,
             else => |err| return unexpectedErrno(err),
         }
     }
@@ -3504,11 +3506,11 @@ pub fn fstat(fd: fd_t) FStatError!Stat {
 
     var stat = mem.zeroes(Stat);
     switch (errno(fstat_sym(fd, &stat))) {
-        0 => return stat,
-        EINVAL => unreachable,
-        EBADF => unreachable, // Always a race condition.
-        ENOMEM => return error.SystemResources,
-        EACCES => return error.AccessDenied,
+        .SUCCESS => return stat,
+        .INVAL => unreachable,
+        .BADF => unreachable, // Always a race condition.
+        .NOMEM => return error.SystemResources,
+        .ACCES => return error.AccessDenied,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -3536,16 +3538,16 @@ pub const fstatatC = @compileError("deprecated: renamed to fstatatZ");
 pub fn fstatatWasi(dirfd: fd_t, pathname: []const u8, flags: u32) FStatAtError!Stat {
     var stat: wasi.filestat_t = undefined;
     switch (wasi.path_filestat_get(dirfd, flags, pathname.ptr, pathname.len, &stat)) {
-        wasi.ESUCCESS => return Stat.fromFilestat(stat),
-        wasi.EINVAL => unreachable,
-        wasi.EBADF => unreachable, // Always a race condition.
-        wasi.ENOMEM => return error.SystemResources,
-        wasi.EACCES => return error.AccessDenied,
-        wasi.EFAULT => unreachable,
-        wasi.ENAMETOOLONG => return error.NameTooLong,
-        wasi.ENOENT => return error.FileNotFound,
-        wasi.ENOTDIR => return error.FileNotFound,
-        wasi.ENOTCAPABLE => return error.AccessDenied,
+        .SUCCESS => return Stat.fromFilestat(stat),
+        .INVAL => unreachable,
+        .BADF => unreachable, // Always a race condition.
+        .NOMEM => return error.SystemResources,
+        .ACCES => return error.AccessDenied,
+        .FAULT => unreachable,
+        .NAMETOOLONG => return error.NameTooLong,
+        .NOENT => return error.FileNotFound,
+        .NOTDIR => return error.FileNotFound,
+        .NOTCAPABLE => return error.AccessDenied,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -3560,17 +3562,17 @@ pub fn fstatatZ(dirfd: fd_t, pathname: [*:0]const u8, flags: u32) FStatAtError!S
 
     var stat = mem.zeroes(Stat);
     switch (errno(fstatat_sym(dirfd, pathname, &stat, flags))) {
-        0 => return stat,
-        EINVAL => unreachable,
-        EBADF => unreachable, // Always a race condition.
-        ENOMEM => return error.SystemResources,
-        EACCES => return error.AccessDenied,
-        EPERM => return error.AccessDenied,
-        EFAULT => unreachable,
-        ENAMETOOLONG => return error.NameTooLong,
-        ELOOP => return error.SymLinkLoop,
-        ENOENT => return error.FileNotFound,
-        ENOTDIR => return error.FileNotFound,
+        .SUCCESS => return stat,
+        .INVAL => unreachable,
+        .BADF => unreachable, // Always a race condition.
+        .NOMEM => return error.SystemResources,
+        .ACCES => return error.AccessDenied,
+        .PERM => return error.AccessDenied,
+        .FAULT => unreachable,
+        .NAMETOOLONG => return error.NameTooLong,
+        .LOOP => return error.SymLinkLoop,
+        .NOENT => return error.FileNotFound,
+        .NOTDIR => return error.FileNotFound,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -3586,9 +3588,9 @@ pub const KQueueError = error{
 pub fn kqueue() KQueueError!i32 {
     const rc = system.kqueue();
     switch (errno(rc)) {
-        0 => return @intCast(i32, rc),
-        EMFILE => return error.ProcessFdQuotaExceeded,
-        ENFILE => return error.SystemFdQuotaExceeded,
+        .SUCCESS => return @intCast(i32, rc),
+        .MFILE => return error.ProcessFdQuotaExceeded,
+        .NFILE => return error.SystemFdQuotaExceeded,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -3627,15 +3629,15 @@ pub fn kevent(
             timeout,
         );
         switch (errno(rc)) {
-            0 => return @intCast(usize, rc),
-            EACCES => return error.AccessDenied,
-            EFAULT => unreachable,
-            EBADF => unreachable, // Always a race condition.
-            EINTR => continue,
-            EINVAL => unreachable,
-            ENOENT => return error.EventNotFound,
-            ENOMEM => return error.SystemResources,
-            ESRCH => return error.ProcessNotFound,
+            .SUCCESS => return @intCast(usize, rc),
+            .ACCES => return error.AccessDenied,
+            .FAULT => unreachable,
+            .BADF => unreachable, // Always a race condition.
+            .INTR => continue,
+            .INVAL => unreachable,
+            .NOENT => return error.EventNotFound,
+            .NOMEM => return error.SystemResources,
+            .SRCH => return error.ProcessNotFound,
             else => unreachable,
         }
     }
@@ -3651,11 +3653,11 @@ pub const INotifyInitError = error{
 pub fn inotify_init1(flags: u32) INotifyInitError!i32 {
     const rc = system.inotify_init1(flags);
     switch (errno(rc)) {
-        0 => return @intCast(i32, rc),
-        EINVAL => unreachable,
-        EMFILE => return error.ProcessFdQuotaExceeded,
-        ENFILE => return error.SystemFdQuotaExceeded,
-        ENOMEM => return error.SystemResources,
+        .SUCCESS => return @intCast(i32, rc),
+        .INVAL => unreachable,
+        .MFILE => return error.ProcessFdQuotaExceeded,
+        .NFILE => return error.SystemFdQuotaExceeded,
+        .NOMEM => return error.SystemResources,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -3681,16 +3683,16 @@ pub const inotify_add_watchC = @compileError("deprecated: renamed to inotify_add
 pub fn inotify_add_watchZ(inotify_fd: i32, pathname: [*:0]const u8, mask: u32) INotifyAddWatchError!i32 {
     const rc = system.inotify_add_watch(inotify_fd, pathname, mask);
     switch (errno(rc)) {
-        0 => return @intCast(i32, rc),
-        EACCES => return error.AccessDenied,
-        EBADF => unreachable,
-        EFAULT => unreachable,
-        EINVAL => unreachable,
-        ENAMETOOLONG => return error.NameTooLong,
-        ENOENT => return error.FileNotFound,
-        ENOMEM => return error.SystemResources,
-        ENOSPC => return error.UserResourceLimitReached,
-        ENOTDIR => return error.NotDir,
+        .SUCCESS => return @intCast(i32, rc),
+        .ACCES => return error.AccessDenied,
+        .BADF => unreachable,
+        .FAULT => unreachable,
+        .INVAL => unreachable,
+        .NAMETOOLONG => return error.NameTooLong,
+        .NOENT => return error.FileNotFound,
+        .NOMEM => return error.SystemResources,
+        .NOSPC => return error.UserResourceLimitReached,
+        .NOTDIR => return error.NotDir,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -3698,9 +3700,9 @@ pub fn inotify_add_watchZ(inotify_fd: i32, pathname: [*:0]const u8, mask: u32) I
 /// remove an existing watch from an inotify instance
 pub fn inotify_rm_watch(inotify_fd: i32, wd: i32) void {
     switch (errno(system.inotify_rm_watch(inotify_fd, wd))) {
-        0 => return,
-        EBADF => unreachable,
-        EINVAL => unreachable,
+        .SUCCESS => return,
+        .BADF => unreachable,
+        .INVAL => unreachable,
         else => unreachable,
     }
 }
@@ -3723,10 +3725,10 @@ pub const MProtectError = error{
 pub fn mprotect(memory: []align(mem.page_size) u8, protection: u32) MProtectError!void {
     assert(mem.isAligned(memory.len, mem.page_size));
     switch (errno(system.mprotect(memory.ptr, memory.len, protection))) {
-        0 => return,
-        EINVAL => unreachable,
-        EACCES => return error.AccessDenied,
-        ENOMEM => return error.OutOfMemory,
+        .SUCCESS => return,
+        .INVAL => unreachable,
+        .ACCES => return error.AccessDenied,
+        .NOMEM => return error.OutOfMemory,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -3736,9 +3738,9 @@ pub const ForkError = error{SystemResources} || UnexpectedError;
 pub fn fork() ForkError!pid_t {
     const rc = system.fork();
     switch (errno(rc)) {
-        0 => return @intCast(pid_t, rc),
-        EAGAIN => return error.SystemResources,
-        ENOMEM => return error.SystemResources,
+        .SUCCESS => return @intCast(pid_t, rc),
+        .AGAIN => return error.SystemResources,
+        .NOMEM => return error.SystemResources,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -3782,22 +3784,23 @@ pub fn mmap(
     const rc = mmap_sym(ptr, length, prot, flags, fd, ioffset);
     const err = if (builtin.link_libc) blk: {
         if (rc != std.c.MAP_FAILED) return @ptrCast([*]align(mem.page_size) u8, @alignCast(mem.page_size, rc))[0..length];
-        break :blk system._errno().*;
+        break :blk @intToEnum(E, system._errno().*);
     } else blk: {
         const err = errno(rc);
-        if (err == 0) return @intToPtr([*]align(mem.page_size) u8, rc)[0..length];
+        if (err == .SUCCESS) return @intToPtr([*]align(mem.page_size) u8, rc)[0..length];
         break :blk err;
     };
     switch (err) {
-        ETXTBSY => return error.AccessDenied,
-        EACCES => return error.AccessDenied,
-        EPERM => return error.PermissionDenied,
-        EAGAIN => return error.LockedMemoryLimitExceeded,
-        EBADF => unreachable, // Always a race condition.
-        EOVERFLOW => unreachable, // The number of pages used for length + offset would overflow.
-        ENODEV => return error.MemoryMappingNotSupported,
-        EINVAL => unreachable, // Invalid parameters to mmap()
-        ENOMEM => return error.OutOfMemory,
+        .SUCCESS => unreachable,
+        .TXTBSY => return error.AccessDenied,
+        .ACCES => return error.AccessDenied,
+        .PERM => return error.PermissionDenied,
+        .AGAIN => return error.LockedMemoryLimitExceeded,
+        .BADF => unreachable, // Always a race condition.
+        .OVERFLOW => unreachable, // The number of pages used for length + offset would overflow.
+        .NODEV => return error.MemoryMappingNotSupported,
+        .INVAL => unreachable, // Invalid parameters to mmap()
+        .NOMEM => return error.OutOfMemory,
         else => return unexpectedErrno(err),
     }
 }
@@ -3810,9 +3813,9 @@ pub fn mmap(
 /// * The Windows function, VirtualFree, has this restriction.
 pub fn munmap(memory: []align(mem.page_size) const u8) void {
     switch (errno(system.munmap(memory.ptr, memory.len))) {
-        0 => return,
-        EINVAL => unreachable, // Invalid parameters.
-        ENOMEM => unreachable, // Attempted to unmap a region in the middle of an existing mapping.
+        .SUCCESS => return,
+        .INVAL => unreachable, // Invalid parameters.
+        .NOMEM => unreachable, // Attempted to unmap a region in the middle of an existing mapping.
         else => unreachable,
     }
 }
@@ -3854,18 +3857,18 @@ pub fn accessZ(path: [*:0]const u8, mode: u32) AccessError!void {
         return;
     }
     switch (errno(system.access(path, mode))) {
-        0 => return,
-        EACCES => return error.PermissionDenied,
-        EROFS => return error.ReadOnlyFileSystem,
-        ELOOP => return error.SymLinkLoop,
-        ETXTBSY => return error.FileBusy,
-        ENOTDIR => return error.FileNotFound,
-        ENOENT => return error.FileNotFound,
-        ENAMETOOLONG => return error.NameTooLong,
-        EINVAL => unreachable,
-        EFAULT => unreachable,
-        EIO => return error.InputOutput,
-        ENOMEM => return error.SystemResources,
+        .SUCCESS => return,
+        .ACCES => return error.PermissionDenied,
+        .ROFS => return error.ReadOnlyFileSystem,
+        .LOOP => return error.SymLinkLoop,
+        .TXTBSY => return error.FileBusy,
+        .NOTDIR => return error.FileNotFound,
+        .NOENT => return error.FileNotFound,
+        .NAMETOOLONG => return error.NameTooLong,
+        .INVAL => unreachable,
+        .FAULT => unreachable,
+        .IO => return error.InputOutput,
+        .NOMEM => return error.SystemResources,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -3905,18 +3908,18 @@ pub fn faccessatZ(dirfd: fd_t, path: [*:0]const u8, mode: u32, flags: u32) Acces
         return faccessatW(dirfd, path_w.span().ptr, mode, flags);
     }
     switch (errno(system.faccessat(dirfd, path, mode, flags))) {
-        0 => return,
-        EACCES => return error.PermissionDenied,
-        EROFS => return error.ReadOnlyFileSystem,
-        ELOOP => return error.SymLinkLoop,
-        ETXTBSY => return error.FileBusy,
-        ENOTDIR => return error.FileNotFound,
-        ENOENT => return error.FileNotFound,
-        ENAMETOOLONG => return error.NameTooLong,
-        EINVAL => unreachable,
-        EFAULT => unreachable,
-        EIO => return error.InputOutput,
-        ENOMEM => return error.SystemResources,
+        .SUCCESS => return,
+        .ACCES => return error.PermissionDenied,
+        .ROFS => return error.ReadOnlyFileSystem,
+        .LOOP => return error.SymLinkLoop,
+        .TXTBSY => return error.FileBusy,
+        .NOTDIR => return error.FileNotFound,
+        .NOENT => return error.FileNotFound,
+        .NAMETOOLONG => return error.NameTooLong,
+        .INVAL => unreachable,
+        .FAULT => unreachable,
+        .IO => return error.InputOutput,
+        .NOMEM => return error.SystemResources,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -3972,11 +3975,11 @@ pub const PipeError = error{
 pub fn pipe() PipeError![2]fd_t {
     var fds: [2]fd_t = undefined;
     switch (errno(system.pipe(&fds))) {
-        0 => return fds,
-        EINVAL => unreachable, // Invalid parameters to pipe()
-        EFAULT => unreachable, // Invalid fds pointer
-        ENFILE => return error.SystemFdQuotaExceeded,
-        EMFILE => return error.ProcessFdQuotaExceeded,
+        .SUCCESS => return fds,
+        .INVAL => unreachable, // Invalid parameters to pipe()
+        .FAULT => unreachable, // Invalid fds pointer
+        .NFILE => return error.SystemFdQuotaExceeded,
+        .MFILE => return error.ProcessFdQuotaExceeded,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -3985,11 +3988,11 @@ pub fn pipe2(flags: u32) PipeError![2]fd_t {
     if (@hasDecl(system, "pipe2")) {
         var fds: [2]fd_t = undefined;
         switch (errno(system.pipe2(&fds, flags))) {
-            0 => return fds,
-            EINVAL => unreachable, // Invalid flags
-            EFAULT => unreachable, // Invalid fds pointer
-            ENFILE => return error.SystemFdQuotaExceeded,
-            EMFILE => return error.ProcessFdQuotaExceeded,
+            .SUCCESS => return fds,
+            .INVAL => unreachable, // Invalid flags
+            .FAULT => unreachable, // Invalid fds pointer
+            .NFILE => return error.SystemFdQuotaExceeded,
+            .MFILE => return error.ProcessFdQuotaExceeded,
             else => |err| return unexpectedErrno(err),
         }
     }
@@ -4008,9 +4011,9 @@ pub fn pipe2(flags: u32) PipeError![2]fd_t {
     if (flags & O_CLOEXEC != 0) {
         for (fds) |fd| {
             switch (errno(system.fcntl(fd, F_SETFD, @as(u32, FD_CLOEXEC)))) {
-                0 => {},
-                EINVAL => unreachable, // Invalid flags
-                EBADF => unreachable, // Always a race condition
+                .SUCCESS => {},
+                .INVAL => unreachable, // Invalid flags
+                .BADF => unreachable, // Always a race condition
                 else => |err| return unexpectedErrno(err),
             }
         }
@@ -4021,9 +4024,9 @@ pub fn pipe2(flags: u32) PipeError![2]fd_t {
     if (new_flags != 0) {
         for (fds) |fd| {
             switch (errno(system.fcntl(fd, F_SETFL, new_flags))) {
-                0 => {},
-                EINVAL => unreachable, // Invalid flags
-                EBADF => unreachable, // Always a race condition
+                .SUCCESS => {},
+                .INVAL => unreachable, // Invalid flags
+                .BADF => unreachable, // Always a race condition
                 else => |err| return unexpectedErrno(err),
             }
         }
@@ -4055,11 +4058,11 @@ pub fn sysctl(
 
     const name_len = math.cast(c_uint, name.len) catch return error.NameTooLong;
     switch (errno(system.sysctl(name.ptr, name_len, oldp, oldlenp, newp, newlen))) {
-        0 => return,
-        EFAULT => unreachable,
-        EPERM => return error.PermissionDenied,
-        ENOMEM => return error.SystemResources,
-        ENOENT => return error.UnknownName,
+        .SUCCESS => return,
+        .FAULT => unreachable,
+        .PERM => return error.PermissionDenied,
+        .NOMEM => return error.SystemResources,
+        .NOENT => return error.UnknownName,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -4081,19 +4084,19 @@ pub fn sysctlbynameZ(
     }
 
     switch (errno(system.sysctlbyname(name, oldp, oldlenp, newp, newlen))) {
-        0 => return,
-        EFAULT => unreachable,
-        EPERM => return error.PermissionDenied,
-        ENOMEM => return error.SystemResources,
-        ENOENT => return error.UnknownName,
+        .SUCCESS => return,
+        .FAULT => unreachable,
+        .PERM => return error.PermissionDenied,
+        .NOMEM => return error.SystemResources,
+        .NOENT => return error.UnknownName,
         else => |err| return unexpectedErrno(err),
     }
 }
 
 pub fn gettimeofday(tv: ?*timeval, tz: ?*timezone) void {
     switch (errno(system.gettimeofday(tv, tz))) {
-        0 => return,
-        EINVAL => unreachable,
+        .SUCCESS => return,
+        .INVAL => unreachable,
         else => unreachable,
     }
 }
@@ -4111,12 +4114,12 @@ pub fn lseek_SET(fd: fd_t, offset: u64) SeekError!void {
     if (builtin.os.tag == .linux and !builtin.link_libc and @sizeOf(usize) == 4) {
         var result: u64 = undefined;
         switch (errno(system.llseek(fd, offset, &result, SEEK_SET))) {
-            0 => return,
-            EBADF => unreachable, // always a race condition
-            EINVAL => return error.Unseekable,
-            EOVERFLOW => return error.Unseekable,
-            ESPIPE => return error.Unseekable,
-            ENXIO => return error.Unseekable,
+            .SUCCESS => return,
+            .BADF => unreachable, // always a race condition
+            .INVAL => return error.Unseekable,
+            .OVERFLOW => return error.Unseekable,
+            .SPIPE => return error.Unseekable,
+            .NXIO => return error.Unseekable,
             else => |err| return unexpectedErrno(err),
         }
     }
@@ -4126,13 +4129,13 @@ pub fn lseek_SET(fd: fd_t, offset: u64) SeekError!void {
     if (builtin.os.tag == .wasi and !builtin.link_libc) {
         var new_offset: wasi.filesize_t = undefined;
         switch (wasi.fd_seek(fd, @bitCast(wasi.filedelta_t, offset), wasi.WHENCE_SET, &new_offset)) {
-            wasi.ESUCCESS => return,
-            wasi.EBADF => unreachable, // always a race condition
-            wasi.EINVAL => return error.Unseekable,
-            wasi.EOVERFLOW => return error.Unseekable,
-            wasi.ESPIPE => return error.Unseekable,
-            wasi.ENXIO => return error.Unseekable,
-            wasi.ENOTCAPABLE => return error.AccessDenied,
+            .SUCCESS => return,
+            .BADF => unreachable, // always a race condition
+            .INVAL => return error.Unseekable,
+            .OVERFLOW => return error.Unseekable,
+            .SPIPE => return error.Unseekable,
+            .NXIO => return error.Unseekable,
+            .NOTCAPABLE => return error.AccessDenied,
             else => |err| return unexpectedErrno(err),
         }
     }
@@ -4144,12 +4147,12 @@ pub fn lseek_SET(fd: fd_t, offset: u64) SeekError!void {
 
     const ioffset = @bitCast(i64, offset); // the OS treats this as unsigned
     switch (errno(lseek_sym(fd, ioffset, SEEK_SET))) {
-        0 => return,
-        EBADF => unreachable, // always a race condition
-        EINVAL => return error.Unseekable,
-        EOVERFLOW => return error.Unseekable,
-        ESPIPE => return error.Unseekable,
-        ENXIO => return error.Unseekable,
+        .SUCCESS => return,
+        .BADF => unreachable, // always a race condition
+        .INVAL => return error.Unseekable,
+        .OVERFLOW => return error.Unseekable,
+        .SPIPE => return error.Unseekable,
+        .NXIO => return error.Unseekable,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -4159,12 +4162,12 @@ pub fn lseek_CUR(fd: fd_t, offset: i64) SeekError!void {
     if (builtin.os.tag == .linux and !builtin.link_libc and @sizeOf(usize) == 4) {
         var result: u64 = undefined;
         switch (errno(system.llseek(fd, @bitCast(u64, offset), &result, SEEK_CUR))) {
-            0 => return,
-            EBADF => unreachable, // always a race condition
-            EINVAL => return error.Unseekable,
-            EOVERFLOW => return error.Unseekable,
-            ESPIPE => return error.Unseekable,
-            ENXIO => return error.Unseekable,
+            .SUCCESS => return,
+            .BADF => unreachable, // always a race condition
+            .INVAL => return error.Unseekable,
+            .OVERFLOW => return error.Unseekable,
+            .SPIPE => return error.Unseekable,
+            .NXIO => return error.Unseekable,
             else => |err| return unexpectedErrno(err),
         }
     }
@@ -4174,13 +4177,13 @@ pub fn lseek_CUR(fd: fd_t, offset: i64) SeekError!void {
     if (builtin.os.tag == .wasi and !builtin.link_libc) {
         var new_offset: wasi.filesize_t = undefined;
         switch (wasi.fd_seek(fd, offset, wasi.WHENCE_CUR, &new_offset)) {
-            wasi.ESUCCESS => return,
-            wasi.EBADF => unreachable, // always a race condition
-            wasi.EINVAL => return error.Unseekable,
-            wasi.EOVERFLOW => return error.Unseekable,
-            wasi.ESPIPE => return error.Unseekable,
-            wasi.ENXIO => return error.Unseekable,
-            wasi.ENOTCAPABLE => return error.AccessDenied,
+            .SUCCESS => return,
+            .BADF => unreachable, // always a race condition
+            .INVAL => return error.Unseekable,
+            .OVERFLOW => return error.Unseekable,
+            .SPIPE => return error.Unseekable,
+            .NXIO => return error.Unseekable,
+            .NOTCAPABLE => return error.AccessDenied,
             else => |err| return unexpectedErrno(err),
         }
     }
@@ -4191,12 +4194,12 @@ pub fn lseek_CUR(fd: fd_t, offset: i64) SeekError!void {
 
     const ioffset = @bitCast(i64, offset); // the OS treats this as unsigned
     switch (errno(lseek_sym(fd, ioffset, SEEK_CUR))) {
-        0 => return,
-        EBADF => unreachable, // always a race condition
-        EINVAL => return error.Unseekable,
-        EOVERFLOW => return error.Unseekable,
-        ESPIPE => return error.Unseekable,
-        ENXIO => return error.Unseekable,
+        .SUCCESS => return,
+        .BADF => unreachable, // always a race condition
+        .INVAL => return error.Unseekable,
+        .OVERFLOW => return error.Unseekable,
+        .SPIPE => return error.Unseekable,
+        .NXIO => return error.Unseekable,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -4206,12 +4209,12 @@ pub fn lseek_END(fd: fd_t, offset: i64) SeekError!void {
     if (builtin.os.tag == .linux and !builtin.link_libc and @sizeOf(usize) == 4) {
         var result: u64 = undefined;
         switch (errno(system.llseek(fd, @bitCast(u64, offset), &result, SEEK_END))) {
-            0 => return,
-            EBADF => unreachable, // always a race condition
-            EINVAL => return error.Unseekable,
-            EOVERFLOW => return error.Unseekable,
-            ESPIPE => return error.Unseekable,
-            ENXIO => return error.Unseekable,
+            .SUCCESS => return,
+            .BADF => unreachable, // always a race condition
+            .INVAL => return error.Unseekable,
+            .OVERFLOW => return error.Unseekable,
+            .SPIPE => return error.Unseekable,
+            .NXIO => return error.Unseekable,
             else => |err| return unexpectedErrno(err),
         }
     }
@@ -4221,13 +4224,13 @@ pub fn lseek_END(fd: fd_t, offset: i64) SeekError!void {
     if (builtin.os.tag == .wasi and !builtin.link_libc) {
         var new_offset: wasi.filesize_t = undefined;
         switch (wasi.fd_seek(fd, offset, wasi.WHENCE_END, &new_offset)) {
-            wasi.ESUCCESS => return,
-            wasi.EBADF => unreachable, // always a race condition
-            wasi.EINVAL => return error.Unseekable,
-            wasi.EOVERFLOW => return error.Unseekable,
-            wasi.ESPIPE => return error.Unseekable,
-            wasi.ENXIO => return error.Unseekable,
-            wasi.ENOTCAPABLE => return error.AccessDenied,
+            .SUCCESS => return,
+            .BADF => unreachable, // always a race condition
+            .INVAL => return error.Unseekable,
+            .OVERFLOW => return error.Unseekable,
+            .SPIPE => return error.Unseekable,
+            .NXIO => return error.Unseekable,
+            .NOTCAPABLE => return error.AccessDenied,
             else => |err| return unexpectedErrno(err),
         }
     }
@@ -4238,12 +4241,12 @@ pub fn lseek_END(fd: fd_t, offset: i64) SeekError!void {
 
     const ioffset = @bitCast(i64, offset); // the OS treats this as unsigned
     switch (errno(lseek_sym(fd, ioffset, SEEK_END))) {
-        0 => return,
-        EBADF => unreachable, // always a race condition
-        EINVAL => return error.Unseekable,
-        EOVERFLOW => return error.Unseekable,
-        ESPIPE => return error.Unseekable,
-        ENXIO => return error.Unseekable,
+        .SUCCESS => return,
+        .BADF => unreachable, // always a race condition
+        .INVAL => return error.Unseekable,
+        .OVERFLOW => return error.Unseekable,
+        .SPIPE => return error.Unseekable,
+        .NXIO => return error.Unseekable,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -4253,12 +4256,12 @@ pub fn lseek_CUR_get(fd: fd_t) SeekError!u64 {
     if (builtin.os.tag == .linux and !builtin.link_libc and @sizeOf(usize) == 4) {
         var result: u64 = undefined;
         switch (errno(system.llseek(fd, 0, &result, SEEK_CUR))) {
-            0 => return result,
-            EBADF => unreachable, // always a race condition
-            EINVAL => return error.Unseekable,
-            EOVERFLOW => return error.Unseekable,
-            ESPIPE => return error.Unseekable,
-            ENXIO => return error.Unseekable,
+            .SUCCESS => return result,
+            .BADF => unreachable, // always a race condition
+            .INVAL => return error.Unseekable,
+            .OVERFLOW => return error.Unseekable,
+            .SPIPE => return error.Unseekable,
+            .NXIO => return error.Unseekable,
             else => |err| return unexpectedErrno(err),
         }
     }
@@ -4268,13 +4271,13 @@ pub fn lseek_CUR_get(fd: fd_t) SeekError!u64 {
     if (builtin.os.tag == .wasi and !builtin.link_libc) {
         var new_offset: wasi.filesize_t = undefined;
         switch (wasi.fd_seek(fd, 0, wasi.WHENCE_CUR, &new_offset)) {
-            wasi.ESUCCESS => return new_offset,
-            wasi.EBADF => unreachable, // always a race condition
-            wasi.EINVAL => return error.Unseekable,
-            wasi.EOVERFLOW => return error.Unseekable,
-            wasi.ESPIPE => return error.Unseekable,
-            wasi.ENXIO => return error.Unseekable,
-            wasi.ENOTCAPABLE => return error.AccessDenied,
+            .SUCCESS => return new_offset,
+            .BADF => unreachable, // always a race condition
+            .INVAL => return error.Unseekable,
+            .OVERFLOW => return error.Unseekable,
+            .SPIPE => return error.Unseekable,
+            .NXIO => return error.Unseekable,
+            .NOTCAPABLE => return error.AccessDenied,
             else => |err| return unexpectedErrno(err),
         }
     }
@@ -4285,12 +4288,12 @@ pub fn lseek_CUR_get(fd: fd_t) SeekError!u64 {
 
     const rc = lseek_sym(fd, 0, SEEK_CUR);
     switch (errno(rc)) {
-        0 => return @bitCast(u64, rc),
-        EBADF => unreachable, // always a race condition
-        EINVAL => return error.Unseekable,
-        EOVERFLOW => return error.Unseekable,
-        ESPIPE => return error.Unseekable,
-        ENXIO => return error.Unseekable,
+        .SUCCESS => return @bitCast(u64, rc),
+        .BADF => unreachable, // always a race condition
+        .INVAL => return error.Unseekable,
+        .OVERFLOW => return error.Unseekable,
+        .SPIPE => return error.Unseekable,
+        .NXIO => return error.Unseekable,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -4306,15 +4309,15 @@ pub fn fcntl(fd: fd_t, cmd: i32, arg: usize) FcntlError!usize {
     while (true) {
         const rc = system.fcntl(fd, cmd, arg);
         switch (errno(rc)) {
-            0 => return @intCast(usize, rc),
-            EINTR => continue,
-            EACCES => return error.Locked,
-            EBADF => unreachable,
-            EBUSY => return error.FileBusy,
-            EINVAL => unreachable, // invalid parameters
-            EPERM => return error.PermissionDenied,
-            EMFILE => return error.ProcessFdQuotaExceeded,
-            ENOTDIR => unreachable, // invalid parameter
+            .SUCCESS => return @intCast(usize, rc),
+            .INTR => continue,
+            .ACCES => return error.Locked,
+            .BADF => unreachable,
+            .BUSY => return error.FileBusy,
+            .INVAL => unreachable, // invalid parameters
+            .PERM => return error.PermissionDenied,
+            .MFILE => return error.ProcessFdQuotaExceeded,
+            .NOTDIR => unreachable, // invalid parameter
             else => |err| return unexpectedErrno(err),
         }
     }
@@ -4381,12 +4384,12 @@ pub fn flock(fd: fd_t, operation: i32) FlockError!void {
     while (true) {
         const rc = system.flock(fd, operation);
         switch (errno(rc)) {
-            0 => return,
-            EBADF => unreachable,
-            EINTR => continue,
-            EINVAL => unreachable, // invalid parameters
-            ENOLCK => return error.SystemResources,
-            EWOULDBLOCK => return error.WouldBlock, // TODO: integrate with async instead of just returning an error
+            .SUCCESS => return,
+            .BADF => unreachable,
+            .INTR => continue,
+            .INVAL => unreachable, // invalid parameters
+            .NOLCK => return error.SystemResources,
+            .AGAIN => return error.WouldBlock, // TODO: integrate with async instead of just returning an error
             else => |err| return unexpectedErrno(err),
         }
     }
@@ -4456,17 +4459,18 @@ pub fn realpathZ(pathname: [*:0]const u8, out_buffer: *[MAX_PATH_BYTES]u8) RealP
 
         return getFdPath(fd, out_buffer);
     }
-    const result_path = std.c.realpath(pathname, out_buffer) orelse switch (std.c._errno().*) {
-        EINVAL => unreachable,
-        EBADF => unreachable,
-        EFAULT => unreachable,
-        EACCES => return error.AccessDenied,
-        ENOENT => return error.FileNotFound,
-        ENOTSUP => return error.NotSupported,
-        ENOTDIR => return error.NotDir,
-        ENAMETOOLONG => return error.NameTooLong,
-        ELOOP => return error.SymLinkLoop,
-        EIO => return error.InputOutput,
+    const result_path = std.c.realpath(pathname, out_buffer) orelse switch (@intToEnum(E, std.c._errno().*)) {
+        .SUCCESS => unreachable,
+        .INVAL => unreachable,
+        .BADF => unreachable,
+        .FAULT => unreachable,
+        .ACCES => return error.AccessDenied,
+        .NOENT => return error.FileNotFound,
+        .OPNOTSUPP => return error.NotSupported,
+        .NOTDIR => return error.NotDir,
+        .NAMETOOLONG => return error.NameTooLong,
+        .LOOP => return error.SymLinkLoop,
+        .IO => return error.InputOutput,
         else => |err| return unexpectedErrno(err),
     };
     return mem.spanZ(result_path);
@@ -4528,8 +4532,8 @@ pub fn getFdPath(fd: fd_t, out_buffer: *[MAX_PATH_BYTES]u8) RealPathError![]u8 {
             // the path to the file descriptor.
             @memset(out_buffer, 0, MAX_PATH_BYTES);
             switch (errno(system.fcntl(fd, F_GETPATH, out_buffer))) {
-                0 => {},
-                EBADF => return error.FileNotFound,
+                .SUCCESS => {},
+                .BADF => return error.FileNotFound,
                 // TODO man pages for fcntl on macOS don't really tell you what
                 // errno values to expect when command is F_GETPATH...
                 else => |err| return unexpectedErrno(err),
@@ -4562,13 +4566,13 @@ pub fn nanosleep(seconds: u64, nanoseconds: u64) void {
     var rem: timespec = undefined;
     while (true) {
         switch (errno(system.nanosleep(&req, &rem))) {
-            EFAULT => unreachable,
-            EINVAL => {
+            .FAULT => unreachable,
+            .INVAL => {
                 // Sometimes Darwin returns EINVAL for no reason.
                 // We treat it as a spurious wakeup.
                 return;
             },
-            EINTR => {
+            .INTR => {
                 req = rem;
                 continue;
             },
@@ -4668,13 +4672,13 @@ pub fn clock_gettime(clk_id: i32, tp: *timespec) ClockGetTimeError!void {
     if (std.Target.current.os.tag == .wasi and !builtin.link_libc) {
         var ts: timestamp_t = undefined;
         switch (system.clock_time_get(@bitCast(u32, clk_id), 1, &ts)) {
-            0 => {
+            .SUCCESS => {
                 tp.* = .{
                     .tv_sec = @intCast(i64, ts / std.time.ns_per_s),
                     .tv_nsec = @intCast(isize, ts % std.time.ns_per_s),
                 };
             },
-            EINVAL => return error.UnsupportedClock,
+            .INVAL => return error.UnsupportedClock,
             else => |err| return unexpectedErrno(err),
         }
         return;
@@ -4698,9 +4702,9 @@ pub fn clock_gettime(clk_id: i32, tp: *timespec) ClockGetTimeError!void {
     }
 
     switch (errno(system.clock_gettime(clk_id, tp))) {
-        0 => return,
-        EFAULT => unreachable,
-        EINVAL => return error.UnsupportedClock,
+        .SUCCESS => return,
+        .FAULT => unreachable,
+        .INVAL => return error.UnsupportedClock,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -4709,20 +4713,20 @@ pub fn clock_getres(clk_id: i32, res: *timespec) ClockGetTimeError!void {
     if (std.Target.current.os.tag == .wasi and !builtin.link_libc) {
         var ts: timestamp_t = undefined;
         switch (system.clock_res_get(@bitCast(u32, clk_id), &ts)) {
-            0 => res.* = .{
+            .SUCCESS => res.* = .{
                 .tv_sec = @intCast(i64, ts / std.time.ns_per_s),
                 .tv_nsec = @intCast(isize, ts % std.time.ns_per_s),
             },
-            EINVAL => return error.UnsupportedClock,
+            .INVAL => return error.UnsupportedClock,
             else => |err| return unexpectedErrno(err),
         }
         return;
     }
 
     switch (errno(system.clock_getres(clk_id, res))) {
-        0 => return,
-        EFAULT => unreachable,
-        EINVAL => return error.UnsupportedClock,
+        .SUCCESS => return,
+        .FAULT => unreachable,
+        .INVAL => return error.UnsupportedClock,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -4732,11 +4736,11 @@ pub const SchedGetAffinityError = error{PermissionDenied} || UnexpectedError;
 pub fn sched_getaffinity(pid: pid_t) SchedGetAffinityError!cpu_set_t {
     var set: cpu_set_t = undefined;
     switch (errno(system.sched_getaffinity(pid, @sizeOf(cpu_set_t), &set))) {
-        0 => return set,
-        EFAULT => unreachable,
-        EINVAL => unreachable,
-        ESRCH => unreachable,
-        EPERM => return error.PermissionDenied,
+        .SUCCESS => return set,
+        .FAULT => unreachable,
+        .INVAL => unreachable,
+        .SRCH => unreachable,
+        .PERM => return error.PermissionDenied,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -4768,13 +4772,9 @@ pub const UnexpectedError = error{
 
 /// Call this when you made a syscall or something that sets errno
 /// and you get an unexpected error.
-pub fn unexpectedErrno(err: anytype) UnexpectedError {
-    if (@typeInfo(@TypeOf(err)) != .Int) {
-        @compileError("err is expected to be an integer");
-    }
-
+pub fn unexpectedErrno(err: E) UnexpectedError {
     if (unexpected_error_tracing) {
-        std.debug.warn("unexpected errno: {d}\n", .{err});
+        std.debug.warn("unexpected errno: {d}\n", .{@enumToInt(err)});
         std.debug.dumpCurrentStackTrace(null);
     }
     return error.Unexpected;
@@ -4790,11 +4790,11 @@ pub const SigaltstackError = error{
 
 pub fn sigaltstack(ss: ?*stack_t, old_ss: ?*stack_t) SigaltstackError!void {
     switch (errno(system.sigaltstack(ss, old_ss))) {
-        0 => return,
-        EFAULT => unreachable,
-        EINVAL => unreachable,
-        ENOMEM => return error.SizeTooSmall,
-        EPERM => return error.PermissionDenied,
+        .SUCCESS => return,
+        .FAULT => unreachable,
+        .INVAL => unreachable,
+        .NOMEM => return error.SizeTooSmall,
+        .PERM => return error.PermissionDenied,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -4802,9 +4802,9 @@ pub fn sigaltstack(ss: ?*stack_t, old_ss: ?*stack_t) SigaltstackError!void {
 /// Examine and change a signal action.
 pub fn sigaction(sig: u6, act: ?*const Sigaction, oact: ?*Sigaction) void {
     switch (errno(system.sigaction(sig, act, oact))) {
-        0 => return,
-        EFAULT => unreachable,
-        EINVAL => unreachable,
+        .SUCCESS => return,
+        .FAULT => unreachable,
+        .INVAL => unreachable,
         else => unreachable,
     }
 }
@@ -4841,25 +4841,25 @@ pub fn futimens(fd: fd_t, times: *const [2]timespec) FutimensError!void {
         const atim = times[0].toTimestamp();
         const mtim = times[1].toTimestamp();
         switch (wasi.fd_filestat_set_times(fd, atim, mtim, wasi.FILESTAT_SET_ATIM | wasi.FILESTAT_SET_MTIM)) {
-            wasi.ESUCCESS => return,
-            wasi.EACCES => return error.AccessDenied,
-            wasi.EPERM => return error.PermissionDenied,
-            wasi.EBADF => unreachable, // always a race condition
-            wasi.EFAULT => unreachable,
-            wasi.EINVAL => unreachable,
-            wasi.EROFS => return error.ReadOnlyFileSystem,
+            .SUCCESS => return,
+            .ACCES => return error.AccessDenied,
+            .PERM => return error.PermissionDenied,
+            .BADF => unreachable, // always a race condition
+            .FAULT => unreachable,
+            .INVAL => unreachable,
+            .ROFS => return error.ReadOnlyFileSystem,
             else => |err| return unexpectedErrno(err),
         }
     }
 
     switch (errno(system.futimens(fd, times))) {
-        0 => return,
-        EACCES => return error.AccessDenied,
-        EPERM => return error.PermissionDenied,
-        EBADF => unreachable, // always a race condition
-        EFAULT => unreachable,
-        EINVAL => unreachable,
-        EROFS => return error.ReadOnlyFileSystem,
+        .SUCCESS => return,
+        .ACCES => return error.AccessDenied,
+        .PERM => return error.PermissionDenied,
+        .BADF => unreachable, // always a race condition
+        .FAULT => unreachable,
+        .INVAL => unreachable,
+        .ROFS => return error.ReadOnlyFileSystem,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -4869,10 +4869,10 @@ pub const GetHostNameError = error{PermissionDenied} || UnexpectedError;
 pub fn gethostname(name_buffer: *[HOST_NAME_MAX]u8) GetHostNameError![]u8 {
     if (builtin.link_libc) {
         switch (errno(system.gethostname(name_buffer, name_buffer.len))) {
-            0 => return mem.spanZ(std.meta.assumeSentinel(name_buffer, 0)),
-            EFAULT => unreachable,
-            ENAMETOOLONG => unreachable, // HOST_NAME_MAX prevents this
-            EPERM => return error.PermissionDenied,
+            .SUCCESS => return mem.spanZ(std.meta.assumeSentinel(name_buffer, 0)),
+            .FAULT => unreachable,
+            .NAMETOOLONG => unreachable, // HOST_NAME_MAX prevents this
+            .PERM => return error.PermissionDenied,
             else => |err| return unexpectedErrno(err),
         }
     }
@@ -4889,8 +4889,8 @@ pub fn gethostname(name_buffer: *[HOST_NAME_MAX]u8) GetHostNameError![]u8 {
 pub fn uname() utsname {
     var uts: utsname = undefined;
     switch (errno(system.uname(&uts))) {
-        0 => return uts,
-        EFAULT => unreachable,
+        .SUCCESS => return uts,
+        .FAULT => unreachable,
         else => unreachable,
     }
 }
@@ -5049,33 +5049,33 @@ pub fn sendmsg(
             }
         } else {
             switch (errno(rc)) {
-                0 => return @intCast(usize, rc),
+                .SUCCESS => return @intCast(usize, rc),
 
-                EACCES => return error.AccessDenied,
-                EAGAIN => return error.WouldBlock,
-                EALREADY => return error.FastOpenAlreadyInProgress,
-                EBADF => unreachable, // always a race condition
-                ECONNRESET => return error.ConnectionResetByPeer,
-                EDESTADDRREQ => unreachable, // The socket is not connection-mode, and no peer address is set.
-                EFAULT => unreachable, // An invalid user space address was specified for an argument.
-                EINTR => continue,
-                EINVAL => unreachable, // Invalid argument passed.
-                EISCONN => unreachable, // connection-mode socket was connected already but a recipient was specified
-                EMSGSIZE => return error.MessageTooBig,
-                ENOBUFS => return error.SystemResources,
-                ENOMEM => return error.SystemResources,
-                ENOTSOCK => unreachable, // The file descriptor sockfd does not refer to a socket.
-                EOPNOTSUPP => unreachable, // Some bit in the flags argument is inappropriate for the socket type.
-                EPIPE => return error.BrokenPipe,
-                EAFNOSUPPORT => return error.AddressFamilyNotSupported,
-                ELOOP => return error.SymLinkLoop,
-                ENAMETOOLONG => return error.NameTooLong,
-                ENOENT => return error.FileNotFound,
-                ENOTDIR => return error.NotDir,
-                EHOSTUNREACH => return error.NetworkUnreachable,
-                ENETUNREACH => return error.NetworkUnreachable,
-                ENOTCONN => return error.SocketNotConnected,
-                ENETDOWN => return error.NetworkSubsystemFailed,
+                .ACCES => return error.AccessDenied,
+                .AGAIN => return error.WouldBlock,
+                .ALREADY => return error.FastOpenAlreadyInProgress,
+                .BADF => unreachable, // always a race condition
+                .CONNRESET => return error.ConnectionResetByPeer,
+                .DESTADDRREQ => unreachable, // The socket is not connection-mode, and no peer address is set.
+                .FAULT => unreachable, // An invalid user space address was specified for an argument.
+                .INTR => continue,
+                .INVAL => unreachable, // Invalid argument passed.
+                .ISCONN => unreachable, // connection-mode socket was connected already but a recipient was specified
+                .MSGSIZE => return error.MessageTooBig,
+                .NOBUFS => return error.SystemResources,
+                .NOMEM => return error.SystemResources,
+                .NOTSOCK => unreachable, // The file descriptor sockfd does not refer to a socket.
+                .OPNOTSUPP => unreachable, // Some bit in the flags argument is inappropriate for the socket type.
+                .PIPE => return error.BrokenPipe,
+                .AFNOSUPPORT => return error.AddressFamilyNotSupported,
+                .LOOP => return error.SymLinkLoop,
+                .NAMETOOLONG => return error.NameTooLong,
+                .NOENT => return error.FileNotFound,
+                .NOTDIR => return error.NotDir,
+                .HOSTUNREACH => return error.NetworkUnreachable,
+                .NETUNREACH => return error.NetworkUnreachable,
+                .NOTCONN => return error.SocketNotConnected,
+                .NETDOWN => return error.NetworkSubsystemFailed,
                 else => |err| return unexpectedErrno(err),
             }
         }
@@ -5149,33 +5149,33 @@ pub fn sendto(
             }
         } else {
             switch (errno(rc)) {
-                0 => return @intCast(usize, rc),
+                .SUCCESS => return @intCast(usize, rc),
 
-                EACCES => return error.AccessDenied,
-                EAGAIN => return error.WouldBlock,
-                EALREADY => return error.FastOpenAlreadyInProgress,
-                EBADF => unreachable, // always a race condition
-                ECONNRESET => return error.ConnectionResetByPeer,
-                EDESTADDRREQ => unreachable, // The socket is not connection-mode, and no peer address is set.
-                EFAULT => unreachable, // An invalid user space address was specified for an argument.
-                EINTR => continue,
-                EINVAL => unreachable, // Invalid argument passed.
-                EISCONN => unreachable, // connection-mode socket was connected already but a recipient was specified
-                EMSGSIZE => return error.MessageTooBig,
-                ENOBUFS => return error.SystemResources,
-                ENOMEM => return error.SystemResources,
-                ENOTSOCK => unreachable, // The file descriptor sockfd does not refer to a socket.
-                EOPNOTSUPP => unreachable, // Some bit in the flags argument is inappropriate for the socket type.
-                EPIPE => return error.BrokenPipe,
-                EAFNOSUPPORT => return error.AddressFamilyNotSupported,
-                ELOOP => return error.SymLinkLoop,
-                ENAMETOOLONG => return error.NameTooLong,
-                ENOENT => return error.FileNotFound,
-                ENOTDIR => return error.NotDir,
-                EHOSTUNREACH => return error.NetworkUnreachable,
-                ENETUNREACH => return error.NetworkUnreachable,
-                ENOTCONN => return error.SocketNotConnected,
-                ENETDOWN => return error.NetworkSubsystemFailed,
+                .ACCES => return error.AccessDenied,
+                .AGAIN => return error.WouldBlock,
+                .ALREADY => return error.FastOpenAlreadyInProgress,
+                .BADF => unreachable, // always a race condition
+                .CONNRESET => return error.ConnectionResetByPeer,
+                .DESTADDRREQ => unreachable, // The socket is not connection-mode, and no peer address is set.
+                .FAULT => unreachable, // An invalid user space address was specified for an argument.
+                .INTR => continue,
+                .INVAL => unreachable, // Invalid argument passed.
+                .ISCONN => unreachable, // connection-mode socket was connected already but a recipient was specified
+                .MSGSIZE => return error.MessageTooBig,
+                .NOBUFS => return error.SystemResources,
+                .NOMEM => return error.SystemResources,
+                .NOTSOCK => unreachable, // The file descriptor sockfd does not refer to a socket.
+                .OPNOTSUPP => unreachable, // Some bit in the flags argument is inappropriate for the socket type.
+                .PIPE => return error.BrokenPipe,
+                .AFNOSUPPORT => return error.AddressFamilyNotSupported,
+                .LOOP => return error.SymLinkLoop,
+                .NAMETOOLONG => return error.NameTooLong,
+                .NOENT => return error.FileNotFound,
+                .NOTDIR => return error.NotDir,
+                .HOSTUNREACH => return error.NetworkUnreachable,
+                .NETUNREACH => return error.NetworkUnreachable,
+                .NOTCONN => return error.SocketNotConnected,
+                .NETDOWN => return error.NetworkSubsystemFailed,
                 else => |err| return unexpectedErrno(err),
             }
         }
@@ -5312,7 +5312,7 @@ pub fn sendfile(
                 var offset: off_t = @bitCast(off_t, in_offset);
                 const rc = sendfile_sym(out_fd, in_fd, &offset, adjusted_count);
                 switch (errno(rc)) {
-                    0 => {
+                    .SUCCESS => {
                         const amt = @bitCast(usize, rc);
                         total_written += amt;
                         if (in_len == 0 and amt == 0) {
@@ -5325,12 +5325,12 @@ pub fn sendfile(
                         }
                     },
 
-                    EBADF => unreachable, // Always a race condition.
-                    EFAULT => unreachable, // Segmentation fault.
-                    EOVERFLOW => unreachable, // We avoid passing too large of a `count`.
-                    ENOTCONN => unreachable, // `out_fd` is an unconnected socket.
+                    .BADF => unreachable, // Always a race condition.
+                    .FAULT => unreachable, // Segmentation fault.
+                    .OVERFLOW => unreachable, // We avoid passing too large of a `count`.
+                    .NOTCONN => unreachable, // `out_fd` is an unconnected socket.
 
-                    EINVAL, ENOSYS => {
+                    .INVAL, .NOSYS => {
                         // EINVAL could be any of the following situations:
                         // * Descriptor is not valid or locked
                         // * an mmap(2)-like operation is  not  available  for in_fd
@@ -5340,17 +5340,17 @@ pub fn sendfile(
                         // manually, the same as ENOSYS.
                         break :sf;
                     },
-                    EAGAIN => if (std.event.Loop.instance) |loop| {
+                    .AGAIN => if (std.event.Loop.instance) |loop| {
                         loop.waitUntilFdWritable(out_fd);
                         continue;
                     } else {
                         return error.WouldBlock;
                     },
-                    EIO => return error.InputOutput,
-                    EPIPE => return error.BrokenPipe,
-                    ENOMEM => return error.SystemResources,
-                    ENXIO => return error.Unseekable,
-                    ESPIPE => return error.Unseekable,
+                    .IO => return error.InputOutput,
+                    .PIPE => return error.BrokenPipe,
+                    .NOMEM => return error.SystemResources,
+                    .NXIO => return error.Unseekable,
+                    .SPIPE => return error.Unseekable,
                     else => |err| {
                         unexpectedErrno(err) catch {};
                         break :sf;
@@ -5392,13 +5392,13 @@ pub fn sendfile(
                 const err = errno(system.sendfile(in_fd, out_fd, offset, adjusted_count, hdtr, &sbytes, flags));
                 const amt = @bitCast(usize, sbytes);
                 switch (err) {
-                    0 => return amt,
+                    .SUCCESS => return amt,
 
-                    EBADF => unreachable, // Always a race condition.
-                    EFAULT => unreachable, // Segmentation fault.
-                    ENOTCONN => unreachable, // `out_fd` is an unconnected socket.
+                    .BADF => unreachable, // Always a race condition.
+                    .FAULT => unreachable, // Segmentation fault.
+                    .NOTCONN => unreachable, // `out_fd` is an unconnected socket.
 
-                    EINVAL, EOPNOTSUPP, ENOTSOCK, ENOSYS => {
+                    .INVAL, .OPNOTSUPP, .NOTSOCK, .NOSYS => {
                         // EINVAL could be any of the following situations:
                         // * The fd argument is not a regular file.
                         // * The s argument is not a SOCK_STREAM type socket.
@@ -5408,9 +5408,9 @@ pub fn sendfile(
                         break :sf;
                     },
 
-                    EINTR => if (amt != 0) return amt else continue,
+                    .INTR => if (amt != 0) return amt else continue,
 
-                    EAGAIN => if (amt != 0) {
+                    .AGAIN => if (amt != 0) {
                         return amt;
                     } else if (std.event.Loop.instance) |loop| {
                         loop.waitUntilFdWritable(out_fd);
@@ -5419,7 +5419,7 @@ pub fn sendfile(
                         return error.WouldBlock;
                     },
 
-                    EBUSY => if (amt != 0) {
+                    .BUSY => if (amt != 0) {
                         return amt;
                     } else if (std.event.Loop.instance) |loop| {
                         loop.waitUntilFdReadable(in_fd);
@@ -5428,9 +5428,9 @@ pub fn sendfile(
                         return error.WouldBlock;
                     },
 
-                    EIO => return error.InputOutput,
-                    ENOBUFS => return error.SystemResources,
-                    EPIPE => return error.BrokenPipe,
+                    .IO => return error.InputOutput,
+                    .NOBUFS => return error.SystemResources,
+                    .PIPE => return error.BrokenPipe,
 
                     else => {
                         unexpectedErrno(err) catch {};
@@ -5471,18 +5471,18 @@ pub fn sendfile(
                 const err = errno(system.sendfile(in_fd, out_fd, signed_offset, &sbytes, hdtr, flags));
                 const amt = @bitCast(usize, sbytes);
                 switch (err) {
-                    0 => return amt,
+                    .SUCCESS => return amt,
 
-                    EBADF => unreachable, // Always a race condition.
-                    EFAULT => unreachable, // Segmentation fault.
-                    EINVAL => unreachable,
-                    ENOTCONN => unreachable, // `out_fd` is an unconnected socket.
+                    .BADF => unreachable, // Always a race condition.
+                    .FAULT => unreachable, // Segmentation fault.
+                    .INVAL => unreachable,
+                    .NOTCONN => unreachable, // `out_fd` is an unconnected socket.
 
-                    ENOTSUP, ENOTSOCK, ENOSYS => break :sf,
+                    .OPNOTSUPP, .NOTSOCK, .NOSYS => break :sf,
 
-                    EINTR => if (amt != 0) return amt else continue,
+                    .INTR => if (amt != 0) return amt else continue,
 
-                    EAGAIN => if (amt != 0) {
+                    .AGAIN => if (amt != 0) {
                         return amt;
                     } else if (std.event.Loop.instance) |loop| {
                         loop.waitUntilFdWritable(out_fd);
@@ -5491,8 +5491,8 @@ pub fn sendfile(
                         return error.WouldBlock;
                     },
 
-                    EIO => return error.InputOutput,
-                    EPIPE => return error.BrokenPipe,
+                    .IO => return error.InputOutput,
+                    .PIPE => return error.BrokenPipe,
 
                     else => {
                         unexpectedErrno(err) catch {};
@@ -5595,22 +5595,22 @@ pub fn copy_file_range(fd_in: fd_t, off_in: u64, fd_out: fd_t, off_out: u64, len
 
         const rc = system.copy_file_range(fd_in, &off_in_copy, fd_out, &off_out_copy, len, flags);
         switch (system.getErrno(rc)) {
-            0 => return @intCast(usize, rc),
-            EBADF => return error.FilesOpenedWithWrongFlags,
-            EFBIG => return error.FileTooBig,
-            EIO => return error.InputOutput,
-            EISDIR => return error.IsDir,
-            ENOMEM => return error.OutOfMemory,
-            ENOSPC => return error.NoSpaceLeft,
-            EOVERFLOW => return error.Unseekable,
-            EPERM => return error.PermissionDenied,
-            ETXTBSY => return error.FileBusy,
+            .SUCCESS => return @intCast(usize, rc),
+            .BADF => return error.FilesOpenedWithWrongFlags,
+            .FBIG => return error.FileTooBig,
+            .IO => return error.InputOutput,
+            .ISDIR => return error.IsDir,
+            .NOMEM => return error.OutOfMemory,
+            .NOSPC => return error.NoSpaceLeft,
+            .OVERFLOW => return error.Unseekable,
+            .PERM => return error.PermissionDenied,
+            .TXTBSY => return error.FileBusy,
             // these may not be regular files, try fallback
-            EINVAL => {},
+            .INVAL => {},
             // support for cross-filesystem copy added in Linux 5.3, use fallback
-            EXDEV => {},
+            .XDEV => {},
             // syscall added in Linux 4.5, use fallback
-            ENOSYS => {
+            .NOSYS => {
                 has_copy_file_range_syscall.store(false, .Monotonic);
             },
             else => |err| return unexpectedErrno(err),
@@ -5652,11 +5652,11 @@ pub fn poll(fds: []pollfd, timeout: i32) PollError!usize {
             }
         } else {
             switch (errno(rc)) {
-                0 => return @intCast(usize, rc),
-                EFAULT => unreachable,
-                EINTR => continue,
-                EINVAL => unreachable,
-                ENOMEM => return error.SystemResources,
+                .SUCCESS => return @intCast(usize, rc),
+                .FAULT => unreachable,
+                .INTR => continue,
+                .INVAL => unreachable,
+                .NOMEM => return error.SystemResources,
                 else => |err| return unexpectedErrno(err),
             }
         }
@@ -5681,11 +5681,11 @@ pub fn ppoll(fds: []pollfd, timeout: ?*const timespec, mask: ?*const sigset_t) P
     }
     const rc = system.ppoll(fds.ptr, fds.len, ts_ptr, mask);
     switch (errno(rc)) {
-        0 => return @intCast(usize, rc),
-        EFAULT => unreachable,
-        EINTR => return error.SignalInterrupt,
-        EINVAL => unreachable,
-        ENOMEM => return error.SystemResources,
+        .SUCCESS => return @intCast(usize, rc),
+        .FAULT => unreachable,
+        .INTR => return error.SignalInterrupt,
+        .INVAL => unreachable,
+        .NOMEM => return error.SystemResources,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -5750,17 +5750,17 @@ pub fn recvfrom(
             }
         } else {
             switch (errno(rc)) {
-                0 => return @intCast(usize, rc),
-                EBADF => unreachable, // always a race condition
-                EFAULT => unreachable,
-                EINVAL => unreachable,
-                ENOTCONN => unreachable,
-                ENOTSOCK => unreachable,
-                EINTR => continue,
-                EAGAIN => return error.WouldBlock,
-                ENOMEM => return error.SystemResources,
-                ECONNREFUSED => return error.ConnectionRefused,
-                ECONNRESET => return error.ConnectionResetByPeer,
+                .SUCCESS => return @intCast(usize, rc),
+                .BADF => unreachable, // always a race condition
+                .FAULT => unreachable,
+                .INVAL => unreachable,
+                .NOTCONN => unreachable,
+                .NOTSOCK => unreachable,
+                .INTR => continue,
+                .AGAIN => return error.WouldBlock,
+                .NOMEM => return error.SystemResources,
+                .CONNREFUSED => return error.ConnectionRefused,
+                .CONNRESET => return error.ConnectionResetByPeer,
                 else => |err| return unexpectedErrno(err),
             }
         }
@@ -5830,8 +5830,8 @@ pub fn sched_yield() SchedYieldError!void {
         return;
     }
     switch (errno(system.sched_yield())) {
-        0 => return,
-        ENOSYS => return error.SystemCannotYield,
+        .SUCCESS => return,
+        .NOSYS => return error.SystemCannotYield,
         else => return error.SystemCannotYield,
     }
 }
@@ -5874,17 +5874,17 @@ pub fn setsockopt(fd: socket_t, level: u32, optname: u32, opt: []const u8) SetSo
         return;
     } else {
         switch (errno(system.setsockopt(fd, level, optname, opt.ptr, @intCast(socklen_t, opt.len)))) {
-            0 => {},
-            EBADF => unreachable, // always a race condition
-            ENOTSOCK => unreachable, // always a race condition
-            EINVAL => unreachable,
-            EFAULT => unreachable,
-            EDOM => return error.TimeoutTooBig,
-            EISCONN => return error.AlreadyConnected,
-            ENOPROTOOPT => return error.InvalidProtocolOption,
-            ENOMEM => return error.SystemResources,
-            ENOBUFS => return error.SystemResources,
-            EPERM => return error.PermissionDenied,
+            .SUCCESS => {},
+            .BADF => unreachable, // always a race condition
+            .NOTSOCK => unreachable, // always a race condition
+            .INVAL => unreachable,
+            .FAULT => unreachable,
+            .DOM => return error.TimeoutTooBig,
+            .ISCONN => return error.AlreadyConnected,
+            .NOPROTOOPT => return error.InvalidProtocolOption,
+            .NOMEM => return error.SystemResources,
+            .NOBUFS => return error.SystemResources,
+            .PERM => return error.PermissionDenied,
             else => |err| return unexpectedErrno(err),
         }
     }
@@ -5909,13 +5909,13 @@ pub fn memfd_createZ(name: [*:0]const u8, flags: u32) MemFdCreateError!fd_t {
     const getErrno = if (use_c) std.c.getErrno else linux.getErrno;
     const rc = sys.memfd_create(name, flags);
     switch (getErrno(rc)) {
-        0 => return @intCast(fd_t, rc),
-        EFAULT => unreachable, // name has invalid memory
-        EINVAL => unreachable, // name/flags are faulty
-        ENFILE => return error.SystemFdQuotaExceeded,
-        EMFILE => return error.ProcessFdQuotaExceeded,
-        ENOMEM => return error.OutOfMemory,
-        ENOSYS => return error.SystemOutdated,
+        .SUCCESS => return @intCast(fd_t, rc),
+        .FAULT => unreachable, // name has invalid memory
+        .INVAL => unreachable, // name/flags are faulty
+        .NFILE => return error.SystemFdQuotaExceeded,
+        .MFILE => return error.ProcessFdQuotaExceeded,
+        .NOMEM => return error.OutOfMemory,
+        .NOSYS => return error.SystemOutdated,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -5940,9 +5940,9 @@ pub fn getrusage(who: i32) rusage {
     var result: rusage = undefined;
     const rc = system.getrusage(who, &result);
     switch (errno(rc)) {
-        0 => return result,
-        EINVAL => unreachable,
-        EFAULT => unreachable,
+        .SUCCESS => return result,
+        .INVAL => unreachable,
+        .FAULT => unreachable,
         else => unreachable,
     }
 }
@@ -5953,10 +5953,10 @@ pub fn tcgetattr(handle: fd_t) TermiosGetError!termios {
     while (true) {
         var term: termios = undefined;
         switch (errno(system.tcgetattr(handle, &term))) {
-            0 => return term,
-            EINTR => continue,
-            EBADF => unreachable,
-            ENOTTY => return error.NotATerminal,
+            .SUCCESS => return term,
+            .INTR => continue,
+            .BADF => unreachable,
+            .NOTTY => return error.NotATerminal,
             else => |err| return unexpectedErrno(err),
         }
     }
@@ -5967,12 +5967,12 @@ pub const TermiosSetError = TermiosGetError || error{ProcessOrphaned};
 pub fn tcsetattr(handle: fd_t, optional_action: TCSA, termios_p: termios) TermiosSetError!void {
     while (true) {
         switch (errno(system.tcsetattr(handle, optional_action, &termios_p))) {
-            0 => return,
-            EBADF => unreachable,
-            EINTR => continue,
-            EINVAL => unreachable,
-            ENOTTY => return error.NotATerminal,
-            EIO => return error.ProcessOrphaned,
+            .SUCCESS => return,
+            .BADF => unreachable,
+            .INTR => continue,
+            .INVAL => unreachable,
+            .NOTTY => return error.NotATerminal,
+            .IO => return error.ProcessOrphaned,
             else => |err| return unexpectedErrno(err),
         }
     }
@@ -5986,15 +5986,15 @@ pub const IoCtl_SIOCGIFINDEX_Error = error{
 pub fn ioctl_SIOCGIFINDEX(fd: fd_t, ifr: *ifreq) IoCtl_SIOCGIFINDEX_Error!void {
     while (true) {
         switch (errno(system.ioctl(fd, SIOCGIFINDEX, @ptrToInt(ifr)))) {
-            0 => return,
-            EINVAL => unreachable, // Bad parameters.
-            ENOTTY => unreachable,
-            ENXIO => unreachable,
-            EBADF => unreachable, // Always a race condition.
-            EFAULT => unreachable, // Bad pointer parameter.
-            EINTR => continue,
-            EIO => return error.FileSystem,
-            ENODEV => return error.InterfaceNotFound,
+            .SUCCESS => return,
+            .INVAL => unreachable, // Bad parameters.
+            .NOTTY => unreachable,
+            .NXIO => unreachable,
+            .BADF => unreachable, // Always a race condition.
+            .FAULT => unreachable, // Bad pointer parameter.
+            .INTR => continue,
+            .IO => return error.FileSystem,
+            .NODEV => return error.InterfaceNotFound,
             else => |err| return unexpectedErrno(err),
         }
     }
@@ -6003,13 +6003,13 @@ pub fn ioctl_SIOCGIFINDEX(fd: fd_t, ifr: *ifreq) IoCtl_SIOCGIFINDEX_Error!void {
 pub fn signalfd(fd: fd_t, mask: *const sigset_t, flags: u32) !fd_t {
     const rc = system.signalfd(fd, mask, flags);
     switch (errno(rc)) {
-        0 => return @intCast(fd_t, rc),
-        EBADF, EINVAL => unreachable,
-        ENFILE => return error.SystemFdQuotaExceeded,
-        ENOMEM => return error.SystemResources,
-        EMFILE => return error.ProcessResources,
-        ENODEV => return error.InodeMountFail,
-        ENOSYS => return error.SystemOutdated,
+        .SUCCESS => return @intCast(fd_t, rc),
+        .BADF, .INVAL => unreachable,
+        .NFILE => return error.SystemFdQuotaExceeded,
+        .NOMEM => return error.SystemResources,
+        .MFILE => return error.ProcessResources,
+        .NODEV => return error.InodeMountFail,
+        .NOSYS => return error.SystemOutdated,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -6030,11 +6030,11 @@ pub fn sync() void {
 pub fn syncfs(fd: fd_t) SyncError!void {
     const rc = system.syncfs(fd);
     switch (errno(rc)) {
-        0 => return,
-        EBADF, EINVAL, EROFS => unreachable,
-        EIO => return error.InputOutput,
-        ENOSPC => return error.NoSpaceLeft,
-        EDQUOT => return error.DiskQuota,
+        .SUCCESS => return,
+        .BADF, .INVAL, .ROFS => unreachable,
+        .IO => return error.InputOutput,
+        .NOSPC => return error.NoSpaceLeft,
+        .DQUOT => return error.DiskQuota,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -6054,11 +6054,11 @@ pub fn fsync(fd: fd_t) SyncError!void {
     }
     const rc = system.fsync(fd);
     switch (errno(rc)) {
-        0 => return,
-        EBADF, EINVAL, EROFS => unreachable,
-        EIO => return error.InputOutput,
-        ENOSPC => return error.NoSpaceLeft,
-        EDQUOT => return error.DiskQuota,
+        .SUCCESS => return,
+        .BADF, .INVAL, .ROFS => unreachable,
+        .IO => return error.InputOutput,
+        .NOSPC => return error.NoSpaceLeft,
+        .DQUOT => return error.DiskQuota,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -6073,11 +6073,11 @@ pub fn fdatasync(fd: fd_t) SyncError!void {
     }
     const rc = system.fdatasync(fd);
     switch (errno(rc)) {
-        0 => return,
-        EBADF, EINVAL, EROFS => unreachable,
-        EIO => return error.InputOutput,
-        ENOSPC => return error.NoSpaceLeft,
-        EDQUOT => return error.DiskQuota,
+        .SUCCESS => return,
+        .BADF, .INVAL, .ROFS => unreachable,
+        .IO => return error.InputOutput,
+        .NOSPC => return error.NoSpaceLeft,
+        .DQUOT => return error.DiskQuota,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -6111,15 +6111,15 @@ pub fn prctl(option: PR, args: anytype) PrctlError!u31 {
 
     const rc = system.prctl(@enumToInt(option), buf[0], buf[1], buf[2], buf[3]);
     switch (errno(rc)) {
-        0 => return @intCast(u31, rc),
-        EACCES => return error.AccessDenied,
-        EBADF => return error.InvalidFileDescriptor,
-        EFAULT => return error.InvalidAddress,
-        EINVAL => unreachable,
-        ENODEV, ENXIO => return error.UnsupportedFeature,
-        EOPNOTSUPP => return error.OperationNotSupported,
-        EPERM, EBUSY => return error.PermissionDenied,
-        ERANGE => unreachable,
+        .SUCCESS => return @intCast(u31, rc),
+        .ACCES => return error.AccessDenied,
+        .BADF => return error.InvalidFileDescriptor,
+        .FAULT => return error.InvalidAddress,
+        .INVAL => unreachable,
+        .NODEV, .NXIO => return error.UnsupportedFeature,
+        .OPNOTSUPP => return error.OperationNotSupported,
+        .PERM, .BUSY => return error.PermissionDenied,
+        .RANGE => unreachable,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -6134,9 +6134,9 @@ pub fn getrlimit(resource: rlimit_resource) GetrlimitError!rlimit {
 
     var limits: rlimit = undefined;
     switch (errno(getrlimit_sym(resource, &limits))) {
-        0 => return limits,
-        EFAULT => unreachable, // bogus pointer
-        EINVAL => unreachable,
+        .SUCCESS => return limits,
+        .FAULT => unreachable, // bogus pointer
+        .INVAL => unreachable,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -6150,10 +6150,10 @@ pub fn setrlimit(resource: rlimit_resource, limits: rlimit) SetrlimitError!void
         system.setrlimit;
 
     switch (errno(setrlimit_sym(resource, &limits))) {
-        0 => return,
-        EFAULT => unreachable, // bogus pointer
-        EINVAL => return error.LimitTooBig, // this could also mean "invalid resource", but that would be unreachable
-        EPERM => return error.PermissionDenied,
+        .SUCCESS => return,
+        .FAULT => unreachable, // bogus pointer
+        .INVAL => return error.LimitTooBig, // this could also mean "invalid resource", but that would be unreachable
+        .PERM => return error.PermissionDenied,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -6194,14 +6194,14 @@ pub const MadviseError = error{
 /// This syscall is optional and is sometimes configured to be disabled.
 pub fn madvise(ptr: [*]align(mem.page_size) u8, length: usize, advice: u32) MadviseError!void {
     switch (errno(system.madvise(ptr, length, advice))) {
-        0 => return,
-        EACCES => return error.AccessDenied,
-        EAGAIN => return error.SystemResources,
-        EBADF => unreachable, // The map exists, but the area maps something that isn't a file.
-        EINVAL => return error.InvalidSyscall,
-        EIO => return error.WouldExceedMaximumResidentSetSize,
-        ENOMEM => return error.OutOfMemory,
-        ENOSYS => return error.MadviseUnavailable,
+        .SUCCESS => return,
+        .ACCES => return error.AccessDenied,
+        .AGAIN => return error.SystemResources,
+        .BADF => unreachable, // The map exists, but the area maps something that isn't a file.
+        .INVAL => return error.InvalidSyscall,
+        .IO => return error.WouldExceedMaximumResidentSetSize,
+        .NOMEM => return error.OutOfMemory,
+        .NOSYS => return error.MadviseUnavailable,
         else => |err| return unexpectedErrno(err),
     }
 }
diff --git a/lib/std/os/bits/darwin.zig b/lib/std/os/bits/darwin.zig
index f39b5948d7..35d507541e 100644
--- a/lib/std/os/bits/darwin.zig
+++ b/lib/std/os/bits/darwin.zig
@@ -866,337 +866,342 @@ pub fn WIFSIGNALED(x: u32) bool {
     return wstatus(x) != wstopped and wstatus(x) != 0;
 }
 
-/// Operation not permitted
-pub const EPERM = 1;
+pub const E = enum(u16) {
+    /// No error occurred.
+    SUCCESS = 0,
 
-/// No such file or directory
-pub const ENOENT = 2;
+    /// Operation not permitted
+    PERM = 1,
 
-/// No such process
-pub const ESRCH = 3;
+    /// No such file or directory
+    NOENT = 2,
 
-/// Interrupted system call
-pub const EINTR = 4;
+    /// No such process
+    SRCH = 3,
 
-/// Input/output error
-pub const EIO = 5;
+    /// Interrupted system call
+    INTR = 4,
 
-/// Device not configured
-pub const ENXIO = 6;
+    /// Input/output error
+    IO = 5,
 
-/// Argument list too long
-pub const E2BIG = 7;
+    /// Device not configured
+    NXIO = 6,
 
-/// Exec format error
-pub const ENOEXEC = 8;
+    /// Argument list too long
+    @"2BIG" = 7,
 
-/// Bad file descriptor
-pub const EBADF = 9;
+    /// Exec format error
+    NOEXEC = 8,
 
-/// No child processes
-pub const ECHILD = 10;
+    /// Bad file descriptor
+    BADF = 9,
 
-/// Resource deadlock avoided
-pub const EDEADLK = 11;
+    /// No child processes
+    CHILD = 10,
 
-/// Cannot allocate memory
-pub const ENOMEM = 12;
+    /// Resource deadlock avoided
+    DEADLK = 11,
 
-/// Permission denied
-pub const EACCES = 13;
+    /// Cannot allocate memory
+    NOMEM = 12,
 
-/// Bad address
-pub const EFAULT = 14;
+    /// Permission denied
+    ACCES = 13,
 
-/// Block device required
-pub const ENOTBLK = 15;
+    /// Bad address
+    FAULT = 14,
 
-/// Device / Resource busy
-pub const EBUSY = 16;
+    /// Block device required
+    NOTBLK = 15,
 
-/// File exists
-pub const EEXIST = 17;
+    /// Device / Resource busy
+    BUSY = 16,
 
-/// Cross-device link
-pub const EXDEV = 18;
+    /// File exists
+    EXIST = 17,
 
-/// Operation not supported by device
-pub const ENODEV = 19;
+    /// Cross-device link
+    XDEV = 18,
 
-/// Not a directory
-pub const ENOTDIR = 20;
+    /// Operation not supported by device
+    NODEV = 19,
 
-/// Is a directory
-pub const EISDIR = 21;
+    /// Not a directory
+    NOTDIR = 20,
 
-/// Invalid argument
-pub const EINVAL = 22;
+    /// Is a directory
+    ISDIR = 21,
 
-/// Too many open files in system
-pub const ENFILE = 23;
+    /// Invalid argument
+    INVAL = 22,
 
-/// Too many open files
-pub const EMFILE = 24;
+    /// Too many open files in system
+    NFILE = 23,
 
-/// Inappropriate ioctl for device
-pub const ENOTTY = 25;
+    /// Too many open files
+    MFILE = 24,
 
-/// Text file busy
-pub const ETXTBSY = 26;
+    /// Inappropriate ioctl for device
+    NOTTY = 25,
 
-/// File too large
-pub const EFBIG = 27;
+    /// Text file busy
+    TXTBSY = 26,
 
-/// No space left on device
-pub const ENOSPC = 28;
+    /// File too large
+    FBIG = 27,
 
-/// Illegal seek
-pub const ESPIPE = 29;
+    /// No space left on device
+    NOSPC = 28,
 
-/// Read-only file system
-pub const EROFS = 30;
+    /// Illegal seek
+    SPIPE = 29,
 
-/// Too many links
-pub const EMLINK = 31;
-/// Broken pipe
+    /// Read-only file system
+    ROFS = 30,
 
-// math software
-pub const EPIPE = 32;
+    /// Too many links
+    MLINK = 31,
 
-/// Numerical argument out of domain
-pub const EDOM = 33;
-/// Result too large
+    /// Broken pipe
+    PIPE = 32,
 
-// non-blocking and interrupt i/o
-pub const ERANGE = 34;
+    // math software
 
-/// Resource temporarily unavailable
-pub const EAGAIN = 35;
+    /// Numerical argument out of domain
+    DOM = 33,
 
-/// Operation would block
-pub const EWOULDBLOCK = EAGAIN;
+    /// Result too large
+    RANGE = 34,
 
-/// Operation now in progress
-pub const EINPROGRESS = 36;
-/// Operation already in progress
+    // non-blocking and interrupt i/o
 
-// ipc/network software -- argument errors
-pub const EALREADY = 37;
+    /// Resource temporarily unavailable
+    /// This is the same code used for `WOULDBLOCK`.
+    AGAIN = 35,
 
-/// Socket operation on non-socket
-pub const ENOTSOCK = 38;
+    /// Operation now in progress
+    INPROGRESS = 36,
 
-/// Destination address required
-pub const EDESTADDRREQ = 39;
+    /// Operation already in progress
+    ALREADY = 37,
 
-/// Message too long
-pub const EMSGSIZE = 40;
+    // ipc/network software -- argument errors
 
-/// Protocol wrong type for socket
-pub const EPROTOTYPE = 41;
+    /// Socket operation on non-socket
+    NOTSOCK = 38,
 
-/// Protocol not available
-pub const ENOPROTOOPT = 42;
+    /// Destination address required
+    DESTADDRREQ = 39,
 
-/// Protocol not supported
-pub const EPROTONOSUPPORT = 43;
+    /// Message too long
+    MSGSIZE = 40,
 
-/// Socket type not supported
-pub const ESOCKTNOSUPPORT = 44;
+    /// Protocol wrong type for socket
+    PROTOTYPE = 41,
 
-/// Operation not supported
-pub const ENOTSUP = 45;
+    /// Protocol not available
+    NOPROTOOPT = 42,
 
-/// Operation not supported. Alias of `ENOTSUP`.
-pub const EOPNOTSUPP = ENOTSUP;
+    /// Protocol not supported
+    PROTONOSUPPORT = 43,
 
-/// Protocol family not supported
-pub const EPFNOSUPPORT = 46;
+    /// Socket type not supported
+    SOCKTNOSUPPORT = 44,
 
-/// Address family not supported by protocol family
-pub const EAFNOSUPPORT = 47;
+    /// Operation not supported
+    /// The same code is used for `NOTSUP`.
+    OPNOTSUPP = 45,
 
-/// Address already in use
-pub const EADDRINUSE = 48;
-/// Can't assign requested address
+    /// Protocol family not supported
+    PFNOSUPPORT = 46,
 
-// ipc/network software -- operational errors
-pub const EADDRNOTAVAIL = 49;
+    /// Address family not supported by protocol family
+    AFNOSUPPORT = 47,
 
-/// Network is down
-pub const ENETDOWN = 50;
+    /// Address already in use
+    ADDRINUSE = 48,
+    /// Can't assign requested address
 
-/// Network is unreachable
-pub const ENETUNREACH = 51;
+    // ipc/network software -- operational errors
+    ADDRNOTAVAIL = 49,
 
-/// Network dropped connection on reset
-pub const ENETRESET = 52;
+    /// Network is down
+    NETDOWN = 50,
 
-/// Software caused connection abort
-pub const ECONNABORTED = 53;
+    /// Network is unreachable
+    NETUNREACH = 51,
 
-/// Connection reset by peer
-pub const ECONNRESET = 54;
+    /// Network dropped connection on reset
+    NETRESET = 52,
 
-/// No buffer space available
-pub const ENOBUFS = 55;
+    /// Software caused connection abort
+    CONNABORTED = 53,
 
-/// Socket is already connected
-pub const EISCONN = 56;
+    /// Connection reset by peer
+    CONNRESET = 54,
 
-/// Socket is not connected
-pub const ENOTCONN = 57;
+    /// No buffer space available
+    NOBUFS = 55,
 
-/// Can't send after socket shutdown
-pub const ESHUTDOWN = 58;
+    /// Socket is already connected
+    ISCONN = 56,
 
-/// Too many references: can't splice
-pub const ETOOMANYREFS = 59;
+    /// Socket is not connected
+    NOTCONN = 57,
 
-/// Operation timed out
-pub const ETIMEDOUT = 60;
+    /// Can't send after socket shutdown
+    SHUTDOWN = 58,
 
-/// Connection refused
-pub const ECONNREFUSED = 61;
+    /// Too many references: can't splice
+    TOOMANYREFS = 59,
 
-/// Too many levels of symbolic links
-pub const ELOOP = 62;
+    /// Operation timed out
+    TIMEDOUT = 60,
 
-/// File name too long
-pub const ENAMETOOLONG = 63;
+    /// Connection refused
+    CONNREFUSED = 61,
 
-/// Host is down
-pub const EHOSTDOWN = 64;
+    /// Too many levels of symbolic links
+    LOOP = 62,
 
-/// No route to host
-pub const EHOSTUNREACH = 65;
-/// Directory not empty
+    /// File name too long
+    NAMETOOLONG = 63,
 
-// quotas & mush
-pub const ENOTEMPTY = 66;
+    /// Host is down
+    HOSTDOWN = 64,
 
-/// Too many processes
-pub const EPROCLIM = 67;
+    /// No route to host
+    HOSTUNREACH = 65,
+    /// Directory not empty
 
-/// Too many users
-pub const EUSERS = 68;
-/// Disc quota exceeded
+    // quotas & mush
+    NOTEMPTY = 66,
 
-// Network File System
-pub const EDQUOT = 69;
+    /// Too many processes
+    PROCLIM = 67,
 
-/// Stale NFS file handle
-pub const ESTALE = 70;
+    /// Too many users
+    USERS = 68,
+    /// Disc quota exceeded
 
-/// Too many levels of remote in path
-pub const EREMOTE = 71;
+    // Network File System
+    DQUOT = 69,
 
-/// RPC struct is bad
-pub const EBADRPC = 72;
+    /// Stale NFS file handle
+    STALE = 70,
 
-/// RPC version wrong
-pub const ERPCMISMATCH = 73;
+    /// Too many levels of remote in path
+    REMOTE = 71,
 
-/// RPC prog. not avail
-pub const EPROGUNAVAIL = 74;
+    /// RPC struct is bad
+    BADRPC = 72,
 
-/// Program version wrong
-pub const EPROGMISMATCH = 75;
+    /// RPC version wrong
+    RPCMISMATCH = 73,
 
-/// Bad procedure for program
-pub const EPROCUNAVAIL = 76;
+    /// RPC prog. not avail
+    PROGUNAVAIL = 74,
 
-/// No locks available
-pub const ENOLCK = 77;
+    /// Program version wrong
+    PROGMISMATCH = 75,
 
-/// Function not implemented
-pub const ENOSYS = 78;
+    /// Bad procedure for program
+    PROCUNAVAIL = 76,
 
-/// Inappropriate file type or format
-pub const EFTYPE = 79;
+    /// No locks available
+    NOLCK = 77,
 
-/// Authentication error
-pub const EAUTH = 80;
-/// Need authenticator
+    /// Function not implemented
+    NOSYS = 78,
 
-// Intelligent device errors
-pub const ENEEDAUTH = 81;
+    /// Inappropriate file type or format
+    FTYPE = 79,
 
-/// Device power is off
-pub const EPWROFF = 82;
+    /// Authentication error
+    AUTH = 80,
 
-/// Device error, e.g. paper out
-pub const EDEVERR = 83;
-/// Value too large to be stored in data type
+    /// Need authenticator
+    NEEDAUTH = 81,
 
-// Program loading errors
-pub const EOVERFLOW = 84;
+    // Intelligent device errors
 
-/// Bad executable
-pub const EBADEXEC = 85;
+    /// Device power is off
+    PWROFF = 82,
 
-/// Bad CPU type in executable
-pub const EBADARCH = 86;
+    /// Device error, e.g. paper out
+    DEVERR = 83,
 
-/// Shared library version mismatch
-pub const ESHLIBVERS = 87;
+    /// Value too large to be stored in data type
+    OVERFLOW = 84,
 
-/// Malformed Macho file
-pub const EBADMACHO = 88;
+    // Program loading errors
 
-/// Operation canceled
-pub const ECANCELED = 89;
+    /// Bad executable
+    BADEXEC = 85,
 
-/// Identifier removed
-pub const EIDRM = 90;
+    /// Bad CPU type in executable
+    BADARCH = 86,
 
-/// No message of desired type
-pub const ENOMSG = 91;
+    /// Shared library version mismatch
+    SHLIBVERS = 87,
 
-/// Illegal byte sequence
-pub const EILSEQ = 92;
+    /// Malformed Macho file
+    BADMACHO = 88,
 
-/// Attribute not found
-pub const ENOATTR = 93;
+    /// Operation canceled
+    CANCELED = 89,
 
-/// Bad message
-pub const EBADMSG = 94;
+    /// Identifier removed
+    IDRM = 90,
 
-/// Reserved
-pub const EMULTIHOP = 95;
+    /// No message of desired type
+    NOMSG = 91,
 
-/// No message available on STREAM
-pub const ENODATA = 96;
+    /// Illegal byte sequence
+    ILSEQ = 92,
 
-/// Reserved
-pub const ENOLINK = 97;
+    /// Attribute not found
+    NOATTR = 93,
 
-/// No STREAM resources
-pub const ENOSR = 98;
+    /// Bad message
+    BADMSG = 94,
 
-/// Not a STREAM
-pub const ENOSTR = 99;
+    /// Reserved
+    MULTIHOP = 95,
 
-/// Protocol error
-pub const EPROTO = 100;
+    /// No message available on STREAM
+    NODATA = 96,
 
-/// STREAM ioctl timeout
-pub const ETIME = 101;
+    /// Reserved
+    NOLINK = 97,
 
-/// No such policy registered
-pub const ENOPOLICY = 103;
+    /// No STREAM resources
+    NOSR = 98,
 
-/// State not recoverable
-pub const ENOTRECOVERABLE = 104;
+    /// Not a STREAM
+    NOSTR = 99,
 
-/// Previous owner died
-pub const EOWNERDEAD = 105;
+    /// Protocol error
+    PROTO = 100,
 
-/// Interface output queue is full
-pub const EQFULL = 106;
+    /// STREAM ioctl timeout
+    TIME = 101,
 
-/// Must be equal largest errno
-pub const ELAST = 106;
+    /// No such policy registered
+    NOPOLICY = 103,
+
+    /// State not recoverable
+    NOTRECOVERABLE = 104,
+
+    /// Previous owner died
+    OWNERDEAD = 105,
+
+    /// Interface output queue is full
+    QFULL = 106,
+
+    _,
+};
 
 pub const SIGSTKSZ = 131072;
 pub const MINSIGSTKSZ = 32768;
diff --git a/lib/std/os/bits/dragonfly.zig b/lib/std/os/bits/dragonfly.zig
index dfa54972f3..cf647a8438 100644
--- a/lib/std/os/bits/dragonfly.zig
+++ b/lib/std/os/bits/dragonfly.zig
@@ -25,103 +25,108 @@ pub const gid_t = u32;
 pub const time_t = isize;
 pub const suseconds_t = c_long;
 
-pub const ENOTSUP = EOPNOTSUPP;
-pub const EWOULDBLOCK = EAGAIN;
-pub const EPERM = 1;
-pub const ENOENT = 2;
-pub const ESRCH = 3;
-pub const EINTR = 4;
-pub const EIO = 5;
-pub const ENXIO = 6;
-pub const E2BIG = 7;
-pub const ENOEXEC = 8;
-pub const EBADF = 9;
-pub const ECHILD = 10;
-pub const EDEADLK = 11;
-pub const ENOMEM = 12;
-pub const EACCES = 13;
-pub const EFAULT = 14;
-pub const ENOTBLK = 15;
-pub const EBUSY = 16;
-pub const EEXIST = 17;
-pub const EXDEV = 18;
-pub const ENODEV = 19;
-pub const ENOTDIR = 20;
-pub const EISDIR = 21;
-pub const EINVAL = 22;
-pub const ENFILE = 23;
-pub const EMFILE = 24;
-pub const ENOTTY = 25;
-pub const ETXTBSY = 26;
-pub const EFBIG = 27;
-pub const ENOSPC = 28;
-pub const ESPIPE = 29;
-pub const EROFS = 30;
-pub const EMLINK = 31;
-pub const EPIPE = 32;
-pub const EDOM = 33;
-pub const ERANGE = 34;
-pub const EAGAIN = 35;
-pub const EINPROGRESS = 36;
-pub const EALREADY = 37;
-pub const ENOTSOCK = 38;
-pub const EDESTADDRREQ = 39;
-pub const EMSGSIZE = 40;
-pub const EPROTOTYPE = 41;
-pub const ENOPROTOOPT = 42;
-pub const EPROTONOSUPPORT = 43;
-pub const ESOCKTNOSUPPORT = 44;
-pub const EOPNOTSUPP = 45;
-pub const EPFNOSUPPORT = 46;
-pub const EAFNOSUPPORT = 47;
-pub const EADDRINUSE = 48;
-pub const EADDRNOTAVAIL = 49;
-pub const ENETDOWN = 50;
-pub const ENETUNREACH = 51;
-pub const ENETRESET = 52;
-pub const ECONNABORTED = 53;
-pub const ECONNRESET = 54;
-pub const ENOBUFS = 55;
-pub const EISCONN = 56;
-pub const ENOTCONN = 57;
-pub const ESHUTDOWN = 58;
-pub const ETOOMANYREFS = 59;
-pub const ETIMEDOUT = 60;
-pub const ECONNREFUSED = 61;
-pub const ELOOP = 62;
-pub const ENAMETOOLONG = 63;
-pub const EHOSTDOWN = 64;
-pub const EHOSTUNREACH = 65;
-pub const ENOTEMPTY = 66;
-pub const EPROCLIM = 67;
-pub const EUSERS = 68;
-pub const EDQUOT = 69;
-pub const ESTALE = 70;
-pub const EREMOTE = 71;
-pub const EBADRPC = 72;
-pub const ERPCMISMATCH = 73;
-pub const EPROGUNAVAIL = 74;
-pub const EPROGMISMATCH = 75;
-pub const EPROCUNAVAIL = 76;
-pub const ENOLCK = 77;
-pub const ENOSYS = 78;
-pub const EFTYPE = 79;
-pub const EAUTH = 80;
-pub const ENEEDAUTH = 81;
-pub const EIDRM = 82;
-pub const ENOMSG = 83;
-pub const EOVERFLOW = 84;
-pub const ECANCELED = 85;
-pub const EILSEQ = 86;
-pub const ENOATTR = 87;
-pub const EDOOFUS = 88;
-pub const EBADMSG = 89;
-pub const EMULTIHOP = 90;
-pub const ENOLINK = 91;
-pub const EPROTO = 92;
-pub const ENOMEDIUM = 93;
-pub const ELAST = 99;
-pub const EASYNC = 99;
+pub const E = enum(u16) {
+    /// No error occurred.
+    SUCCESS = 0,
+
+    PERM = 1,
+    NOENT = 2,
+    SRCH = 3,
+    INTR = 4,
+    IO = 5,
+    NXIO = 6,
+    @"2BIG" = 7,
+    NOEXEC = 8,
+    BADF = 9,
+    CHILD = 10,
+    DEADLK = 11,
+    NOMEM = 12,
+    ACCES = 13,
+    FAULT = 14,
+    NOTBLK = 15,
+    BUSY = 16,
+    EXIST = 17,
+    XDEV = 18,
+    NODEV = 19,
+    NOTDIR = 20,
+    ISDIR = 21,
+    INVAL = 22,
+    NFILE = 23,
+    MFILE = 24,
+    NOTTY = 25,
+    TXTBSY = 26,
+    FBIG = 27,
+    NOSPC = 28,
+    SPIPE = 29,
+    ROFS = 30,
+    MLINK = 31,
+    PIPE = 32,
+    DOM = 33,
+    RANGE = 34,
+    /// This code is also used for `WOULDBLOCK`.
+    AGAIN = 35,
+    INPROGRESS = 36,
+    ALREADY = 37,
+    NOTSOCK = 38,
+    DESTADDRREQ = 39,
+    MSGSIZE = 40,
+    PROTOTYPE = 41,
+    NOPROTOOPT = 42,
+    PROTONOSUPPORT = 43,
+    SOCKTNOSUPPORT = 44,
+    /// This code is also used for `NOTSUP`.
+    OPNOTSUPP = 45,
+    PFNOSUPPORT = 46,
+    AFNOSUPPORT = 47,
+    ADDRINUSE = 48,
+    ADDRNOTAVAIL = 49,
+    NETDOWN = 50,
+    NETUNREACH = 51,
+    NETRESET = 52,
+    CONNABORTED = 53,
+    CONNRESET = 54,
+    NOBUFS = 55,
+    ISCONN = 56,
+    NOTCONN = 57,
+    SHUTDOWN = 58,
+    TOOMANYREFS = 59,
+    TIMEDOUT = 60,
+    CONNREFUSED = 61,
+    LOOP = 62,
+    NAMETOOLONG = 63,
+    HOSTDOWN = 64,
+    HOSTUNREACH = 65,
+    NOTEMPTY = 66,
+    PROCLIM = 67,
+    USERS = 68,
+    DQUOT = 69,
+    STALE = 70,
+    REMOTE = 71,
+    BADRPC = 72,
+    RPCMISMATCH = 73,
+    PROGUNAVAIL = 74,
+    PROGMISMATCH = 75,
+    PROCUNAVAIL = 76,
+    NOLCK = 77,
+    NOSYS = 78,
+    FTYPE = 79,
+    AUTH = 80,
+    NEEDAUTH = 81,
+    IDRM = 82,
+    NOMSG = 83,
+    OVERFLOW = 84,
+    CANCELED = 85,
+    ILSEQ = 86,
+    NOATTR = 87,
+    DOOFUS = 88,
+    BADMSG = 89,
+    MULTIHOP = 90,
+    NOLINK = 91,
+    PROTO = 92,
+    NOMEDIUM = 93,
+    ASYNC = 99,
+    _,
+};
 
 pub const STDIN_FILENO = 0;
 pub const STDOUT_FILENO = 1;
diff --git a/lib/std/os/bits/freebsd.zig b/lib/std/os/bits/freebsd.zig
index b08c31c8e3..b60676e266 100644
--- a/lib/std/os/bits/freebsd.zig
+++ b/lib/std/os/bits/freebsd.zig
@@ -887,127 +887,134 @@ pub usingnamespace switch (builtin.target.cpu.arch) {
     else => struct {},
 };
 
-pub const EPERM = 1; // Operation not permitted
-pub const ENOENT = 2; // No such file or directory
-pub const ESRCH = 3; // No such process
-pub const EINTR = 4; // Interrupted system call
-pub const EIO = 5; // Input/output error
-pub const ENXIO = 6; // Device not configured
-pub const E2BIG = 7; // Argument list too long
-pub const ENOEXEC = 8; // Exec format error
-pub const EBADF = 9; // Bad file descriptor
-pub const ECHILD = 10; // No child processes
-pub const EDEADLK = 11; // Resource deadlock avoided
-// 11 was EAGAIN
-pub const ENOMEM = 12; // Cannot allocate memory
-pub const EACCES = 13; // Permission denied
-pub const EFAULT = 14; // Bad address
-pub const ENOTBLK = 15; // Block device required
-pub const EBUSY = 16; // Device busy
-pub const EEXIST = 17; // File exists
-pub const EXDEV = 18; // Cross-device link
-pub const ENODEV = 19; // Operation not supported by device
-pub const ENOTDIR = 20; // Not a directory
-pub const EISDIR = 21; // Is a directory
-pub const EINVAL = 22; // Invalid argument
-pub const ENFILE = 23; // Too many open files in system
-pub const EMFILE = 24; // Too many open files
-pub const ENOTTY = 25; // Inappropriate ioctl for device
-pub const ETXTBSY = 26; // Text file busy
-pub const EFBIG = 27; // File too large
-pub const ENOSPC = 28; // No space left on device
-pub const ESPIPE = 29; // Illegal seek
-pub const EROFS = 30; // Read-only filesystem
-pub const EMLINK = 31; // Too many links
-pub const EPIPE = 32; // Broken pipe
+pub const E = enum(u16) {
+    /// No error occurred.
+    SUCCESS = 0,
 
-// math software
-pub const EDOM = 33; // Numerical argument out of domain
-pub const ERANGE = 34; // Result too large
+    PERM = 1, // Operation not permitted
+    NOENT = 2, // No such file or directory
+    SRCH = 3, // No such process
+    INTR = 4, // Interrupted system call
+    IO = 5, // Input/output error
+    NXIO = 6, // Device not configured
+    @"2BIG" = 7, // Argument list too long
+    NOEXEC = 8, // Exec format error
+    BADF = 9, // Bad file descriptor
+    CHILD = 10, // No child processes
+    DEADLK = 11, // Resource deadlock avoided
+    // 11 was AGAIN
+    NOMEM = 12, // Cannot allocate memory
+    ACCES = 13, // Permission denied
+    FAULT = 14, // Bad address
+    NOTBLK = 15, // Block device required
+    BUSY = 16, // Device busy
+    EXIST = 17, // File exists
+    XDEV = 18, // Cross-device link
+    NODEV = 19, // Operation not supported by device
+    NOTDIR = 20, // Not a directory
+    ISDIR = 21, // Is a directory
+    INVAL = 22, // Invalid argument
+    NFILE = 23, // Too many open files in system
+    MFILE = 24, // Too many open files
+    NOTTY = 25, // Inappropriate ioctl for device
+    TXTBSY = 26, // Text file busy
+    FBIG = 27, // File too large
+    NOSPC = 28, // No space left on device
+    SPIPE = 29, // Illegal seek
+    ROFS = 30, // Read-only filesystem
+    MLINK = 31, // Too many links
+    PIPE = 32, // Broken pipe
 
-// non-blocking and interrupt i/o
-pub const EAGAIN = 35; // Resource temporarily unavailable
-pub const EWOULDBLOCK = EAGAIN; // Operation would block
-pub const EINPROGRESS = 36; // Operation now in progress
-pub const EALREADY = 37; // Operation already in progress
+    // math software
+    DOM = 33, // Numerical argument out of domain
+    RANGE = 34, // Result too large
 
-// ipc/network software -- argument errors
-pub const ENOTSOCK = 38; // Socket operation on non-socket
-pub const EDESTADDRREQ = 39; // Destination address required
-pub const EMSGSIZE = 40; // Message too long
-pub const EPROTOTYPE = 41; // Protocol wrong type for socket
-pub const ENOPROTOOPT = 42; // Protocol not available
-pub const EPROTONOSUPPORT = 43; // Protocol not supported
-pub const ESOCKTNOSUPPORT = 44; // Socket type not supported
-pub const EOPNOTSUPP = 45; // Operation not supported
-pub const ENOTSUP = EOPNOTSUPP; // Operation not supported
-pub const EPFNOSUPPORT = 46; // Protocol family not supported
-pub const EAFNOSUPPORT = 47; // Address family not supported by protocol family
-pub const EADDRINUSE = 48; // Address already in use
-pub const EADDRNOTAVAIL = 49; // Can't assign requested address
+    // non-blocking and interrupt i/o
 
-// ipc/network software -- operational errors
-pub const ENETDOWN = 50; // Network is down
-pub const ENETUNREACH = 51; // Network is unreachable
-pub const ENETRESET = 52; // Network dropped connection on reset
-pub const ECONNABORTED = 53; // Software caused connection abort
-pub const ECONNRESET = 54; // Connection reset by peer
-pub const ENOBUFS = 55; // No buffer space available
-pub const EISCONN = 56; // Socket is already connected
-pub const ENOTCONN = 57; // Socket is not connected
-pub const ESHUTDOWN = 58; // Can't send after socket shutdown
-pub const ETOOMANYREFS = 59; // Too many references: can't splice
-pub const ETIMEDOUT = 60; // Operation timed out
-pub const ECONNREFUSED = 61; // Connection refused
+    /// Resource temporarily unavailable
+    /// This code is also used for `WOULDBLOCK`: operation would block.
+    AGAIN = 35,
+    INPROGRESS = 36, // Operation now in progress
+    ALREADY = 37, // Operation already in progress
 
-pub const ELOOP = 62; // Too many levels of symbolic links
-pub const ENAMETOOLONG = 63; // File name too long
+    // ipc/network software -- argument errors
+    NOTSOCK = 38, // Socket operation on non-socket
+    DESTADDRREQ = 39, // Destination address required
+    MSGSIZE = 40, // Message too long
+    PROTOTYPE = 41, // Protocol wrong type for socket
+    NOPROTOOPT = 42, // Protocol not available
+    PROTONOSUPPORT = 43, // Protocol not supported
+    SOCKTNOSUPPORT = 44, // Socket type not supported
+    /// Operation not supported
+    /// This code is also used for `NOTSUP`.
+    OPNOTSUPP = 45,
+    PFNOSUPPORT = 46, // Protocol family not supported
+    AFNOSUPPORT = 47, // Address family not supported by protocol family
+    ADDRINUSE = 48, // Address already in use
+    ADDRNOTAVAIL = 49, // Can't assign requested address
 
-// should be rearranged
-pub const EHOSTDOWN = 64; // Host is down
-pub const EHOSTUNREACH = 65; // No route to host
-pub const ENOTEMPTY = 66; // Directory not empty
+    // ipc/network software -- operational errors
+    NETDOWN = 50, // Network is down
+    NETUNREACH = 51, // Network is unreachable
+    NETRESET = 52, // Network dropped connection on reset
+    CONNABORTED = 53, // Software caused connection abort
+    CONNRESET = 54, // Connection reset by peer
+    NOBUFS = 55, // No buffer space available
+    ISCONN = 56, // Socket is already connected
+    NOTCONN = 57, // Socket is not connected
+    SHUTDOWN = 58, // Can't send after socket shutdown
+    TOOMANYREFS = 59, // Too many references: can't splice
+    TIMEDOUT = 60, // Operation timed out
+    CONNREFUSED = 61, // Connection refused
 
-// quotas & mush
-pub const EPROCLIM = 67; // Too many processes
-pub const EUSERS = 68; // Too many users
-pub const EDQUOT = 69; // Disc quota exceeded
+    LOOP = 62, // Too many levels of symbolic links
+    NAMETOOLONG = 63, // File name too long
 
-// Network File System
-pub const ESTALE = 70; // Stale NFS file handle
-pub const EREMOTE = 71; // Too many levels of remote in path
-pub const EBADRPC = 72; // RPC struct is bad
-pub const ERPCMISMATCH = 73; // RPC version wrong
-pub const EPROGUNAVAIL = 74; // RPC prog. not avail
-pub const EPROGMISMATCH = 75; // Program version wrong
-pub const EPROCUNAVAIL = 76; // Bad procedure for program
+    // should be rearranged
+    HOSTDOWN = 64, // Host is down
+    HOSTUNREACH = 65, // No route to host
+    NOTEMPTY = 66, // Directory not empty
 
-pub const ENOLCK = 77; // No locks available
-pub const ENOSYS = 78; // Function not implemented
+    // quotas & mush
+    PROCLIM = 67, // Too many processes
+    USERS = 68, // Too many users
+    DQUOT = 69, // Disc quota exceeded
 
-pub const EFTYPE = 79; // Inappropriate file type or format
-pub const EAUTH = 80; // Authentication error
-pub const ENEEDAUTH = 81; // Need authenticator
-pub const EIDRM = 82; // Identifier removed
-pub const ENOMSG = 83; // No message of desired type
-pub const EOVERFLOW = 84; // Value too large to be stored in data type
-pub const ECANCELED = 85; // Operation canceled
-pub const EILSEQ = 86; // Illegal byte sequence
-pub const ENOATTR = 87; // Attribute not found
+    // Network File System
+    STALE = 70, // Stale NFS file handle
+    REMOTE = 71, // Too many levels of remote in path
+    BADRPC = 72, // RPC struct is bad
+    RPCMISMATCH = 73, // RPC version wrong
+    PROGUNAVAIL = 74, // RPC prog. not avail
+    PROGMISMATCH = 75, // Program version wrong
+    PROCUNAVAIL = 76, // Bad procedure for program
 
-pub const EDOOFUS = 88; // Programming error
+    NOLCK = 77, // No locks available
+    NOSYS = 78, // Function not implemented
 
-pub const EBADMSG = 89; // Bad message
-pub const EMULTIHOP = 90; // Multihop attempted
-pub const ENOLINK = 91; // Link has been severed
-pub const EPROTO = 92; // Protocol error
+    FTYPE = 79, // Inappropriate file type or format
+    AUTH = 80, // Authentication error
+    NEEDAUTH = 81, // Need authenticator
+    IDRM = 82, // Identifier removed
+    NOMSG = 83, // No message of desired type
+    OVERFLOW = 84, // Value too large to be stored in data type
+    CANCELED = 85, // Operation canceled
+    ILSEQ = 86, // Illegal byte sequence
+    NOATTR = 87, // Attribute not found
 
-pub const ENOTCAPABLE = 93; // Capabilities insufficient
-pub const ECAPMODE = 94; // Not permitted in capability mode
-pub const ENOTRECOVERABLE = 95; // State not recoverable
-pub const EOWNERDEAD = 96; // Previous owner died
+    DOOFUS = 88, // Programming error
 
-pub const ELAST = 96; // Must be equal largest errno
+    BADMSG = 89, // Bad message
+    MULTIHOP = 90, // Multihop attempted
+    NOLINK = 91, // Link has been severed
+    PROTO = 92, // Protocol error
+
+    NOTCAPABLE = 93, // Capabilities insufficient
+    CAPMODE = 94, // Not permitted in capability mode
+    NOTRECOVERABLE = 95, // State not recoverable
+    OWNERDEAD = 96, // Previous owner died
+    _,
+};
 
 pub const MINSIGSTKSZ = switch (builtin.target.cpu.arch) {
     .i386, .x86_64 => 2048,
diff --git a/lib/std/os/bits/haiku.zig b/lib/std/os/bits/haiku.zig
index b3ea4aa0e2..8421c80a52 100644
--- a/lib/std/os/bits/haiku.zig
+++ b/lib/std/os/bits/haiku.zig
@@ -734,125 +734,130 @@ pub const sigset_t = extern struct {
     __bits: [_SIG_WORDS]u32,
 };
 
-pub const EPERM = -0x7ffffff1; // Operation not permitted
-pub const ENOENT = -0x7fff9ffd; // No such file or directory
-pub const ESRCH = -0x7fff8ff3; // No such process
-pub const EINTR = -0x7ffffff6; // Interrupted system call
-pub const EIO = -0x7fffffff; // Input/output error
-pub const ENXIO = -0x7fff8ff5; // Device not configured
-pub const E2BIG = -0x7fff8fff; // Argument list too long
-pub const ENOEXEC = -0x7fffecfe; // Exec format error
-pub const ECHILD = -0x7fff8ffe; // No child processes
-pub const EDEADLK = -0x7fff8ffd; // Resource deadlock avoided
-pub const ENOMEM = -0x80000000; // Cannot allocate memory
-pub const EACCES = -0x7ffffffe; // Permission denied
-pub const EFAULT = -0x7fffecff; // Bad address
-pub const EBUSY = -0x7ffffff2; // Device busy
-pub const EEXIST = -0x7fff9ffe; // File exists
-pub const EXDEV = -0x7fff9ff5; // Cross-device link
-pub const ENODEV = -0x7fff8ff9; // Operation not supported by device
-pub const ENOTDIR = -0x7fff9ffb; // Not a directory
-pub const EISDIR = -0x7fff9ff7; // Is a directory
-pub const EINVAL = -0x7ffffffb; // Invalid argument
-pub const ENFILE = -0x7fff8ffa; // Too many open files in system
-pub const EMFILE = -0x7fff9ff6; // Too many open files
-pub const ENOTTY = -0x7fff8ff6; // Inappropriate ioctl for device
-pub const ETXTBSY = -0x7fff8fc5; // Text file busy
-pub const EFBIG = -0x7fff8ffc; // File too large
-pub const ENOSPC = -0x7fff9ff9; // No space left on device
-pub const ESPIPE = -0x7fff8ff4; // Illegal seek
-pub const EROFS = -0x7fff9ff8; // Read-only filesystem
-pub const EMLINK = -0x7fff8ffb; // Too many links
-pub const EPIPE = -0x7fff9ff3; // Broken pipe
-pub const EBADF = -0x7fffa000; // Bad file descriptor
+pub const E = enum(i32) {
+    /// No error occurred.
+    SUCCESS = 0,
+    PERM = -0x7ffffff1, // Operation not permitted
+    NOENT = -0x7fff9ffd, // No such file or directory
+    SRCH = -0x7fff8ff3, // No such process
+    INTR = -0x7ffffff6, // Interrupted system call
+    IO = -0x7fffffff, // Input/output error
+    NXIO = -0x7fff8ff5, // Device not configured
+    @"2BIG" = -0x7fff8fff, // Argument list too long
+    NOEXEC = -0x7fffecfe, // Exec format error
+    CHILD = -0x7fff8ffe, // No child processes
+    DEADLK = -0x7fff8ffd, // Resource deadlock avoided
+    NOMEM = -0x80000000, // Cannot allocate memory
+    ACCES = -0x7ffffffe, // Permission denied
+    FAULT = -0x7fffecff, // Bad address
+    BUSY = -0x7ffffff2, // Device busy
+    EXIST = -0x7fff9ffe, // File exists
+    XDEV = -0x7fff9ff5, // Cross-device link
+    NODEV = -0x7fff8ff9, // Operation not supported by device
+    NOTDIR = -0x7fff9ffb, // Not a directory
+    ISDIR = -0x7fff9ff7, // Is a directory
+    INVAL = -0x7ffffffb, // Invalid argument
+    NFILE = -0x7fff8ffa, // Too many open files in system
+    MFILE = -0x7fff9ff6, // Too many open files
+    NOTTY = -0x7fff8ff6, // Inappropriate ioctl for device
+    TXTBSY = -0x7fff8fc5, // Text file busy
+    FBIG = -0x7fff8ffc, // File too large
+    NOSPC = -0x7fff9ff9, // No space left on device
+    SPIPE = -0x7fff8ff4, // Illegal seek
+    ROFS = -0x7fff9ff8, // Read-only filesystem
+    MLINK = -0x7fff8ffb, // Too many links
+    PIPE = -0x7fff9ff3, // Broken pipe
+    BADF = -0x7fffa000, // Bad file descriptor
 
-// math software
-pub const EDOM = 33; // Numerical argument out of domain
-pub const ERANGE = 34; // Result too large
+    // math software
+    DOM = 33, // Numerical argument out of domain
+    RANGE = 34, // Result too large
 
-// non-blocking and interrupt i/o
-pub const EAGAIN = -0x7ffffff5;
-pub const EWOULDBLOCK = -0x7ffffff5;
-pub const EINPROGRESS = -0x7fff8fdc;
-pub const EALREADY = -0x7fff8fdb;
+    // non-blocking and interrupt i/o
 
-// ipc/network software -- argument errors
-pub const ENOTSOCK = 38; // Socket operation on non-socket
-pub const EDESTADDRREQ = 39; // Destination address required
-pub const EMSGSIZE = 40; // Message too long
-pub const EPROTOTYPE = 41; // Protocol wrong type for socket
-pub const ENOPROTOOPT = 42; // Protocol not available
-pub const EPROTONOSUPPORT = 43; // Protocol not supported
-pub const ESOCKTNOSUPPORT = 44; // Socket type not supported
-pub const EOPNOTSUPP = 45; // Operation not supported
-pub const ENOTSUP = EOPNOTSUPP; // Operation not supported
-pub const EPFNOSUPPORT = 46; // Protocol family not supported
-pub const EAFNOSUPPORT = 47; // Address family not supported by protocol family
-pub const EADDRINUSE = 48; // Address already in use
-pub const EADDRNOTAVAIL = 49; // Can't assign requested address
+    /// Also used for `WOULDBLOCK`.
+    AGAIN = -0x7ffffff5,
+    INPROGRESS = -0x7fff8fdc,
+    ALREADY = -0x7fff8fdb,
 
-// ipc/network software -- operational errors
-pub const ENETDOWN = 50; // Network is down
-pub const ENETUNREACH = 51; // Network is unreachable
-pub const ENETRESET = 52; // Network dropped connection on reset
-pub const ECONNABORTED = 53; // Software caused connection abort
-pub const ECONNRESET = 54; // Connection reset by peer
-pub const ENOBUFS = 55; // No buffer space available
-pub const EISCONN = 56; // Socket is already connected
-pub const ENOTCONN = 57; // Socket is not connected
-pub const ESHUTDOWN = 58; // Can't send after socket shutdown
-pub const ETOOMANYREFS = 59; // Too many references: can't splice
-pub const ETIMEDOUT = 60; // Operation timed out
-pub const ECONNREFUSED = 61; // Connection refused
+    // ipc/network software -- argument errors
+    NOTSOCK = 38, // Socket operation on non-socket
+    DESTADDRREQ = 39, // Destination address required
+    MSGSIZE = 40, // Message too long
+    PROTOTYPE = 41, // Protocol wrong type for socket
+    NOPROTOOPT = 42, // Protocol not available
+    PROTONOSUPPORT = 43, // Protocol not supported
+    SOCKTNOSUPPORT = 44, // Socket type not supported
+    /// Also used for `NOTSUP`.
+    OPNOTSUPP = 45, // Operation not supported
+    PFNOSUPPORT = 46, // Protocol family not supported
+    AFNOSUPPORT = 47, // Address family not supported by protocol family
+    ADDRINUSE = 48, // Address already in use
+    ADDRNOTAVAIL = 49, // Can't assign requested address
 
-pub const ELOOP = 62; // Too many levels of symbolic links
-pub const ENAMETOOLONG = 63; // File name too long
+    // ipc/network software -- operational errors
+    NETDOWN = 50, // Network is down
+    NETUNREACH = 51, // Network is unreachable
+    NETRESET = 52, // Network dropped connection on reset
+    CONNABORTED = 53, // Software caused connection abort
+    CONNRESET = 54, // Connection reset by peer
+    NOBUFS = 55, // No buffer space available
+    ISCONN = 56, // Socket is already connected
+    NOTCONN = 57, // Socket is not connected
+    SHUTDOWN = 58, // Can't send after socket shutdown
+    TOOMANYREFS = 59, // Too many references: can't splice
+    TIMEDOUT = 60, // Operation timed out
+    CONNREFUSED = 61, // Connection refused
 
-// should be rearranged
-pub const EHOSTDOWN = 64; // Host is down
-pub const EHOSTUNREACH = 65; // No route to host
-pub const ENOTEMPTY = 66; // Directory not empty
+    LOOP = 62, // Too many levels of symbolic links
+    NAMETOOLONG = 63, // File name too long
 
-// quotas & mush
-pub const EPROCLIM = 67; // Too many processes
-pub const EUSERS = 68; // Too many users
-pub const EDQUOT = 69; // Disc quota exceeded
+    // should be rearranged
+    HOSTDOWN = 64, // Host is down
+    HOSTUNREACH = 65, // No route to host
+    NOTEMPTY = 66, // Directory not empty
 
-// Network File System
-pub const ESTALE = 70; // Stale NFS file handle
-pub const EREMOTE = 71; // Too many levels of remote in path
-pub const EBADRPC = 72; // RPC struct is bad
-pub const ERPCMISMATCH = 73; // RPC version wrong
-pub const EPROGUNAVAIL = 74; // RPC prog. not avail
-pub const EPROGMISMATCH = 75; // Program version wrong
-pub const EPROCUNAVAIL = 76; // Bad procedure for program
+    // quotas & mush
+    PROCLIM = 67, // Too many processes
+    USERS = 68, // Too many users
+    DQUOT = 69, // Disc quota exceeded
 
-pub const ENOLCK = 77; // No locks available
-pub const ENOSYS = 78; // Function not implemented
+    // Network File System
+    STALE = 70, // Stale NFS file handle
+    REMOTE = 71, // Too many levels of remote in path
+    BADRPC = 72, // RPC struct is bad
+    RPCMISMATCH = 73, // RPC version wrong
+    PROGUNAVAIL = 74, // RPC prog. not avail
+    PROGMISMATCH = 75, // Program version wrong
+    PROCUNAVAIL = 76, // Bad procedure for program
 
-pub const EFTYPE = 79; // Inappropriate file type or format
-pub const EAUTH = 80; // Authentication error
-pub const ENEEDAUTH = 81; // Need authenticator
-pub const EIDRM = 82; // Identifier removed
-pub const ENOMSG = 83; // No message of desired type
-pub const EOVERFLOW = 84; // Value too large to be stored in data type
-pub const ECANCELED = 85; // Operation canceled
-pub const EILSEQ = 86; // Illegal byte sequence
-pub const ENOATTR = 87; // Attribute not found
+    NOLCK = 77, // No locks available
+    NOSYS = 78, // Function not implemented
 
-pub const EDOOFUS = 88; // Programming error
+    FTYPE = 79, // Inappropriate file type or format
+    AUTH = 80, // Authentication error
+    NEEDAUTH = 81, // Need authenticator
+    IDRM = 82, // Identifier removed
+    NOMSG = 83, // No message of desired type
+    OVERFLOW = 84, // Value too large to be stored in data type
+    CANCELED = 85, // Operation canceled
+    ILSEQ = 86, // Illegal byte sequence
+    NOATTR = 87, // Attribute not found
 
-pub const EBADMSG = 89; // Bad message
-pub const EMULTIHOP = 90; // Multihop attempted
-pub const ENOLINK = 91; // Link has been severed
-pub const EPROTO = 92; // Protocol error
+    DOOFUS = 88, // Programming error
 
-pub const ENOTCAPABLE = 93; // Capabilities insufficient
-pub const ECAPMODE = 94; // Not permitted in capability mode
-pub const ENOTRECOVERABLE = 95; // State not recoverable
-pub const EOWNERDEAD = 96; // Previous owner died
+    BADMSG = 89, // Bad message
+    MULTIHOP = 90, // Multihop attempted
+    NOLINK = 91, // Link has been severed
+    PROTO = 92, // Protocol error
 
-pub const ELAST = 96; // Must be equal largest errno
+    NOTCAPABLE = 93, // Capabilities insufficient
+    CAPMODE = 94, // Not permitted in capability mode
+    NOTRECOVERABLE = 95, // State not recoverable
+    OWNERDEAD = 96, // Previous owner died
+
+    _,
+};
 
 pub const MINSIGSTKSZ = switch (builtin.cpu.arch) {
     .i386, .x86_64 => 2048,
diff --git a/lib/std/os/bits/linux.zig b/lib/std/os/bits/linux.zig
index ffe74b74e9..1dbc552b3c 100644
--- a/lib/std/os/bits/linux.zig
+++ b/lib/std/os/bits/linux.zig
@@ -8,10 +8,10 @@ const maxInt = std.math.maxInt;
 const arch = @import("builtin").target.cpu.arch;
 pub usingnamespace @import("posix.zig");
 
-pub usingnamespace switch (arch) {
-    .mips, .mipsel => @import("linux/errno-mips.zig"),
-    .sparc, .sparcel, .sparcv9 => @import("linux/errno-sparc.zig"),
-    else => @import("linux/errno-generic.zig"),
+pub const E = switch (arch) {
+    .mips, .mipsel => @import("linux/errno/mips.zig").E,
+    .sparc, .sparcel, .sparcv9 => @import("linux/errno/sparc.zig").E,
+    else => @import("linux/errno/generic.zig").E,
 };
 
 pub usingnamespace switch (arch) {
@@ -1665,6 +1665,13 @@ pub const io_uring_cqe = extern struct {
     /// result code for this event
     res: i32,
     flags: u32,
+
+    pub fn err(self: io_uring_cqe) E {
+        if (self.res > -4096 and self.res < 0) {
+            return @intToEnum(E, -self.res);
+        }
+        return .SUCCESS;
+    }
 };
 
 // io_uring_cqe.flags
diff --git a/lib/std/os/bits/linux/errno-generic.zig b/lib/std/os/bits/linux/errno-generic.zig
deleted file mode 100644
index f55aa3698e..0000000000
--- a/lib/std/os/bits/linux/errno-generic.zig
+++ /dev/null
@@ -1,462 +0,0 @@
-// SPDX-License-Identifier: MIT
-// Copyright (c) 2015-2021 Zig Contributors
-// This file is part of [zig](https://ziglang.org/), which is MIT licensed.
-// The MIT license requires this copyright notice to be included in all copies
-// and substantial portions of the software.
-/// Operation not permitted
-pub const EPERM = 1;
-
-/// No such file or directory
-pub const ENOENT = 2;
-
-/// No such process
-pub const ESRCH = 3;
-
-/// Interrupted system call
-pub const EINTR = 4;
-
-/// I/O error
-pub const EIO = 5;
-
-/// No such device or address
-pub const ENXIO = 6;
-
-/// Arg list too long
-pub const E2BIG = 7;
-
-/// Exec format error
-pub const ENOEXEC = 8;
-
-/// Bad file number
-pub const EBADF = 9;
-
-/// No child processes
-pub const ECHILD = 10;
-
-/// Try again
-pub const EAGAIN = 11;
-
-/// Out of memory
-pub const ENOMEM = 12;
-
-/// Permission denied
-pub const EACCES = 13;
-
-/// Bad address
-pub const EFAULT = 14;
-
-/// Block device required
-pub const ENOTBLK = 15;
-
-/// Device or resource busy
-pub const EBUSY = 16;
-
-/// File exists
-pub const EEXIST = 17;
-
-/// Cross-device link
-pub const EXDEV = 18;
-
-/// No such device
-pub const ENODEV = 19;
-
-/// Not a directory
-pub const ENOTDIR = 20;
-
-/// Is a directory
-pub const EISDIR = 21;
-
-/// Invalid argument
-pub const EINVAL = 22;
-
-/// File table overflow
-pub const ENFILE = 23;
-
-/// Too many open files
-pub const EMFILE = 24;
-
-/// Not a typewriter
-pub const ENOTTY = 25;
-
-/// Text file busy
-pub const ETXTBSY = 26;
-
-/// File too large
-pub const EFBIG = 27;
-
-/// No space left on device
-pub const ENOSPC = 28;
-
-/// Illegal seek
-pub const ESPIPE = 29;
-
-/// Read-only file system
-pub const EROFS = 30;
-
-/// Too many links
-pub const EMLINK = 31;
-
-/// Broken pipe
-pub const EPIPE = 32;
-
-/// Math argument out of domain of func
-pub const EDOM = 33;
-
-/// Math result not representable
-pub const ERANGE = 34;
-
-/// Resource deadlock would occur
-pub const EDEADLK = 35;
-
-/// File name too long
-pub const ENAMETOOLONG = 36;
-
-/// No record locks available
-pub const ENOLCK = 37;
-
-/// Function not implemented
-pub const ENOSYS = 38;
-
-/// Directory not empty
-pub const ENOTEMPTY = 39;
-
-/// Too many symbolic links encountered
-pub const ELOOP = 40;
-
-/// Operation would block
-pub const EWOULDBLOCK = EAGAIN;
-
-/// No message of desired type
-pub const ENOMSG = 42;
-
-/// Identifier removed
-pub const EIDRM = 43;
-
-/// Channel number out of range
-pub const ECHRNG = 44;
-
-/// Level 2 not synchronized
-pub const EL2NSYNC = 45;
-
-/// Level 3 halted
-pub const EL3HLT = 46;
-
-/// Level 3 reset
-pub const EL3RST = 47;
-
-/// Link number out of range
-pub const ELNRNG = 48;
-
-/// Protocol driver not attached
-pub const EUNATCH = 49;
-
-/// No CSI structure available
-pub const ENOCSI = 50;
-
-/// Level 2 halted
-pub const EL2HLT = 51;
-
-/// Invalid exchange
-pub const EBADE = 52;
-
-/// Invalid request descriptor
-pub const EBADR = 53;
-
-/// Exchange full
-pub const EXFULL = 54;
-
-/// No anode
-pub const ENOANO = 55;
-
-/// Invalid request code
-pub const EBADRQC = 56;
-
-/// Invalid slot
-pub const EBADSLT = 57;
-
-/// Bad font file format
-pub const EBFONT = 59;
-
-/// Device not a stream
-pub const ENOSTR = 60;
-
-/// No data available
-pub const ENODATA = 61;
-
-/// Timer expired
-pub const ETIME = 62;
-
-/// Out of streams resources
-pub const ENOSR = 63;
-
-/// Machine is not on the network
-pub const ENONET = 64;
-
-/// Package not installed
-pub const ENOPKG = 65;
-
-/// Object is remote
-pub const EREMOTE = 66;
-
-/// Link has been severed
-pub const ENOLINK = 67;
-
-/// Advertise error
-pub const EADV = 68;
-
-/// Srmount error
-pub const ESRMNT = 69;
-
-/// Communication error on send
-pub const ECOMM = 70;
-
-/// Protocol error
-pub const EPROTO = 71;
-
-/// Multihop attempted
-pub const EMULTIHOP = 72;
-
-/// RFS specific error
-pub const EDOTDOT = 73;
-
-/// Not a data message
-pub const EBADMSG = 74;
-
-/// Value too large for defined data type
-pub const EOVERFLOW = 75;
-
-/// Name not unique on network
-pub const ENOTUNIQ = 76;
-
-/// File descriptor in bad state
-pub const EBADFD = 77;
-
-/// Remote address changed
-pub const EREMCHG = 78;
-
-/// Can not access a needed shared library
-pub const ELIBACC = 79;
-
-/// Accessing a corrupted shared library
-pub const ELIBBAD = 80;
-
-/// .lib section in a.out corrupted
-pub const ELIBSCN = 81;
-
-/// Attempting to link in too many shared libraries
-pub const ELIBMAX = 82;
-
-/// Cannot exec a shared library directly
-pub const ELIBEXEC = 83;
-
-/// Illegal byte sequence
-pub const EILSEQ = 84;
-
-/// Interrupted system call should be restarted
-pub const ERESTART = 85;
-
-/// Streams pipe error
-pub const ESTRPIPE = 86;
-
-/// Too many users
-pub const EUSERS = 87;
-
-/// Socket operation on non-socket
-pub const ENOTSOCK = 88;
-
-/// Destination address required
-pub const EDESTADDRREQ = 89;
-
-/// Message too long
-pub const EMSGSIZE = 90;
-
-/// Protocol wrong type for socket
-pub const EPROTOTYPE = 91;
-
-/// Protocol not available
-pub const ENOPROTOOPT = 92;
-
-/// Protocol not supported
-pub const EPROTONOSUPPORT = 93;
-
-/// Socket type not supported
-pub const ESOCKTNOSUPPORT = 94;
-
-/// Operation not supported on transport endpoint
-pub const EOPNOTSUPP = 95;
-pub const ENOTSUP = EOPNOTSUPP;
-
-/// Protocol family not supported
-pub const EPFNOSUPPORT = 96;
-
-/// Address family not supported by protocol
-pub const EAFNOSUPPORT = 97;
-
-/// Address already in use
-pub const EADDRINUSE = 98;
-
-/// Cannot assign requested address
-pub const EADDRNOTAVAIL = 99;
-
-/// Network is down
-pub const ENETDOWN = 100;
-
-/// Network is unreachable
-pub const ENETUNREACH = 101;
-
-/// Network dropped connection because of reset
-pub const ENETRESET = 102;
-
-/// Software caused connection abort
-pub const ECONNABORTED = 103;
-
-/// Connection reset by peer
-pub const ECONNRESET = 104;
-
-/// No buffer space available
-pub const ENOBUFS = 105;
-
-/// Transport endpoint is already connected
-pub const EISCONN = 106;
-
-/// Transport endpoint is not connected
-pub const ENOTCONN = 107;
-
-/// Cannot send after transport endpoint shutdown
-pub const ESHUTDOWN = 108;
-
-/// Too many references: cannot splice
-pub const ETOOMANYREFS = 109;
-
-/// Connection timed out
-pub const ETIMEDOUT = 110;
-
-/// Connection refused
-pub const ECONNREFUSED = 111;
-
-/// Host is down
-pub const EHOSTDOWN = 112;
-
-/// No route to host
-pub const EHOSTUNREACH = 113;
-
-/// Operation already in progress
-pub const EALREADY = 114;
-
-/// Operation now in progress
-pub const EINPROGRESS = 115;
-
-/// Stale NFS file handle
-pub const ESTALE = 116;
-
-/// Structure needs cleaning
-pub const EUCLEAN = 117;
-
-/// Not a XENIX named type file
-pub const ENOTNAM = 118;
-
-/// No XENIX semaphores available
-pub const ENAVAIL = 119;
-
-/// Is a named type file
-pub const EISNAM = 120;
-
-/// Remote I/O error
-pub const EREMOTEIO = 121;
-
-/// Quota exceeded
-pub const EDQUOT = 122;
-
-/// No medium found
-pub const ENOMEDIUM = 123;
-
-/// Wrong medium type
-pub const EMEDIUMTYPE = 124;
-
-/// Operation canceled
-pub const ECANCELED = 125;
-
-/// Required key not available
-pub const ENOKEY = 126;
-
-/// Key has expired
-pub const EKEYEXPIRED = 127;
-
-/// Key has been revoked
-pub const EKEYREVOKED = 128;
-
-/// Key was rejected by service
-pub const EKEYREJECTED = 129;
-
-// for robust mutexes
-
-/// Owner died
-pub const EOWNERDEAD = 130;
-
-/// State not recoverable
-pub const ENOTRECOVERABLE = 131;
-
-/// Operation not possible due to RF-kill
-pub const ERFKILL = 132;
-
-/// Memory page has hardware error
-pub const EHWPOISON = 133;
-
-// nameserver query return codes
-
-/// DNS server returned answer with no data
-pub const ENSROK = 0;
-
-/// DNS server returned answer with no data
-pub const ENSRNODATA = 160;
-
-/// DNS server claims query was misformatted
-pub const ENSRFORMERR = 161;
-
-/// DNS server returned general failure
-pub const ENSRSERVFAIL = 162;
-
-/// Domain name not found
-pub const ENSRNOTFOUND = 163;
-
-/// DNS server does not implement requested operation
-pub const ENSRNOTIMP = 164;
-
-/// DNS server refused query
-pub const ENSRREFUSED = 165;
-
-/// Misformatted DNS query
-pub const ENSRBADQUERY = 166;
-
-/// Misformatted domain name
-pub const ENSRBADNAME = 167;
-
-/// Unsupported address family
-pub const ENSRBADFAMILY = 168;
-
-/// Misformatted DNS reply
-pub const ENSRBADRESP = 169;
-
-/// Could not contact DNS servers
-pub const ENSRCONNREFUSED = 170;
-
-/// Timeout while contacting DNS servers
-pub const ENSRTIMEOUT = 171;
-
-/// End of file
-pub const ENSROF = 172;
-
-/// Error reading file
-pub const ENSRFILE = 173;
-
-/// Out of memory
-pub const ENSRNOMEM = 174;
-
-/// Application terminated lookup
-pub const ENSRDESTRUCTION = 175;
-
-/// Domain name is too long
-pub const ENSRQUERYDOMAINTOOLONG = 176;
-
-/// Domain name is too long
-pub const ENSRCNAMELOOP = 177;
diff --git a/lib/std/os/bits/linux/errno-mips.zig b/lib/std/os/bits/linux/errno-mips.zig
deleted file mode 100644
index 2c22290288..0000000000
--- a/lib/std/os/bits/linux/errno-mips.zig
+++ /dev/null
@@ -1,143 +0,0 @@
-// SPDX-License-Identifier: MIT
-// Copyright (c) 2015-2021 Zig Contributors
-// This file is part of [zig](https://ziglang.org/), which is MIT licensed.
-// The MIT license requires this copyright notice to be included in all copies
-// and substantial portions of the software.
-
-// These are MIPS ABI compatible.
-
-pub const EPERM = 1;
-pub const ENOENT = 2;
-pub const ESRCH = 3;
-pub const EINTR = 4;
-pub const EIO = 5;
-pub const ENXIO = 6;
-pub const E2BIG = 7;
-pub const ENOEXEC = 8;
-pub const EBADF = 9;
-pub const ECHILD = 10;
-pub const EAGAIN = 11;
-pub const ENOMEM = 12;
-pub const EACCES = 13;
-pub const EFAULT = 14;
-pub const ENOTBLK = 15;
-pub const EBUSY = 16;
-pub const EEXIST = 17;
-pub const EXDEV = 18;
-pub const ENODEV = 19;
-pub const ENOTDIR = 20;
-pub const EISDIR = 21;
-pub const EINVAL = 22;
-pub const ENFILE = 23;
-pub const EMFILE = 24;
-pub const ENOTTY = 25;
-pub const ETXTBSY = 26;
-pub const EFBIG = 27;
-pub const ENOSPC = 28;
-pub const ESPIPE = 29;
-pub const EROFS = 30;
-pub const EMLINK = 31;
-pub const EPIPE = 32;
-pub const EDOM = 33;
-pub const ERANGE = 34;
-
-pub const ENOMSG = 35;
-pub const EIDRM = 36;
-pub const ECHRNG = 37;
-pub const EL2NSYNC = 38;
-pub const EL3HLT = 39;
-pub const EL3RST = 40;
-pub const ELNRNG = 41;
-pub const EUNATCH = 42;
-pub const ENOCSI = 43;
-pub const EL2HLT = 44;
-pub const EDEADLK = 45;
-pub const ENOLCK = 46;
-pub const EBADE = 50;
-pub const EBADR = 51;
-pub const EXFULL = 52;
-pub const ENOANO = 53;
-pub const EBADRQC = 54;
-pub const EBADSLT = 55;
-pub const EDEADLOCK = 56;
-pub const EBFONT = 59;
-pub const ENOSTR = 60;
-pub const ENODATA = 61;
-pub const ETIME = 62;
-pub const ENOSR = 63;
-pub const ENONET = 64;
-pub const ENOPKG = 65;
-pub const EREMOTE = 66;
-pub const ENOLINK = 67;
-pub const EADV = 68;
-pub const ESRMNT = 69;
-pub const ECOMM = 70;
-pub const EPROTO = 71;
-pub const EDOTDOT = 73;
-pub const EMULTIHOP = 74;
-pub const EBADMSG = 77;
-pub const ENAMETOOLONG = 78;
-pub const EOVERFLOW = 79;
-pub const ENOTUNIQ = 80;
-pub const EBADFD = 81;
-pub const EREMCHG = 82;
-pub const ELIBACC = 83;
-pub const ELIBBAD = 84;
-pub const ELIBSCN = 85;
-pub const ELIBMAX = 86;
-pub const ELIBEXEC = 87;
-pub const EILSEQ = 88;
-pub const ENOSYS = 89;
-pub const ELOOP = 90;
-pub const ERESTART = 91;
-pub const ESTRPIPE = 92;
-pub const ENOTEMPTY = 93;
-pub const EUSERS = 94;
-pub const ENOTSOCK = 95;
-pub const EDESTADDRREQ = 96;
-pub const EMSGSIZE = 97;
-pub const EPROTOTYPE = 98;
-pub const ENOPROTOOPT = 99;
-pub const EPROTONOSUPPORT = 120;
-pub const ESOCKTNOSUPPORT = 121;
-pub const EOPNOTSUPP = 122;
-pub const ENOTSUP = EOPNOTSUPP;
-pub const EPFNOSUPPORT = 123;
-pub const EAFNOSUPPORT = 124;
-pub const EADDRINUSE = 125;
-pub const EADDRNOTAVAIL = 126;
-pub const ENETDOWN = 127;
-pub const ENETUNREACH = 128;
-pub const ENETRESET = 129;
-pub const ECONNABORTED = 130;
-pub const ECONNRESET = 131;
-pub const ENOBUFS = 132;
-pub const EISCONN = 133;
-pub const ENOTCONN = 134;
-pub const EUCLEAN = 135;
-pub const ENOTNAM = 137;
-pub const ENAVAIL = 138;
-pub const EISNAM = 139;
-pub const EREMOTEIO = 140;
-pub const ESHUTDOWN = 143;
-pub const ETOOMANYREFS = 144;
-pub const ETIMEDOUT = 145;
-pub const ECONNREFUSED = 146;
-pub const EHOSTDOWN = 147;
-pub const EHOSTUNREACH = 148;
-pub const EWOULDBLOCK = EAGAIN;
-pub const EALREADY = 149;
-pub const EINPROGRESS = 150;
-pub const ESTALE = 151;
-pub const ECANCELED = 158;
-pub const ENOMEDIUM = 159;
-pub const EMEDIUMTYPE = 160;
-pub const ENOKEY = 161;
-pub const EKEYEXPIRED = 162;
-pub const EKEYREVOKED = 163;
-pub const EKEYREJECTED = 164;
-pub const EOWNERDEAD = 165;
-pub const ENOTRECOVERABLE = 166;
-pub const ERFKILL = 167;
-pub const EHWPOISON = 168;
-pub const EDQUOT = 1133;
diff --git a/lib/std/os/bits/linux/errno-sparc.zig b/lib/std/os/bits/linux/errno-sparc.zig
deleted file mode 100644
index 94b696fc35..0000000000
--- a/lib/std/os/bits/linux/errno-sparc.zig
+++ /dev/null
@@ -1,145 +0,0 @@
-// SPDX-License-Identifier: MIT
-// Copyright (c) 2015-2021 Zig Contributors
-// This file is part of [zig](https://ziglang.org/), which is MIT licensed.
-// The MIT license requires this copyright notice to be included in all copies
-// and substantial portions of the software.
-
-// These match the SunOS error numbering scheme.
-
-pub const EPERM = 1;
-pub const ENOENT = 2;
-pub const ESRCH = 3;
-pub const EINTR = 4;
-pub const EIO = 5;
-pub const ENXIO = 6;
-pub const E2BIG = 7;
-pub const ENOEXEC = 8;
-pub const EBADF = 9;
-pub const ECHILD = 10;
-pub const EAGAIN = 11;
-pub const ENOMEM = 12;
-pub const EACCES = 13;
-pub const EFAULT = 14;
-pub const ENOTBLK = 15;
-pub const EBUSY = 16;
-pub const EEXIST = 17;
-pub const EXDEV = 18;
-pub const ENODEV = 19;
-pub const ENOTDIR = 20;
-pub const EISDIR = 21;
-pub const EINVAL = 22;
-pub const ENFILE = 23;
-pub const EMFILE = 24;
-pub const ENOTTY = 25;
-pub const ETXTBSY = 26;
-pub const EFBIG = 27;
-pub const ENOSPC = 28;
-pub const ESPIPE = 29;
-pub const EROFS = 30;
-pub const EMLINK = 31;
-pub const EPIPE = 32;
-pub const EDOM = 33;
-pub const ERANGE = 34;
-
-pub const EWOULDBLOCK = EAGAIN;
-pub const EINPROGRESS = 36;
-pub const EALREADY = 37;
-pub const ENOTSOCK = 38;
-pub const EDESTADDRREQ = 39;
-pub const EMSGSIZE = 40;
-pub const EPROTOTYPE = 41;
-pub const ENOPROTOOPT = 42;
-pub const EPROTONOSUPPORT = 43;
-pub const ESOCKTNOSUPPORT = 44;
-pub const EOPNOTSUPP = 45;
-pub const ENOTSUP = EOPNOTSUPP;
-pub const EPFNOSUPPORT = 46;
-pub const EAFNOSUPPORT = 47;
-pub const EADDRINUSE = 48;
-pub const EADDRNOTAVAIL = 49;
-pub const ENETDOWN = 50;
-pub const ENETUNREACH = 51;
-pub const ENETRESET = 52;
-pub const ECONNABORTED = 53;
-pub const ECONNRESET = 54;
-pub const ENOBUFS = 55;
-pub const EISCONN = 56;
-pub const ENOTCONN = 57;
-pub const ESHUTDOWN = 58;
-pub const ETOOMANYREFS = 59;
-pub const ETIMEDOUT = 60;
-pub const ECONNREFUSED = 61;
-pub const ELOOP = 62;
-pub const ENAMETOOLONG = 63;
-pub const EHOSTDOWN = 64;
-pub const EHOSTUNREACH = 65;
-pub const ENOTEMPTY = 66;
-pub const EPROCLIM = 67;
-pub const EUSERS = 68;
-pub const EDQUOT = 69;
-pub const ESTALE = 70;
-pub const EREMOTE = 71;
-pub const ENOSTR = 72;
-pub const ETIME = 73;
-pub const ENOSR = 74;
-pub const ENOMSG = 75;
-pub const EBADMSG = 76;
-pub const EIDRM = 77;
-pub const EDEADLK = 78;
-pub const ENOLCK = 79;
-pub const ENONET = 80;
-pub const ERREMOTE = 81;
-pub const ENOLINK = 82;
-pub const EADV = 83;
-pub const ESRMNT = 84;
-pub const ECOMM = 85;
-pub const EPROTO = 86;
-pub const EMULTIHOP = 87;
-pub const EDOTDOT = 88;
-pub const EREMCHG = 89;
-pub const ENOSYS = 90;
-pub const ESTRPIPE = 91;
-pub const EOVERFLOW = 92;
-pub const EBADFD = 93;
-pub const ECHRNG = 94;
-pub const EL2NSYNC = 95;
-pub const EL3HLT = 96;
-pub const EL3RST = 97;
-pub const ELNRNG = 98;
-pub const EUNATCH = 99;
-pub const ENOCSI = 100;
-pub const EL2HLT = 101;
-pub const EBADE = 102;
-pub const EBADR = 103;
-pub const EXFULL = 104;
-pub const ENOANO = 105;
-pub const EBADRQC = 106;
-pub const EBADSLT = 107;
-pub const EDEADLOCK = 108;
-pub const EBFONT = 109;
-pub const ELIBEXEC = 110;
-pub const ENODATA = 111;
-pub const ELIBBAD = 112;
-pub const ENOPKG = 113;
-pub const ELIBACC = 114;
-pub const ENOTUNIQ = 115;
-pub const ERESTART = 116;
-pub const EUCLEAN = 117;
-pub const ENOTNAM = 118;
-pub const ENAVAIL = 119;
-pub const EISNAM = 120;
-pub const EREMOTEIO = 121;
-pub const EILSEQ = 122;
-pub const ELIBMAX = 123;
-pub const ELIBSCN = 124;
-pub const ENOMEDIUM = 125;
-pub const EMEDIUMTYPE = 126;
-pub const ECANCELED = 127;
-pub const ENOKEY = 128;
-pub const EKEYEXPIRED = 129;
-pub const EKEYREVOKED = 130;
-pub const EKEYREJECTED = 131;
-pub const EOWNERDEAD = 132;
-pub const ENOTRECOVERABLE = 133;
-pub const ERFKILL = 134;
-pub const EHWPOISON = 135;
diff --git a/lib/std/os/bits/linux/errno/generic.zig b/lib/std/os/bits/linux/errno/generic.zig
new file mode 100644
index 0000000000..49b35f6501
--- /dev/null
+++ b/lib/std/os/bits/linux/errno/generic.zig
@@ -0,0 +1,466 @@
+// SPDX-License-Identifier: MIT
+// Copyright (c) 2015-2021 Zig Contributors
+// This file is part of [zig](https://ziglang.org/), which is MIT licensed.
+// The MIT license requires this copyright notice to be included in all copies
+// and substantial portions of the software.
+
+pub const E = enum(u16) {
+    /// No error occurred.
+    /// Same code used for `NSROK`.
+    SUCCESS = 0,
+
+    /// Operation not permitted
+    PERM = 1,
+
+    /// No such file or directory
+    NOENT = 2,
+
+    /// No such process
+    SRCH = 3,
+
+    /// Interrupted system call
+    INTR = 4,
+
+    /// I/O error
+    IO = 5,
+
+    /// No such device or address
+    NXIO = 6,
+
+    /// Arg list too long
+    @"2BIG" = 7,
+
+    /// Exec format error
+    NOEXEC = 8,
+
+    /// Bad file number
+    BADF = 9,
+
+    /// No child processes
+    CHILD = 10,
+
+    /// Try again
+    /// Also means: WOULDBLOCK: operation would block
+    AGAIN = 11,
+
+    /// Out of memory
+    NOMEM = 12,
+
+    /// Permission denied
+    ACCES = 13,
+
+    /// Bad address
+    FAULT = 14,
+
+    /// Block device required
+    NOTBLK = 15,
+
+    /// Device or resource busy
+    BUSY = 16,
+
+    /// File exists
+    EXIST = 17,
+
+    /// Cross-device link
+    XDEV = 18,
+
+    /// No such device
+    NODEV = 19,
+
+    /// Not a directory
+    NOTDIR = 20,
+
+    /// Is a directory
+    ISDIR = 21,
+
+    /// Invalid argument
+    INVAL = 22,
+
+    /// File table overflow
+    NFILE = 23,
+
+    /// Too many open files
+    MFILE = 24,
+
+    /// Not a typewriter
+    NOTTY = 25,
+
+    /// Text file busy
+    TXTBSY = 26,
+
+    /// File too large
+    FBIG = 27,
+
+    /// No space left on device
+    NOSPC = 28,
+
+    /// Illegal seek
+    SPIPE = 29,
+
+    /// Read-only file system
+    ROFS = 30,
+
+    /// Too many links
+    MLINK = 31,
+
+    /// Broken pipe
+    PIPE = 32,
+
+    /// Math argument out of domain of func
+    DOM = 33,
+
+    /// Math result not representable
+    RANGE = 34,
+
+    /// Resource deadlock would occur
+    DEADLK = 35,
+
+    /// File name too long
+    NAMETOOLONG = 36,
+
+    /// No record locks available
+    NOLCK = 37,
+
+    /// Function not implemented
+    NOSYS = 38,
+
+    /// Directory not empty
+    NOTEMPTY = 39,
+
+    /// Too many symbolic links encountered
+    LOOP = 40,
+
+    /// No message of desired type
+    NOMSG = 42,
+
+    /// Identifier removed
+    IDRM = 43,
+
+    /// Channel number out of range
+    CHRNG = 44,
+
+    /// Level 2 not synchronized
+    L2NSYNC = 45,
+
+    /// Level 3 halted
+    L3HLT = 46,
+
+    /// Level 3 reset
+    L3RST = 47,
+
+    /// Link number out of range
+    LNRNG = 48,
+
+    /// Protocol driver not attached
+    UNATCH = 49,
+
+    /// No CSI structure available
+    NOCSI = 50,
+
+    /// Level 2 halted
+    L2HLT = 51,
+
+    /// Invalid exchange
+    BADE = 52,
+
+    /// Invalid request descriptor
+    BADR = 53,
+
+    /// Exchange full
+    XFULL = 54,
+
+    /// No anode
+    NOANO = 55,
+
+    /// Invalid request code
+    BADRQC = 56,
+
+    /// Invalid slot
+    BADSLT = 57,
+
+    /// Bad font file format
+    BFONT = 59,
+
+    /// Device not a stream
+    NOSTR = 60,
+
+    /// No data available
+    NODATA = 61,
+
+    /// Timer expired
+    TIME = 62,
+
+    /// Out of streams resources
+    NOSR = 63,
+
+    /// Machine is not on the network
+    NONET = 64,
+
+    /// Package not installed
+    NOPKG = 65,
+
+    /// Object is remote
+    REMOTE = 66,
+
+    /// Link has been severed
+    NOLINK = 67,
+
+    /// Advertise error
+    ADV = 68,
+
+    /// Srmount error
+    SRMNT = 69,
+
+    /// Communication error on send
+    COMM = 70,
+
+    /// Protocol error
+    PROTO = 71,
+
+    /// Multihop attempted
+    MULTIHOP = 72,
+
+    /// RFS specific error
+    DOTDOT = 73,
+
+    /// Not a data message
+    BADMSG = 74,
+
+    /// Value too large for defined data type
+    OVERFLOW = 75,
+
+    /// Name not unique on network
+    NOTUNIQ = 76,
+
+    /// File descriptor in bad state
+    BADFD = 77,
+
+    /// Remote address changed
+    REMCHG = 78,
+
+    /// Can not access a needed shared library
+    LIBACC = 79,
+
+    /// Accessing a corrupted shared library
+    LIBBAD = 80,
+
+    /// .lib section in a.out corrupted
+    LIBSCN = 81,
+
+    /// Attempting to link in too many shared libraries
+    LIBMAX = 82,
+
+    /// Cannot exec a shared library directly
+    LIBEXEC = 83,
+
+    /// Illegal byte sequence
+    ILSEQ = 84,
+
+    /// Interrupted system call should be restarted
+    RESTART = 85,
+
+    /// Streams pipe error
+    STRPIPE = 86,
+
+    /// Too many users
+    USERS = 87,
+
+    /// Socket operation on non-socket
+    NOTSOCK = 88,
+
+    /// Destination address required
+    DESTADDRREQ = 89,
+
+    /// Message too long
+    MSGSIZE = 90,
+
+    /// Protocol wrong type for socket
+    PROTOTYPE = 91,
+
+    /// Protocol not available
+    NOPROTOOPT = 92,
+
+    /// Protocol not supported
+    PROTONOSUPPORT = 93,
+
+    /// Socket type not supported
+    SOCKTNOSUPPORT = 94,
+
+    /// Operation not supported on transport endpoint
+    /// This code also means `NOTSUP`.
+    OPNOTSUPP = 95,
+
+    /// Protocol family not supported
+    PFNOSUPPORT = 96,
+
+    /// Address family not supported by protocol
+    AFNOSUPPORT = 97,
+
+    /// Address already in use
+    ADDRINUSE = 98,
+
+    /// Cannot assign requested address
+    ADDRNOTAVAIL = 99,
+
+    /// Network is down
+    NETDOWN = 100,
+
+    /// Network is unreachable
+    NETUNREACH = 101,
+
+    /// Network dropped connection because of reset
+    NETRESET = 102,
+
+    /// Software caused connection abort
+    CONNABORTED = 103,
+
+    /// Connection reset by peer
+    CONNRESET = 104,
+
+    /// No buffer space available
+    NOBUFS = 105,
+
+    /// Transport endpoint is already connected
+    ISCONN = 106,
+
+    /// Transport endpoint is not connected
+    NOTCONN = 107,
+
+    /// Cannot send after transport endpoint shutdown
+    SHUTDOWN = 108,
+
+    /// Too many references: cannot splice
+    TOOMANYREFS = 109,
+
+    /// Connection timed out
+    TIMEDOUT = 110,
+
+    /// Connection refused
+    CONNREFUSED = 111,
+
+    /// Host is down
+    HOSTDOWN = 112,
+
+    /// No route to host
+    HOSTUNREACH = 113,
+
+    /// Operation already in progress
+    ALREADY = 114,
+
+    /// Operation now in progress
+    INPROGRESS = 115,
+
+    /// Stale NFS file handle
+    STALE = 116,
+
+    /// Structure needs cleaning
+    UCLEAN = 117,
+
+    /// Not a XENIX named type file
+    NOTNAM = 118,
+
+    /// No XENIX semaphores available
+    NAVAIL = 119,
+
+    /// Is a named type file
+    ISNAM = 120,
+
+    /// Remote I/O error
+    REMOTEIO = 121,
+
+    /// Quota exceeded
+    DQUOT = 122,
+
+    /// No medium found
+    NOMEDIUM = 123,
+
+    /// Wrong medium type
+    MEDIUMTYPE = 124,
+
+    /// Operation canceled
+    CANCELED = 125,
+
+    /// Required key not available
+    NOKEY = 126,
+
+    /// Key has expired
+    KEYEXPIRED = 127,
+
+    /// Key has been revoked
+    KEYREVOKED = 128,
+
+    /// Key was rejected by service
+    KEYREJECTED = 129,
+
+    // for robust mutexes
+
+    /// Owner died
+    OWNERDEAD = 130,
+
+    /// State not recoverable
+    NOTRECOVERABLE = 131,
+
+    /// Operation not possible due to RF-kill
+    RFKILL = 132,
+
+    /// Memory page has hardware error
+    HWPOISON = 133,
+
+    // nameserver query return codes
+
+    /// DNS server returned answer with no data
+    NSRNODATA = 160,
+
+    /// DNS server claims query was misformatted
+    NSRFORMERR = 161,
+
+    /// DNS server returned general failure
+    NSRSERVFAIL = 162,
+
+    /// Domain name not found
+    NSRNOTFOUND = 163,
+
+    /// DNS server does not implement requested operation
+    NSRNOTIMP = 164,
+
+    /// DNS server refused query
+    NSRREFUSED = 165,
+
+    /// Misformatted DNS query
+    NSRBADQUERY = 166,
+
+    /// Misformatted domain name
+    NSRBADNAME = 167,
+
+    /// Unsupported address family
+    NSRBADFAMILY = 168,
+
+    /// Misformatted DNS reply
+    NSRBADRESP = 169,
+
+    /// Could not contact DNS servers
+    NSRCONNREFUSED = 170,
+
+    /// Timeout while contacting DNS servers
+    NSRTIMEOUT = 171,
+
+    /// End of file
+    NSROF = 172,
+
+    /// Error reading file
+    NSRFILE = 173,
+
+    /// Out of memory
+    NSRNOMEM = 174,
+
+    /// Application terminated lookup
+    NSRDESTRUCTION = 175,
+
+    /// Domain name is too long
+    NSRQUERYDOMAINTOOLONG = 176,
+
+    /// Domain name is too long
+    NSRCNAMELOOP = 177,
+
+    _,
+};
diff --git a/lib/std/os/bits/linux/errno/mips.zig b/lib/std/os/bits/linux/errno/mips.zig
new file mode 100644
index 0000000000..4f14db65ee
--- /dev/null
+++ b/lib/std/os/bits/linux/errno/mips.zig
@@ -0,0 +1,147 @@
+// SPDX-License-Identifier: MIT
+// Copyright (c) 2015-2021 Zig Contributors
+// This file is part of [zig](https://ziglang.org/), which is MIT licensed.
+// The MIT license requires this copyright notice to be included in all copies
+// and substantial portions of the software.
+
+//! These are MIPS ABI compatible.
+pub const E = enum(i32) {
+    /// No error occurred.
+    SUCCESS = 0,
+
+    PERM = 1,
+    NOENT = 2,
+    SRCH = 3,
+    INTR = 4,
+    IO = 5,
+    NXIO = 6,
+    @"2BIG" = 7,
+    NOEXEC = 8,
+    BADF = 9,
+    CHILD = 10,
+    /// Also used for WOULDBLOCK.
+    AGAIN = 11,
+    NOMEM = 12,
+    ACCES = 13,
+    FAULT = 14,
+    NOTBLK = 15,
+    BUSY = 16,
+    EXIST = 17,
+    XDEV = 18,
+    NODEV = 19,
+    NOTDIR = 20,
+    ISDIR = 21,
+    INVAL = 22,
+    NFILE = 23,
+    MFILE = 24,
+    NOTTY = 25,
+    TXTBSY = 26,
+    FBIG = 27,
+    NOSPC = 28,
+    SPIPE = 29,
+    ROFS = 30,
+    MLINK = 31,
+    PIPE = 32,
+    DOM = 33,
+    RANGE = 34,
+
+    NOMSG = 35,
+    IDRM = 36,
+    CHRNG = 37,
+    L2NSYNC = 38,
+    L3HLT = 39,
+    L3RST = 40,
+    LNRNG = 41,
+    UNATCH = 42,
+    NOCSI = 43,
+    L2HLT = 44,
+    DEADLK = 45,
+    NOLCK = 46,
+    BADE = 50,
+    BADR = 51,
+    XFULL = 52,
+    NOANO = 53,
+    BADRQC = 54,
+    BADSLT = 55,
+    DEADLOCK = 56,
+    BFONT = 59,
+    NOSTR = 60,
+    NODATA = 61,
+    TIME = 62,
+    NOSR = 63,
+    NONET = 64,
+    NOPKG = 65,
+    REMOTE = 66,
+    NOLINK = 67,
+    ADV = 68,
+    SRMNT = 69,
+    COMM = 70,
+    PROTO = 71,
+    DOTDOT = 73,
+    MULTIHOP = 74,
+    BADMSG = 77,
+    NAMETOOLONG = 78,
+    OVERFLOW = 79,
+    NOTUNIQ = 80,
+    BADFD = 81,
+    REMCHG = 82,
+    LIBACC = 83,
+    LIBBAD = 84,
+    LIBSCN = 85,
+    LIBMAX = 86,
+    LIBEXEC = 87,
+    ILSEQ = 88,
+    NOSYS = 89,
+    LOOP = 90,
+    RESTART = 91,
+    STRPIPE = 92,
+    NOTEMPTY = 93,
+    USERS = 94,
+    NOTSOCK = 95,
+    DESTADDRREQ = 96,
+    MSGSIZE = 97,
+    PROTOTYPE = 98,
+    NOPROTOOPT = 99,
+    PROTONOSUPPORT = 120,
+    SOCKTNOSUPPORT = 121,
+    OPNOTSUPP = 122,
+    PFNOSUPPORT = 123,
+    AFNOSUPPORT = 124,
+    ADDRINUSE = 125,
+    ADDRNOTAVAIL = 126,
+    NETDOWN = 127,
+    NETUNREACH = 128,
+    NETRESET = 129,
+    CONNABORTED = 130,
+    CONNRESET = 131,
+    NOBUFS = 132,
+    ISCONN = 133,
+    NOTCONN = 134,
+    UCLEAN = 135,
+    NOTNAM = 137,
+    NAVAIL = 138,
+    ISNAM = 139,
+    REMOTEIO = 140,
+    SHUTDOWN = 143,
+    TOOMANYREFS = 144,
+    TIMEDOUT = 145,
+    CONNREFUSED = 146,
+    HOSTDOWN = 147,
+    HOSTUNREACH = 148,
+    ALREADY = 149,
+    INPROGRESS = 150,
+    STALE = 151,
+    CANCELED = 158,
+    NOMEDIUM = 159,
+    MEDIUMTYPE = 160,
+    NOKEY = 161,
+    KEYEXPIRED = 162,
+    KEYREVOKED = 163,
+    KEYREJECTED = 164,
+    OWNERDEAD = 165,
+    NOTRECOVERABLE = 166,
+    RFKILL = 167,
+    HWPOISON = 168,
+    DQUOT = 1133,
+    _,
+};
diff --git a/lib/std/os/bits/linux/errno/sparc.zig b/lib/std/os/bits/linux/errno/sparc.zig
new file mode 100644
index 0000000000..cc43ce1a94
--- /dev/null
+++ b/lib/std/os/bits/linux/errno/sparc.zig
@@ -0,0 +1,150 @@
+// SPDX-License-Identifier: MIT
+// Copyright (c) 2015-2021 Zig Contributors
+// This file is part of [zig](https://ziglang.org/), which is MIT licensed.
+// The MIT license requires this copyright notice to be included in all copies
+// and substantial portions of the software.
+
+//! These match the SunOS error numbering scheme.
+pub const E = enum(i32) {
+    /// No error occurred.
+    SUCCESS = 0,
+
+    PERM = 1,
+    NOENT = 2,
+    SRCH = 3,
+    INTR = 4,
+    IO = 5,
+    NXIO = 6,
+    @"2BIG" = 7,
+    NOEXEC = 8,
+    BADF = 9,
+    CHILD = 10,
+    /// Also used for WOULDBLOCK
+    AGAIN = 11,
+    NOMEM = 12,
+    ACCES = 13,
+    FAULT = 14,
+    NOTBLK = 15,
+    BUSY = 16,
+    EXIST = 17,
+    XDEV = 18,
+    NODEV = 19,
+    NOTDIR = 20,
+    ISDIR = 21,
+    INVAL = 22,
+    NFILE = 23,
+    MFILE = 24,
+    NOTTY = 25,
+    TXTBSY = 26,
+    FBIG = 27,
+    NOSPC = 28,
+    SPIPE = 29,
+    ROFS = 30,
+    MLINK = 31,
+    PIPE = 32,
+    DOM = 33,
+    RANGE = 34,
+
+    INPROGRESS = 36,
+    ALREADY = 37,
+    NOTSOCK = 38,
+    DESTADDRREQ = 39,
+    MSGSIZE = 40,
+    PROTOTYPE = 41,
+    NOPROTOOPT = 42,
+    PROTONOSUPPORT = 43,
+    SOCKTNOSUPPORT = 44,
+    /// Also used for NOTSUP
+    OPNOTSUPP = 45,
+    PFNOSUPPORT = 46,
+    AFNOSUPPORT = 47,
+    ADDRINUSE = 48,
+    ADDRNOTAVAIL = 49,
+    NETDOWN = 50,
+    NETUNREACH = 51,
+    NETRESET = 52,
+    CONNABORTED = 53,
+    CONNRESET = 54,
+    NOBUFS = 55,
+    ISCONN = 56,
+    NOTCONN = 57,
+    SHUTDOWN = 58,
+    TOOMANYREFS = 59,
+    TIMEDOUT = 60,
+    CONNREFUSED = 61,
+    LOOP = 62,
+    NAMETOOLONG = 63,
+    HOSTDOWN = 64,
+    HOSTUNREACH = 65,
+    NOTEMPTY = 66,
+    PROCLIM = 67,
+    USERS = 68,
+    DQUOT = 69,
+    STALE = 70,
+    REMOTE = 71,
+    NOSTR = 72,
+    TIME = 73,
+    NOSR = 74,
+    NOMSG = 75,
+    BADMSG = 76,
+    IDRM = 77,
+    DEADLK = 78,
+    NOLCK = 79,
+    NONET = 80,
+    RREMOTE = 81,
+    NOLINK = 82,
+    ADV = 83,
+    SRMNT = 84,
+    COMM = 85,
+    PROTO = 86,
+    MULTIHOP = 87,
+    DOTDOT = 88,
+    REMCHG = 89,
+    NOSYS = 90,
+    STRPIPE = 91,
+    OVERFLOW = 92,
+    BADFD = 93,
+    CHRNG = 94,
+    L2NSYNC = 95,
+    L3HLT = 96,
+    L3RST = 97,
+    LNRNG = 98,
+    UNATCH = 99,
+    NOCSI = 100,
+    L2HLT = 101,
+    BADE = 102,
+    BADR = 103,
+    XFULL = 104,
+    NOANO = 105,
+    BADRQC = 106,
+    BADSLT = 107,
+    DEADLOCK = 108,
+    BFONT = 109,
+    LIBEXEC = 110,
+    NODATA = 111,
+    LIBBAD = 112,
+    NOPKG = 113,
+    LIBACC = 114,
+    NOTUNIQ = 115,
+    RESTART = 116,
+    UCLEAN = 117,
+    NOTNAM = 118,
+    NAVAIL = 119,
+    ISNAM = 120,
+    REMOTEIO = 121,
+    ILSEQ = 122,
+    LIBMAX = 123,
+    LIBSCN = 124,
+    NOMEDIUM = 125,
+    MEDIUMTYPE = 126,
+    CANCELED = 127,
+    NOKEY = 128,
+    KEYEXPIRED = 129,
+    KEYREVOKED = 130,
+    KEYREJECTED = 131,
+    OWNERDEAD = 132,
+    NOTRECOVERABLE = 133,
+    RFKILL = 134,
+    HWPOISON = 135,
+    _,
+};
diff --git a/lib/std/os/bits/netbsd.zig b/lib/std/os/bits/netbsd.zig
index af04d0536b..f1bfe1b958 100644
--- a/lib/std/os/bits/netbsd.zig
+++ b/lib/std/os/bits/netbsd.zig
@@ -933,140 +933,144 @@ pub const ucontext_t = extern struct {
     ]u32,
 };
 
-pub const EPERM = 1; // Operation not permitted
-pub const ENOENT = 2; // No such file or directory
-pub const ESRCH = 3; // No such process
-pub const EINTR = 4; // Interrupted system call
-pub const EIO = 5; // Input/output error
-pub const ENXIO = 6; // Device not configured
-pub const E2BIG = 7; // Argument list too long
-pub const ENOEXEC = 8; // Exec format error
-pub const EBADF = 9; // Bad file descriptor
-pub const ECHILD = 10; // No child processes
-pub const EDEADLK = 11; // Resource deadlock avoided
-// 11 was EAGAIN
-pub const ENOMEM = 12; // Cannot allocate memory
-pub const EACCES = 13; // Permission denied
-pub const EFAULT = 14; // Bad address
-pub const ENOTBLK = 15; // Block device required
-pub const EBUSY = 16; // Device busy
-pub const EEXIST = 17; // File exists
-pub const EXDEV = 18; // Cross-device link
-pub const ENODEV = 19; // Operation not supported by device
-pub const ENOTDIR = 20; // Not a directory
-pub const EISDIR = 21; // Is a directory
-pub const EINVAL = 22; // Invalid argument
-pub const ENFILE = 23; // Too many open files in system
-pub const EMFILE = 24; // Too many open files
-pub const ENOTTY = 25; // Inappropriate ioctl for device
-pub const ETXTBSY = 26; // Text file busy
-pub const EFBIG = 27; // File too large
-pub const ENOSPC = 28; // No space left on device
-pub const ESPIPE = 29; // Illegal seek
-pub const EROFS = 30; // Read-only file system
-pub const EMLINK = 31; // Too many links
-pub const EPIPE = 32; // Broken pipe
+pub const E = enum(u16) {
+    /// No error occurred.
+    SUCCESS = 0,
+    PERM = 1, // Operation not permitted
+    NOENT = 2, // No such file or directory
+    SRCH = 3, // No such process
+    INTR = 4, // Interrupted system call
+    IO = 5, // Input/output error
+    NXIO = 6, // Device not configured
+    @"2BIG" = 7, // Argument list too long
+    NOEXEC = 8, // Exec format error
+    BADF = 9, // Bad file descriptor
+    CHILD = 10, // No child processes
+    DEADLK = 11, // Resource deadlock avoided
+    // 11 was AGAIN
+    NOMEM = 12, // Cannot allocate memory
+    ACCES = 13, // Permission denied
+    FAULT = 14, // Bad address
+    NOTBLK = 15, // Block device required
+    BUSY = 16, // Device busy
+    EXIST = 17, // File exists
+    XDEV = 18, // Cross-device link
+    NODEV = 19, // Operation not supported by device
+    NOTDIR = 20, // Not a directory
+    ISDIR = 21, // Is a directory
+    INVAL = 22, // Invalid argument
+    NFILE = 23, // Too many open files in system
+    MFILE = 24, // Too many open files
+    NOTTY = 25, // Inappropriate ioctl for device
+    TXTBSY = 26, // Text file busy
+    FBIG = 27, // File too large
+    NOSPC = 28, // No space left on device
+    SPIPE = 29, // Illegal seek
+    ROFS = 30, // Read-only file system
+    MLINK = 31, // Too many links
+    PIPE = 32, // Broken pipe
 
-// math software
-pub const EDOM = 33; // Numerical argument out of domain
-pub const ERANGE = 34; // Result too large or too small
+    // math software
+    DOM = 33, // Numerical argument out of domain
+    RANGE = 34, // Result too large or too small
 
-// non-blocking and interrupt i/o
-pub const EAGAIN = 35; // Resource temporarily unavailable
-pub const EWOULDBLOCK = EAGAIN; // Operation would block
-pub const EINPROGRESS = 36; // Operation now in progress
-pub const EALREADY = 37; // Operation already in progress
+    // non-blocking and interrupt i/o
+    // also: WOULDBLOCK: operation would block
+    AGAIN = 35, // Resource temporarily unavailable
+    INPROGRESS = 36, // Operation now in progress
+    ALREADY = 37, // Operation already in progress
 
-// ipc/network software -- argument errors
-pub const ENOTSOCK = 38; // Socket operation on non-socket
-pub const EDESTADDRREQ = 39; // Destination address required
-pub const EMSGSIZE = 40; // Message too long
-pub const EPROTOTYPE = 41; // Protocol wrong type for socket
-pub const ENOPROTOOPT = 42; // Protocol option not available
-pub const EPROTONOSUPPORT = 43; // Protocol not supported
-pub const ESOCKTNOSUPPORT = 44; // Socket type not supported
-pub const EOPNOTSUPP = 45; // Operation not supported
-pub const EPFNOSUPPORT = 46; // Protocol family not supported
-pub const EAFNOSUPPORT = 47; // Address family not supported by protocol family
-pub const EADDRINUSE = 48; // Address already in use
-pub const EADDRNOTAVAIL = 49; // Can't assign requested address
+    // ipc/network software -- argument errors
+    NOTSOCK = 38, // Socket operation on non-socket
+    DESTADDRREQ = 39, // Destination address required
+    MSGSIZE = 40, // Message too long
+    PROTOTYPE = 41, // Protocol wrong type for socket
+    NOPROTOOPT = 42, // Protocol option not available
+    PROTONOSUPPORT = 43, // Protocol not supported
+    SOCKTNOSUPPORT = 44, // Socket type not supported
+    OPNOTSUPP = 45, // Operation not supported
+    PFNOSUPPORT = 46, // Protocol family not supported
+    AFNOSUPPORT = 47, // Address family not supported by protocol family
+    ADDRINUSE = 48, // Address already in use
+    ADDRNOTAVAIL = 49, // Can't assign requested address
 
-// ipc/network software -- operational errors
-pub const ENETDOWN = 50; // Network is down
-pub const ENETUNREACH = 51; // Network is unreachable
-pub const ENETRESET = 52; // Network dropped connection on reset
-pub const ECONNABORTED = 53; // Software caused connection abort
-pub const ECONNRESET = 54; // Connection reset by peer
-pub const ENOBUFS = 55; // No buffer space available
-pub const EISCONN = 56; // Socket is already connected
-pub const ENOTCONN = 57; // Socket is not connected
-pub const ESHUTDOWN = 58; // Can't send after socket shutdown
-pub const ETOOMANYREFS = 59; // Too many references: can't splice
-pub const ETIMEDOUT = 60; // Operation timed out
-pub const ECONNREFUSED = 61; // Connection refused
+    // ipc/network software -- operational errors
+    NETDOWN = 50, // Network is down
+    NETUNREACH = 51, // Network is unreachable
+    NETRESET = 52, // Network dropped connection on reset
+    CONNABORTED = 53, // Software caused connection abort
+    CONNRESET = 54, // Connection reset by peer
+    NOBUFS = 55, // No buffer space available
+    ISCONN = 56, // Socket is already connected
+    NOTCONN = 57, // Socket is not connected
+    SHUTDOWN = 58, // Can't send after socket shutdown
+    TOOMANYREFS = 59, // Too many references: can't splice
+    TIMEDOUT = 60, // Operation timed out
+    CONNREFUSED = 61, // Connection refused
 
-pub const ELOOP = 62; // Too many levels of symbolic links
-pub const ENAMETOOLONG = 63; // File name too long
+    LOOP = 62, // Too many levels of symbolic links
+    NAMETOOLONG = 63, // File name too long
 
-// should be rearranged
-pub const EHOSTDOWN = 64; // Host is down
-pub const EHOSTUNREACH = 65; // No route to host
-pub const ENOTEMPTY = 66; // Directory not empty
+    // should be rearranged
+    HOSTDOWN = 64, // Host is down
+    HOSTUNREACH = 65, // No route to host
+    NOTEMPTY = 66, // Directory not empty
 
-// quotas & mush
-pub const EPROCLIM = 67; // Too many processes
-pub const EUSERS = 68; // Too many users
-pub const EDQUOT = 69; // Disc quota exceeded
+    // quotas & mush
+    PROCLIM = 67, // Too many processes
+    USERS = 68, // Too many users
+    DQUOT = 69, // Disc quota exceeded
 
-// Network File System
-pub const ESTALE = 70; // Stale NFS file handle
-pub const EREMOTE = 71; // Too many levels of remote in path
-pub const EBADRPC = 72; // RPC struct is bad
-pub const ERPCMISMATCH = 73; // RPC version wrong
-pub const EPROGUNAVAIL = 74; // RPC prog. not avail
-pub const EPROGMISMATCH = 75; // Program version wrong
-pub const EPROCUNAVAIL = 76; // Bad procedure for program
+    // Network File System
+    STALE = 70, // Stale NFS file handle
+    REMOTE = 71, // Too many levels of remote in path
+    BADRPC = 72, // RPC struct is bad
+    RPCMISMATCH = 73, // RPC version wrong
+    PROGUNAVAIL = 74, // RPC prog. not avail
+    PROGMISMATCH = 75, // Program version wrong
+    PROCUNAVAIL = 76, // Bad procedure for program
 
-pub const ENOLCK = 77; // No locks available
-pub const ENOSYS = 78; // Function not implemented
+    NOLCK = 77, // No locks available
+    NOSYS = 78, // Function not implemented
 
-pub const EFTYPE = 79; // Inappropriate file type or format
-pub const EAUTH = 80; // Authentication error
-pub const ENEEDAUTH = 81; // Need authenticator
+    FTYPE = 79, // Inappropriate file type or format
+    AUTH = 80, // Authentication error
+    NEEDAUTH = 81, // Need authenticator
 
-// SystemV IPC
-pub const EIDRM = 82; // Identifier removed
-pub const ENOMSG = 83; // No message of desired type
-pub const EOVERFLOW = 84; // Value too large to be stored in data type
+    // SystemV IPC
+    IDRM = 82, // Identifier removed
+    NOMSG = 83, // No message of desired type
+    OVERFLOW = 84, // Value too large to be stored in data type
 
-// Wide/multibyte-character handling, ISO/IEC 9899/AMD1:1995
-pub const EILSEQ = 85; // Illegal byte sequence
+    // Wide/multibyte-character handling, ISO/IEC 9899/AMD1:1995
+    ILSEQ = 85, // Illegal byte sequence
 
-// From IEEE Std 1003.1-2001
-// Base, Realtime, Threads or Thread Priority Scheduling option errors
-pub const ENOTSUP = 86; // Not supported
+    // From IEEE Std 1003.1-2001
+    // Base, Realtime, Threads or Thread Priority Scheduling option errors
+    NOTSUP = 86, // Not supported
 
-// Realtime option errors
-pub const ECANCELED = 87; // Operation canceled
+    // Realtime option errors
+    CANCELED = 87, // Operation canceled
 
-// Realtime, XSI STREAMS option errors
-pub const EBADMSG = 88; // Bad or Corrupt message
+    // Realtime, XSI STREAMS option errors
+    BADMSG = 88, // Bad or Corrupt message
 
-// XSI STREAMS option errors
-pub const ENODATA = 89; // No message available
-pub const ENOSR = 90; // No STREAM resources
-pub const ENOSTR = 91; // Not a STREAM
-pub const ETIME = 92; // STREAM ioctl timeout
+    // XSI STREAMS option errors
+    NODATA = 89, // No message available
+    NOSR = 90, // No STREAM resources
+    NOSTR = 91, // Not a STREAM
+    TIME = 92, // STREAM ioctl timeout
 
-// File system extended attribute errors
-pub const ENOATTR = 93; // Attribute not found
+    // File system extended attribute errors
+    NOATTR = 93, // Attribute not found
 
-// Realtime, XSI STREAMS option errors
-pub const EMULTIHOP = 94; // Multihop attempted
-pub const ENOLINK = 95; // Link has been severed
-pub const EPROTO = 96; // Protocol error
+    // Realtime, XSI STREAMS option errors
+    MULTIHOP = 94, // Multihop attempted
+    NOLINK = 95, // Link has been severed
+    PROTO = 96, // Protocol error
 
-pub const ELAST = 96; // Must equal largest errno
+    _,
+};
 
 pub const MINSIGSTKSZ = 8192;
 pub const SIGSTKSZ = MINSIGSTKSZ + 32768;
diff --git a/lib/std/os/bits/openbsd.zig b/lib/std/os/bits/openbsd.zig
index 233ebcbd68..5ad1f8980b 100644
--- a/lib/std/os/bits/openbsd.zig
+++ b/lib/std/os/bits/openbsd.zig
@@ -295,6 +295,7 @@ pub const AI_NUMERICSERV = 16;
 pub const AI_ADDRCONFIG = 64;
 
 pub const PATH_MAX = 1024;
+pub const IOV_MAX = 1024;
 
 pub const STDIN_FILENO = 0;
 pub const STDOUT_FILENO = 1;
@@ -824,125 +825,129 @@ pub usingnamespace switch (builtin.target.cpu.arch) {
 pub const sigset_t = c_uint;
 pub const empty_sigset: sigset_t = 0;
 
-pub const EPERM = 1; // Operation not permitted
-pub const ENOENT = 2; // No such file or directory
-pub const ESRCH = 3; // No such process
-pub const EINTR = 4; // Interrupted system call
-pub const EIO = 5; // Input/output error
-pub const ENXIO = 6; // Device not configured
-pub const E2BIG = 7; // Argument list too long
-pub const ENOEXEC = 8; // Exec format error
-pub const EBADF = 9; // Bad file descriptor
-pub const ECHILD = 10; // No child processes
-pub const EDEADLK = 11; // Resource deadlock avoided
-// 11 was EAGAIN
-pub const ENOMEM = 12; // Cannot allocate memory
-pub const EACCES = 13; // Permission denied
-pub const EFAULT = 14; // Bad address
-pub const ENOTBLK = 15; // Block device required
-pub const EBUSY = 16; // Device busy
-pub const EEXIST = 17; // File exists
-pub const EXDEV = 18; // Cross-device link
-pub const ENODEV = 19; // Operation not supported by device
-pub const ENOTDIR = 20; // Not a directory
-pub const EISDIR = 21; // Is a directory
-pub const EINVAL = 22; // Invalid argument
-pub const ENFILE = 23; // Too many open files in system
-pub const EMFILE = 24; // Too many open files
-pub const ENOTTY = 25; // Inappropriate ioctl for device
-pub const ETXTBSY = 26; // Text file busy
-pub const EFBIG = 27; // File too large
-pub const ENOSPC = 28; // No space left on device
-pub const ESPIPE = 29; // Illegal seek
-pub const EROFS = 30; // Read-only file system
-pub const EMLINK = 31; // Too many links
-pub const EPIPE = 32; // Broken pipe
+pub const E = enum(u16) {
+    /// No error occurred.
+    SUCCESS = 0,
+    PERM = 1, // Operation not permitted
+    NOENT = 2, // No such file or directory
+    SRCH = 3, // No such process
+    INTR = 4, // Interrupted system call
+    IO = 5, // Input/output error
+    NXIO = 6, // Device not configured
+    @"2BIG" = 7, // Argument list too long
+    NOEXEC = 8, // Exec format error
+    BADF = 9, // Bad file descriptor
+    CHILD = 10, // No child processes
+    DEADLK = 11, // Resource deadlock avoided
+    // 11 was AGAIN
+    NOMEM = 12, // Cannot allocate memory
+    ACCES = 13, // Permission denied
+    FAULT = 14, // Bad address
+    NOTBLK = 15, // Block device required
+    BUSY = 16, // Device busy
+    EXIST = 17, // File exists
+    XDEV = 18, // Cross-device link
+    NODEV = 19, // Operation not supported by device
+    NOTDIR = 20, // Not a directory
+    ISDIR = 21, // Is a directory
+    INVAL = 22, // Invalid argument
+    NFILE = 23, // Too many open files in system
+    MFILE = 24, // Too many open files
+    NOTTY = 25, // Inappropriate ioctl for device
+    TXTBSY = 26, // Text file busy
+    FBIG = 27, // File too large
+    NOSPC = 28, // No space left on device
+    SPIPE = 29, // Illegal seek
+    ROFS = 30, // Read-only file system
+    MLINK = 31, // Too many links
+    PIPE = 32, // Broken pipe
 
-// math software
-pub const EDOM = 33; // Numerical argument out of domain
-pub const ERANGE = 34; // Result too large or too small
+    // math software
+    DOM = 33, // Numerical argument out of domain
+    RANGE = 34, // Result too large or too small
 
-// non-blocking and interrupt i/o
-pub const EAGAIN = 35; // Resource temporarily unavailable
-pub const EWOULDBLOCK = EAGAIN; // Operation would block
-pub const EINPROGRESS = 36; // Operation now in progress
-pub const EALREADY = 37; // Operation already in progress
+    // non-blocking and interrupt i/o
+    // also: WOULDBLOCK: operation would block
+    AGAIN = 35, // Resource temporarily unavailable
+    INPROGRESS = 36, // Operation now in progress
+    ALREADY = 37, // Operation already in progress
 
-// ipc/network software -- argument errors
-pub const ENOTSOCK = 38; // Socket operation on non-socket
-pub const EDESTADDRREQ = 39; // Destination address required
-pub const EMSGSIZE = 40; // Message too long
-pub const EPROTOTYPE = 41; // Protocol wrong type for socket
-pub const ENOPROTOOPT = 42; // Protocol option not available
-pub const EPROTONOSUPPORT = 43; // Protocol not supported
-pub const ESOCKTNOSUPPORT = 44; // Socket type not supported
-pub const EOPNOTSUPP = 45; // Operation not supported
-pub const EPFNOSUPPORT = 46; // Protocol family not supported
-pub const EAFNOSUPPORT = 47; // Address family not supported by protocol family
-pub const EADDRINUSE = 48; // Address already in use
-pub const EADDRNOTAVAIL = 49; // Can't assign requested address
+    // ipc/network software -- argument errors
+    NOTSOCK = 38, // Socket operation on non-socket
+    DESTADDRREQ = 39, // Destination address required
+    MSGSIZE = 40, // Message too long
+    PROTOTYPE = 41, // Protocol wrong type for socket
+    NOPROTOOPT = 42, // Protocol option not available
+    PROTONOSUPPORT = 43, // Protocol not supported
+    SOCKTNOSUPPORT = 44, // Socket type not supported
+    OPNOTSUPP = 45, // Operation not supported
+    PFNOSUPPORT = 46, // Protocol family not supported
+    AFNOSUPPORT = 47, // Address family not supported by protocol family
+    ADDRINUSE = 48, // Address already in use
+    ADDRNOTAVAIL = 49, // Can't assign requested address
 
-// ipc/network software -- operational errors
-pub const ENETDOWN = 50; // Network is down
-pub const ENETUNREACH = 51; // Network is unreachable
-pub const ENETRESET = 52; // Network dropped connection on reset
-pub const ECONNABORTED = 53; // Software caused connection abort
-pub const ECONNRESET = 54; // Connection reset by peer
-pub const ENOBUFS = 55; // No buffer space available
-pub const EISCONN = 56; // Socket is already connected
-pub const ENOTCONN = 57; // Socket is not connected
-pub const ESHUTDOWN = 58; // Can't send after socket shutdown
-pub const ETOOMANYREFS = 59; // Too many references: can't splice
-pub const ETIMEDOUT = 60; // Operation timed out
-pub const ECONNREFUSED = 61; // Connection refused
+    // ipc/network software -- operational errors
+    NETDOWN = 50, // Network is down
+    NETUNREACH = 51, // Network is unreachable
+    NETRESET = 52, // Network dropped connection on reset
+    CONNABORTED = 53, // Software caused connection abort
+    CONNRESET = 54, // Connection reset by peer
+    NOBUFS = 55, // No buffer space available
+    ISCONN = 56, // Socket is already connected
+    NOTCONN = 57, // Socket is not connected
+    SHUTDOWN = 58, // Can't send after socket shutdown
+    TOOMANYREFS = 59, // Too many references: can't splice
+    TIMEDOUT = 60, // Operation timed out
+    CONNREFUSED = 61, // Connection refused
 
-pub const ELOOP = 62; // Too many levels of symbolic links
-pub const ENAMETOOLONG = 63; // File name too long
+    LOOP = 62, // Too many levels of symbolic links
+    NAMETOOLONG = 63, // File name too long
 
-// should be rearranged
-pub const EHOSTDOWN = 64; // Host is down
-pub const EHOSTUNREACH = 65; // No route to host
-pub const ENOTEMPTY = 66; // Directory not empty
+    // should be rearranged
+    HOSTDOWN = 64, // Host is down
+    HOSTUNREACH = 65, // No route to host
+    NOTEMPTY = 66, // Directory not empty
 
-// quotas & mush
-pub const EPROCLIM = 67; // Too many processes
-pub const EUSERS = 68; // Too many users
-pub const EDQUOT = 69; // Disc quota exceeded
+    // quotas & mush
+    PROCLIM = 67, // Too many processes
+    USERS = 68, // Too many users
+    DQUOT = 69, // Disc quota exceeded
 
-// Network File System
-pub const ESTALE = 70; // Stale NFS file handle
-pub const EREMOTE = 71; // Too many levels of remote in path
-pub const EBADRPC = 72; // RPC struct is bad
-pub const ERPCMISMATCH = 73; // RPC version wrong
-pub const EPROGUNAVAIL = 74; // RPC prog. not avail
-pub const EPROGMISMATCH = 75; // Program version wrong
-pub const EPROCUNAVAIL = 76; // Bad procedure for program
+    // Network File System
+    STALE = 70, // Stale NFS file handle
+    REMOTE = 71, // Too many levels of remote in path
+    BADRPC = 72, // RPC struct is bad
+    RPCMISMATCH = 73, // RPC version wrong
+    PROGUNAVAIL = 74, // RPC prog. not avail
+    PROGMISMATCH = 75, // Program version wrong
+    PROCUNAVAIL = 76, // Bad procedure for program
 
-pub const ENOLCK = 77; // No locks available
-pub const ENOSYS = 78; // Function not implemented
+    NOLCK = 77, // No locks available
+    NOSYS = 78, // Function not implemented
 
-pub const EFTYPE = 79; // Inappropriate file type or format
-pub const EAUTH = 80; // Authentication error
-pub const ENEEDAUTH = 81; // Need authenticator
-pub const EIPSEC = 82; // IPsec processing failure
-pub const ENOATTR = 83; // Attribute not found
+    FTYPE = 79, // Inappropriate file type or format
+    AUTH = 80, // Authentication error
+    NEEDAUTH = 81, // Need authenticator
+    IPSEC = 82, // IPsec processing failure
+    NOATTR = 83, // Attribute not found
 
-// Wide/multibyte-character handling, ISO/IEC 9899/AMD1:1995
-pub const EILSEQ = 84; // Illegal byte sequence
+    // Wide/multibyte-character handling, ISO/IEC 9899/AMD1:1995
+    ILSEQ = 84, // Illegal byte sequence
 
-pub const ENOMEDIUM = 85; // No medium found
-pub const EMEDIUMTYPE = 86; // Wrong medium type
-pub const EOVERFLOW = 87; // Value too large to be stored in data type
-pub const ECANCELED = 88; // Operation canceled
-pub const EIDRM = 89; // Identifier removed
-pub const ENOMSG = 90; // No message of desired type
-pub const ENOTSUP = 91; // Not supported
-pub const EBADMSG = 92; // Bad or Corrupt message
-pub const ENOTRECOVERABLE = 93; // State not recoverable
-pub const EOWNERDEAD = 94; // Previous owner died
-pub const EPROTO = 95; // Protocol error
+    NOMEDIUM = 85, // No medium found
+    MEDIUMTYPE = 86, // Wrong medium type
+    OVERFLOW = 87, // Value too large to be stored in data type
+    CANCELED = 88, // Operation canceled
+    IDRM = 89, // Identifier removed
+    NOMSG = 90, // No message of desired type
+    NOTSUP = 91, // Not supported
+    BADMSG = 92, // Bad or Corrupt message
+    NOTRECOVERABLE = 93, // State not recoverable
+    OWNERDEAD = 94, // Previous owner died
+    PROTO = 95, // Protocol error
 
-pub const ELAST = 95; // Must equal largest errno
+    _,
+};
 
 const _MAX_PAGE_SHIFT = switch (builtin.target.cpu.arch) {
     .i386 => 12,
diff --git a/lib/std/os/bits/wasi.zig b/lib/std/os/bits/wasi.zig
index ece97eacce..eb68946f05 100644
--- a/lib/std/os/bits/wasi.zig
+++ b/lib/std/os/bits/wasi.zig
@@ -111,86 +111,89 @@ pub const dirent_t = extern struct {
     d_type: filetype_t,
 };
 
-pub const errno_t = u16;
-pub const ESUCCESS: errno_t = 0;
-pub const E2BIG: errno_t = 1;
-pub const EACCES: errno_t = 2;
-pub const EADDRINUSE: errno_t = 3;
-pub const EADDRNOTAVAIL: errno_t = 4;
-pub const EAFNOSUPPORT: errno_t = 5;
-pub const EAGAIN: errno_t = 6;
-pub const EWOULDBLOCK = EAGAIN;
-pub const EALREADY: errno_t = 7;
-pub const EBADF: errno_t = 8;
-pub const EBADMSG: errno_t = 9;
-pub const EBUSY: errno_t = 10;
-pub const ECANCELED: errno_t = 11;
-pub const ECHILD: errno_t = 12;
-pub const ECONNABORTED: errno_t = 13;
-pub const ECONNREFUSED: errno_t = 14;
-pub const ECONNRESET: errno_t = 15;
-pub const EDEADLK: errno_t = 16;
-pub const EDESTADDRREQ: errno_t = 17;
-pub const EDOM: errno_t = 18;
-pub const EDQUOT: errno_t = 19;
-pub const EEXIST: errno_t = 20;
-pub const EFAULT: errno_t = 21;
-pub const EFBIG: errno_t = 22;
-pub const EHOSTUNREACH: errno_t = 23;
-pub const EIDRM: errno_t = 24;
-pub const EILSEQ: errno_t = 25;
-pub const EINPROGRESS: errno_t = 26;
-pub const EINTR: errno_t = 27;
-pub const EINVAL: errno_t = 28;
-pub const EIO: errno_t = 29;
-pub const EISCONN: errno_t = 30;
-pub const EISDIR: errno_t = 31;
-pub const ELOOP: errno_t = 32;
-pub const EMFILE: errno_t = 33;
-pub const EMLINK: errno_t = 34;
-pub const EMSGSIZE: errno_t = 35;
-pub const EMULTIHOP: errno_t = 36;
-pub const ENAMETOOLONG: errno_t = 37;
-pub const ENETDOWN: errno_t = 38;
-pub const ENETRESET: errno_t = 39;
-pub const ENETUNREACH: errno_t = 40;
-pub const ENFILE: errno_t = 41;
-pub const ENOBUFS: errno_t = 42;
-pub const ENODEV: errno_t = 43;
-pub const ENOENT: errno_t = 44;
-pub const ENOEXEC: errno_t = 45;
-pub const ENOLCK: errno_t = 46;
-pub const ENOLINK: errno_t = 47;
-pub const ENOMEM: errno_t = 48;
-pub const ENOMSG: errno_t = 49;
-pub const ENOPROTOOPT: errno_t = 50;
-pub const ENOSPC: errno_t = 51;
-pub const ENOSYS: errno_t = 52;
-pub const ENOTCONN: errno_t = 53;
-pub const ENOTDIR: errno_t = 54;
-pub const ENOTEMPTY: errno_t = 55;
-pub const ENOTRECOVERABLE: errno_t = 56;
-pub const ENOTSOCK: errno_t = 57;
-pub const ENOTSUP: errno_t = 58;
-pub const EOPNOTSUPP = ENOTSUP;
-pub const ENOTTY: errno_t = 59;
-pub const ENXIO: errno_t = 60;
-pub const EOVERFLOW: errno_t = 61;
-pub const EOWNERDEAD: errno_t = 62;
-pub const EPERM: errno_t = 63;
-pub const EPIPE: errno_t = 64;
-pub const EPROTO: errno_t = 65;
-pub const EPROTONOSUPPORT: errno_t = 66;
-pub const EPROTOTYPE: errno_t = 67;
-pub const ERANGE: errno_t = 68;
-pub const EROFS: errno_t = 69;
-pub const ESPIPE: errno_t = 70;
-pub const ESRCH: errno_t = 71;
-pub const ESTALE: errno_t = 72;
-pub const ETIMEDOUT: errno_t = 73;
-pub const ETXTBSY: errno_t = 74;
-pub const EXDEV: errno_t = 75;
-pub const ENOTCAPABLE: errno_t = 76;
+pub const errno_t = enum(u16) {
+    SUCCESS = 0,
+    @"2BIG" = 1,
+    ACCES = 2,
+    ADDRINUSE = 3,
+    ADDRNOTAVAIL = 4,
+    AFNOSUPPORT = 5,
+    /// This is also the error code used for `WOULDBLOCK`.
+    AGAIN = 6,
+    ALREADY = 7,
+    BADF = 8,
+    BADMSG = 9,
+    BUSY = 10,
+    CANCELED = 11,
+    CHILD = 12,
+    CONNABORTED = 13,
+    CONNREFUSED = 14,
+    CONNRESET = 15,
+    DEADLK = 16,
+    DESTADDRREQ = 17,
+    DOM = 18,
+    DQUOT = 19,
+    EXIST = 20,
+    FAULT = 21,
+    FBIG = 22,
+    HOSTUNREACH = 23,
+    IDRM = 24,
+    ILSEQ = 25,
+    INPROGRESS = 26,
+    INTR = 27,
+    INVAL = 28,
+    IO = 29,
+    ISCONN = 30,
+    ISDIR = 31,
+    LOOP = 32,
+    MFILE = 33,
+    MLINK = 34,
+    MSGSIZE = 35,
+    MULTIHOP = 36,
+    NAMETOOLONG = 37,
+    NETDOWN = 38,
+    NETRESET = 39,
+    NETUNREACH = 40,
+    NFILE = 41,
+    NOBUFS = 42,
+    NODEV = 43,
+    NOENT = 44,
+    NOEXEC = 45,
+    NOLCK = 46,
+    NOLINK = 47,
+    NOMEM = 48,
+    NOMSG = 49,
+    NOPROTOOPT = 50,
+    NOSPC = 51,
+    NOSYS = 52,
+    NOTCONN = 53,
+    NOTDIR = 54,
+    NOTEMPTY = 55,
+    NOTRECOVERABLE = 56,
+    NOTSOCK = 57,
+    /// This is also the code used for `NOTSUP`.
+    OPNOTSUPP = 58,
+    NOTTY = 59,
+    NXIO = 60,
+    OVERFLOW = 61,
+    OWNERDEAD = 62,
+    PERM = 63,
+    PIPE = 64,
+    PROTO = 65,
+    PROTONOSUPPORT = 66,
+    PROTOTYPE = 67,
+    RANGE = 68,
+    ROFS = 69,
+    SPIPE = 70,
+    SRCH = 71,
+    STALE = 72,
+    TIMEDOUT = 73,
+    TXTBSY = 74,
+    XDEV = 75,
+    NOTCAPABLE = 76,
+    _,
+};
+pub const E = errno_t;
 
 pub const event_t = extern struct {
     userdata: userdata_t,
diff --git a/lib/std/os/bits/windows.zig b/lib/std/os/bits/windows.zig
index 05c50ffe47..3943d1fd3d 100644
--- a/lib/std/os/bits/windows.zig
+++ b/lib/std/os/bits/windows.zig
@@ -87,94 +87,98 @@ pub const SEEK_SET = 0;
 pub const SEEK_CUR = 1;
 pub const SEEK_END = 2;
 
-pub const EPERM = 1;
-pub const ENOENT = 2;
-pub const ESRCH = 3;
-pub const EINTR = 4;
-pub const EIO = 5;
-pub const ENXIO = 6;
-pub const E2BIG = 7;
-pub const ENOEXEC = 8;
-pub const EBADF = 9;
-pub const ECHILD = 10;
-pub const EAGAIN = 11;
-pub const ENOMEM = 12;
-pub const EACCES = 13;
-pub const EFAULT = 14;
-pub const EBUSY = 16;
-pub const EEXIST = 17;
-pub const EXDEV = 18;
-pub const ENODEV = 19;
-pub const ENOTDIR = 20;
-pub const EISDIR = 21;
-pub const ENFILE = 23;
-pub const EMFILE = 24;
-pub const ENOTTY = 25;
-pub const EFBIG = 27;
-pub const ENOSPC = 28;
-pub const ESPIPE = 29;
-pub const EROFS = 30;
-pub const EMLINK = 31;
-pub const EPIPE = 32;
-pub const EDOM = 33;
-pub const EDEADLK = 36;
-pub const ENAMETOOLONG = 38;
-pub const ENOLCK = 39;
-pub const ENOSYS = 40;
-pub const ENOTEMPTY = 41;
+pub const E = enum(u16) {
+    /// No error occurred.
+    SUCCESS = 0,
+    PERM = 1,
+    NOENT = 2,
+    SRCH = 3,
+    INTR = 4,
+    IO = 5,
+    NXIO = 6,
+    @"2BIG" = 7,
+    NOEXEC = 8,
+    BADF = 9,
+    CHILD = 10,
+    AGAIN = 11,
+    NOMEM = 12,
+    ACCES = 13,
+    FAULT = 14,
+    BUSY = 16,
+    EXIST = 17,
+    XDEV = 18,
+    NODEV = 19,
+    NOTDIR = 20,
+    ISDIR = 21,
+    NFILE = 23,
+    MFILE = 24,
+    NOTTY = 25,
+    FBIG = 27,
+    NOSPC = 28,
+    SPIPE = 29,
+    ROFS = 30,
+    MLINK = 31,
+    PIPE = 32,
+    DOM = 33,
+    /// Also means `DEADLOCK`.
+    DEADLK = 36,
+    NAMETOOLONG = 38,
+    NOLCK = 39,
+    NOSYS = 40,
+    NOTEMPTY = 41,
+
+    INVAL = 22,
+    RANGE = 34,
+    ILSEQ = 42,
+
+    // POSIX Supplement
+    ADDRINUSE = 100,
+    ADDRNOTAVAIL = 101,
+    AFNOSUPPORT = 102,
+    ALREADY = 103,
+    BADMSG = 104,
+    CANCELED = 105,
+    CONNABORTED = 106,
+    CONNREFUSED = 107,
+    CONNRESET = 108,
+    DESTADDRREQ = 109,
+    HOSTUNREACH = 110,
+    IDRM = 111,
+    INPROGRESS = 112,
+    ISCONN = 113,
+    LOOP = 114,
+    MSGSIZE = 115,
+    NETDOWN = 116,
+    NETRESET = 117,
+    NETUNREACH = 118,
+    NOBUFS = 119,
+    NODATA = 120,
+    NOLINK = 121,
+    NOMSG = 122,
+    NOPROTOOPT = 123,
+    NOSR = 124,
+    NOSTR = 125,
+    NOTCONN = 126,
+    NOTRECOVERABLE = 127,
+    NOTSOCK = 128,
+    NOTSUP = 129,
+    OPNOTSUPP = 130,
+    OTHER = 131,
+    OVERFLOW = 132,
+    OWNERDEAD = 133,
+    PROTO = 134,
+    PROTONOSUPPORT = 135,
+    PROTOTYPE = 136,
+    TIME = 137,
+    TIMEDOUT = 138,
+    TXTBSY = 139,
+    WOULDBLOCK = 140,
+    DQUOT = 10069,
+    _,
+};
 
-pub const EINVAL = 22;
-pub const ERANGE = 34;
-pub const EILSEQ = 42;
 pub const STRUNCATE = 80;
 
-// Support EDEADLOCK for compatibility with older Microsoft C versions
-pub const EDEADLOCK = EDEADLK;
-
-// POSIX Supplement
-pub const EADDRINUSE = 100;
-pub const EADDRNOTAVAIL = 101;
-pub const EAFNOSUPPORT = 102;
-pub const EALREADY = 103;
-pub const EBADMSG = 104;
-pub const ECANCELED = 105;
-pub const ECONNABORTED = 106;
-pub const ECONNREFUSED = 107;
-pub const ECONNRESET = 108;
-pub const EDESTADDRREQ = 109;
-pub const EHOSTUNREACH = 110;
-pub const EIDRM = 111;
-pub const EINPROGRESS = 112;
-pub const EISCONN = 113;
-pub const ELOOP = 114;
-pub const EMSGSIZE = 115;
-pub const ENETDOWN = 116;
-pub const ENETRESET = 117;
-pub const ENETUNREACH = 118;
-pub const ENOBUFS = 119;
-pub const ENODATA = 120;
-pub const ENOLINK = 121;
-pub const ENOMSG = 122;
-pub const ENOPROTOOPT = 123;
-pub const ENOSR = 124;
-pub const ENOSTR = 125;
-pub const ENOTCONN = 126;
-pub const ENOTRECOVERABLE = 127;
-pub const ENOTSOCK = 128;
-pub const ENOTSUP = 129;
-pub const EOPNOTSUPP = 130;
-pub const EOTHER = 131;
-pub const EOVERFLOW = 132;
-pub const EOWNERDEAD = 133;
-pub const EPROTO = 134;
-pub const EPROTONOSUPPORT = 135;
-pub const EPROTOTYPE = 136;
-pub const ETIME = 137;
-pub const ETIMEDOUT = 138;
-pub const ETXTBSY = 139;
-pub const EWOULDBLOCK = 140;
-pub const EDQUOT = 10069;
-
 pub const F_OK = 0;
 
 /// Remove directory instead of unlinking file
diff --git a/lib/std/os/linux.zig b/lib/std/os/linux.zig
index ca8f0907e1..841f77467c 100644
--- a/lib/std/os/linux.zig
+++ b/lib/std/os/linux.zig
@@ -91,9 +91,10 @@ fn splitValue64(val: i64) [2]u32 {
 }
 
 /// Get the errno from a syscall return value, or 0 for no error.
-pub fn getErrno(r: usize) u12 {
+pub fn getErrno(r: usize) E {
     const signed_r = @bitCast(isize, r);
-    return if (signed_r > -4096 and signed_r < 0) @intCast(u12, -signed_r) else 0;
+    const int = if (signed_r > -4096 and signed_r < 0) -signed_r else 0;
+    return @intToEnum(E, int);
 }
 
 pub fn dup(old: i32) usize {
@@ -281,7 +282,7 @@ pub fn mmap(address: ?[*]u8, length: usize, prot: usize, flags: u32, fd: i32, of
     if (@hasField(SYS, "mmap2")) {
         // Make sure the offset is also specified in multiples of page size
         if ((offset & (MMAP2_UNIT - 1)) != 0)
-            return @bitCast(usize, @as(isize, -EINVAL));
+            return @bitCast(usize, -@as(isize, @enumToInt(E.INVAL)));
 
         return syscall6(
             .mmap2,
@@ -746,7 +747,7 @@ pub fn clock_gettime(clk_id: i32, tp: *timespec) usize {
             const f = @ptrCast(vdso_clock_gettime_ty, fn_ptr);
             const rc = f(clk_id, tp);
             switch (rc) {
-                0, @bitCast(usize, @as(isize, -EINVAL)) => return rc,
+                0, @bitCast(usize, -@as(isize, @enumToInt(E.INVAL))) => return rc,
                 else => {},
             }
         }
@@ -764,7 +765,7 @@ fn init_vdso_clock_gettime(clk: i32, ts: *timespec) callconv(.C) usize {
         const f = @ptrCast(vdso_clock_gettime_ty, fn_ptr);
         return f(clk, ts);
     }
-    return @bitCast(usize, @as(isize, -ENOSYS));
+    return @bitCast(usize, -@as(isize, @enumToInt(E.NOSYS)));
 }
 
 pub fn clock_getres(clk_id: i32, tp: *timespec) usize {
@@ -961,7 +962,7 @@ pub fn sigaction(sig: u6, noalias act: ?*const Sigaction, noalias oact: ?*Sigact
         .sparc, .sparcv9 => syscall5(.rt_sigaction, sig, ksa_arg, oldksa_arg, @ptrToInt(ksa.restorer), mask_size),
         else => syscall4(.rt_sigaction, sig, ksa_arg, oldksa_arg, mask_size),
     };
-    if (getErrno(result) != 0) return result;
+    if (getErrno(result) != .SUCCESS) return result;
 
     if (oact) |old| {
         old.handler.handler = oldksa.handler;
@@ -1202,7 +1203,7 @@ pub fn statx(dirfd: i32, path: [*]const u8, flags: u32, mask: u32, statx_buf: *S
             @ptrToInt(statx_buf),
         );
     }
-    return @bitCast(usize, @as(isize, -ENOSYS));
+    return @bitCast(usize, -@as(isize, @enumToInt(E.NOSYS)));
 }
 
 pub fn listxattr(path: [*:0]const u8, list: [*]u8, size: usize) usize {
diff --git a/lib/std/os/linux/bpf.zig b/lib/std/os/linux/bpf.zig
index 86993083e3..8afd851629 100644
--- a/lib/std/os/linux/bpf.zig
+++ b/lib/std/os/linux/bpf.zig
@@ -1508,13 +1508,13 @@ pub fn map_create(map_type: MapType, key_size: u32, value_size: u32, max_entries
     attr.map_create.max_entries = max_entries;
 
     const rc = bpf(.map_create, &attr, @sizeOf(MapCreateAttr));
-    return switch (errno(rc)) {
-        0 => @intCast(fd_t, rc),
-        EINVAL => error.MapTypeOrAttrInvalid,
-        ENOMEM => error.SystemResources,
-        EPERM => error.AccessDenied,
-        else => |err| unexpectedErrno(err),
-    };
+    switch (errno(rc)) {
+        .SUCCESS => return @intCast(fd_t, rc),
+        .INVAL => return error.MapTypeOrAttrInvalid,
+        .NOMEM => return error.SystemResources,
+        .PERM => return error.AccessDenied,
+        else => |err| return unexpectedErrno(err),
+    }
 }
 
 test "map_create" {
@@ -1533,12 +1533,12 @@ pub fn map_lookup_elem(fd: fd_t, key: []const u8, value: []u8) !void {
 
     const rc = bpf(.map_lookup_elem, &attr, @sizeOf(MapElemAttr));
     switch (errno(rc)) {
-        0 => return,
-        EBADF => return error.BadFd,
-        EFAULT => unreachable,
-        EINVAL => return error.FieldInAttrNeedsZeroing,
-        ENOENT => return error.NotFound,
-        EPERM => return error.AccessDenied,
+        .SUCCESS => return,
+        .BADF => return error.BadFd,
+        .FAULT => unreachable,
+        .INVAL => return error.FieldInAttrNeedsZeroing,
+        .NOENT => return error.NotFound,
+        .PERM => return error.AccessDenied,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -1555,13 +1555,13 @@ pub fn map_update_elem(fd: fd_t, key: []const u8, value: []const u8, flags: u64)
 
     const rc = bpf(.map_update_elem, &attr, @sizeOf(MapElemAttr));
     switch (errno(rc)) {
-        0 => return,
-        E2BIG => return error.ReachedMaxEntries,
-        EBADF => return error.BadFd,
-        EFAULT => unreachable,
-        EINVAL => return error.FieldInAttrNeedsZeroing,
-        ENOMEM => return error.SystemResources,
-        EPERM => return error.AccessDenied,
+        .SUCCESS => return,
+        .@"2BIG" => return error.ReachedMaxEntries,
+        .BADF => return error.BadFd,
+        .FAULT => unreachable,
+        .INVAL => return error.FieldInAttrNeedsZeroing,
+        .NOMEM => return error.SystemResources,
+        .PERM => return error.AccessDenied,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -1576,12 +1576,12 @@ pub fn map_delete_elem(fd: fd_t, key: []const u8) !void {
 
     const rc = bpf(.map_delete_elem, &attr, @sizeOf(MapElemAttr));
     switch (errno(rc)) {
-        0 => return,
-        EBADF => return error.BadFd,
-        EFAULT => unreachable,
-        EINVAL => return error.FieldInAttrNeedsZeroing,
-        ENOENT => return error.NotFound,
-        EPERM => return error.AccessDenied,
+        .SUCCESS => return,
+        .BADF => return error.BadFd,
+        .FAULT => unreachable,
+        .INVAL => return error.FieldInAttrNeedsZeroing,
+        .NOENT => return error.NotFound,
+        .PERM => return error.AccessDenied,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -1639,11 +1639,11 @@ pub fn prog_load(
 
     const rc = bpf(.prog_load, &attr, @sizeOf(ProgLoadAttr));
     return switch (errno(rc)) {
-        0 => @intCast(fd_t, rc),
-        EACCES => error.UnsafeProgram,
-        EFAULT => unreachable,
-        EINVAL => error.InvalidProgram,
-        EPERM => error.AccessDenied,
+        .SUCCESS => @intCast(fd_t, rc),
+        .ACCES => error.UnsafeProgram,
+        .FAULT => unreachable,
+        .INVAL => error.InvalidProgram,
+        .PERM => error.AccessDenied,
         else => |err| unexpectedErrno(err),
     };
 }
diff --git a/lib/std/os/linux/io_uring.zig b/lib/std/os/linux/io_uring.zig
index b6bde34b7d..1db4c30d2a 100644
--- a/lib/std/os/linux/io_uring.zig
+++ b/lib/std/os/linux/io_uring.zig
@@ -54,19 +54,19 @@ pub const IO_Uring = struct {
 
         const res = linux.io_uring_setup(entries, p);
         switch (linux.getErrno(res)) {
-            0 => {},
-            linux.EFAULT => return error.ParamsOutsideAccessibleAddressSpace,
+            .SUCCESS => {},
+            .FAULT => return error.ParamsOutsideAccessibleAddressSpace,
             // The resv array contains non-zero data, p.flags contains an unsupported flag,
             // entries out of bounds, IORING_SETUP_SQ_AFF was specified without IORING_SETUP_SQPOLL,
             // or IORING_SETUP_CQSIZE was specified but io_uring_params.cq_entries was invalid:
-            linux.EINVAL => return error.ArgumentsInvalid,
-            linux.EMFILE => return error.ProcessFdQuotaExceeded,
-            linux.ENFILE => return error.SystemFdQuotaExceeded,
-            linux.ENOMEM => return error.SystemResources,
+            .INVAL => return error.ArgumentsInvalid,
+            .MFILE => return error.ProcessFdQuotaExceeded,
+            .NFILE => return error.SystemFdQuotaExceeded,
+            .NOMEM => return error.SystemResources,
             // IORING_SETUP_SQPOLL was specified but effective user ID lacks sufficient privileges,
             // or a container seccomp policy prohibits io_uring syscalls:
-            linux.EPERM => return error.PermissionDenied,
-            linux.ENOSYS => return error.SystemOutdated,
+            .PERM => return error.PermissionDenied,
+            .NOSYS => return error.SystemOutdated,
             else => |errno| return os.unexpectedErrno(errno),
         }
         const fd = @intCast(os.fd_t, res);
@@ -180,31 +180,31 @@ pub const IO_Uring = struct {
         assert(self.fd >= 0);
         const res = linux.io_uring_enter(self.fd, to_submit, min_complete, flags, null);
         switch (linux.getErrno(res)) {
-            0 => {},
+            .SUCCESS => {},
             // The kernel was unable to allocate memory or ran out of resources for the request.
             // The application should wait for some completions and try again:
-            linux.EAGAIN => return error.SystemResources,
+            .AGAIN => return error.SystemResources,
             // The SQE `fd` is invalid, or IOSQE_FIXED_FILE was set but no files were registered:
-            linux.EBADF => return error.FileDescriptorInvalid,
+            .BADF => return error.FileDescriptorInvalid,
             // The file descriptor is valid, but the ring is not in the right state.
             // See io_uring_register(2) for how to enable the ring.
-            linux.EBADFD => return error.FileDescriptorInBadState,
+            .BADFD => return error.FileDescriptorInBadState,
             // The application attempted to overcommit the number of requests it can have pending.
             // The application should wait for some completions and try again:
-            linux.EBUSY => return error.CompletionQueueOvercommitted,
+            .BUSY => return error.CompletionQueueOvercommitted,
             // The SQE is invalid, or valid but the ring was setup with IORING_SETUP_IOPOLL:
-            linux.EINVAL => return error.SubmissionQueueEntryInvalid,
+            .INVAL => return error.SubmissionQueueEntryInvalid,
             // The buffer is outside the process' accessible address space, or IORING_OP_READ_FIXED
             // or IORING_OP_WRITE_FIXED was specified but no buffers were registered, or the range
             // described by `addr` and `len` is not within the buffer registered at `buf_index`:
-            linux.EFAULT => return error.BufferInvalid,
-            linux.ENXIO => return error.RingShuttingDown,
+            .FAULT => return error.BufferInvalid,
+            .NXIO => return error.RingShuttingDown,
             // The kernel believes our `self.fd` does not refer to an io_uring instance,
             // or the opcode is valid but not supported by this kernel (more likely):
-            linux.EOPNOTSUPP => return error.OpcodeNotSupported,
+            .OPNOTSUPP => return error.OpcodeNotSupported,
             // The operation was interrupted by a delivery of a signal before it could complete.
             // This can happen while waiting for events with IORING_ENTER_GETEVENTS:
-            linux.EINTR => return error.SignalInterrupt,
+            .INTR => return error.SignalInterrupt,
             else => |errno| return os.unexpectedErrno(errno),
         }
         return @intCast(u32, res);
@@ -681,22 +681,22 @@ pub const IO_Uring = struct {
 
     fn handle_registration_result(res: usize) !void {
         switch (linux.getErrno(res)) {
-            0 => {},
+            .SUCCESS => {},
             // One or more fds in the array are invalid, or the kernel does not support sparse sets:
-            linux.EBADF => return error.FileDescriptorInvalid,
-            linux.EBUSY => return error.FilesAlreadyRegistered,
-            linux.EINVAL => return error.FilesEmpty,
+            .BADF => return error.FileDescriptorInvalid,
+            .BUSY => return error.FilesAlreadyRegistered,
+            .INVAL => return error.FilesEmpty,
             // Adding `nr_args` file references would exceed the maximum allowed number of files the
             // user is allowed to have according to the per-user RLIMIT_NOFILE resource limit and
             // the CAP_SYS_RESOURCE capability is not set, or `nr_args` exceeds the maximum allowed
             // for a fixed file set (older kernels have a limit of 1024 files vs 64K files):
-            linux.EMFILE => return error.UserFdQuotaExceeded,
+            .MFILE => return error.UserFdQuotaExceeded,
             // Insufficient kernel resources, or the caller had a non-zero RLIMIT_MEMLOCK soft
             // resource limit but tried to lock more memory than the limit permitted (not enforced
             // when the process is privileged with CAP_IPC_LOCK):
-            linux.ENOMEM => return error.SystemResources,
+            .NOMEM => return error.SystemResources,
             // Attempt to register files on a ring already registering files or being torn down:
-            linux.ENXIO => return error.RingShuttingDownOrAlreadyRegisteringFiles,
+            .NXIO => return error.RingShuttingDownOrAlreadyRegisteringFiles,
             else => |errno| return os.unexpectedErrno(errno),
         }
     }
@@ -706,8 +706,8 @@ pub const IO_Uring = struct {
         assert(self.fd >= 0);
         const res = linux.io_uring_register(self.fd, .UNREGISTER_FILES, null, 0);
         switch (linux.getErrno(res)) {
-            0 => {},
-            linux.ENXIO => return error.FilesNotRegistered,
+            .SUCCESS => {},
+            .NXIO => return error.FilesNotRegistered,
             else => |errno| return os.unexpectedErrno(errno),
         }
     }
@@ -1272,8 +1272,8 @@ test "write/read" {
     const cqe_read = try ring.copy_cqe();
     // Prior to Linux Kernel 5.6 this is the only way to test for read/write support:
     // https://lwn.net/Articles/809820/
-    if (cqe_write.res == -linux.EINVAL) return error.SkipZigTest;
-    if (cqe_read.res == -linux.EINVAL) return error.SkipZigTest;
+    if (cqe_write.err() == .INVAL) return error.SkipZigTest;
+    if (cqe_read.err() == .INVAL) return error.SkipZigTest;
     try testing.expectEqual(linux.io_uring_cqe{
         .user_data = 0x11111111,
         .res = buffer_write.len,
@@ -1322,11 +1322,11 @@ test "openat" {
 
     const cqe_openat = try ring.copy_cqe();
     try testing.expectEqual(@as(u64, 0x33333333), cqe_openat.user_data);
-    if (cqe_openat.res == -linux.EINVAL) return error.SkipZigTest;
+    if (cqe_openat.err() == .INVAL) return error.SkipZigTest;
     // AT_FDCWD is not fully supported before kernel 5.6:
     // See https://lore.kernel.org/io-uring/20200207155039.12819-1-axboe@kernel.dk/T/
     // We use IORING_FEAT_RW_CUR_POS to know if we are pre-5.6 since that feature was added in 5.6.
-    if (cqe_openat.res == -linux.EBADF and (ring.features & linux.IORING_FEAT_RW_CUR_POS) == 0) {
+    if (cqe_openat.err() == .BADF and (ring.features & linux.IORING_FEAT_RW_CUR_POS) == 0) {
         return error.SkipZigTest;
     }
     if (cqe_openat.res <= 0) std.debug.print("\ncqe_openat.res={}\n", .{cqe_openat.res});
@@ -1357,7 +1357,7 @@ test "close" {
     try testing.expectEqual(@as(u32, 1), try ring.submit());
 
     const cqe_close = try ring.copy_cqe();
-    if (cqe_close.res == -linux.EINVAL) return error.SkipZigTest;
+    if (cqe_close.err() == .INVAL) return error.SkipZigTest;
     try testing.expectEqual(linux.io_uring_cqe{
         .user_data = 0x44444444,
         .res = 0,
@@ -1397,9 +1397,9 @@ test "accept/connect/send/recv" {
     try testing.expectEqual(@as(u32, 1), try ring.submit());
 
     var cqe_accept = try ring.copy_cqe();
-    if (cqe_accept.res == -linux.EINVAL) return error.SkipZigTest;
+    if (cqe_accept.err() == .INVAL) return error.SkipZigTest;
     var cqe_connect = try ring.copy_cqe();
-    if (cqe_connect.res == -linux.EINVAL) return error.SkipZigTest;
+    if (cqe_connect.err() == .INVAL) return error.SkipZigTest;
 
     // The accept/connect CQEs may arrive in any order, the connect CQE will sometimes come first:
     if (cqe_accept.user_data == 0xcccccccc and cqe_connect.user_data == 0xaaaaaaaa) {
@@ -1425,7 +1425,7 @@ test "accept/connect/send/recv" {
     try testing.expectEqual(@as(u32, 2), try ring.submit());
 
     const cqe_send = try ring.copy_cqe();
-    if (cqe_send.res == -linux.EINVAL) return error.SkipZigTest;
+    if (cqe_send.err() == .INVAL) return error.SkipZigTest;
     try testing.expectEqual(linux.io_uring_cqe{
         .user_data = 0xeeeeeeee,
         .res = buffer_send.len,
@@ -1433,7 +1433,7 @@ test "accept/connect/send/recv" {
     }, cqe_send);
 
     const cqe_recv = try ring.copy_cqe();
-    if (cqe_recv.res == -linux.EINVAL) return error.SkipZigTest;
+    if (cqe_recv.err() == .INVAL) return error.SkipZigTest;
     try testing.expectEqual(linux.io_uring_cqe{
         .user_data = 0xffffffff,
         .res = buffer_recv.len,
@@ -1466,7 +1466,7 @@ test "timeout (after a relative time)" {
 
     try testing.expectEqual(linux.io_uring_cqe{
         .user_data = 0x55555555,
-        .res = -linux.ETIME,
+        .res = -@as(i32, @enumToInt(linux.E.TIME)),
         .flags = 0,
     }, cqe);
 
@@ -1535,14 +1535,14 @@ test "timeout_remove" {
     // We use IORING_FEAT_RW_CUR_POS as a safety check here to make sure we are at least pre-5.6.
     // We don't want to skip this test for newer kernels.
     if (cqe_timeout.user_data == 0x99999999 and
-        cqe_timeout.res == -linux.EBADF and
+        cqe_timeout.err() == .BADF and
         (ring.features & linux.IORING_FEAT_RW_CUR_POS) == 0)
     {
         return error.SkipZigTest;
     }
     try testing.expectEqual(linux.io_uring_cqe{
         .user_data = 0x88888888,
-        .res = -linux.ECANCELED,
+        .res = -@as(i32, @enumToInt(linux.E.CANCELED)),
         .flags = 0,
     }, cqe_timeout);
 
@@ -1578,15 +1578,15 @@ test "fallocate" {
     try testing.expectEqual(@as(u32, 1), try ring.submit());
 
     const cqe = try ring.copy_cqe();
-    switch (-cqe.res) {
-        0 => {},
+    switch (cqe.err()) {
+        .SUCCESS => {},
         // This kernel's io_uring does not yet implement fallocate():
-        linux.EINVAL => return error.SkipZigTest,
+        .INVAL => return error.SkipZigTest,
         // This kernel does not implement fallocate():
-        linux.ENOSYS => return error.SkipZigTest,
+        .NOSYS => return error.SkipZigTest,
         // The filesystem containing the file referred to by fd does not support this operation;
         // or the mode is not supported by the filesystem containing the file referred to by fd:
-        linux.EOPNOTSUPP => return error.SkipZigTest,
+        .OPNOTSUPP => return error.SkipZigTest,
         else => |errno| std.debug.panic("unhandled errno: {}", .{errno}),
     }
     try testing.expectEqual(linux.io_uring_cqe{
diff --git a/lib/std/os/linux/test.zig b/lib/std/os/linux/test.zig
index 2e98fe359d..8efa6c754f 100644
--- a/lib/std/os/linux/test.zig
+++ b/lib/std/os/linux/test.zig
@@ -22,9 +22,9 @@ test "fallocate" {
 
     const len: i64 = 65536;
     switch (linux.getErrno(linux.fallocate(file.handle, 0, 0, len))) {
-        0 => {},
-        linux.ENOSYS => return error.SkipZigTest,
-        linux.EOPNOTSUPP => return error.SkipZigTest,
+        .SUCCESS => {},
+        .NOSYS => return error.SkipZigTest,
+        .OPNOTSUPP => return error.SkipZigTest,
         else => |errno| std.debug.panic("unhandled errno: {}", .{errno}),
     }
 
@@ -37,11 +37,11 @@ test "getpid" {
 
 test "timer" {
     const epoll_fd = linux.epoll_create();
-    var err: usize = linux.getErrno(epoll_fd);
-    try expect(err == 0);
+    var err: linux.E = linux.getErrno(epoll_fd);
+    try expect(err == .SUCCESS);
 
     const timer_fd = linux.timerfd_create(linux.CLOCK_MONOTONIC, 0);
-    try expect(linux.getErrno(timer_fd) == 0);
+    try expect(linux.getErrno(timer_fd) == .SUCCESS);
 
     const time_interval = linux.timespec{
         .tv_sec = 0,
@@ -53,22 +53,22 @@ test "timer" {
         .it_value = time_interval,
     };
 
-    err = linux.timerfd_settime(@intCast(i32, timer_fd), 0, &new_time, null);
-    try expect(err == 0);
+    err = linux.getErrno(linux.timerfd_settime(@intCast(i32, timer_fd), 0, &new_time, null));
+    try expect(err == .SUCCESS);
 
     var event = linux.epoll_event{
         .events = linux.EPOLLIN | linux.EPOLLOUT | linux.EPOLLET,
         .data = linux.epoll_data{ .ptr = 0 },
     };
 
-    err = linux.epoll_ctl(@intCast(i32, epoll_fd), linux.EPOLL_CTL_ADD, @intCast(i32, timer_fd), &event);
-    try expect(err == 0);
+    err = linux.getErrno(linux.epoll_ctl(@intCast(i32, epoll_fd), linux.EPOLL_CTL_ADD, @intCast(i32, timer_fd), &event));
+    try expect(err == .SUCCESS);
 
     const events_one: linux.epoll_event = undefined;
     var events = [_]linux.epoll_event{events_one} ** 8;
 
-    // TODO implicit cast from *[N]T to [*]T
-    err = linux.epoll_wait(@intCast(i32, epoll_fd), @ptrCast([*]linux.epoll_event, &events), 8, -1);
+    err = linux.getErrno(linux.epoll_wait(@intCast(i32, epoll_fd), &events, 8, -1));
+    try expect(err == .SUCCESS);
 }
 
 test "statx" {
@@ -81,15 +81,15 @@ test "statx" {
 
     var statx_buf: linux.Statx = undefined;
     switch (linux.getErrno(linux.statx(file.handle, "", linux.AT_EMPTY_PATH, linux.STATX_BASIC_STATS, &statx_buf))) {
-        0 => {},
+        .SUCCESS => {},
         // The statx syscall was only introduced in linux 4.11
-        linux.ENOSYS => return error.SkipZigTest,
+        .NOSYS => return error.SkipZigTest,
         else => unreachable,
     }
 
     var stat_buf: linux.kernel_stat = undefined;
     switch (linux.getErrno(linux.fstatat(file.handle, "", &stat_buf, linux.AT_EMPTY_PATH))) {
-        0 => {},
+        .SUCCESS => {},
         else => unreachable,
     }
 
diff --git a/lib/std/os/wasi.zig b/lib/std/os/wasi.zig
index 3965ae77a0..e99d2b820b 100644
--- a/lib/std/os/wasi.zig
+++ b/lib/std/os/wasi.zig
@@ -83,6 +83,6 @@ pub extern "wasi_snapshot_preview1" fn sock_send(sock: fd_t, si_data: *const cio
 pub extern "wasi_snapshot_preview1" fn sock_shutdown(sock: fd_t, how: sdflags_t) errno_t;
 
 /// Get the errno from a syscall return value, or 0 for no error.
-pub fn getErrno(r: errno_t) usize {
+pub fn getErrno(r: errno_t) errno_t {
     return r;
 }
diff --git a/lib/std/process.zig b/lib/std/process.zig
index 47e800c124..db9f442e56 100644
--- a/lib/std/process.zig
+++ b/lib/std/process.zig
@@ -93,7 +93,7 @@ pub fn getEnvMap(allocator: *Allocator) !BufMap {
         var environ_buf_size: usize = undefined;
 
         const environ_sizes_get_ret = os.wasi.environ_sizes_get(&environ_count, &environ_buf_size);
-        if (environ_sizes_get_ret != os.wasi.ESUCCESS) {
+        if (environ_sizes_get_ret != .SUCCESS) {
             return os.unexpectedErrno(environ_sizes_get_ret);
         }
 
@@ -103,7 +103,7 @@ pub fn getEnvMap(allocator: *Allocator) !BufMap {
         defer allocator.free(environ_buf);
 
         const environ_get_ret = os.wasi.environ_get(environ.ptr, environ_buf.ptr);
-        if (environ_get_ret != os.wasi.ESUCCESS) {
+        if (environ_get_ret != .SUCCESS) {
             return os.unexpectedErrno(environ_get_ret);
         }
 
@@ -255,7 +255,7 @@ pub const ArgIteratorWasi = struct {
         var buf_size: usize = undefined;
 
         switch (w.args_sizes_get(&count, &buf_size)) {
-            w.ESUCCESS => {},
+            .SUCCESS => {},
             else => |err| return os.unexpectedErrno(err),
         }
 
@@ -265,7 +265,7 @@ pub const ArgIteratorWasi = struct {
         var argv_buf = try allocator.alloc(u8, buf_size);
 
         switch (w.args_get(argv.ptr, argv_buf.ptr)) {
-            w.ESUCCESS => {},
+            .SUCCESS => {},
             else => |err| return os.unexpectedErrno(err),
         }
 
diff --git a/lib/std/special/compiler_rt/emutls.zig b/lib/std/special/compiler_rt/emutls.zig
index 46d0dd98e8..d51550c0d5 100644
--- a/lib/std/special/compiler_rt/emutls.zig
+++ b/lib/std/special/compiler_rt/emutls.zig
@@ -201,7 +201,7 @@ const current_thread_storage = struct {
 
     /// Initialize pthread_key_t.
     fn init() void {
-        if (std.c.pthread_key_create(&current_thread_storage.key, current_thread_storage.deinit) != 0) {
+        if (std.c.pthread_key_create(&current_thread_storage.key, current_thread_storage.deinit) != .SUCCESS) {
             abort();
         }
     }
@@ -248,14 +248,14 @@ const emutls_control = extern struct {
 
     /// Simple wrapper for global lock.
     fn lock() void {
-        if (std.c.pthread_mutex_lock(&emutls_control.mutex) != 0) {
+        if (std.c.pthread_mutex_lock(&emutls_control.mutex) != .SUCCESS) {
             abort();
         }
     }
 
     /// Simple wrapper for global unlock.
     fn unlock() void {
-        if (std.c.pthread_mutex_unlock(&emutls_control.mutex) != 0) {
+        if (std.c.pthread_mutex_unlock(&emutls_control.mutex) != .SUCCESS) {
             abort();
         }
     }
diff --git a/lib/std/time.zig b/lib/std/time.zig
index 99304af46a..a0430049cf 100644
--- a/lib/std/time.zig
+++ b/lib/std/time.zig
@@ -92,7 +92,7 @@ pub fn nanoTimestamp() i128 {
     if (builtin.os.tag == .wasi and !builtin.link_libc) {
         var ns: os.wasi.timestamp_t = undefined;
         const err = os.wasi.clock_time_get(os.wasi.CLOCK_REALTIME, 1, &ns);
-        assert(err == os.wasi.ESUCCESS);
+        assert(err == .SUCCESS);
         return ns;
     }
     var ts: os.timespec = undefined;
diff --git a/lib/std/x/os/socket_posix.zig b/lib/std/x/os/socket_posix.zig
index 5deff22317..59e4b177f7 100644
--- a/lib/std/x/os/socket_posix.zig
+++ b/lib/std/x/os/socket_posix.zig
@@ -82,32 +82,32 @@ pub fn Mixin(comptime Socket: type) type {
             while (true) {
                 const rc = os.system.sendmsg(self.fd, &msg, @intCast(c_int, flags));
                 return switch (os.errno(rc)) {
-                    0 => return @intCast(usize, rc),
-                    os.EACCES => error.AccessDenied,
-                    os.EAGAIN => error.WouldBlock,
-                    os.EALREADY => error.FastOpenAlreadyInProgress,
-                    os.EBADF => unreachable, // always a race condition
-                    os.ECONNRESET => error.ConnectionResetByPeer,
-                    os.EDESTADDRREQ => unreachable, // The socket is not connection-mode, and no peer address is set.
-                    os.EFAULT => unreachable, // An invalid user space address was specified for an argument.
-                    os.EINTR => continue,
-                    os.EINVAL => unreachable, // Invalid argument passed.
-                    os.EISCONN => unreachable, // connection-mode socket was connected already but a recipient was specified
-                    os.EMSGSIZE => error.MessageTooBig,
-                    os.ENOBUFS => error.SystemResources,
-                    os.ENOMEM => error.SystemResources,
-                    os.ENOTSOCK => unreachable, // The file descriptor sockfd does not refer to a socket.
-                    os.EOPNOTSUPP => unreachable, // Some bit in the flags argument is inappropriate for the socket type.
-                    os.EPIPE => error.BrokenPipe,
-                    os.EAFNOSUPPORT => error.AddressFamilyNotSupported,
-                    os.ELOOP => error.SymLinkLoop,
-                    os.ENAMETOOLONG => error.NameTooLong,
-                    os.ENOENT => error.FileNotFound,
-                    os.ENOTDIR => error.NotDir,
-                    os.EHOSTUNREACH => error.NetworkUnreachable,
-                    os.ENETUNREACH => error.NetworkUnreachable,
-                    os.ENOTCONN => error.SocketNotConnected,
-                    os.ENETDOWN => error.NetworkSubsystemFailed,
+                    .SUCCESS => return @intCast(usize, rc),
+                    .ACCES => error.AccessDenied,
+                    .AGAIN => error.WouldBlock,
+                    .ALREADY => error.FastOpenAlreadyInProgress,
+                    .BADF => unreachable, // always a race condition
+                    .CONNRESET => error.ConnectionResetByPeer,
+                    .DESTADDRREQ => unreachable, // The socket is not connection-mode, and no peer address is set.
+                    .FAULT => unreachable, // An invalid user space address was specified for an argument.
+                    .INTR => continue,
+                    .INVAL => unreachable, // Invalid argument passed.
+                    .ISCONN => unreachable, // connection-mode socket was connected already but a recipient was specified
+                    .MSGSIZE => error.MessageTooBig,
+                    .NOBUFS => error.SystemResources,
+                    .NOMEM => error.SystemResources,
+                    .NOTSOCK => unreachable, // The file descriptor sockfd does not refer to a socket.
+                    .OPNOTSUPP => unreachable, // Some bit in the flags argument is inappropriate for the socket type.
+                    .PIPE => error.BrokenPipe,
+                    .AFNOSUPPORT => error.AddressFamilyNotSupported,
+                    .LOOP => error.SymLinkLoop,
+                    .NAMETOOLONG => error.NameTooLong,
+                    .NOENT => error.FileNotFound,
+                    .NOTDIR => error.NotDir,
+                    .HOSTUNREACH => error.NetworkUnreachable,
+                    .NETUNREACH => error.NetworkUnreachable,
+                    .NOTCONN => error.SocketNotConnected,
+                    .NETDOWN => error.NetworkSubsystemFailed,
                     else => |err| os.unexpectedErrno(err),
                 };
             }
@@ -120,17 +120,17 @@ pub fn Mixin(comptime Socket: type) type {
             while (true) {
                 const rc = os.system.recvmsg(self.fd, msg, @intCast(c_int, flags));
                 return switch (os.errno(rc)) {
-                    0 => @intCast(usize, rc),
-                    os.EBADF => unreachable, // always a race condition
-                    os.EFAULT => unreachable,
-                    os.EINVAL => unreachable,
-                    os.ENOTCONN => unreachable,
-                    os.ENOTSOCK => unreachable,
-                    os.EINTR => continue,
-                    os.EAGAIN => error.WouldBlock,
-                    os.ENOMEM => error.SystemResources,
-                    os.ECONNREFUSED => error.ConnectionRefused,
-                    os.ECONNRESET => error.ConnectionResetByPeer,
+                    .SUCCESS => @intCast(usize, rc),
+                    .BADF => unreachable, // always a race condition
+                    .FAULT => unreachable,
+                    .INVAL => unreachable,
+                    .NOTCONN => unreachable,
+                    .NOTSOCK => unreachable,
+                    .INTR => continue,
+                    .AGAIN => error.WouldBlock,
+                    .NOMEM => error.SystemResources,
+                    .CONNREFUSED => error.ConnectionRefused,
+                    .CONNRESET => error.ConnectionResetByPeer,
                     else => |err| os.unexpectedErrno(err),
                 };
             }
@@ -164,12 +164,12 @@ pub fn Mixin(comptime Socket: type) type {
 
             const rc = os.system.getsockopt(self.fd, os.SOL_SOCKET, os.SO_RCVBUF, mem.asBytes(&value), &value_len);
             return switch (os.errno(rc)) {
-                0 => value,
-                os.EBADF => error.BadFileDescriptor,
-                os.EFAULT => error.InvalidAddressSpace,
-                os.EINVAL => error.InvalidSocketOption,
-                os.ENOPROTOOPT => error.UnknownSocketOption,
-                os.ENOTSOCK => error.NotASocket,
+                .SUCCESS => value,
+                .BADF => error.BadFileDescriptor,
+                .FAULT => error.InvalidAddressSpace,
+                .INVAL => error.InvalidSocketOption,
+                .NOPROTOOPT => error.UnknownSocketOption,
+                .NOTSOCK => error.NotASocket,
                 else => |err| os.unexpectedErrno(err),
             };
         }
@@ -181,12 +181,12 @@ pub fn Mixin(comptime Socket: type) type {
 
             const rc = os.system.getsockopt(self.fd, os.SOL_SOCKET, os.SO_SNDBUF, mem.asBytes(&value), &value_len);
             return switch (os.errno(rc)) {
-                0 => value,
-                os.EBADF => error.BadFileDescriptor,
-                os.EFAULT => error.InvalidAddressSpace,
-                os.EINVAL => error.InvalidSocketOption,
-                os.ENOPROTOOPT => error.UnknownSocketOption,
-                os.ENOTSOCK => error.NotASocket,
+                .SUCCESS => value,
+                .BADF => error.BadFileDescriptor,
+                .FAULT => error.InvalidAddressSpace,
+                .INVAL => error.InvalidSocketOption,
+                .NOPROTOOPT => error.UnknownSocketOption,
+                .NOTSOCK => error.NotASocket,
                 else => |err| os.unexpectedErrno(err),
             };
         }