diff mbox series

[bpf-next,v2,2/3] bpftool: Prevent setting duplicate _GNU_SOURCE in Makefile

Message ID 820bd20ea460548828ae9a50f5bdbad0700591e5.1729233447.git.vmalik@redhat.com (mailing list archive)
State New
Delegated to: BPF
Headers show
Series selftests/bpf: Improve building with extra | expand

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bpf/vmtest-bpf-next-PR success PR summary
netdev/series_format success Posting correctly formatted
netdev/tree_selection success Clearly marked for bpf-next, async
netdev/ynl success Generated files up to date; no warnings/errors; no diff in generated;
netdev/fixes_present success Fixes tag not required for -next series
netdev/header_inline success No static functions without inline keyword in header files
netdev/build_32bit success Errors and warnings before: 6 this patch: 6
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netdev/cc_maintainers warning 2 maintainers not CCed: llvm@lists.linux.dev qmo@kernel.org
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Commit Message

Viktor Malik Oct. 18, 2024, 6:49 a.m. UTC 
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>
---
 tools/bpf/bpftool/Makefile | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

Comments

Quentin Monnet Oct. 18, 2024, 9:17 a.m. UTC | #1 
2024-10-18 08:49 UTC+0200 ~ Viktor Malik <vmalik@redhat.com>
> 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>

I am not aware of any extension in use in bpftool that would require the
use of -D_GNU_SOURCE, so I suppose it's fine to remove it
unconditionally, even when it's not in CFLAGS before we append the flags
from llvm-config. Thanks!

Acked-by: Quentin Monnet <qmo@kernel.org>
diff mbox series

Patch

diff --git a/tools/bpf/bpftool/Makefile b/tools/bpf/bpftool/Makefile
index ba927379eb20..a4263dfb5e03 100644
--- a/tools/bpf/bpftool/Makefile
+++ b/tools/bpf/bpftool/Makefile
@@ -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))