netdev - Re: [xdp-hints] Re: [PATCH bpf-next 00/11] xdp: hints via kfuncs

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Message-ID: <87zgcrdd54.fsf@toke.dk>
Date:   Wed, 16 Nov 2022 00:13:59 +0100
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Stanislav Fomichev <sdf@...gle.com>
Cc:     bpf <bpf@...r.kernel.org>, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>, Hao Luo <haoluo@...gle.com>,
        Jiri Olsa <jolsa@...nel.org>, David Ahern <dsahern@...il.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Willem de Bruijn <willemb@...gle.com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Anatoly Burakov <anatoly.burakov@...el.com>,
        Alexander Lobakin <alexandr.lobakin@...el.com>,
        Magnus Karlsson <magnus.karlsson@...il.com>,
        Maryam Tahhan <mtahhan@...hat.com>, xdp-hints@...-project.net,
        Network Development <netdev@...r.kernel.org>
Subject: Re: [xdp-hints] Re: [PATCH bpf-next 00/11] xdp: hints via kfuncs

Alexei Starovoitov <alexei.starovoitov@...il.com> writes:

> On Tue, Nov 15, 2022 at 10:38 AM Stanislav Fomichev <sdf@...gle.com> wrote:
>>
>> On Tue, Nov 15, 2022 at 7:54 AM Toke Høiland-Jørgensen <toke@...hat.com> wrote:
>> >
>> > Stanislav Fomichev <sdf@...gle.com> writes:
>> >
>> > > - drop __randomize_layout
>> > >
>> > >   Not sure it's possible to sanely expose it via UAPI. Because every
>> > >   .o potentially gets its own randomized layout, test_progs
>> > >   refuses to link.
>> >
>> > So this won't work if the struct is in a kernel-supplied UAPI header
>> > (which would include the __randomize_layout tag). But if it's *not* in a
>> > UAPI header it should still be included in a stable form (i.e., without
>> > the randomize tag) in vmlinux.h, right? Which would be the point:
>> > consumers would be forced to read it from there and do CO-RE on it...
>>
>> So you're suggesting something like the following in the uapi header?
>>
>> #ifndef __KERNEL__
>> #define __randomize_layout
>> #endif
>>
>
> 1.
> __randomize_layout in uapi header makes no sense.

I agree, which is why I wanted it to be only in vmlinux.h...

> 2.
> It's supported by gcc plugin and afaik that plugin is broken
> vs debug info, so dwarf is broken, hence BTF is broken too,
> and CO-RE doesn't work on kernels compiled with that gcc plugin.

...however this one seems a deal breaker. Ah well, too bad, seemed like
a neat trick to enforce CO-RE :(

-Toke