From b44e0cc9f456449e1378e4b03bcb7ad3db094725 Mon Sep 17 00:00:00 2001 From: Simon McVittie Date: Fri, 10 Dec 2021 15:12:59 +0000 Subject: [PATCH] internals: Use Standard C offsetof macro if available clang 13 fails to compile our current implementation with: .../dbus/dbus-message.c:2070:3: error: variable length array folded to constant array as an extension [-Werror,-Wgnu-folding-constant] _DBUS_STATIC_ASSERT (_DBUS_ALIGNOF (DBusMessageRealIter) <= ^ .../dbus/dbus-internals.h:460:25: note: expanded from macro '_DBUS_STATIC_ASSERT' typedef struct { char _assertion[(expr) ? 1 : -1]; } \ This appears to be because the "traditional" definition of offsetof(), which we're hard-coding here, does not qualify as a constant expression under C rules due to its use of pointer casts. Modern compilers like gcc and clang have a built-in implementation of offsetof that *is* a constant expression. Signed-off-by: Simon McVittie (cherry picked from commit a24cf746e2a8191070efd1300a15d37284aaf2fa) --- dbus/dbus-internals.h | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/dbus/dbus-internals.h b/dbus/dbus-internals.h index e7649e1..281d6af 100644 --- a/dbus/dbus-internals.h +++ b/dbus/dbus-internals.h @@ -192,8 +192,13 @@ void _dbus_real_assert_not_reached (const char *explanation, #define _DBUS_ZERO(object) (memset (&(object), '\0', sizeof ((object)))) +#ifdef offsetof +#define _DBUS_STRUCT_OFFSET(struct_type, member) \ + (offsetof (struct_type, member)) +#else #define _DBUS_STRUCT_OFFSET(struct_type, member) \ ((intptr_t) ((unsigned char*) &((struct_type*) 0)->member)) +#endif #define _DBUS_ALIGNOF(type) \ (_DBUS_STRUCT_OFFSET (struct { char _1; type _2; }, _2)) -- 2.7.4