From b72d55ea5fa1de0c55e2cfb9aa65f4ec80986bc9 Mon Sep 17 00:00:00 2001
From: LemonBoy <thatlemon@gmail.com>
Date: Fri, 18 Jun 2021 10:27:37 +0200
Subject: [PATCH] std: Make copy_file_range checks run at compile-time

* Avoid emitting the copy_file_range symbol at all to prevent link-time
  errors.
* Fix a bug in the check logic, the has_copy_file_range_syscall was
  set to the wrong value in case of ENOSYS
* If link_libc is true don't fall-back to the raw syscall approach,
  there's no policy about what to do in this case but let's follow what
  the other impls do.

Fixes #9146
---
 lib/std/os.zig | 22 +++++++++-------------
 1 file changed, 9 insertions(+), 13 deletions(-)

diff --git a/lib/std/os.zig b/lib/std/os.zig
index 072771b000..321c44a919 100644
--- a/lib/std/os.zig
+++ b/lib/std/os.zig
@@ -5532,10 +5532,7 @@ pub const CopyFileRangeError = error{
     FileBusy,
 } || PReadError || PWriteError || UnexpectedError;
 
-var has_copy_file_range_syscall = init: {
-    const kernel_has_syscall = std.Target.current.os.isAtLeast(.linux, .{ .major = 4, .minor = 5 }) orelse true;
-    break :init std.atomic.Atomic(bool).init(kernel_has_syscall);
-};
+var has_copy_file_range_syscall = std.atomic.Atomic(bool).init(true);
 
 /// Transfer data between file descriptors at specified offsets.
 /// Returns the number of bytes written, which can less than requested.
@@ -5563,18 +5560,17 @@ var has_copy_file_range_syscall = init: {
 ///
 /// Maximum offsets on Linux are `math.maxInt(i64)`.
 pub fn copy_file_range(fd_in: fd_t, off_in: u64, fd_out: fd_t, off_out: u64, len: usize, flags: u32) CopyFileRangeError!usize {
-    const use_c = std.c.versionCheck(.{ .major = 2, .minor = 27, .patch = 0 }).ok;
-
-    if (std.Target.current.os.tag == .linux and
-        (use_c or has_copy_file_range_syscall.load(.Monotonic)))
-    {
-        const sys = if (use_c) std.c else linux;
+    const call_cfr = comptime if (builtin.link_libc)
+        std.c.versionCheck(.{ .major = 2, .minor = 27, .patch = 0 }).ok
+    else
+        std.Target.current.os.isAtLeast(.linux, .{ .major = 4, .minor = 5 }) orelse true;
 
+    if (call_cfr and has_copy_file_range_syscall.load(.Monotonic)) {
         var off_in_copy = @bitCast(i64, off_in);
         var off_out_copy = @bitCast(i64, off_out);
 
-        const rc = sys.copy_file_range(fd_in, &off_in_copy, fd_out, &off_out_copy, len, flags);
-        switch (sys.getErrno(rc)) {
+        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,
@@ -5591,7 +5587,7 @@ pub fn copy_file_range(fd_in: fd_t, off_in: u64, fd_out: fd_t, off_out: u64, len
             EXDEV => {},
             // syscall added in Linux 4.5, use fallback
             ENOSYS => {
-                has_copy_file_range_syscall.store(true, .Monotonic);
+                has_copy_file_range_syscall.store(false, .Monotonic);
             },
             else => |err| return unexpectedErrno(err),
         }