Re: [PATCH] perf build: Support passing extra Clang options via EXTRA_BPF_FLAGS

[Namhyung Kim <namhyung@kernel.org>]

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@gmail.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?

Thanks,
Namhyung

> +CLANG_OPTIONS += $(EXTRA_BPF_FLAGS)
> +
>  $(SKEL_TMP_OUT)/%.bpf.o: $(OUTPUT)PERF-VERSION-FILE util/bpf_skel/perf_version.h | $(SKEL_TMP_OUT)
>  $(SKEL_TMP_OUT)/%.bpf.o: util/bpf_skel/%.bpf.c $(LIBBPF) $(SKEL_OUT)/vmlinux.h
>  	$(QUIET_CLANG)$(CLANG) -g -O2 -fno-stack-protector --target=bpf \
> -- 
> 2.43.0
>