linux-kernel - Re: [PATCH] perf build: Support passing extra Clang options via EXTRA_BPF

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Message-ID: <CADHxFxQF033b97sBx8rtRHAo5Ou5Uc3WLUH1Y5+qA3f1i2MMjw@mail.gmail.com>
Date: Mon, 20 Oct 2025 16:00:10 +0800
From: hupu <hupu.gm@...il.com>
To: Namhyung Kim <namhyung@...nel.org>
Cc: acme@...nel.org, adrian.hunter@...el.com, 
	alexander.shishkin@...ux.intel.com, irogers@...gle.com, jolsa@...nel.org, 
	justinstitt@...gle.com, leo.yan@....com, linux-kernel@...r.kernel.org, 
	linux-perf-users@...r.kernel.org, mark.rutland@....com, mingo@...hat.com, 
	morbo@...gle.com, nathan@...nel.org, nick.desaulniers+lkml@...il.com, 
	peterz@...radead.org
Subject: Re: [PATCH] perf build: Support passing extra Clang options via EXTRA_BPF_FLAGS

Hi Namhyung,
Thanks for your review.

On Mon, Oct 20, 2025 at 12:16 PM Namhyung Kim <namhyung@...nel.org> wrote:
>
> On Mon, Oct 20, 2025 at 10:40:49AM +0800, hupu wrote:
> > When cross-compiling perf with BPF enabled, Clang is invoked during the
> > build. Some cross-compilation environments require additional compiler
> > options, such as `--sysroot` or custom include paths.
> >
> > This patch introduces a new Make variable, `EXTRA_BPF_FLAGS`. During BPF
> > skeleton builds, it appends user-provided options to `CLANG_OPTIONS`,
> > allowing extra Clang flags to be set without modifying Makefile.perf
> > directly.
> >
> > Example usage:
> >     EXTRA_BPF_FLAGS="--sysroot=$SYSROOT"
> >     make perf ARCH="$ARCH" EXTRA_BPF_FLAGS="$EXTRA_BPF_FLAGS"
>
> Why not just:
>
>   make perf ARCH="arm64" EXTRA_BPF_FLAGS="--sysroot=..."
>
> >
> > Change history:
> >   v2:
> >     - Rename EXTRA_CLANG_FLAGS to EXTRA_BPF_FLAGS
> >     - Update commit message
> >   v1:
> >     - Introduce EXTRA_CLANG_FLAGS to allow passing extra Clang options
> >
> > Signed-off-by: hupu <hupu.gm@...il.com>
>
> Leo, are you ok with this?
>
> > ---
> >  tools/perf/Makefile.perf | 5 +++++
> >  1 file changed, 5 insertions(+)
> >
> > diff --git a/tools/perf/Makefile.perf b/tools/perf/Makefile.perf
> > index 47c906b807ef..f1f2efdbab8c 100644
> > --- a/tools/perf/Makefile.perf
> > +++ b/tools/perf/Makefile.perf
> > @@ -1249,6 +1249,11 @@ else
> >       $(Q)cp "$(VMLINUX_H)" $@
> >  endif
> >
> > +# Allow users to specify additional Clang options (e.g. --sysroot)
> > +# when cross-compiling BPF skeletons, enabling more flexible
> > +# build configurations.
>
> Can you please move this comment or add new one at the top of the file
> along with EXTRA_CFLAGS?
>

Alright, I will prepare a v3 patch based on your review comments.

Thanks,
hupu