Messages in this thread | | | Date | Wed, 6 Sep 2017 16:33:02 -0500 | From | Josh Poimboeuf <> | Subject | Re: [PATCH 3/3] locking/rwsem/x86: Add stack frame dependency for __downgrade_write() |
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On Wed, Sep 06, 2017 at 12:26:13AM -0500, Miguel Bernal Marin wrote: > kernel/locking/rwsem.o: warning: objtool: downgrade_write()+0x22: call without frame pointer save/setup > > The warning means gcc 7.2.0 placed the __downgrade_write() inline asm (and > its call instruction) before the frame pointer setup in downgrade_write(), > which breaks frame pointer convention and can result in incorrect > stack traces. > > Force a stack frame to be created before the call instruction by listing > the stack pointer as an output operand in the inline asm statement. > > Signed-off-by: Miguel Bernal Marin <miguel.bernal.marin@linux.intel.com> > --- > 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 d26b6916b935..a749dc6a3103 100644 > --- a/arch/x86/include/asm/rwsem.h > +++ b/arch/x86/include/asm/rwsem.h > @@ -205,8 +205,10 @@ static inline void __up_write(struct rw_semaphore *sem) > */ > static inline void __downgrade_write(struct rw_semaphore *sem) > { > + register void *__sp asm(_ASM_SP); > + > asm volatile("# beginning __downgrade_write\n\t" > - LOCK_PREFIX _ASM_ADD "%2,(%1)\n\t" > + LOCK_PREFIX _ASM_ADD "%2,(%2)\n\t"
The '%2' should be changed to '%3'
LOCK_PREFIX _ASM_ADD "%3,(%2)\n\t"
because both inputs' indices are shifted by the new output constraint.
> /* > * transitions 0xZZZZ0001 -> 0xYYYY0001 (i386) > * 0xZZZZZZZZ00000001 -> 0xYYYYYYYY00000001 (x86_64) > @@ -215,7 +217,7 @@ static inline void __downgrade_write(struct rw_semaphore *sem) > " call call_rwsem_downgrade_wake\n" > "1:\n\t" > "# ending __downgrade_write\n" > - : "+m" (sem->count) > + : "+m" (sem->count), "+r" (__sp) > : "a" (sem), "er" (-RWSEM_WAITING_BIAS) > : "memory", "cc");
-- Josh
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