The patch titled Subject: kernel.h: add BUILD_BUG() macro has been added to the -mm tree. Its filename is kernelh-add-build_bug-macro.patch Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/SubmitChecklist when testing your code *** See http://userweb.kernel.org/~akpm/stuff/added-to-mm.txt to find out what to do about this The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/ ------------------------------------------------------ From: David Daney <david.daney@xxxxxxxxxx> Subject: kernel.h: add BUILD_BUG() macro We can place this in definitions that we expect the compiler to remove by dead code elimination. If this assertion fails, we get a nice error message at build time. The GCC function attribute error("message") was added in version 4.3, so we define a new macro __linktime_error(message) to expand to this for GCC-4.3 and later. This will give us an error diagnostic from the compiler on the line that fails. For other compilers __linktime_error(message) expands to nothing, and we have to be content with a link time error, but at least we will still get a build error. BUILD_BUG() expands to the undefined function __build_bug_failed() and will fail at link time if the compiler ever emits code for it. On GCC-4.3 and later, attribute((error())) is used so that the failure will be noted at compile time instead. Signed-off-by: David Daney <david.daney@xxxxxxxxxx> Cc: David Rientjes <rientjes@xxxxxxxxxx> Cc: DM <dm.n9107@xxxxxxxxx> Cc: Ralf Baechle <ralf@xxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- include/linux/compiler-gcc4.h | 1 + include/linux/compiler.h | 4 +++- include/linux/kernel.h | 16 ++++++++++++++++ 3 files changed, 20 insertions(+), 1 deletion(-) diff -puN include/linux/compiler-gcc4.h~kernelh-add-build_bug-macro include/linux/compiler-gcc4.h --- a/include/linux/compiler-gcc4.h~kernelh-add-build_bug-macro +++ a/include/linux/compiler-gcc4.h @@ -29,6 +29,7 @@ the kernel context */ #define __cold __attribute__((__cold__)) +#define __linktime_error(message) __attribute__((__error__(message))) #if __GNUC_MINOR__ >= 5 /* diff -puN include/linux/compiler.h~kernelh-add-build_bug-macro include/linux/compiler.h --- a/include/linux/compiler.h~kernelh-add-build_bug-macro +++ a/include/linux/compiler.h @@ -293,7 +293,9 @@ void ftrace_likely_update(struct ftrace_ #ifndef __compiletime_error # define __compiletime_error(message) #endif - +#ifndef __linktime_error +# define __linktime_error(message) +#endif /* * Prevent the compiler from merging or refetching accesses. The compiler * is also forbidden from reordering successive instances of ACCESS_ONCE(), diff -puN include/linux/kernel.h~kernelh-add-build_bug-macro include/linux/kernel.h --- a/include/linux/kernel.h~kernelh-add-build_bug-macro +++ a/include/linux/kernel.h @@ -665,6 +665,7 @@ static inline void ftrace_dump(enum ftra #define BUILD_BUG_ON_ZERO(e) (0) #define BUILD_BUG_ON_NULL(e) ((void*)0) #define BUILD_BUG_ON(condition) +#define BUILD_BUG() (0) #else /* __CHECKER__ */ /* Force a compilation error if a constant expression is not a power of 2 */ @@ -703,6 +704,21 @@ extern int __build_bug_on_failed; if (condition) __build_bug_on_failed = 1; \ } while(0) #endif + +/** + * BUILD_BUG - break compile if used. + * + * If you have some code that you expect the compiler to eliminate at + * build time, you should use BUILD_BUG_ON_USED to detect if it is + * unexpectedly used. + */ +#define BUILD_BUG() \ + do { \ + extern void __build_bug_failed(void) \ + __linktime_error("BUILD_BUG failed"); \ + __build_bug_failed(); \ + } while (0) + #endif /* __CHECKER__ */ /* Trap pasters of __FUNCTION__ at compile-time */ _ Subject: Subject: kernel.h: add BUILD_BUG() macro Patches currently in -mm which might be from david.daney@xxxxxxxxxx are origin.patch linux-next.patch kernelh-add-build_bug-macro.patch hugetlb-replace-bug-with-build_bug-for-dummy-definitions.patch -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html