@@ -4,17 +4,17 @@
#include <linux/compiler.h>
-#ifdef __CHECKER__
-#define BUILD_BUG_ON_ZERO(e) (0)
-#else /* __CHECKER__ */
/*
* Force a compilation error if condition is true, but also produce a
* result (of value 0 and type int), so the expression can be used
* e.g. in a structure initializer (or where-ever else comma expressions
* aren't permitted).
+ *
+ * Take an error message as an optional second argument. If omitted,
+ * default to the stringification of the tested expression.
*/
-#define BUILD_BUG_ON_ZERO(e) ((int)(sizeof(struct { int:(-!!(e)); })))
-#endif /* __CHECKER__ */
+#define BUILD_BUG_ON_ZERO(e, ...) \
+ __BUILD_BUG_ON_ZERO_MSG(e, ##__VA_ARGS__, #e " is true")
/* Force a compilation error if a constant expression is not a power of 2 */
#define __BUILD_BUG_ON_NOT_POWER_OF_2(n) \
@@ -192,9 +192,9 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
})
#ifdef __CHECKER__
-#define __BUILD_BUG_ON_ZERO_MSG(e, msg) (0)
+#define __BUILD_BUG_ON_ZERO_MSG(e, msg, ...) (0)
#else /* __CHECKER__ */
-#define __BUILD_BUG_ON_ZERO_MSG(e, msg) ((int)sizeof(struct {_Static_assert(!(e), msg);}))
+#define __BUILD_BUG_ON_ZERO_MSG(e, msg, ...) ((int)sizeof(struct {_Static_assert(!(e), msg);}))
#endif /* __CHECKER__ */
/* &a[0] degrades to a pointer: a different type from an array */
__BUILD_BUG_ON_ZERO_MSG(), as introduced in [1], makes it possible to do a static assertions in expressions. The direct benefit is to provide a meaningful error message instead of the cryptic negative bitfield size error message currently returned by BUILD_BUG_ON_ZERO(): ./include/linux/build_bug.h:16:51: error: negative width in bit-field '<anonymous>' 16 | #define BUILD_BUG_ON_ZERO(e) ((int)(sizeof(struct { int:(-!!(e)); }))) | ^ Get rid of BUILD_BUG_ON_ZERO()'s bitfield size hack. Instead rely on __BUILD_BUG_ON_ZERO_MSG() which in turn relies on C11's _Static_assert(). Use some macro magic, similarly to static_assert(), to either use an optional error message provided by the user or, when omitted, to produce a default error message by stringifying the tested expression. With this, for example: BUILD_BUG_ON_ZERO(1 > 0) would now throw: ./include/linux/compiler.h:197:62: error: static assertion failed: "1 > 0 is true" 197 | define __BUILD_BUG_ON_ZERO_MSG(e, msg) ((int)sizeof(struct {_Static_assert(!(e), msg);})) | ^~~~~~~~~~~~~~ Finally, __BUILD_BUG_ON_ZERO_MSG() is already guarded by an: #ifdef __CHECKER__ So no need any more for that guard clause for BUILD_BUG_ON_ZERO(). Remove it. [1] commit d7a516c6eeae ("compiler.h: Fix undefined BUILD_BUG_ON_ZERO()") Link: https://git.kernel.org/torvalds/c/d7a516c6eeae Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr> --- ** Prerequisite ** This patch depends on: commit b88937277df ("drm/i915: Convert REG_GENMASK*() to fixed-width GENMASK_U*()") Link: https://git.kernel.org/next/linux-next/c/b88937277df Changelog: v1 -> v2: - The patch caused an issue because of a conflict in drm/i915: Link: https://lore.kernel.org/all/202412080849.sPp82jSi-lkp@intel.com/ Above conflict is indirectly resolved by commit b88937277df (c.f. above prerequisite). Now that the conflict is resolved, resend the patch. - Remove the intermediary __BUILD_BUG_ON_ZERO() macro, instead, make __BUILD_BUG_ON_ZERO_MSG() variadic. Link to v1: https://lore.kernel.org/all/20241205151316.1480255-2-mailhol.vincent@wanadoo.fr/ --- include/linux/build_bug.h | 10 +++++----- include/linux/compiler.h | 4 ++-- 2 files changed, 7 insertions(+), 7 deletions(-) --- base-commit: de305063001d5624138a452bdb2d56e68dc2301c change-id: 20250327-build_bug-a55c1812ce51 Best regards,