WG14 N2350 made very clear that it is an UB having type definitions within "offsetof" [1]. This patch enhances the implementation of macro ALIGN_OF to use builtin "_Alignof" to avoid undefined behavior when using std=c11 or newer clang 16+ has started to flag this [2] Fixes build when using -std >= gnu11 and using clang16+ Older compilers gcc < 4.9 or clang < 8 has buggy _Alignof even though it may support C11, exclude those compiler versions [1] https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2350.htm [2] https://reviews.llvm.org/D133574 Signed-off-by: Khem Raj <raj.khem@gmail.com> --- ext/fiddle/fiddle.h | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) diff --git a/ext/fiddle/fiddle.h b/ext/fiddle/fiddle.h index 10eb9ce..ffb395e 100644 --- a/ext/fiddle/fiddle.h +++ b/ext/fiddle/fiddle.h @@ -196,7 +196,17 @@ #endif #define TYPE_UINTPTR_T (-TYPE_INTPTR_T) -#define ALIGN_OF(type) offsetof(struct {char align_c; type align_x;}, align_x) +/* GCC releases before GCC 4.9 had a bug in _Alignof. See GCC bug 52023 + <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52023>. + clang versions < 8.0.0 have the same bug. */ +#if (!defined __STDC_VERSION__ || __STDC_VERSION__ < 201112 \ + || (defined __GNUC__ && __GNUC__ < 4 + (__GNUC_MINOR__ < 9) \ + && !defined __clang__) \ + || (defined __clang__ && __clang_major__ < 8)) +# define ALIGN_OF(type) offsetof(struct {char align_c; type align_x;}, align_x) +#else +# define ALIGN_OF(type) _Alignof(type) +#endif #define ALIGN_VOIDP ALIGN_OF(void*) #define ALIGN_CHAR ALIGN_OF(char) -- 2.39.0