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

[Yonghong Song <yhs@meta.com>]

On 10/27/22 11:43 AM, Yonghong Song wrote:
> 
> 
> 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.

handling arguments for infer_header_guards.pl should also take
care of full file path.

+ /home/yhs/work/bpf-next/scripts/infer_header_guards.pl include/uapi 
include/generated/uapi arch/x86/include/uapi arch/x86/include/generated/uapi
+ return 1

> 
>> +            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