[Buildroot] [PATCH] package/libbpf: Don't remove bpf.h on host

[Francis Laniel]

Hi.

Le lundi 28 novembre 2022, 16:06:20 CET Lang Daniel a écrit :
> libbpf >1.0.0 defines libbpf_bpf_link_type_str(enum bpf_link_type) in
> src/libbpf.h, which is included by host-pahole.
> bpf_link_type is defined in linux/bpf.h, therefore the comment stating
> that pahole doesn't need bpf.h is no longer valid.
> 
> Fixes:
> -
> http://autobuild.buildroot.net/results/d126a4b6eca786402dc362c86f8df3addec3
> d217/
> 
> Signed-off-by: Daniel Lang <d.lang at abatec.at>
> ---
> I wasn't able to reproduce the mentioned compile error in the kernel.
> The mentioned file (tools/lib/bpf/strset.c) shouldn't be compiled when
> compiling the kernel as it would recompile libbpf.
> ---
>  package/libbpf/libbpf.mk | 17 +----------------
>  1 file changed, 1 insertion(+), 16 deletions(-)
> 
> diff --git a/package/libbpf/libbpf.mk b/package/libbpf/libbpf.mk
> index 820f1dc4bf..0381fd833a 100644
> --- a/package/libbpf/libbpf.mk
> +++ b/package/libbpf/libbpf.mk
> @@ -39,26 +39,11 @@ define LIBBPF_INSTALL_TARGET_CMDS
>  		-C $(@D)/src install DESTDIR=$(TARGET_DIR)
>  endef
> 
> -# We need to install_uapi_headers so we have btf.h to compile
> -# host-pahole.
> -# Nonetheless, this target adds bpf.h which generates a conflict when
> -# building the kernel:
> -# In file included from libbpf_internal.h:17:0, from strset.c:9:
> -# relo_core.h:10:6: error: nested redefinition of 'enum bpf_core_relo_kind'
> -# enum bpf_core_relo_kind {
> -# ^~~~~~~~~~~~~~~~~~
> -# relo_core.h:10:6: error: redeclaration of 'enum bpf_core_relo_kind'
> -# In file included from libbpf_legacy.h:13:0,
> -# 		from libbpf_internal.h:16,
> -# 		from strset.c:9:
> -# /home/francis/buildroot/output/host/include/linux/bpf.h:6497:6: note:
> originally defined here -# enum bpf_core_relo_kind {
> -# So, better to remove remove it now since we do not need it to build
> +# We need to install_uapi_headers so we have bpf.h and btf.h to compile
>  # host-pahole, the only user of host-libbpf.
>  define HOST_LIBBPF_INSTALL_CMDS
>  	$(HOST_MAKE_ENV) $(HOST_CONFIGURE_OPTS) $(MAKE) \
>  		-C $(@D)/src install install_uapi_headers DESTDIR=$(HOST_DIR)
> -	rm $(HOST_DIR)/include/linux/bpf.h
>  endef
> 
>  $(eval $(generic-package))

Thank you for this patch and sorry for my very late reply.
Sadly, I do not think the patch addresses the underlying issue.
Indeed, this is not pahole which does not need this file, as pahole relies on 
<linux/bpf.h> to be built.
So, the whole point of this comment and the rm is to avoid a problem when 
building the kernel when pahole was built before.

Sadly, I tested your patch and I hit the problem described in the comment 
regarding redefinition of bpf_core_relo_kind.

Did you also hit it or you were able to build the kernel with 
BR2_LINUX_KERNEL_NEEDS_HOST_PAHOLE?


Best regards and thank you in advance.