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bpftool: Prevent setting duplicate _GNU_SOURCE in Makefile

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When building selftests with CFLAGS set via env variable, the value of
CFLAGS is propagated into bpftool Makefile (called from selftests
Makefile). This makes the compilation fail as _GNU_SOURCE is defined two
times - once from selftests Makefile (by including lib.mk) and once from
bpftool Makefile (by calling `llvm-config --cflags`):

    $ CFLAGS="" make -C tools/testing/selftests/bpf
    [...]
    CC      /bpf-next/tools/testing/selftests/bpf/tools/build/bpftool/btf.o
    <command-line>: error: "_GNU_SOURCE" redefined [-Werror]
    <command-line>: note: this is the location of the previous definition
    cc1: all warnings being treated as errors
    [...]

Filter out -D_GNU_SOURCE from the result of `llvm-config --cflags` in
bpftool Makefile to prevent this error.

Signed-off-by: Viktor Malik <vmalik@redhat.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Quentin Monnet <qmo@kernel.org>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Link: https://lore.kernel.org/bpf/acec3108b62d4df1436cda777e58e93e033ac7a7.1730449390.git.vmalik@redhat.com
This commit is contained in:
Viktor Malik 2024-11-01 09:27:12 +01:00 committed by Andrii Nakryiko
parent 4d99e509c1
commit 0513eeee86
1 changed files with 5 additions and 1 deletions
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6
tools/bpf/bpftool/Makefile
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@ -147,7 +147,11 @@ ifeq ($(feature-llvm),1)
# If LLVM is available, use it for JIT disassembly
CFLAGS += -DHAVE_LLVM_SUPPORT
LLVM_CONFIG_LIB_COMPONENTS := mcdisassembler all-targets
CFLAGS += $(shell $(LLVM_CONFIG) --cflags)
# llvm-config always adds -D_GNU_SOURCE, however, it may already be in CFLAGS
# (e.g. when bpftool build is called from selftests build as selftests
# Makefile includes lib.mk which sets -D_GNU_SOURCE) which would cause
# compilation error due to redefinition. Let's filter it out here.
CFLAGS += $(filter-out -D_GNU_SOURCE,$(shell $(LLVM_CONFIG) --cflags))
LIBS += $(shell $(LLVM_CONFIG) --libs $(LLVM_CONFIG_LIB_COMPONENTS))
ifeq ($(shell $(LLVM_CONFIG) --shared-mode),static)
LIBS += $(shell $(LLVM_CONFIG) --system-libs $(LLVM_CONFIG_LIB_COMPONENTS))