>>> On 05.11.12 at 03:19, Rusty Russell <ru...@rustcorp.com.au> wrote:
> Jan Beulich <jbeul...@suse.com> writes:
>> @@ -54,6 +61,15 @@ struct pt_regs;
>> */
>> #ifndef __OPTIMIZE__
>> #define BUILD_BUG_ON(condition) ((void)sizeof(char[1 - 2*!!(condition)]))
>> +#elif __GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 3)
>> +#define __build_bug_on_failed(n) __build_bug_on_##n##_failed
>> +#define _BUILD_BUG_ON(n, condition) \
>> + do { \
>> + extern void __compiletime_error(#condition) \
>> + __build_bug_on_failed(n)(void); \
>> + if (condition) __build_bug_on_failed(n)(); \
>> + } while(0)
>> +#define BUILD_BUG_ON(condition...) _BUILD_BUG_ON(__COUNTER__, ##condition)
>> #else
>> extern int __build_bug_on_failed;
>> #define BUILD_BUG_ON(condition) \
>
> Why does this depend on gcc version? Looks like residue from an attempt
> to use _Static_assert here?
That was the original hope, yes, but didn't work because of
certain uses BUILD_BUG_ON() in inline functions. Hence the
next best solution was to use __compiletime_error(), which
still gives a better diagnostic than what we have so far, but is
- see include/linux/compiler-gcc4.h - available only with gcc 4.3
and newer (simply using the construct even when expanding to
nothing - in include/linux/compile.h - wouldn't have the intended
effect of producing a compiler diagnostic at all, it would get
deferred to link time in _all_ cases, even if the compiler can tell
it's a constant).
Jan
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
