Re: [PATCH v2 1/2] arm64: revamp unwind_frame for interrupt stack

[AKASHI Takahiro]

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@xxxxxxxxxx>
> > ---
> > 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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