Re: [RFC PATCH 1/2] perf/core: Let an arch prepare the user stack before it is dumped

[sashiko-bot@kernel.org]

> PERF_SAMPLE_STACK_USER copies the user stack as it is in memory, which
> assumes the whole call chain is there. On sparc the sampled window's
> %l and %i registers, including the frame pointer and return address an
> unwinder starts from, may still be in the register file: they only
> reach the stack when a window spills. perf_callchain_user() already
> handles this for the callchain by calling flushw_user() first; the user
> stack dump has no equivalent arch entry point.
> 
> Add perf_arch_prepare_ustack(), a no-op by default, called from
> perf_prepare_sample() before the dump size is computed, so an arch can
> write back whatever part of the user's stack state it still holds in
> registers. Doing this in the arch PMU interrupt handler would not do:
> software events such as cpu-clock reach perf_event_overflow() without
> passing through it.
> 
> Signed-off-by: Stian Halseth <stian@itx.no>

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

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Sashiko AI review · https://sashiko.dev/#/patchset/20260922135653.1622301-1-stian@itx.no?part=1