Re: [PATCH 2/2] perf build: compile BPF skeletons with -mcpu=v3

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] Adding `-mcpu=v3` to `CLANG_OPTIONS` forces all BPF skeletons to use the BPF v3 ISA, breaking backward compatibility for perf tools designed to run on older kernels.
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commit 2e8791aeccf694e1ae9ed9fda46e3a6f73332838
Author: Suchit Karunakaran <suchitkarunakaran@gmail.com>

perf build: compile BPF skeletons with -mcpu=v3

This commit adds -mcpu=v3 to CLANG_OPTIONS to support the atomic
cmpxchg instruction required by the lock_contention BPF program.
This forces Clang to emit BPF ISA v3 instructions during skeleton
compilation.

> diff --git a/tools/perf/Makefile.perf b/tools/perf/Makefile.perf
> index cee19c923c060..a9a8c84b6b006 100644
> --- a/tools/perf/Makefile.perf
> +++ b/tools/perf/Makefile.perf

[ ... ]

> @@ -1195,7 +1195,7 @@ ifneq ($(CROSS_COMPILE),)
>  CLANG_TARGET_ARCH = --target=$(notdir $(CROSS_COMPILE:%-=%))
>  endif
>  
> -CLANG_OPTIONS = -Wall
> +CLANG_OPTIONS = -Wall -mcpu=v3

Does this change break backward compatibility for other perf tools running
on older kernels?

Since CLANG_OPTIONS is used in the pattern rule for compiling all BPF
skeletons, this forces every BPF program in perf (such as
augmented_raw_syscalls.bpf.c and off_cpu.bpf.c) to target the BPF ISA v3.

Kernels older than 5.1 do not support v3 instructions and will reject
these programs during the verifier load phase.

Should the -mcpu=v3 flag be restricted exclusively to the target that
needs it, perhaps using a target-specific append for lock_contention.bpf.o?

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Sashiko AI review · https://sashiko.dev/#/patchset/20260507184238.65280-1-suchitkarunakaran@gmail.com?part=2