linux-kernel - [PATCH 8/10] bug.h: Make BUILD_BUG

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <1348874411-28288-9-git-send-email-daniel.santos@pobox.com>
Date:	Fri, 28 Sep 2012 18:20:09 -0500
From:	Daniel Santos <daniel.santos@...ox.com>
To:	LKML <linux-kernel@...r.kernel.org>,
	Andi Kleen <ak@...ux.intel.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Christopher Li <sparse@...isli.org>,
	Daniel Santos <daniel.santos@...ox.com>,
	David Daney <david.daney@...ium.com>,
	David Howells <dhowells@...hat.com>,
	Joe Perches <joe@...ches.com>,
	Konstantin Khlebnikov <khlebnikov@...nvz.org>,
	linux-sparse@...r.kernel.org,
	Michel Lespinasse <walken@...gle.com>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Pavel Pisa <pisa@....felk.cvut.cz>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: [PATCH 8/10] bug.h: Make BUILD_BUG_ON generate compile-time error

Negative sized arrays wont create a compile-time error in some cases
starting with gcc 4.4 (e.g., inlined functions), but gcc 4.3 introduced
the error function attribute that will.  This patch modifies
BUILD_BUG_ON to behave like BUILD_BUG already does, using the error
function attribute so that you don't have to build the entire kernel to
discover that you have a problem, and then enjoy trying to track it down
from a link-time error.

Signed-off-by: Daniel Santos <daniel.santos@...ox.com>
---
 include/linux/bug.h |   24 ++++++++++++++----------
 1 files changed, 14 insertions(+), 10 deletions(-)

diff --git a/include/linux/bug.h b/include/linux/bug.h
index 298a916..c70b833 100644
--- a/include/linux/bug.h
+++ b/include/linux/bug.h
@@ -42,24 +42,28 @@ struct pt_regs;
  * @condition: the condition which the compiler should know is false.
  *
  * If you have some code which relies on certain constants being equal, or
- * other compile-time-evaluated condition, you should use BUILD_BUG_ON to
+ * some other compile-time-evaluated condition, you should use BUILD_BUG_ON to
  * detect if someone changes it.
  *
  * The implementation uses gcc's reluctance to create a negative array, but
  * gcc (as of 4.4) only emits that error for obvious cases (eg. not arguments
- * to inline functions).  So as a fallback we use the optimizer; if it can't
- * prove the condition is false, it will cause a link error on the undefined
- * "__build_bug_on_failed".  This error message can be harder to track down
- * though, hence the two different methods.
+ * to inline functions).  Luckily, in 4.3 they added the "error" function
+ * attribute just for this type of case.  Thus, we use a negative sized array
+ * (should always create an error pre-gcc-4.4) and then call an undefined
+ * function with the error attribute (should always creates an error 4.3+).  If
+ * for some reason, neither creates a compile-time error, we'll still have a
+ * link-time error, which is harder to track down.
  */
 #ifndef __OPTIMIZE__
 #define BUILD_BUG_ON(condition) ((void)sizeof(char[1 - 2*!!(condition)]))
 #else
-extern int __build_bug_on_failed;
-#define BUILD_BUG_ON(condition)					\
-	do {							\
-		((void)sizeof(char[1 - 2*!!(condition)]));	\
-		if (condition) __build_bug_on_failed = 1;	\
+#define BUILD_BUG_ON(condition)						\
+	do {								\
+		extern void __build_bug_on_failed(void)			\
+			__compiletime_error("BUILD_BUG_ON failed");	\
+		((void)sizeof(char[1 - 2*!!(condition)]));		\
+		if (condition)						\
+			__build_bug_on_failed();			\
 	} while(0)
 #endif
 
-- 
1.7.3.4

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/