linux-kernel - [PATCH 2/2] x86: Annotate WARN-related UD2 as reachable

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Date:   Thu,  8 Feb 2018 17:09:26 -0600
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     x86@...nel.org
Cc:     Borislav Petkov <bp@...en8.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        kbuild test robot <fengguang.wu@...el.com>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org,
        Arjan van de Ven <arjan@...ux.intel.com>
Subject: [PATCH 2/2] x86: Annotate WARN-related UD2 as reachable

By default, objtool assumes that a UD2 is a dead end.  This is mainly
because GCC 7+ sometimes inserts a UD2 when it detects a divide-by-zero
condition.

Now that WARN() is moving back to UD2, annotate the code after it as
reachable so objtool can follow the code flow.

Reported-by: Borislav Petkov <bp@...en8.de>
Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
---
 arch/x86/include/asm/bug.h | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/bug.h b/arch/x86/include/asm/bug.h
index f2da5fc90e5c..697d89d6fa76 100644
--- a/arch/x86/include/asm/bug.h
+++ b/arch/x86/include/asm/bug.h
@@ -74,7 +74,11 @@ do {								\
 	unreachable();						\
 } while (0)
 
-#define __WARN_FLAGS(flags)	_BUG_FLAGS(ASM_UD2, BUGFLAG_WARNING|(flags))
+#define __WARN_FLAGS(flags)					\
+do {								\
+	_BUG_FLAGS(ASM_UD2, BUGFLAG_WARNING|(flags));		\
+	annotate_reachable();					\
+} while (0)
 
 #include <asm-generic/bug.h>
 
-- 
2.14.3