Re: [RFC][PATCH] Implement perf_callchain_user for o32 ABI (on mipsel)

[David Daney <david.daney@cavium.com>]

On 08/10/2011 12:24 AM, Holger Hans Peter Freyther wrote:
> Hi all,
>
> I wanted to use perf to profile my userspace application on MIPS but I saw
> that there is no solution for that. I have written some code to scan the
> prologue of the function to identify the stack size and where in the stack the
> return address is stored.
>
>     0:	27bdffd8 	addiu	sp,sp,-40<-- used to find prev. stack
>     4:	afbf0024 	sw	ra,36(sp)<-- stored return addr.
>     8:	afbe0020 	sw	s8,32(sp)
>     c:	03a0f021 	move	s8,sp
>    10:	3c1c0000 	lui	gp,0x0
>    14:	279c0000 	addiu	gp,gp,0
>
> The code appears to work in qemu-system-mipsel (not where I am going to do my
> profiling) with my simple test application.
>
> The code is missing a S-o-b because I would like to get feedback if something
> like this would ever be accepted upstream. The other question is also about
> security, other ABIs, 32/64 bit...
>
> comments more than welcome
> 	holger

You need to reconcile your patches with these:

http://patchwork.linux-mips.org/patch/2579/
http://patchwork.linux-mips.org/patch/2376/
http://patchwork.linux-mips.org/patch/2375/

We probably could use some sort of backtrace code in the kernel, but 
three seperate implementations are too many.

Also separating most of the unwinder into a separate file would be 
preferable to mixing it into the perf counter driver.

David Daney