From: behanw@converseincode•com (Behan Webster)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH 2/5] arm: LLVMLinux: use current_stack_pointer for percpu
Date: Fri, 06 Sep 2013 18:59:35 -0400 [thread overview]
Message-ID: <522A5E57.2050505@converseincode.com> (raw)
In-Reply-To: <yw1xioyd1t1d.fsf@unicorn.mansr.com>
On 09/06/13 18:31, M?ns Rullg?rd wrote:
> behanw at converseincode.com writes:
>
>> From: Behan Webster <behanw@converseincode•com>
>>
>> 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 <charlebm@gmail•com>
>> Signed-off-by: Behan Webster <behanw@converseincode•com>
>> Reviewed-by: Jan-Simon M?ller <dl9pf@gmx•de>
>> ---
>> 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
next prev parent reply other threads:[~2013-09-06 22:59 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-09-06 21:28 [PATCH 0/5] arm: LLVMLinux: Add current_stack_pointer behanw at converseincode.com
2013-09-06 21:28 ` [PATCH 1/5] arm: LLVMLinux: Add current_stack_pointer macro for ARM behanw at converseincode.com
2013-09-06 22:12 ` Måns Rullgård
2013-09-06 22:50 ` Behan Webster
2013-09-06 22:20 ` Russell King - ARM Linux
2013-09-06 22:54 ` Behan Webster
2013-09-06 21:28 ` [PATCH 2/5] arm: LLVMLinux: use current_stack_pointer for percpu behanw at converseincode.com
2013-09-06 22:22 ` Russell King - ARM Linux
2013-09-06 22:56 ` Behan Webster
2013-09-06 22:31 ` Måns Rullgård
2013-09-06 22:59 ` Behan Webster [this message]
2013-09-07 5:12 ` Nicolas Pitre
2013-09-09 9:59 ` Will Deacon
2013-09-06 21:28 ` [PATCH 3/5] arm: LLVMLinux: Use current_stack_pointer for return_address behanw at converseincode.com
2013-09-06 21:28 ` [PATCH 4/5] arm: LLVMLinux: Use current_stack_pointer in save_stack_trace_tsk behanw at converseincode.com
2013-09-06 21:28 ` [PATCH 5/5] arm: LLVMLinux: Use current_stack_pointer in unwind_backtrace behanw at converseincode.com
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