On Wed 13-04-16 12:27:31, Ingo Molnar wrote: > > * Ingo Molnar <[email protected]> wrote: > > > I'm testing your patches today, if they are otherwise OK [...] > > got this build failure: > > ./arch/x86/include/asm/rwsem.h:106:2: error: ‘asm’ operand has impossible > constraints
Hmm, I have no idea why 64b didn't have problem with the asm but 32b complains. Anyway, the following makes both happy. I have checked the generated code for 64b and it hasn't changed after the patch. 32b also seems to be generating a proper code. My gcc asm()-foo is rather weak so I would feel better if somebody double checked after me. --- >From d23f4e6994670bf2c5d864f2190f21022b4499b2 Mon Sep 17 00:00:00 2001 From: Michal Hocko <[email protected]> Date: Wed, 13 Apr 2016 14:21:25 +0200 Subject: [PATCH] x86: __down_read_trylock fix 32b build failure MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Ingo has noticed the following compilation error with CONFIG_X86_32=y ./arch/x86/include/asm/rwsem.h:106:2: error: ‘asm’ operand has impossible constraints The reason seems to be that 32b doesn't like ret being input and output argument sharing the same register with sem which is only the input. Fix this by making ret output only and use %3 (aka sem) for xadd. ret initialization is not needed now because this is done implicitly by the asm even for the fast path as both sem and ret share the same register. Reported-by: Ingo Molnar <[email protected]> Signed-off-by: Michal Hocko <[email protected]> --- arch/x86/include/asm/rwsem.h | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/arch/x86/include/asm/rwsem.h b/arch/x86/include/asm/rwsem.h index d759c5f70f49..453744c1d347 100644 --- a/arch/x86/include/asm/rwsem.h +++ b/arch/x86/include/asm/rwsem.h @@ -102,9 +102,9 @@ static inline int __down_read_trylock(struct rw_semaphore *sem) #define ____down_write(sem, slow_path) \ ({ \ long tmp; \ - struct rw_semaphore* ret = sem; \ + struct rw_semaphore* ret; \ asm volatile("# beginning down_write\n\t" \ - LOCK_PREFIX " xadd %1,(%2)\n\t" \ + LOCK_PREFIX " xadd %1,(%3)\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 +112,7 @@ static inline int __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) \ : "a" (sem), "1" (RWSEM_ACTIVE_WRITE_BIAS) \ : "memory", "cc"); \ ret; \ -- 2.8.0.rc3 -- Michal Hocko SUSE Labs
