From mboxrd@z Thu Jan 1 00:00:00 1970 From: behanw@converseincode.com (Behan Webster) Date: Fri, 06 Sep 2013 18:56:07 -0400 Subject: [PATCH 2/5] arm: LLVMLinux: use current_stack_pointer for percpu In-Reply-To: <20130906222243.GS6617@n2100.arm.linux.org.uk> References: <1378502899-1241-1-git-send-email-behanw@converseincode.com> <1378502899-1241-3-git-send-email-behanw@converseincode.com> <20130906222243.GS6617@n2100.arm.linux.org.uk> Message-ID: <522A5D87.30704@converseincode.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 09/06/13 18:22, Russell King - ARM Linux wrote: > On Fri, Sep 06, 2013 at 05:28:08PM -0400, behanw at converseincode.com wrote: >> 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 looks like it's breaking what's going on here. With the original > code, we're passing the contents of the word at the stack pointer into > the assembly via a "Q" constraint. After this change, we're passing > the _value_ of the stack pointer. > > Also, if you read the comment, it's certainly wrong. This code was rewritten a few times trying to remove the extra copy. I think this bug crept in. Of course you're right. I will fix it. Thanks, Behan -- Behan Webster behanw at converseincode.com