[libc] Use __attribute__((__noreturn__)) for _Noreturn in C < 11 #121252
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When in modes like C99, the _Noreturn keyword is not available in C. But GNU-compatible compilers have a `noreturn` attribute with the same effect on function declarations.
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@llvm/pr-subscribers-libc Author: Roland McGrath (frobtech) ChangesWhen in modes like C99, the _Noreturn keyword is not available in Full diff: https://github.com/llvm/llvm-project/pull/121252.diff 1 Files Affected:
diff --git a/libc/include/__llvm-libc-common.h b/libc/include/__llvm-libc-common.h
index d54ee7b9f91f32..d9d70aff771c08 100644
--- a/libc/include/__llvm-libc-common.h
+++ b/libc/include/__llvm-libc-common.h
@@ -52,6 +52,16 @@
#undef __restrict
#define __restrict restrict // C99 and above support the restrict keyword.
+#undef _Noreturn
+#if __STDC_VERSION__ >= 201112L
+// In C11 and later, _Noreturn is a keyword.
+#elif defined(__GNUC__)
+// GNU-compatible compilers have an equivalent attribute.
+#define _Noreturn __attribute__((__noreturn__))
+#else
+#define _Noreturn
+#endif
+
#undef __NOEXCEPT
#ifdef __GNUC__
#define __NOEXCEPT __attribute__((__nothrow__))
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| @@ -52,6 +52,16 @@ | |||
| #undef __restrict | |||
| #define __restrict restrict // C99 and above support the restrict keyword. | |||
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| #undef _Noreturn | |||
| #if __STDC_VERSION__ >= 201112L | |||
| // In C11 and later, _Noreturn is a keyword. | |||
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woah, so I was familiar with the keyword, but for some reason I had a hunch there was also a function attribute using the C23 [[]] syntax...turns out there is! lol
So there's BOTH they keyword / "function specifier" _Noreturn, AND the function attribute [[noreturn]] (sounds like [[_Noreturn]] is supported but "obsolescent." See footnote 175 of n3220) (and the GNU function attribute syntax). Looks like C23 also added __has_c_attribute preprocessor directive, but I'm guessing that's not yet widely supported by many versions of gcc+clang.
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When in modes like C99, the _Noreturn keyword is not available in
C. But GNU-compatible compilers have a
noreturnattribute withthe same effect on function declarations.