The patch titled Subject: compiler.h, bug.h: Prevent double error messages with BUILD_BUG{,_ON} has been added to the -mm tree. Its filename is compilerh-bugh-prevent-double-error-messages-with-build_bug_on.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 *** The -mm tree is included into linux-next and is updated there every 3-4 working days ------------------------------------------------------ From: Daniel Santos <daniel.santos@xxxxxxxxx> Subject: compiler.h, bug.h: Prevent double error messages with BUILD_BUG{,_ON} Prior to the introduction of __attribute__((error("msg"))) in gcc 4.3, creating compile-time errors required a little trickery. BUILD_BUG{,_ON} uses this attribute when available to generate compile-time errors, but also uses the negative-sized array trick for older compilers, resulting in two error messages in some cases. The reason it's "some" cases is that as of gcc 4.4, the negative-sized array will not create an error in some situations, like inline functions. This patch replaces the negative-sized array code with the new __compiletime_error_fallback() macro which expands to the same thing unless the the error attribute is available, in which case it expands to do{}while(0), resulting in exactly one compile-time error on all versions of gcc. Note that we are not changing the negative-sized array code for the unoptimized version of BUILD_BUG_ON, since it has the potential to catch problems that would be disabled in later versions of gcc were __compiletime_error_fallback used. The reason is that that an unoptimized build can't always remove calls to an error-attributed function call (like we are using) that should effectively become dead code if it were optimized. However, using a negative-sized array with a similar value will not result in an false-positive (error). The only caveat being that it will also fail to catch valid conditions, which we should be expecting in an unoptimized build anyway. Signed-off-by: Daniel Santos <daniel.santos@xxxxxxxxx> Cc: Andi Kleen <ak@xxxxxxxxxxxxxxx> Cc: Borislav Petkov <bp@xxxxxxxxx> Cc: David Rientjes <rientjes@xxxxxxxxxx> Cc: Joe Perches <joe@xxxxxxxxxxx> Cc: Josh Triplett <josh@xxxxxxxxxxxxxxxx> Cc: Paul Gortmaker <paul.gortmaker@xxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- include/linux/bug.h | 2 +- include/linux/compiler.h | 5 +++++ 2 files changed, 6 insertions(+), 1 deletion(-) diff -puN include/linux/bug.h~compilerh-bugh-prevent-double-error-messages-with-build_bug_on include/linux/bug.h --- a/include/linux/bug.h~compilerh-bugh-prevent-double-error-messages-with-build_bug_on +++ a/include/linux/bug.h @@ -67,7 +67,7 @@ struct pt_regs; __compiletime_error("BUILD_BUG_ON failed"); \ if (__cond) \ __build_bug_on_failed(); \ - ((void)sizeof(char[1 - 2 * __cond])); \ + __compiletime_error_fallback(__cond); \ } while(0) #endif diff -puN include/linux/compiler.h~compilerh-bugh-prevent-double-error-messages-with-build_bug_on include/linux/compiler.h --- a/include/linux/compiler.h~compilerh-bugh-prevent-double-error-messages-with-build_bug_on +++ a/include/linux/compiler.h @@ -307,7 +307,12 @@ void ftrace_likely_update(struct ftrace_ #endif #ifndef __compiletime_error # define __compiletime_error(message) +# define __compiletime_error_fallback(condition) \ + do { ((void)sizeof(char[1 - 2*!!(condition)])); } while (0) +#else +# define __compiletime_error_fallback(condition) do { } while (0) #endif + /* * Prevent the compiler from merging or refetching accesses. The compiler * is also forbidden from reordering successive instances of ACCESS_ONCE(), _ Patches currently in -mm which might be from daniel.santos@xxxxxxxxx are compiler-gcc4h-reorder-macros-based-upon-gcc-ver.patch compiler-gcch-add-gcc-recommended-gcc_version-macro.patch compiler-gcc34h-use-gcc_version-macro.patch compiler-gcc4h-bugh-remove-duplicate-macros.patch bugh-fix-build_bug_on-macro-in-__checker__.patch bugh-prevent-double-evaulation-of-in-build_bug_on.patch bugh-make-build_bug_on-generate-compile-time-error.patch compilerh-bugh-prevent-double-error-messages-with-build_bug_on.patch bugh-compilerh-introduce-compiletime_assert-build_bug_on_msg.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