linux-kernel - Re: [PATCH v2 1/2] arm64: revamp unwind

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Message-ID: <562732FC.7010306@linaro.org>
Date:	Wed, 21 Oct 2015 15:38:52 +0900
From:	AKASHI Takahiro <takahiro.akashi@...aro.org>
To:	Jungseok Lee <jungseoklee85@...il.com>
Cc:	catalin.marinas@....com, will.deacon@....com, james.morse@....com,
	mark.rutland@....com, broonie@...nel.org, david.griego@...aro.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] arm64: revamp unwind_frame for interrupt stack

On 10/20/2015 10:26 PM, Jungseok Lee wrote:
> On Oct 20, 2015, at 5:00 PM, AKASHI Takahiro wrote:
>> This patch allows unwind_frame() to traverse from interrupt stack
>> to process stack correctly by having a dummy stack frame for irq
>> exception entry created at its prologue.
>>
>> Signed-off-by: AKASHI Takahiro <takahiro.akashi@...aro.org>
>> ---
>> arch/arm64/kernel/entry.S      |   22 ++++++++++++++++++++--
>> arch/arm64/kernel/stacktrace.c |   14 +++++++++++++-
>> 2 files changed, 33 insertions(+), 3 deletions(-)
>>
>> diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
>> index c8e0bcf..779f807 100644
>> --- a/arch/arm64/kernel/entry.S
>> +++ b/arch/arm64/kernel/entry.S
>> @@ -186,8 +186,26 @@ alternative_endif
>> 	and	x23, x23, #~(IRQ_STACK_SIZE - 1)
>> 	cmp	x20, x23			// check irq re-enterance
>> 	mov	x19, sp
>> -	csel	x23, x19, x24, eq		// x24 = top of irq stack
>> -	mov	sp, x23
>> +	beq	1f
>> +	mov	sp, x24				// x24 = top of irq stack
>> +	stp	x29, x19, [sp, #-16]!		// for sanity check
>> +	stp	x29, x22, [sp, #-16]!		// dummy stack frame
>> +	mov	x29, sp
>> +1:
>> +	/*
>> +	 * Layout of interrupt stack after this macro is invoked:
>> +	 *
>> +	 *     |                |
>> +	 *-0x20+----------------+ <= dummy stack frame
>> +	 *     |      fp        |    : fp on process stack
>> +	 *-0x18+----------------+
>> +	 *     |      lr        |    : return address
>> +	 *-0x10+----------------+
>> +	 *     |    fp (copy)   |    : for sanity check
>> +	 * -0x8+----------------+
>> +	 *     |      sp        |    : sp on process stack
>> +	 *  0x0+----------------+
>> +	 */
>> 	.endm
>>
>> 	/*
>> diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c
>> index 407991b..03611a1 100644
>> --- a/arch/arm64/kernel/stacktrace.c
>> +++ b/arch/arm64/kernel/stacktrace.c
>> @@ -43,12 +43,24 @@ int notrace unwind_frame(struct stackframe *frame)
>> 	low  = frame->sp;
>> 	high = ALIGN(low, THREAD_SIZE);
>>
>> -	if (fp < low || fp > high - 0x18 || fp & 0xf)
>> +	if (fp < low || fp > high - 0x20 || fp & 0xf)
>> 		return -EINVAL;
>>
>> 	frame->sp = fp + 0x10;
>> 	frame->fp = *(unsigned long *)(fp);
>> 	/*
>> +	 * check whether we are going to walk trough from interrupt stack
>> +	 * to process stack
>> +	 * If the previous frame is the initial (dummy) stack frame on
>> +	 * interrupt stack, frame->sp now points to just below the frame
>> +	 * (dummy frame + 0x10).
>> +	 * See entry.S
>> +	 */
>> +#define STACK_LOW(addr) round_down((addr), THREAD_SIZE)
>> +	if ((STACK_LOW(frame->sp) != STACK_LOW(frame->fp)) &&
>> +			(frame->fp == *(unsigned long *)frame->sp))
>> +		frame->sp = *((unsigned long *)(frame->sp + 8));
>> +	/*
>> 	 * -4 here because we care about the PC at time of bl,
>> 	 * not where the return will go.
>> 	 */
>> --
>> 1.7.9.5
>
> How about folding the following hunk into this patch?
> The comment would be helpful for people to follow this code.

Thanks.
A frame pointer(x29) is a frame pointer, and I'm not sure that the comment is
very useful.
But it's much better than "fp on process stack" in my ascii-art.

-Takahiro AKASHI

> ----8<----
>
> diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
> index f1303c5..0ff7db3 100644
> --- a/arch/arm64/kernel/entry.S
> +++ b/arch/arm64/kernel/entry.S
> @@ -122,7 +122,8 @@
>           * x21 - aborted SP
>           * x22 - aborted PC
>           * x23 - aborted PSTATE
> -       */
> +        * x29 - aborted FP
> +        */
>          .endm
>
>          .macro  kernel_exit, el
>
> ----8<----
>
> Best Regards
> Jungseok Lee
>
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