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 18:56:07 -0400 [thread overview]
Message-ID: <522A5D87.30704@converseincode.com> (raw)
In-Reply-To: <20130906222243.GS6617@n2100.arm.linux.org.uk>
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 <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 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
next prev parent reply other threads:[~2013-09-06 22:56 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 [this message]
2013-09-06 22:31 ` Måns Rullgård
2013-09-06 22:59 ` Behan Webster
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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