Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965285AbbEEC3g (ORCPT ); Mon, 4 May 2015 22:29:36 -0400 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:50791 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751921AbbEEBV4 (ORCPT ); Mon, 4 May 2015 21:21:56 -0400 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, "David Howells" , "DM" , "David Rientjes" , "David Daney" , "Ralf Baechle" , "Linus Torvalds" Date: Tue, 05 May 2015 02:16:39 +0100 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) Subject: [PATCH 3.2 008/221] kernel.h: add BUILD_BUG() macro In-Reply-To: X-SA-Exim-Connect-IP: 192.168.4.249 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3364 Lines: 96 3.2.69-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: David Daney commit 1399ff86f2a2bbacbbe68fa00c5f8c752b344723 upstream. 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 Acked-by: David Rientjes Cc: DM Cc: Ralf Baechle Acked-by: David Howells Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds [bwh: Backported to 3.2: adjust context] Signed-off-by: Ben Hutchings --- --- a/include/linux/compiler-gcc4.h +++ b/include/linux/compiler-gcc4.h @@ -29,6 +29,8 @@ the kernel context */ #define __cold __attribute__((__cold__)) +#define __linktime_error(message) __attribute__((__error__(message))) + /* * GCC 'asm goto' miscompiles certain code sequences: * --- a/include/linux/compiler.h +++ b/include/linux/compiler.h @@ -297,7 +297,9 @@ 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(), --- a/include/linux/kernel.h +++ b/include/linux/kernel.h @@ -679,6 +679,7 @@ 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 */ @@ -717,6 +718,21 @@ 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 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 */ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/