Re: [PATCH v4 27/30] selftests/bpf: Append extra cflags

[Ian Rogers]

On Wed, Mar 11, 2026 at 1:33 AM Leo Yan <leo.yan@xxxxxxx> wrote:
>
> Append EXTRA_CFLAGS to CFLAGS so that additional flags can be applied to
> the compiler.
>
> urandom_read is built with clang.  Introduce URANDOM_READ_CFLAGS to copy
> the compiler flags without appending EXTRA_CFLAGS, which may contain
> incompatible options with clang.
>
> Signed-off-by: Leo Yan <leo.yan@xxxxxxx>
> ---
>  tools/testing/selftests/bpf/Makefile | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
> index 72a9ba41f95ebb825d25799c07ba3f0311243e45..27112f08c9a5b6cabc41902207d00897070b41b4 100644
> --- a/tools/testing/selftests/bpf/Makefile
> +++ b/tools/testing/selftests/bpf/Makefile
> @@ -71,6 +71,12 @@ ifneq ($(LLVM),)
>  CFLAGS += -Wno-unused-command-line-argument
>  endif
>
> +# urandom_read is built with clang. Copy $(CFLAGS) before EXTRA_CFLAGS are
> +# appended so that it does not inherit potentially incompatible options.
> +URANDOM_READ_CFLAGS := $(CFLAGS)

Later in the Makefile, include ../lib.mk is executed and it appends
CFLAGS like -D_GNU_SOURCE= which will be missing from
URANDOM_READ_CFLAGS here. Perhaps move these assignments below the
include?

Thanks,
Ian

> +
> +CFLAGS += $(EXTRA_CFLAGS)
> +
>  # Check whether bpf cpu=v4 is supported or not by clang
>  ifneq ($(shell $(CLANG) --target=bpf -mcpu=help 2>&1 | grep 'v4'),)
>  CLANG_CPUV4 := 1
> @@ -255,7 +261,7 @@ endif
>  $(OUTPUT)/liburandom_read.so: urandom_read_lib1.c urandom_read_lib2.c liburandom_read.map
>         $(call msg,LIB,,$@)
>         $(Q)$(CLANG) $(CLANG_TARGET_ARCH) \
> -                    $(filter-out -static,$(CFLAGS) $(LDFLAGS)) \
> +                    $(filter-out -static,$(URANDOM_READ_CFLAGS) $(LDFLAGS)) \
>                      $(filter %.c,$^) $(filter-out -static,$(LDLIBS)) \
>                      -Wno-unused-command-line-argument \
>                      -fuse-ld=$(LLD) -Wl,-znoseparate-code -Wl,--build-id=sha1 \
> @@ -265,7 +271,7 @@ $(OUTPUT)/liburandom_read.so: urandom_read_lib1.c urandom_read_lib2.c liburandom
>  $(OUTPUT)/urandom_read: urandom_read.c urandom_read_aux.c $(OUTPUT)/liburandom_read.so
>         $(call msg,BINARY,,$@)
>         $(Q)$(CLANG) $(CLANG_TARGET_ARCH) \
> -                    $(filter-out -static,$(CFLAGS) $(LDFLAGS)) $(filter %.c,$^) \
> +                    $(filter-out -static,$(URANDOM_READ_CFLAGS) $(LDFLAGS)) $(filter %.c,$^) \
>                      -Wno-unused-command-line-argument \
>                      -lurandom_read $(filter-out -static,$(LDLIBS)) -L$(OUTPUT) \
>                      -fuse-ld=$(LLD) -Wl,-znoseparate-code -Wl,--build-id=sha1 \
>
> --
> 2.34.1
>