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| author | Vincent Mailhol <mailhol.vincent@wanadoo.fr> | 2025-03-29 01:48:50 +0900 |
|---|---|---|
| committer | Yury Norov <yury.norov@gmail.com> | 2025-04-29 15:58:38 -0400 |
| commit | 243c90e917f5cfc99821e5104d1c8a81c11cda4c (patch) | |
| tree | 2abb577edd3b6cd38d429432e646a9bd303f56ab | |
| parent | e289b488256107425591d8e6a402de8fcf6d088c (diff) | |
build_bug.h: more user friendly error messages in BUILD_BUG_ON_ZERO()
__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>
Link: https://git.kernel.org/next/linux-next/c/b88937277df
Reviewed-by: Kees Cook <kees@kernel.org>
Signed-off-by: Yury Norov <yury.norov@gmail.com>
| -rw-r--r-- | include/linux/build_bug.h | 10 | ||||
| -rw-r--r-- | include/linux/compiler.h | 4 |
2 files changed, 7 insertions, 7 deletions
diff --git a/include/linux/build_bug.h b/include/linux/build_bug.h index 3aa3640f8c18..2cfbb4c65c78 100644 --- a/include/linux/build_bug.h +++ b/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 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) \ diff --git a/include/linux/compiler.h b/include/linux/compiler.h index 27725f1ab5ab..6f04a1d8c720 100644 --- a/include/linux/compiler.h +++ b/include/linux/compiler.h @@ -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 */ |