Andrew Geissler | c5535c9 | 2023-01-27 16:10:19 -0600 | [diff] [blame^] | 1 | From b0fd3a58354b1f5ead891907979dfd3dd36840d5 Mon Sep 17 00:00:00 2001 |
| 2 | From: Khem Raj <raj.khem@gmail.com> |
| 3 | Date: Sat, 14 Jan 2023 14:55:03 -0800 |
| 4 | Subject: [PATCH] Define alignof_slot using _Alignof when using C11 or newer |
| 5 | |
| 6 | WG14 N2350 made very clear that it is an UB having type definitions |
| 7 | within "offsetof" [1]. This patch enhances the implementation of macro |
| 8 | alignof_slot to use builtin "_Alignof" to avoid undefined behavior on |
| 9 | when using std=c11 or newer |
| 10 | |
| 11 | clang 16+ has started to flag this [2] |
| 12 | |
| 13 | Fixes build when using -std >= gnu11 and using clang16+ [3] |
| 14 | |
| 15 | [1] https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2350.htm |
| 16 | [2] https://reviews.llvm.org/D133574 |
| 17 | [3] https://public-inbox.org/bug-gnulib/20230114232744.215167-1-raj.khem@gmail.com/T/#u |
| 18 | |
| 19 | Upstream-Status: Backport [https://git.savannah.gnu.org/cgit/gnulib.git/commit/?id=2d404c7dd974cc65f894526f4a1b76bc1dcd8d82] |
| 20 | Signed-off-by: Khem Raj <raj.khem@gmail.com> |
| 21 | --- |
| 22 | lib/alignof.h | 2 ++ |
| 23 | 1 file changed, 2 insertions(+) |
| 24 | |
| 25 | --- a/lib/alignof.h |
| 26 | +++ b/lib/alignof.h |
| 27 | @@ -18,19 +18,19 @@ |
| 28 | #define _ALIGNOF_H |
| 29 | |
| 30 | #include <stddef.h> |
| 31 | +#include "stdalign.h" |
| 32 | |
| 33 | /* alignof_slot (TYPE) |
| 34 | Determine the alignment of a structure slot (field) of a given type, |
| 35 | at compile time. Note that the result depends on the ABI. |
| 36 | - This is the same as alignof (TYPE) and _Alignof (TYPE), defined in |
| 37 | - <stdalign.h> if __alignof_is_defined is 1. |
| 38 | + This is the same as alignof (TYPE). |
| 39 | Note: The result cannot be used as a value for an 'enum' constant, |
| 40 | due to bugs in HP-UX 10.20 cc and AIX 3.2.5 xlc. */ |
| 41 | #if defined __cplusplus |
| 42 | template <class type> struct alignof_helper { char __slot1; type __slot2; }; |
| 43 | # define alignof_slot(type) offsetof (alignof_helper<type>, __slot2) |
| 44 | #else |
| 45 | -# define alignof_slot(type) offsetof (struct { char __slot1; type __slot2; }, __slot2) |
| 46 | +# define alignof_slot(type) alignof (type) |
| 47 | #endif |
| 48 | |
| 49 | /* alignof_type (TYPE) |