linux-kernel - Re: [PATCH v2] btf: support ints larger than 128 bits

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Date:   Tue, 5 Jan 2021 13:58:08 +0000
From:   Sean Young <sean@...s.org>
To:     Yonghong Song <yhs@...com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Nathan Chancellor <natechancellor@...il.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Quentin Monnet <quentin@...valent.com>,
        Toke Høiland-Jørgensen <toke@...hat.com>,
        linux-doc@...r.kernel.org, netdev@...r.kernel.org,
        bpf@...r.kernel.org, linux-kernel@...r.kernel.org,
        clang-built-linux@...glegroups.com
Subject: Re: [PATCH v2] btf: support ints larger than 128 bits

On Wed, Dec 30, 2020 at 10:21:09AM -0800, Yonghong Song wrote:
> On 12/19/20 8:36 AM, Sean Young wrote:
> > clang supports arbitrary length ints using the _ExtInt extension. This
> > can be useful to hold very large values, e.g. 256 bit or 512 bit types.
> > 
> > Larger types (e.g. 1024 bits) are possible but I am unaware of a use
> > case for these.
> > 
> > This requires the _ExtInt extension enabled in clang, which is under
> > review.
> > 
> > Link: https://clang.llvm.org/docs/LanguageExtensions.html#extended-integer-types
> > Link: https://reviews.llvm.org/D93103
> > 
> > Signed-off-by: Sean Young <sean@...s.org>
> > ---
> > changes since v2:
> >   - added tests as suggested by Yonghong Song
> >   - added kernel pretty-printer
> > 
> >   Documentation/bpf/btf.rst                     |   4 +-
> >   include/uapi/linux/btf.h                      |   2 +-
> >   kernel/bpf/btf.c                              |  54 +-
> >   tools/bpf/bpftool/btf_dumper.c                |  40 ++
> >   tools/include/uapi/linux/btf.h                |   2 +-
> >   tools/lib/bpf/btf.c                           |   2 +-
> >   tools/testing/selftests/bpf/Makefile          |   3 +-
> >   tools/testing/selftests/bpf/prog_tests/btf.c  |   3 +-
> >   .../selftests/bpf/progs/test_btf_extint.c     |  50 ++
> >   tools/testing/selftests/bpf/test_extint.py    | 535 ++++++++++++++++++
> 
> For easier review, maybe you can break this patch into a patch series like
> below?
>   patch 1 (kernel related changes and doc)
>       kernel/bpf/btf.c, include/uapi/linux/btf.h,
>       tools/include/uapi/linux/btf.h
>       Documentation/bpf/btf.rst
>   patch 2 (libbpf support)
>       tools/lib/bpf/btf.c
>   patch 3 (bpftool support)
>       tools/bpf/bpftool/btf_dumper.c
>   patch 4 (testing)
>       rest files

That makes sense, I'll send out v3 shortly.

Thanks,

Sean