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

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Date:	Tue, 20 Oct 2015 22:26:29 +0900
From:	Jungseok Lee <jungseoklee85@...il.com>
To:	AKASHI Takahiro <takahiro.akashi@...aro.org>
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 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.

----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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