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locking/rwsem/x86: Add stack frame dependency for ____down_write()

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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 <arnd@arndb.de>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1188b7015f04baf361e59de499ee2d7272c59dce.1476393828.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Josh Poimboeuf 2016-10-13 16:26:15 -05:00 committed by Ingo Molnar
parent 1001354ca3
commit 55a76b59b5
1 changed files with 4 additions and 2 deletions
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6
arch/x86/include/asm/rwsem.h
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@ -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; \