The patch titled
Subject: build_bug.h: more user friendly error messages in BUILD_BUG_ON_ZERO()
has been added to the -mm mm-nonmm-unstable branch. Its filename is
build_bugh-more-user-friendly-error-messages-in-build_bug_on_zero.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/build_bugh-more-user-friendly-error-messages-in-build_bug_on_zero.patch
This patch will later appear in the mm-nonmm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Vincent Mailhol <mailhol.vincent@xxxxxxxxxx>
Subject: build_bug.h: more user friendly error messages in BUILD_BUG_ON_ZERO()
Date: Fri, 6 Dec 2024 00:11:46 +0900
__BUILD_BUG_ON_ZERO_MSG(), as introduced in [1], makes it possible to do a
static assert while still returning a zero value. 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() 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 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_MSG(1 > 0)
would now throw:
./include/linux/compiler.h:245:62: error: static assertion failed: "1 > 0 is true"
245 | #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
Link: https://lkml.kernel.org/r/20241205151316.1480255-2-mailhol.vincent@xxxxxxxxxx
Signed-off-by: Vincent Mailhol <mailhol.vincent@xxxxxxxxxx>
Cc: Kees Cook <kees@xxxxxxxxxx>
Cc: Masahiro Yamada <masahiroy@xxxxxxxxxx>
Cc: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/build_bug.h | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)
--- a/include/linux/build_bug.h~build_bugh-more-user-friendly-error-messages-in-build_bug_on_zero
+++ a/include/linux/build_bug.h
@@ -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 a 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(e, ##__VA_ARGS__, #e)
+#define __BUILD_BUG_ON_ZERO(e, msg) __BUILD_BUG_ON_ZERO_MSG(e, msg " 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) \
_
Patches currently in -mm which might be from mailhol.vincent@xxxxxxxxxx are
build_bugh-more-user-friendly-error-messages-in-build_bug_on_zero.patch
