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 <[email protected]>
Signed-off-by: Josh Poimboeuf <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Arjan van de Ven <[email protected]>
Cc: Brian Gerst <[email protected]>
Cc: Denys Vlasenko <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: kbuild test robot <[email protected]>
Link: http://lkml.kernel.org/r/0e483379275a42626ba8898117f918e1bf661e40.1518130694.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <[email protected]>

diff --git a/arch/x86/include/asm/bug.h b/arch/x86/include/asm/bug.h
index 34d99af43994453e1cec89aa202cc17b052ee690..71e6f4bf9161d82adfec8ebc22d93c1de39ff805 100644 (file)
--- 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>