Re: [PATCH v2 2/3] MIPS: perf: Add SB1 userspace callchain unwinding

[sashiko-bot@kernel.org]

> Restore the userspace callchain capability formerly available through
> MIPS OProfile, exposing it through perf for SB1 and SB1A. Commit
> 5f307491f3a0 ("MIPS: oprofile: Add callgraph support") introduced an
> in-kernel userspace prologue scanner, which disappeared with the removal
> of MIPS OProfile support in e258958945c6 ("arch: mips: Remove CONFIG_OPROFILE
> support"). The MIPS perf userspace callchain hook remained unimplemented.
> 
> Follow the former OProfile approach of examining instructions before the
> sampled PC to find standard MIPS stack adjustments and saved return
> addresses. Bound each scan to 128 instructions, use nofault user reads,
> validate frame data and stack progress, and stop at the perf stack limit.
> Handle o32, n32 and n64 address widths and the actual sw/sd return-address
> slot widths, rather than relying on the kernel's unsigned long size.
> Allow the sampled leaf to use the live return-address register, and permit
> repeated return PCs when the stack advances so recursion is not truncated.
> [ ... ]
> types retain their existing userspace callchain behavior. Nonstandard
> prologues, dynamic stack adjustments and signal trampolines can truncate
> chains.
> 
> Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>

Sashiko has reviewed this patch and found no issues.

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Sashiko AI review · https://sashiko.dev/#/patchset/20261113233358.538698-1-f.fainelli@gmail.com?part=2