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 11:55 AM, Yonghong Song wrote:
> 
> 
> 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

Also, please pay attention to bpf selftest result. I see quite a
few selftest failures with this patch set.

>>
>>> +            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