Re: [PATCH v3 5/5] alpha: fill in pc for software event samples

[sashiko-bot@kernel.org]

> Context switch and tracepoint events have no trap frame, so perf builds
> one with perf_fetch_caller_regs(). Alpha does not define
> perf_arch_fetch_caller_regs(), which leaves that pt_regs zeroed, and
> these samples report pc as 0.
> 
> Record the caller's address as pc. The zero ps already marks the frame
> as kernel mode, and pt_regs has nowhere to keep sp, so pc is all that
> can be filled in.
> 
> perf_fetch_caller_regs() gets that address from CALLER_ADDR0, which
> alpha defines as 0 when CONFIG_FRAME_POINTER is disabled. Finding the
> level zero return address does not need a frame pointer, so make
> alpha_ftrace_return_address0() available in both configurations. Only
> ftrace_return_address(n) still depends on frame pointers.
> 
> Reported-by: Magnus Lindholm <linmag7@gmail.com>
> Suggested-by: Magnus Lindholm <linmag7@gmail.com>
> Closes: https://lore.kernel.org/all/CA%2B%3DFv5S8-Zk8-LUpZnWiBfTGSQXthepmRc_-a9O%2BpEPmVW0mRA@mail.gmail.com/
> Assisted-by: Claude:claude-opus-5-5
> Reviewed-by: Magnus Lindholm <linmag7@gmail.com>
> Acked-by: Ian Rogers <irogers@google.com>
> Signed-off-by: Matt Turner <mattst88@gmail.com>

Sashiko has reviewed this patch and found no issues.

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Sashiko AI review · https://sashiko.dev/#/patchset/20261018-alpha-perf-regs-v3-v3-0-52be85332c57@gmail.com?part=5