[libc-commits] [libc] [libc] fortify jmp buffer for x86-64 (PR #112769)

[Nick Desaulniers via libc-commits]

================
@@ -0,0 +1,91 @@
+//===-- Implementation of longjmp (64-bit) --------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "include/llvm-libc-macros/offsetof-macro.h"
+#include "src/__support/common.h"
+#include "src/__support/macros/config.h"
+#include "src/setjmp/longjmp.h"
+
+#if !defined(LIBC_TARGET_ARCH_IS_X86_64) || !LIBC_COPT_SETJMP_FORTIFICATION
+#error "Invalid file include"
+#endif
+
+#include "src/setjmp/checksum.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+LLVM_LIBC_FUNCTION(void, longjmp, (jmp_buf, int)) {
+  asm(R"(
+      mov %c[rbx](%%rdi), %%rbx
+      xor %%rbx, %%rax
----------------
nickdesaulniers wrote:

If this is relying on `cookie` being allocated to `rax`, I think it would be more readable to do:

```suggestion
      xor %%rbx, %[cookie]
```
here and below. WDYT?

https://github.com/llvm/llvm-project/pull/112769