Re: [RFC bpf-next 09/12] kbuild: Header guards for types from include/uapi/*.h in kernel BTF

[Yonghong Song <yhs@meta.com>]

On 10/25/22 3:27 PM, Eduard Zingerman wrote:
> Use pahole --header_guards_db flag to enable encoding of header guard
> information in kernel BTF. The actual correspondence between header
> file and guard string is computed by the scripts/infer_header_guards.pl.
> 
> The encoded header guard information could be used to restore the
> original guards in the vmlinux.h, e.g.:
> 
>      include/uapi/linux/tcp.h:
> 
>        #ifndef _UAPI_LINUX_TCP_H
>        #define _UAPI_LINUX_TCP_H
>        ...
>        union tcp_word_hdr {
>      	struct tcphdr hdr;
>      	__be32        words[5];
>        };
>        ...
>        #endif /* _UAPI_LINUX_TCP_H */
> 
>      vmlinux.h:
> 
>        ...
>        #ifndef _UAPI_LINUX_TCP_H
> 
>        union tcp_word_hdr {
>      	struct tcphdr hdr;
>      	__be32 words[5];
>        };
> 
>        #endif /* _UAPI_LINUX_TCP_H */
>        ...
> 
> Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
> ---
>   scripts/link-vmlinux.sh | 13 ++++++++++++-
>   1 file changed, 12 insertions(+), 1 deletion(-)
> 
> diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
> index 918470d768e9..f57f621eda1f 100755
> --- a/scripts/link-vmlinux.sh
> +++ b/scripts/link-vmlinux.sh
> @@ -110,6 +110,7 @@ vmlinux_link()
>   gen_btf()
>   {
>   	local pahole_ver
> +	local extra_flags
>   
>   	if ! [ -x "$(command -v ${PAHOLE})" ]; then
>   		echo >&2 "BTF: ${1}: pahole (${PAHOLE}) is not available"
> @@ -122,10 +123,20 @@ gen_btf()
>   		return 1
>   	fi
>   
> +	if [ "${pahole_ver}" -ge "124" ]; then
> +		scripts/infer_header_guards.pl \

We should have full path like
	${srctree}/scripts/infer_header_guards.pl
so it can work if build directory is different from source directory.

> +			include/uapi \
> +			include/generated/uapi \
> +			arch/${SRCARCH}/include/uapi \
> +			arch/${SRCARCH}/include/generated/uapi \
> +			> .btf.uapi_header_guards || return 1;
> +		extra_flags="--header_guards_db .btf.uapi_header_guards"
> +	fi
> +
>   	vmlinux_link ${1}
>   
>   	info "BTF" ${2}
> -	LLVM_OBJCOPY="${OBJCOPY}" ${PAHOLE} -J ${PAHOLE_FLAGS} ${1}
> +	LLVM_OBJCOPY="${OBJCOPY}" ${PAHOLE} -J ${PAHOLE_FLAGS} ${extra_flags} ${1}
>   
>   	# Create ${2} which contains just .BTF section but no symbols. Add
>   	# SHF_ALLOC because .BTF will be part of the vmlinux image. --strip-all