[libc-commits] [libc] [libc] Add `returns_twice` attribute to `setjmp(3)` (PR #124370)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-libc

Author: Alan Zhao (alanzhao1)

<details>
<summary>Changes</summary>

This is to work around a clang bug where clang will incorrectly add a tail call optimization to `setjmp(3)` if `-fno-builtins` is set (#<!-- -->122840).

---
Full diff: https://github.com/llvm/llvm-project/pull/124370.diff


2 Files Affected:

- (modified) libc/include/__llvm-libc-common.h (+6) 
- (modified) libc/include/setjmp.yaml (+2) 


``````````diff
diff --git a/libc/include/__llvm-libc-common.h b/libc/include/__llvm-libc-common.h
index b5a23c5765f4d8..58006a1ffc24fc 100644
--- a/libc/include/__llvm-libc-common.h
+++ b/libc/include/__llvm-libc-common.h
@@ -45,6 +45,9 @@
 #define __NOEXCEPT throw()
 #endif
 
+#undef _Returns_twice
+#define _Returns_twice [[gnu::returns_twice]]
+
 #else // not __cplusplus
 
 #undef __BEGIN_C_DECLS
@@ -80,6 +83,9 @@
 #define __NOEXCEPT
 #endif
 
+#undef _Returns_twice
+#define _Returns_twice __attribute__((returns_twice))
+
 #endif // __cplusplus
 
 #endif // LLVM_LIBC_COMMON_H
diff --git a/libc/include/setjmp.yaml b/libc/include/setjmp.yaml
index 2c4f7fb6dfcc70..5fbb9eb2a47e5b 100644
--- a/libc/include/setjmp.yaml
+++ b/libc/include/setjmp.yaml
@@ -17,5 +17,7 @@ functions:
     standards:
       - stdc
     return_type: int
+    attributes:
+      - _Returns_twice
     arguments:
       - type: jmp_buf

``````````

</details>


https://github.com/llvm/llvm-project/pull/124370