| From b0fd3a58354b1f5ead891907979dfd3dd36840d5 Mon Sep 17 00:00:00 2001 |
| From: Khem Raj <raj.khem@gmail.com> |
| 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 <raj.khem@gmail.com> |
| --- |
| 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 <stddef.h> |
| +#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 |
| - <stdalign.h> 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 <class type> struct alignof_helper { char __slot1; type __slot2; }; |
| # define alignof_slot(type) offsetof (alignof_helper<type>, __slot2) |
| #else |
| -# define alignof_slot(type) offsetof (struct { char __slot1; type __slot2; }, __slot2) |
| +# define alignof_slot(type) alignof (type) |
| #endif |
| |
| /* alignof_type (TYPE) |