Merge pull request #15235 from Vexu/safety

add runtime safety for noreturn function returning

lib/std/builtin.zig

@@ -1006,6 +1006,7 @@ pub const panic_messages = struct {
     pub const for_len_mismatch = "for loop over objects with non-equal lengths";
     pub const memcpy_len_mismatch = "@memcpy arguments have non-equal lengths";
     pub const memcpy_alias = "@memcpy arguments alias";
+    pub const noreturn_returned = "'noreturn' function returned";
 };
 
 pub noinline fn returnError(st: *StackTrace) void {

lib/std/crypto/aes/soft.zig

@@ -739,9 +739,9 @@ inline fn table_lookup(table: *align(64) const [4][256]u32, idx0: u8, idx1: u8,
         std.mem.doNotOptimizeAway(t);
         return [4]u32{
             t[0][idx0 / stride],
-            math.rotl(u32, t[1][idx1 / stride], 8),
-            math.rotl(u32, t[2][idx2 / stride], 16),
-            math.rotl(u32, t[3][idx3 / stride], 24),
+            math.rotl(u32, (&t[1])[idx1 / stride], 8),
+            math.rotl(u32, (&t[2])[idx2 / stride], 16),
+            math.rotl(u32, (&t[3])[idx3 / stride], 24),
         };
     }
 }

src/Sema.zig

@@ -7080,15 +7080,38 @@ fn analyzeCall(
             } },
         });
         sema.appendRefsAssumeCapacity(args);
+
+        if (call_tag == .call_always_tail) {
+            if (ensure_result_used) {
+                try sema.ensureResultUsed(block, sema.typeOf(func_inst), call_src);
+            }
+            return sema.handleTailCall(block, call_src, func_ty, func_inst);
+        } else if (block.wantSafety() and func_ty_info.return_type.isNoReturn()) {
+            // Function pointers and extern functions aren't guaranteed to
+            // actually be noreturn so we add a safety check for them.
+            check: {
+                var func_val = (try sema.resolveMaybeUndefVal(func)) orelse break :check;
+                switch (func_val.tag()) {
+                    .function, .decl_ref => {
+                        _ = try block.addNoOp(.unreach);
+                        return Air.Inst.Ref.unreachable_value;
+                    },
+                    else => break :check,
+                }
+            }
+
+            try sema.safetyPanic(block, .noreturn_returned);
+            return Air.Inst.Ref.unreachable_value;
+        } else if (func_ty_info.return_type.isNoReturn()) {
+            _ = try block.addNoOp(.unreach);
+            return Air.Inst.Ref.unreachable_value;
+        }
         break :res func_inst;
     };
 
     if (ensure_result_used) {
         try sema.ensureResultUsed(block, sema.typeOf(result), call_src);
     }
-    if (call_tag == .call_always_tail) {
-        return sema.handleTailCall(block, call_src, func_ty, result);
-    }
     return result;
 }
 
@@ -7581,6 +7604,10 @@ fn instantiateGenericCall(
     if (call_tag == .call_always_tail) {
         return sema.handleTailCall(block, call_src, func_ty, result);
     }
+    if (new_fn_info.return_type.isNoReturn()) {
+        _ = try block.addNoOp(.unreach);
+        return Air.Inst.Ref.unreachable_value;
+    }
     return result;
 }
 
@@ -23440,6 +23467,7 @@ pub const PanicId = enum {
     for_len_mismatch,
     memcpy_len_mismatch,
     memcpy_alias,
+    noreturn_returned,
 };
 
 fn addSafetyCheck(
@@ -23607,7 +23635,7 @@ fn panicIndexOutOfBounds(
     try sema.safetyCheckFormatted(parent_block, ok, "panicOutOfBounds", &.{ index, len });
 }
 
-fn panicStartLargerThanEnd(
+fn panicStartGreaterThanEnd(
     sema: *Sema,
     parent_block: *Block,
     start: Air.Inst.Ref,
@@ -29464,8 +29492,10 @@ fn analyzeSlice(
     const slice_sentinel = if (sentinel_opt != .none) sentinel else null;
 
     // requirement: start <= end
+    var need_start_gt_end_check = true;
     if (try sema.resolveDefinedValue(block, end_src, end)) |end_val| {
         if (try sema.resolveDefinedValue(block, start_src, start)) |start_val| {
+            need_start_gt_end_check = false;
             if (!by_length and !(try sema.compareAll(start_val, .lte, end_val, Type.usize))) {
                 return sema.fail(
                     block,
@@ -29519,9 +29549,9 @@ fn analyzeSlice(
         }
     }
 
-    if (!by_length and block.wantSafety() and !block.is_comptime) {
+    if (!by_length and block.wantSafety() and !block.is_comptime and need_start_gt_end_check) {
         // requirement: start <= end
-        try sema.panicStartLargerThanEnd(block, start, end);
+        try sema.panicStartGreaterThanEnd(block, start, end);
     }
     const new_len = if (by_length)
         try sema.coerce(block, Type.usize, uncasted_end_opt, end_src)

src/codegen/llvm.zig

@@ -5030,7 +5030,6 @@ pub const FuncGen = struct {
         }
 
         if (return_type.isNoReturn() and attr != .AlwaysTail) {
-            _ = self.builder.buildUnreachable();
             return null;
         }
 

test/cases/safety/noreturn returned.zig

@@ -0,0 +1,23 @@
+const std = @import("std");
+
+pub fn panic(message: []const u8, stack_trace: ?*std.builtin.StackTrace, _: ?usize) noreturn {
+    _ = stack_trace;
+    if (std.mem.eql(u8, message, "'noreturn' function returned")) {
+        std.process.exit(0);
+    }
+    std.process.exit(1);
+}
+const T = struct {
+    export fn bar() void {
+        // ...
+    }
+};
+
+extern fn bar() noreturn;
+pub fn main() void {
+    _ = T.bar;
+    bar();
+}
+// run
+// backend=llvm
+// target=native