From mboxrd@z Thu Jan 1 00:00:00 1970 From: behanw@converseincode.com (Behan Webster) Date: Fri, 06 Sep 2013 18:59:35 -0400 Subject: [PATCH 2/5] arm: LLVMLinux: use current_stack_pointer for percpu In-Reply-To: References: <1378502899-1241-1-git-send-email-behanw@converseincode.com> <1378502899-1241-3-git-send-email-behanw@converseincode.com> Message-ID: <522A5E57.2050505@converseincode.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 09/06/13 18:31, M?ns Rullg?rd wrote: > behanw at converseincode.com writes: > >> From: Behan Webster >> >> The existing code uses named registers to get the value of the stack pointer. >> The new current_stack_pointer macro is more readable and allows for a central >> portable implementation of how to get the stack pointer with ASM. This change >> supports being able to compile the kernel with both gcc and Clang. >> >> Signed-off-by: Mark Charlebois >> Signed-off-by: Behan Webster >> Reviewed-by: Jan-Simon M?ller >> --- >> arch/arm/include/asm/percpu.h | 4 ++-- >> 1 file changed, 2 insertions(+), 2 deletions(-) >> >> diff --git a/arch/arm/include/asm/percpu.h b/arch/arm/include/asm/percpu.h >> index 209e650..629a975 100644 >> --- a/arch/arm/include/asm/percpu.h >> +++ b/arch/arm/include/asm/percpu.h >> @@ -30,14 +30,14 @@ static inline void set_my_cpu_offset(unsigned long off) >> static inline unsigned long __my_cpu_offset(void) >> { >> unsigned long off; >> - register unsigned long *sp asm ("sp"); >> + unsigned long sp = current_stack_pointer; >> >> /* >> * Read TPIDRPRW. >> * We want to allow caching the value, so avoid using volatile and >> * instead use a fake stack read to hazard against barrier(). >> */ >> - asm("mrc p15, 0, %0, c13, c0, 4" : "=r" (off) : "Q" (*sp)); >> + asm("mrc p15, 0, %0, c13, c0, 4" : "=r" (off) : "Q" (sp)); > This doesn't do quite the same thing. The existing code pretends to > read something from the stack in order to create a barrier of some > sort. Your new code stores the value of the stack pointer to a location > on the stack for consumption by the "Q" memory constraint. Agreed. My bug. Will fix. > This store is not necessary and should preferably be avoided. I agree that the extra store should be avoided. I wasn't unable to remove it. Can you suggest how? Thanks, Behan -- Behan Webster behanw at converseincode.com