linux-kernel - [PATCH v2 1/3] locking/rwsem/x86: Add stack frame dependency for __up

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Message-Id: <20170906224501.11816-2-miguel.bernal.marin@linux.intel.com>
Date:   Wed,  6 Sep 2017 17:44:59 -0500
From:   Miguel Bernal Marin <miguel.bernal.marin@...ux.intel.com>
To:     Josh Poimboeuf <jpoimboe@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H . Peter Anvin" <hpa@...or.com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org
Subject: [PATCH v2 1/3] locking/rwsem/x86: Add stack frame dependency for __up_read()

kernel/locking/rwsem.o: warning: objtool: up_read()+0x11: call without frame pointer save/setup

The warning means gcc 7.2.0 placed the __up_read() inline asm (and its
call instruction) before the frame pointer setup in up_read(),
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@...ux.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 a34e0d4b957d..762167afaec0 100644
--- a/arch/x86/include/asm/rwsem.h
+++ b/arch/x86/include/asm/rwsem.h
@@ -166,14 +166,16 @@ static inline bool __down_write_trylock(struct rw_semaphore *sem)
 static inline void __up_read(struct rw_semaphore *sem)
 {
 	long tmp;
+	register void *__sp asm(_ASM_SP);
+
 	asm volatile("# beginning __up_read\n\t"
-		     LOCK_PREFIX "  xadd      %1,(%2)\n\t"
+		     LOCK_PREFIX "  xadd      %1,(%3)\n\t"
 		     /* subtracts 1, returns the old value */
 		     "  jns        1f\n\t"
 		     "  call call_rwsem_wake\n" /* expects old value in %edx */
 		     "1:\n"
 		     "# ending __up_read\n"
-		     : "+m" (sem->count), "=d" (tmp)
+		     : "+m" (sem->count), "=d" (tmp), "+r" (__sp)
 		     : "a" (sem), "1" (-RWSEM_ACTIVE_READ_BIAS)
 		     : "memory", "cc");
 }
-- 
2.14.1