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SubjectRe: [PATCH 19/19] [INCOMPLETE] ARM: make return_address available for ARM_UNWIND
On Mon, Jan 28, 2013 at 11:33:11AM +0900, Keun-O Park wrote:
> Hello guys,
>
> Could you please review the patch of fixing bug first of returning
> wrong address when using frame pointer?
> I am wondering if the first patch is not delivered to the mailing.

I posted a similar patch to alkml a couple of months ago, but I got
no response and it looks like I forgot about it.

http://lists.infradead.org/pipermail/linux-arm-kernel/2012-November/129381.html

[...]

>
> ~~~~~~~~~~~~~~~~~~~~~snip~~~~~~~~~~~~~~~~~~~~~~~~~
> From 3a60b536d22a2043d735c890a9aac9e7cb72de8f Mon Sep 17 00:00:00 2001
> From: sahara <keun-o.park@windriver.com>
> Date: Thu, 3 Jan 2013 17:12:37 +0900
> Subject: [PATCH 1/2] arm: fix returning wrong CALLER_ADDRx
>
> This makes return_address return correct value for ftrace feature.
> unwind_frame does not update frame->lr but frame->pc for backtrace.
> And, the initialization for data.addr was missing so that wrong value
> returned when unwind_frame failed.
>
> Signed-off-by: sahara <keun-o.park@windriver.com>
> ---
> arch/arm/kernel/return_address.c | 5 +++--
> 1 files changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm/kernel/return_address.c b/arch/arm/kernel/return_address.c
> index 8085417..fafedd8 100644
> --- a/arch/arm/kernel/return_address.c
> +++ b/arch/arm/kernel/return_address.c
> @@ -26,7 +26,7 @@ static int save_return_addr(struct stackframe *frame, void *d)
> struct return_address_data *data = d;
>
> if (!data->level) {
> - data->addr = (void *)frame->lr;
> + data->addr = (void *)frame->pc;
>
> return 1;
> } else {
> @@ -41,7 +41,8 @@ void *return_address(unsigned int level)
> struct stackframe frame;
> register unsigned long current_sp asm ("sp");
>
> - data.level = level + 1;
> + data.level = level + 2;
> + data.addr = NULL;

Can you explain why this is needed? I think I concluded it wasn't
necessary, but you may be right -- I think if walk_stackframe()
fails to unwind the next frame just after data.level reaches zero,
then data.addr can remain unset and return_address() may return
uninitialised garbage.

Initialising data.addr to NULL before we start seems a good way
to avoid that.

Cheers
---Dave


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