linux-kernel - Re: [RFC 1/2] perf build: Allow passing extra Clang flags via EXTRA_BPF

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Message-ID: <aUrdUjqVEjJW9VBl@google.com>
Date: Tue, 23 Dec 2025 10:20:02 -0800
From: Namhyung Kim <namhyung@...nel.org>
To: hupu <hupu.gm@...il.com>
Cc: peterz@...radead.org, mingo@...hat.com, acme@...nel.org,
	mark.rutland@....com, alexander.shishkin@...ux.intel.com,
	jolsa@...nel.org, irogers@...gle.com, adrian.hunter@...el.com,
	james.clark@...aro.org, nathan@...nel.org,
	nick.desaulniers+lkml@...il.com, morbo@...gle.com,
	justinstitt@...gle.com, linux-perf-users@...r.kernel.org,
	linux-kernel@...r.kernel.org, llvm@...ts.linux.dev
Subject: Re: [RFC 1/2] perf build: Allow passing extra Clang flags via
 EXTRA_BPF_FLAGS

Hello,

On Tue, Dec 23, 2025 at 04:43:34PM +0800, hupu wrote:
> Add support for EXTRA_BPF_FLAGS in the eBPF skeleton build, allowing
> users to pass additional Clang options such as --sysroot or custom
> include paths when cross-compiling perf.
> 
> This is primarily intended for cross-build scenarios where the default
> host include paths do not match the target kernel version.
> 
> Example usage:
>     make perf ARCH="arm64" EXTRA_BPF_FLAGS="--sysroot=..."
> 
> Change history:
>   v5:
>     - Update commit message
>   v4:
>     - Apply EXTRA_BPF_FLAGS directly to BPF skeleton build command
>       instead of modifying CLANG_OPTIONS
>   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>

Reviewed-by: Namhyung Kim <namhyung@...nel.org>

Thanks,
Namhyung

> ---
>  tools/perf/Makefile.perf | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/perf/Makefile.perf b/tools/perf/Makefile.perf
> index b3f481a626af..8b8647fd4f41 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.
>  #
> @@ -1250,7 +1253,7 @@ endif
>  $(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) $(BPF_INCLUDE) $(TOOLS_UAPI_INCLUDE) \
> +	  $(CLANG_OPTIONS) $(EXTRA_BPF_FLAGS) $(BPF_INCLUDE) $(TOOLS_UAPI_INCLUDE) \
>  	  -include $(OUTPUT)PERF-VERSION-FILE -include util/bpf_skel/perf_version.h \
>  	  -c $(filter util/bpf_skel/%.bpf.c,$^) -o $@
>  
> -- 
> 2.43.0
>