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

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Message-ID: <aSVlQHJ9xcGcZULp@google.com>
Date: Tue, 25 Nov 2025 00:13:52 -0800
From: Namhyung Kim <namhyung@...nel.org>
To: hupu <hupu.gm@...il.com>
Cc: leo.yan@....com, acme@...nel.org, adrian.hunter@...el.com,
	alexander.shishkin@...ux.intel.com, irogers@...gle.com,
	jolsa@...nel.org, justinstitt@...gle.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

Hello,

On Mon, Nov 24, 2025 at 03:34:45PM +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:
>     make perf ARCH="arm64" EXTRA_BPF_FLAGS="--sysroot=..."
> 
> Change history:
>   v3:
>     - Move the variable description comment to the top of Makefile.perf
>     - Update commit message
>   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>
> ---
>  tools/perf/Makefile.perf | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/tools/perf/Makefile.perf b/tools/perf/Makefile.perf
> index 47c906b807ef..c1a66cf3d1a7 100644
> --- a/tools/perf/Makefile.perf
> +++ b/tools/perf/Makefile.perf
> @@ -35,6 +35,9 @@ include ../scripts/utilities.mak
>  #
>  # Define EXTRA_CFLAGS=-m64 or EXTRA_CFLAGS=-m32 as appropriate for cross-builds.
>  #
> +# Define EXTRA_BPF_FLAGS="--sysroot=<path>" or other custom include paths for
> +# cross-compiling BPF skeletons
> +#
>  # Define EXCLUDE_EXTLIBS=-lmylib to exclude libmylib from the auto-generated
>  # EXTLIBS.
>  #
> @@ -1249,6 +1252,8 @@ else
>  	$(Q)cp "$(VMLINUX_H)" $@
>  endif
>  
> +CLANG_OPTIONS += $(EXTRA_BPF_FLAGS)

While it seems CLANG_OPTIONS is used only for BPF skeletons, I think
it's better to add it directly to the below lines instead of adding it
to CLANG_OPTIONS like following.

> +
>  $(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 \

	  $(CLANG_OPTIONS) $(EXTRA_BPF_FLAGS) $(BPF_INCLUDE) $(TOOLS_UAPI_INCLUDE) \

Thanks,
Namhyung