On 10/16/24 22:34, Andrii Nakryiko wrote: > On Mon, Oct 14, 2024 at 11:55 PM Viktor Malik <vmalik@xxxxxxxxxx> wrote: >> >> 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 >> [...] >> >> Let bpftool Makefile check if _GNU_SOURCE is already defined and if so, >> do not let llvm-config add it again. >> >> Signed-off-by: Viktor Malik <vmalik@xxxxxxxxxx> >> --- >> tools/bpf/bpftool/Makefile | 8 +++++++- >> 1 file changed, 7 insertions(+), 1 deletion(-) >> >> diff --git a/tools/bpf/bpftool/Makefile b/tools/bpf/bpftool/Makefile >> index ba927379eb20..2b5a713d71d8 100644 >> --- a/tools/bpf/bpftool/Makefile >> +++ b/tools/bpf/bpftool/Makefile >> @@ -147,7 +147,13 @@ 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 $(LLVM_CONFIG) --cflags) >> + # When bpftool build is called from another Makefile which already sets >> + # -D_GNU_SOURCE, do not let llvm-config add it again as it will cause conflict. >> + ifneq ($(filter -D_GNU_SOURCE=,$(CFLAGS)),) >> + CFLAGS += $(filter-out -D_GNU_SOURCE,$(shell $(LLVM_CONFIG) --cflags)) > > why not always do filter-out and avoid this ugly ifneq? Because in that case, _GNU_SOURCE would not be defined for some builds (e.g. plain bpftool build). I'm not entirely sure what the implications are so I wanted to stay on the safe side. Anyways, I gave it a try and bpftool builds without _GNU_SOURCE just fine so I think that we can drop the ifneq. > >> + else >> + CFLAGS += $(shell $(LLVM_CONFIG) --cflags) >> + endif >> 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)) >> -- >> 2.47.0 >> >
