Re: [PATCH bpf-next] bpf: disable some `attribute ignored' warnings in GCC

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

On 5/6/24 12:09 PM, David Faust wrote:
>
> On 5/6/24 11:32 AM, Yonghong Song wrote:
>> On 5/3/24 5:32 AM, Jose E. Marchesi wrote:
>>> This patch modifies selftests/bpf/Makefile to pass -Wno-attributes to
>>> GCC.  This is because of the following attributes which are ignored:
>>>
>>> - btf_decl_tag
>>> - btf_type_tag
>>>
>>>     There are many of these.  At the moment none of these are
>>>     recognized/handled by gcc-bpf.
>>>
>>>     We are aware that btf_decl_tag is necessary for some of the
>>>     selftest harness to communicate test failure/success.  Support for
>>>     it is in progress in GCC upstream:
>>>
>>>     https://gcc.gnu.org/pipermail/gcc-patches/2024-May/650482.html
>>>
>>>     However, the GCC master branch is not yet open, so the series
>>>     above (currently under review upstream) wont be able to make it
>>>     there until 14.1 gets released, probably mid next week.
>> Thanks. It would be great if the patch can be merged soon.
> A small note here - the above series does not itself contain the patch
> to support decl_tag, it is just some prerequisite structural changes and
> the option to prune BTF before emission similar to clang to slim the
> selftest (and other) program sizes down.
>
> The patch to enable decl_tag for functions in BTF, enough for the
> selftest harness, can go up after that. But, it will require some
> approvals from the C front-end maintainers, since it is a new attribute,
> so it may take longer, and may be contentious.

Thanks for the update! Let me know if I can help from llvm/kernel/bpf
perspective.

>
>>>     As for btf_type_tag, more extensive work will be needed in GCC
>>>     upstream to support it in both BTF and DWARF.  We have a WIP big
>>>     patch for that, but that is not needed to compile/build the
>>>     selftests.
>> Thanks. Eduard has implemented in llvm with agreed new format. Since
>> the old phabricator becomes readonly, he will upstream the original
>> patch to llvm-project soon.
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