[libc] Add _Returns_twice to C++ code #153602
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Fixes issue with <csetjmp> which requires _Returns_twice but in C++ mode
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@llvm/pr-subscribers-libc Author: William Huynh (saturn691) ChangesFixes issue with Full diff: https://github.com/llvm/llvm-project/pull/153602.diff 1 Files Affected:
diff --git a/libc/include/__llvm-libc-common.h b/libc/include/__llvm-libc-common.h
index c6fd33a55532c..b376b05df1678 100644
--- a/libc/include/__llvm-libc-common.h
+++ b/libc/include/__llvm-libc-common.h
@@ -47,6 +47,9 @@
#define __NOEXCEPT throw()
#endif
+#undef _Returns_twice
+#define _Returns_twice [[gnu::returns_twice]]
+
// This macro serves as a generic cast implementation for use in both C and C++,
// similar to `__BIONIC_CAST` in Android.
#undef __LLVM_LIBC_CAST
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libc/include/__llvm-libc-common.h
Outdated
| #undef _Returns_twice | ||
| #define _Returns_twice [[gnu::returns_twice]] | ||
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given that this is on both sides of the #ifdef __cplusplus branch is there a way we can unify it instead of having two copies? Also is there a reason you used the gnu attribute instead of the generic one?
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returns_twiceneeds to be namespaced (https://en.cppreference.com/w/cpp/language/attributes.html)
❯ clang test.c
test.c:3:3: warning: unknown attribute 'returns_twice' ignored [-Wunknown-attributes]
3 | [[returns_twice]] int f() {
| ^~~~~~~~~~~~~
1 warning generated.
[[attribute]]syntax is only supported in C++11. It seems to compile for older versions and this has even been back-ported to C code in clang. I'll push an update to unify this.
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The [[attribute]] syntax was only introduced in C20 so we shouldn't be using it in C code since we want our headers are compatible with older C standards.
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Good point, I've settled with preferring to generate the new attribute syntax if the compiler supports it (C++11) onwards.
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Fixes issue with
<csetjmp>which requires_Returns_twicebut in C++ mode