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

[hupu <hupu.gm@gmail.com>]

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:
  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@gmail.com>
---
 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 47c906b807ef..e1cf6accaa4c 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.
 #
@@ -1252,7 +1255,7 @@ 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