From b0fd3a58354b1f5ead891907979dfd3dd36840d5 Mon Sep 17 00:00:00 2001 From: Khem Raj Date: Sat, 14 Jan 2023 14:55:03 -0800 Subject: [PATCH] Define alignof_slot using _Alignof when using C11 or newer WG14 N2350 made very clear that it is an UB having type definitions within "offsetof" [1]. This patch enhances the implementation of macro alignof_slot to use builtin "_Alignof" to avoid undefined behavior on when using std=c11 or newer clang 16+ has started to flag this [2] Fixes build when using -std >= gnu11 and using clang16+ [3] [1] https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2350.htm [2] https://reviews.llvm.org/D133574 [3] https://public-inbox.org/bug-gnulib/20230114232744.215167-1-raj.khem@gmail.com/T/#u Upstream-Status: Backport [https://git.savannah.gnu.org/cgit/gnulib.git/commit/?id=2d404c7dd974cc65f894526f4a1b76bc1dcd8d82] Signed-off-by: Khem Raj --- lib/alignof.h | 2 ++ 1 file changed, 2 insertions(+) --- a/lib/alignof.h +++ b/lib/alignof.h @@ -18,19 +18,19 @@ #define _ALIGNOF_H #include +#include "stdalign.h" /* alignof_slot (TYPE) Determine the alignment of a structure slot (field) of a given type, at compile time. Note that the result depends on the ABI. - This is the same as alignof (TYPE) and _Alignof (TYPE), defined in - if __alignof_is_defined is 1. + This is the same as alignof (TYPE). Note: The result cannot be used as a value for an 'enum' constant, due to bugs in HP-UX 10.20 cc and AIX 3.2.5 xlc. */ #if defined __cplusplus template struct alignof_helper { char __slot1; type __slot2; }; # define alignof_slot(type) offsetof (alignof_helper, __slot2) #else -# define alignof_slot(type) offsetof (struct { char __slot1; type __slot2; }, __slot2) +# define alignof_slot(type) alignof (type) #endif /* alignof_type (TYPE)