From: sashiko-bot@kernel.org
To: "Suchit Karunakaran" <suchitkarunakaran@gmail.com>
Cc: linux-perf-users@vger.kernel.org, bpf@vger.kernel.org
Subject: Re: [PATCH 2/2] perf build: compile BPF skeletons with -mcpu=v3
Date: Thu, 07 May 2026 23:49:59 +0000 [thread overview]
Message-ID: <20260507234959.EEC5BC2BCB8@smtp.kernel.org> (raw)
In-Reply-To: <20260507184238.65280-2-suchitkarunakaran@gmail.com>
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.
--
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?
--
Sashiko AI review · https://sashiko.dev/#/patchset/20260507184238.65280-1-suchitkarunakaran@gmail.com?part=2
next prev parent reply other threads:[~2026-05-07 23:50 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-05-07 18:42 [PATCH 1/2] perf/lock: Fix non-atomic max/time and min_time updates in contention_data Suchit Karunakaran
2026-05-07 18:42 ` [PATCH 2/2] perf build: compile BPF skeletons with -mcpu=v3 Suchit Karunakaran
2026-05-07 23:49 ` sashiko-bot [this message]
2026-05-10 6:47 ` Namhyung Kim
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