>>> 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/