[PATCH bpf-next v3 2/8] selftests/bpf: don't pass clang-only warning flags to GCC

[Vineet Gupta <vineet.gupta@linux.dev>]

The clang only togges are passed to every BPF object build, including
for BPF_GCC build.

GCC accepts an unknown -Wno-foo silently until some other diagnostic fires,
and then appends a note to it, so every warning in a bpf_gcc build comes with
two lines of noise:

  cc1: note: unrecognized command-line option '-Wno-initializer-overrides' may have been intended to silence earlier diagnostics
  cc1: note: unrecognized command-line option '-Wno-microsoft-anon-tag' may have been intended to silence earlier diagnostics

Collect them in CLANG_BPF_CFLAGS and hand them only to the clang
flavors, through the per-flavor BPF_CC_FLAGS that Makefile.skel appends
after BPF_CFLAGS.

Only these two are clang-only; -Wno-compare-distinct-pointer-types and
-fms-extensions are understood by GCC 14 and later and stay in
BPF_CFLAGS.

Signed-off-by: Vineet Gupta <vineet.gupta@linux.dev>
---
 tools/testing/selftests/bpf/Makefile           | 8 ++++----
 tools/testing/selftests/bpf/Makefile.buildvars | 6 ++++--
 2 files changed, 8 insertions(+), 6 deletions(-)

diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
index c99e0f623e10..77682bf28c6e 100644
--- a/tools/testing/selftests/bpf/Makefile
+++ b/tools/testing/selftests/bpf/Makefile
@@ -376,7 +376,7 @@ CLANG_TARGET_ARCH = --target=$(notdir $(CROSS_COMPILE:%-=%))
 endif
 
 CLANG_SYS_INCLUDES = $(call get_sys_includes,$(CLANG),$(CLANG_TARGET_ARCH))
-CLANG_CFLAGS = $(CLANG_SYS_INCLUDES)
+CLANG_CFLAGS = $(CLANG_SYS_INCLUDES) $(CLANG_BPF_CFLAGS)
 
 # genkey writes both outputs. Pattern rules group them even on make
 # versions before 4.3, preventing concurrent genkey invocations.
@@ -511,7 +511,7 @@ BINARY := test_progs
 BPF_CC := $(CLANG)
 BPF_CC_MSG := CLNG-BPF
 BPF_SYS_INCLUDES := $(CLANG_SYS_INCLUDES)
-BPF_CC_FLAGS := -O2 $(BPF_TARGET_ENDIAN) -mcpu=v3
+BPF_CC_FLAGS := -O2 $(BPF_TARGET_ENDIAN) -mcpu=v3 $(CLANG_BPF_CFLAGS)
 BPF_DEFINES := -DENABLE_ATOMICS_TESTS
 include Makefile.skel
 
@@ -527,12 +527,12 @@ $(OUTPUT)/test_progs: $(RUNNER_PREREQS) $(BPF_OBJS) $(ALL_SKELS) FORCE
 
 $(OUTPUT)/test_progs-no_alu32: $(RUNNER_PREREQS) FORCE
 	+$(Q)$(RUNNER_MAKE) RUNNER=test_progs FLAVOR=no_alu32 TESTS_DIR=prog_tests \
-		$(CLANG_RUNNER_ARGS) BPF_CC_FLAGS='-O2 $(BPF_TARGET_ENDIAN) -mcpu=v2'
+		$(CLANG_RUNNER_ARGS) BPF_CC_FLAGS='-O2 $(BPF_TARGET_ENDIAN) -mcpu=v2 $(CLANG_BPF_CFLAGS)'
 
 ifneq ($(CLANG_CPUV4),)
 $(OUTPUT)/test_progs-cpuv4: $(RUNNER_PREREQS) FORCE
 	+$(Q)$(RUNNER_MAKE) RUNNER=test_progs FLAVOR=cpuv4 TESTS_DIR=prog_tests \
-		$(CLANG_RUNNER_ARGS) BPF_CC_FLAGS='-O2 $(BPF_TARGET_ENDIAN) -mcpu=v4' \
+		$(CLANG_RUNNER_ARGS) BPF_CC_FLAGS='-O2 $(BPF_TARGET_ENDIAN) -mcpu=v4 $(CLANG_BPF_CFLAGS)' \
 		BPF_DEFINES=-DENABLE_ATOMICS_TESTS
 endif
 
diff --git a/tools/testing/selftests/bpf/Makefile.buildvars b/tools/testing/selftests/bpf/Makefile.buildvars
index d2a0c0031b87..4d25a736376c 100644
--- a/tools/testing/selftests/bpf/Makefile.buildvars
+++ b/tools/testing/selftests/bpf/Makefile.buildvars
@@ -132,13 +132,15 @@ BPF_CFLAGS = -g -Wall -Werror -D__TARGET_ARCH_$(SRCARCH) $(MENDIAN)	\
 	     -I$(abspath $(OUTPUT)/../usr/include)			\
 	     -std=gnu11		 					\
 	     -fno-strict-aliasing 					\
-	     -Wno-microsoft-anon-tag					\
 	     -fms-extensions						\
 	     -Wno-compare-distinct-pointer-types			\
-	     -Wno-initializer-overrides					\
 	     #
 # TODO: enable me -Wsign-compare
 
+# Warning flags that only clang has.  GCC accepts an unknown -Wno-foo
+# silently and then notes it on the next diagnostic it emits.
+CLANG_BPF_CFLAGS := -Wno-microsoft-anon-tag -Wno-initializer-overrides
+
 VERIFY_SIG_SETUP := $(CURDIR)/verify_sig_setup.sh
 VERIFICATION_CERT   := $(BUILD_DIR)/signing_key.der
 PRIVATE_KEY := $(BUILD_DIR)/signing_key.pem
-- 
2.53.0-Meta