Re: [PATCH] perf evsel: Improve callchain warning for s390

[sashiko-bot@kernel.org]

> On s390 the kernel uses s390 back chain instead of frame pointers for
> stack tracing of user space since v6.7 commit aa44433ac4ee ("s390: add
> USER_STACKTRACE support").  This is because frame pointers on s390
> cannot be used for stack tracing. [1]
> 
> This requires user space to maintain a s390 back chain.  For instance
> user space to be built with compiler option '-mbackchain' (instead of
> '-fno-omit-frame-pointer' used on other architectures, which should
> better not be used on s390 [1]).  Only few distributions and users build
> user space with '-mbackchain'.  Therefore '--call-graph fp' may in
> practice not produce the expected results.
> 
> Commit ca76fb67ebdd ("perf evlist: Improve default event for s390")
> changed the default '-g' option to 'dwarf' on s390 and added a warning
> for s390 that wrongly claimed that "Framepointer unwinding lacks kernel
> [ ... ]
> [1]: s390: Stack tracing using Frame Pointer, Back Chain, and SFrame,
>      https://conf.gnu-tools-cauldron.org/opo25/talk/Y3CVHY/
> 
> Fixes: ca76fb67ebdd ("perf evlist: Improve default event for s390")
> Signed-off-by: Jens Remus <jremus@linux.ibm.com>

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

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Sashiko AI review · https://sashiko.dev/#/patchset/20260922144300.1217524-1-jremus@linux.ibm.com?part=1