Re: [PATCH v6 04/13] alpha/perf: do not report user registers from the entry code

[sashiko-bot@kernel.org]

> perf_get_regs_user() returns task_pt_regs() whenever a sample of a user
> task lands in the kernel. But exception entry runs with interrupts
> enabled, so the sample can land before the entry code has saved the user
> registers. Only the part PALcode pushed is valid then. An interrupt
> taken on the first instruction of entUna, say, pushes its own frame on
> top of PALcode's, which overlaps the rest of the user frame, so r7 and r8
> read as the interrupt's r23 and r24.
> 
> Report no user registers while the interrupted PC is in the entry code.
> Such a sample also gets no user stack dump. The range is all of the entry
> code from entInt to the end of the save in entSys, so it also drops the
> registers of samples that land after they were saved there.
> 
> An interrupt that nests on one taken in the entry code still reads the
> incomplete frame, as its own PC has left the entry code.
> 
> Fixes: 9280e99d87dd ("alpha: add HAVE_PERF_REGS and HAVE_PERF_USER_STACK_DUMP support")
> Assisted-by: Claude:claude-opus-5-5
> Reviewed-by: Magnus Lindholm <linmag7@gmail.com>
> Tested-by: Magnus Lindholm <linmag7@gmail.com>
> Signed-off-by: Matt Turner <mattst88@gmail.com>

Sashiko has reviewed this patch and found no issues.

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