Re: [PATCH bpf] selftests/bpf: make BPF_TARGET_ENDIAN non-recursive to speed up *.bpf.o build

[Yonghong Song <yonghong.song@linux.dev>]

On 12/12/24 4:32 PM, Eduard Zingerman wrote:
> BPF_TARGET_ENDIAN is used in CLANG_BPF_BUILD_RULE and co macros.
> It is defined as a recursively expanded variable, meaning that it is
> recomputed each time the value is needed. Thus, it is recomputed for
> each *.bpf.o file compilation. The variable is computed by running a C
> compiler in a shell. This significantly hinders parallel build
> performance for *.bpf.o files.
>
> This commit changes BPF_TARGET_ENDIAN to be a simply expanded
> variable.
>
>      # Build performance stats before this commit
>      $ git clean -xfd; time make -j12
>      real	1m0.000s
>      ...
>
>      # Build performance stats after this commit
>      $ git clean -xfd; time make -j12
>      real	0m43.605s
>      ...
>
> Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>

LGTM except should target to bpf-next.

Acked-by: Yonghong Song <yonghong.song@linux.dev>

> ---
>   tools/testing/selftests/bpf/Makefile | 6 +++---
>   1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
> index bb8cf8f5bf11..9e870e519c30 100644
> --- a/tools/testing/selftests/bpf/Makefile
> +++ b/tools/testing/selftests/bpf/Makefile
> @@ -461,10 +461,10 @@ $(shell $(1) $(2) -dM -E - </dev/null | grep -E 'MIPS(EL|EB)|_MIPS_SZ(PTR|LONG)
>   endef
>   
>   # Determine target endianness.
> -IS_LITTLE_ENDIAN = $(shell $(CC) -dM -E - </dev/null | \
> +IS_LITTLE_ENDIAN := $(shell $(CC) -dM -E - </dev/null | \
>   			grep 'define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__')
> -MENDIAN=$(if $(IS_LITTLE_ENDIAN),-mlittle-endian,-mbig-endian)
> -BPF_TARGET_ENDIAN=$(if $(IS_LITTLE_ENDIAN),--target=bpfel,--target=bpfeb)
> +MENDIAN:=$(if $(IS_LITTLE_ENDIAN),-mlittle-endian,-mbig-endian)
> +BPF_TARGET_ENDIAN:=$(if $(IS_LITTLE_ENDIAN),--target=bpfel,--target=bpfeb)
>   
>   ifneq ($(CROSS_COMPILE),)
>   CLANG_TARGET_ARCH = --target=$(notdir $(CROSS_COMPILE:%-=%))