From 55a76b59b5fef408442e16121faa9eb00a65fd50 Mon Sep 17 00:00:00 2001 From: Josh Poimboeuf Date: Thu, 13 Oct 2016 16:26:15 -0500 Subject: [PATCH] locking/rwsem/x86: Add stack frame dependency for ____down_write() Arnd reported the following objtool warning: kernel/locking/rwsem.o: warning: objtool: down_write_killable()+0x16: call without frame pointer save/setup The warning means gcc placed the ____down_write() inline asm (and its call instruction) before the frame pointer setup in down_write_killable(), which breaks frame pointer convention and can result in incorrect stack traces. Force the stack frame to be created before the call instruction by listing the stack pointer as an output operand in the inline asm statement. Reported-by: Arnd Bergmann Signed-off-by: Josh Poimboeuf Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/1188b7015f04baf361e59de499ee2d7272c59dce.1476393828.git.jpoimboe@redhat.com Signed-off-by: Ingo Molnar --- arch/x86/include/asm/rwsem.h | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/arch/x86/include/asm/rwsem.h b/arch/x86/include/asm/rwsem.h index 3d33a719f5c1..a34e0d4b957d 100644 --- a/arch/x86/include/asm/rwsem.h +++ b/arch/x86/include/asm/rwsem.h @@ -103,8 +103,10 @@ static inline bool __down_read_trylock(struct rw_semaphore *sem) ({ \ long tmp; \ struct rw_semaphore* ret; \ + register void *__sp asm(_ASM_SP); \ + \ asm volatile("# beginning down_write\n\t" \ - LOCK_PREFIX " xadd %1,(%3)\n\t" \ + LOCK_PREFIX " xadd %1,(%4)\n\t" \ /* adds 0xffff0001, returns the old value */ \ " test " __ASM_SEL(%w1,%k1) "," __ASM_SEL(%w1,%k1) "\n\t" \ /* was the active mask 0 before? */\ @@ -112,7 +114,7 @@ static inline bool __down_read_trylock(struct rw_semaphore *sem) " call " slow_path "\n" \ "1:\n" \ "# ending down_write" \ - : "+m" (sem->count), "=d" (tmp), "=a" (ret) \ + : "+m" (sem->count), "=d" (tmp), "=a" (ret), "+r" (__sp) \ : "a" (sem), "1" (RWSEM_ACTIVE_WRITE_BIAS) \ : "memory", "cc"); \ ret; \ -- 2.20.1