# Re: \[RFC PATCH v2 06/24\] unwind\_user: Enable archs that define CFA = SP\_callsite + offset

- From: sashiko-bot@kernel.org
- Date: 2026-08-21 20:03:44 
- List: linux-trace-kernel
- Page: https://ratatoskr.run/linux-trace-kernel/2026/08/17446944
- Thread: https://ratatoskr.run/linux-s390/2026/08/17446896/t.md

```text
> Most architectures define their CFA as the value of the stack pointer
> (SP) at the call site in the previous frame, as suggested by the DWARF
> standard.  Therefore the SP at call site can be unwound using an
> implicitly assumed value offset from CFA rule with an offset of zero:
> 
>   .cfi_val_offset <SP>, 0
> 
> As a result the SP at call site computes as follows:
> 
>   SP = CFA
> 
> Enable unwinding of user space for architectures, such as s390, which
> define their CFA as the value of the SP at the call site in the previous
> frame with an offset.  Do so by enabling architectures to override the
> default SP value offset from CFA of zero with an architecture-specific
> one:
> 
>   .cfi_val_offset <SP>, offset
> 
> So that the SP at call site computes as follows:
> 
>   SP = CFA + offset
> 
> Signed-off-by: Jens Remus <redacted>

Sashiko has reviewed this patch and found no issues. It looks great!

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260821195259.2688377-1-jremus@linux.ibm.com?part=6

```