2024-10-15 08:54 UTC+0200 ~ Viktor Malik <vmalik@xxxxxxxxxx>
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 $(LLVM_CONFIG) --cflags)
+ # When bpftool build is called from another Makefile which already sets
+ # -D_GNU_SOURCE, do not let llvm-config add it again as it will cause conflict.
Thanks! Can you please make your comment more explicit and mention the
file tools/testing/selftests/lib.mk and/or the use case addressed
(building bpftool from selftests), given that you match on the exact
string "-D_GNU_SOURCE="? Your check won't skip adding the duplicate
definition if someone passes "-D_GNU_SOURCE", without the "=", by
calling the Makefile from another path; that's fine, but I don't want
users to read the Makefile and expect it to remove the second definition
in such a case.
+ ifneq ($(filter -D_GNU_SOURCE=,$(CFLAGS)),)
+ CFLAGS += $(filter-out -D_GNU_SOURCE,$(shell $(LLVM_CONFIG) --cflags))
+ else
+ CFLAGS += $(shell $(LLVM_CONFIG) --cflags)
+ endif
Looks good otherwise:
Reviewed-by: Quentin Monnet <qmo@xxxxxxxxxx>
