Re: [PATCH v2 00/11] unwind, perf: sframe user space unwinding, deferred perf callchains

[Josh Poimboeuf]

On Wed, Oct 23, 2024 at 03:22:35PM +0200, Jens Remus wrote:
> We are looking forward to implement support for unwinding of user space
> using SFrame in kernel/perf on s390. One major concern is that your x86
> implementation currently relies on a fallback to unwinding using frame
> pointer. On s390 unwinding using frame pointer is unsupported, because
> of lack of proper s390x ABI [1] specification and compiler support. In
> theory there would be a s390-specific alternative of unwinding using
> backchain (compiler option -mbackchain), but this has limitations and
> there is currently no distribution where user space is built with
> backchain.
> 
> How much of an issue would it be if s390 could not provide an unwinding
> fallback implementation? Do you see the possibility to get away without?

No problem, I'll make the fallback dependent on CONFIG_HAVE_UNWIND_USER_FP.

> For s390 support of unwinding using SFrame we would need to make a few
> changes to your generic unwinding framework in the kernel:

Also no problem, I'm sure there will need to be tweaks going forward.

Thanks for looking at it!  v3 will be posted soon.

-- 
Josh