Re: [PATCH v3 06/14] perf cs-etm: Mark branches that were not taken

[sashiko-bot@kernel.org]

> An exception can transfer execution to the kernel after any instruction.
> When this creates a trace boundary, perf may attribute the trace-end
> sample to the last instruction in the range. If that instruction is an
> untaken branch, reporting only its branch type can make the transfer look
> like a taken branch.
> 
> Set PERF_IP_FLAG_NOT_TAKEN for branch ranges when
> last_instr_taken_branch is false. This records the decoded branch
> outcome independently of exception entry.
> 
> For a discontinuity without an exception element, perf script previously
> reported an untaken B.LS as:
> 
>   tr end  jcc             4000f8 => 0       b.ls #0x400118
>   tr strt jmp                  0 => 4000fc
> 
> With the not-taken flag set:
> 
>   tr end  jcc/not_taken/  4000f8 => 0       b.ls #0x400118
>   tr strt jmp                  0 => 4000fc
> 
> Here, 4000f8 remains the last traced instruction and 4000fc is the trace
> restart address. These boundary samples do not establish an IRQ entry or
> an exception return; the not_taken flag records only the branch outcome.
> 
> Reviewed-by: James Clark <james.clark@linaro.org>
> Signed-off-by: Leo Yan <leo.yan@arm.com>

Sashiko has reviewed this patch and found no issues.

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Sashiko AI review · https://sashiko.dev/#/patchset/20261030-perf_cs_etm_fix_non_taken-v3-0-7629b52ab047@arm.com?part=6