[tip:x86/pti] x86/debug, objtool: Annotate WARN()-related UD2 as reachable

[tip-bot for Josh Poimboeuf]

Commit-ID:  30dde5167c432f8e32d3d13fe73a241578a4f259
Gitweb:     https://git.kernel.org/tip/30dde5167c432f8e32d3d13fe73a241578a4f259
Author:     Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
AuthorDate: Thu, 8 Feb 2018 17:09:26 -0600
Committer:  Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Tue, 13 Feb 2018 11:47:00 +0100

x86/debug, objtool: 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@xxxxxxxxx>
Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Arjan van de Ven <arjan@xxxxxxxxxxxxxxx>
Cc: Brian Gerst <brgerst@xxxxxxxxx>
Cc: Denys Vlasenko <dvlasenk@xxxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: kbuild test robot <fengguang.wu@xxxxxxxxx>
Link: http://lkml.kernel.org/r/0e483379275a42626ba8898117f918e1bf661e40.1518130694.git.jpoimboe@xxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 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 34d99af4..71e6f4bf 100644
--- a/arch/x86/include/asm/bug.h
+++ b/arch/x86/include/asm/bug.h
@@ -77,7 +77,11 @@ do {								\
 	unreachable();						\
 } while (0)
 
-#define __WARN_FLAGS(flags)	_BUG_FLAGS(ASM_UD0, BUGFLAG_WARNING|(flags))
+#define __WARN_FLAGS(flags)					\
+do {								\
+	_BUG_FLAGS(ASM_UD0, BUGFLAG_WARNING|(flags));		\
+	annotate_reachable();					\
+} while (0)
 
 #include <asm-generic/bug.h>