From: Stanislav Fomichev <sdf@google.com>
To: "Toke Høiland-Jørgensen" <toke@redhat.com>
Cc: bpf@vger.kernel.org, ast@kernel.org, daniel@iogearbox.net,
andrii@kernel.org, martin.lau@linux.dev, song@kernel.org,
yhs@fb.com, john.fastabend@gmail.com, kpsingh@kernel.org,
haoluo@google.com, jolsa@kernel.org,
David Ahern <dsahern@gmail.com>, Jakub Kicinski <kuba@kernel.org>,
Willem de Bruijn <willemb@google.com>,
Jesper Dangaard Brouer <brouer@redhat.com>,
Anatoly Burakov <anatoly.burakov@intel.com>,
Alexander Lobakin <alexandr.lobakin@intel.com>,
Magnus Karlsson <magnus.karlsson@gmail.com>,
Maryam Tahhan <mtahhan@redhat.com>,
xdp-hints@xdp-project.net, netdev@vger.kernel.org
Subject: [xdp-hints] Re: [PATCH bpf-next v3 03/12] bpf: XDP metadata RX kfuncs
Date: Thu, 8 Dec 2022 18:57:30 -0800 [thread overview]
Message-ID: <CAKH8qBsK1J5HeSgPN_sYzQRY2jZOO=-E+zyKsn4xJ22zv5HRFg@mail.gmail.com> (raw)
In-Reply-To: <87zgbxjv7a.fsf@toke.dk>
On Thu, Dec 8, 2022 at 4:07 PM Toke Høiland-Jørgensen <toke@redhat.com> wrote:
>
> Stanislav Fomichev <sdf@google.com> writes:
>
> >> Another UX thing I ran into is that libbpf will bail out if it can't
> >> find the kfunc in the kernel vmlinux, even if the code calling the
> >> function is behind an always-false if statement (which would be
> >> eliminated as dead code from the verifier). This makes it a bit hard to
> >> conditionally use them. Should libbpf just allow the load without
> >> performing the relocation (and let the verifier worry about it), or
> >> should we have a bpf_core_kfunc_exists() macro to use for checking?
> >> Maybe both?
> >
> > I'm not sure how libbpf can allow the load without performing the
> > relocation; maybe I'm missing something.
> > IIUC, libbpf uses the kfunc name (from the relocation?) and replaces
> > it with the kfunc id, right?
>
> Yeah, so if it can't find the kfunc in vmlinux, just write an id of 0.
> This will trip the check at the top of fixup_kfunc_call() in the
> verifier, but if the code is hidden behind an always-false branch (an
> rodata variable set to zero, say) the instructions should get eliminated
> before they reach that point. That way you can at least turn it off at
> runtime (after having done some kind of feature detection) without
> having to compile it out of your program entirely.
>
> > Having bpf_core_kfunc_exists would help, but this probably needs
> > compiler work first to preserve some of the kfunc traces in vmlinux.h?
>
> I am not sure how the existing macros work, TBH. Hopefully someone else
> can chime in :)
+1
I think we need to poke Andrii as a follow up :-)
> -Toke
>
next prev parent reply other threads:[~2022-12-09 2:57 UTC|newest]
Thread overview: 61+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-12-06 2:45 [xdp-hints] [PATCH bpf-next v3 00/12] xdp: hints via kfuncs Stanislav Fomichev
2022-12-06 2:45 ` [xdp-hints] [PATCH bpf-next v3 01/12] bpf: Document XDP RX metadata Stanislav Fomichev
2022-12-08 4:25 ` [xdp-hints] " Jakub Kicinski
2022-12-08 19:06 ` Stanislav Fomichev
2022-12-06 2:45 ` [xdp-hints] [PATCH bpf-next v3 02/12] bpf: Rename bpf_{prog,map}_is_dev_bound to is_offloaded Stanislav Fomichev
2022-12-08 4:26 ` [xdp-hints] " Jakub Kicinski
2022-12-06 2:45 ` [xdp-hints] [PATCH bpf-next v3 03/12] bpf: XDP metadata RX kfuncs Stanislav Fomichev
2022-12-07 4:29 ` [xdp-hints] " Alexei Starovoitov
2022-12-07 4:52 ` Stanislav Fomichev
2022-12-07 7:23 ` Martin KaFai Lau
2022-12-07 18:05 ` Stanislav Fomichev
2022-12-08 2:47 ` Martin KaFai Lau
2022-12-08 19:07 ` Stanislav Fomichev
2022-12-08 22:53 ` Martin KaFai Lau
2022-12-08 23:45 ` Stanislav Fomichev
2022-12-08 5:00 ` Jakub Kicinski
2022-12-08 19:07 ` Stanislav Fomichev
2022-12-09 1:30 ` Jakub Kicinski
2022-12-09 2:57 ` Stanislav Fomichev
2022-12-08 22:39 ` Toke Høiland-Jørgensen
2022-12-08 23:46 ` Stanislav Fomichev
2022-12-09 0:07 ` Toke Høiland-Jørgensen
2022-12-09 2:57 ` Stanislav Fomichev [this message]
2022-12-10 0:42 ` Martin KaFai Lau
2022-12-10 1:12 ` Martin KaFai Lau
2022-12-09 11:10 ` Jesper Dangaard Brouer
2022-12-09 17:47 ` Stanislav Fomichev
2022-12-11 11:09 ` Jesper Dangaard Brouer
2022-12-06 2:45 ` [xdp-hints] [PATCH bpf-next v3 04/12] veth: Introduce veth_xdp_buff wrapper for xdp_buff Stanislav Fomichev
2022-12-06 2:45 ` [xdp-hints] [PATCH bpf-next v3 05/12] veth: Support RX XDP metadata Stanislav Fomichev
2022-12-06 2:45 ` [xdp-hints] [PATCH bpf-next v3 06/12] selftests/bpf: Verify xdp_metadata xdp->af_xdp path Stanislav Fomichev
2022-12-06 2:45 ` [xdp-hints] [PATCH bpf-next v3 07/12] mlx4: Introduce mlx4_xdp_buff wrapper for xdp_buff Stanislav Fomichev
2022-12-08 6:11 ` [xdp-hints] " Tariq Toukan
2022-12-08 19:07 ` Stanislav Fomichev
2022-12-06 2:45 ` [xdp-hints] [PATCH bpf-next v3 08/12] mxl4: Support RX XDP metadata Stanislav Fomichev
2022-12-08 6:09 ` [xdp-hints] " Tariq Toukan
2022-12-08 19:07 ` Stanislav Fomichev
2022-12-08 20:23 ` Tariq Toukan
2022-12-06 2:45 ` [xdp-hints] [PATCH bpf-next v3 09/12] xsk: Add cb area to struct xdp_buff_xsk Stanislav Fomichev
2022-12-06 2:45 ` [xdp-hints] [PATCH bpf-next v3 10/12] mlx5: Introduce mlx5_xdp_buff wrapper for xdp_buff Stanislav Fomichev
2022-12-06 2:45 ` [xdp-hints] [PATCH bpf-next v3 11/12] mlx5: Support RX XDP metadata Stanislav Fomichev
2022-12-08 22:59 ` [xdp-hints] " Toke Høiland-Jørgensen
2022-12-08 23:45 ` Stanislav Fomichev
2022-12-09 0:02 ` Toke Høiland-Jørgensen
2022-12-09 0:07 ` Alexei Starovoitov
2022-12-09 0:29 ` Toke Høiland-Jørgensen
2022-12-09 0:32 ` Alexei Starovoitov
2022-12-09 0:53 ` Toke Høiland-Jørgensen
2022-12-09 2:57 ` Stanislav Fomichev
2022-12-09 5:24 ` Saeed Mahameed
2022-12-09 12:59 ` Jesper Dangaard Brouer
2022-12-09 14:37 ` Toke Høiland-Jørgensen
2022-12-09 15:19 ` Dave Taht
2022-12-09 14:42 ` Toke Høiland-Jørgensen
2022-12-09 16:45 ` Jakub Kicinski
2022-12-09 17:46 ` Stanislav Fomichev
2022-12-09 22:13 ` Jakub Kicinski
2022-12-06 2:45 ` [xdp-hints] [PATCH bpf-next v3 12/12] selftests/bpf: Simple program to dump XDP RX metadata Stanislav Fomichev
2022-12-08 22:28 ` [xdp-hints] Re: [PATCH bpf-next v3 00/12] xdp: hints via kfuncs Toke Høiland-Jørgensen
2022-12-08 23:47 ` Stanislav Fomichev
2022-12-09 0:14 ` Toke Høiland-Jørgensen
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
List information: https://lists.xdp-project.net/postorius/lists/xdp-hints.xdp-project.net/
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to='CAKH8qBsK1J5HeSgPN_sYzQRY2jZOO=-E+zyKsn4xJ22zv5HRFg@mail.gmail.com' \
--to=sdf@google.com \
--cc=alexandr.lobakin@intel.com \
--cc=anatoly.burakov@intel.com \
--cc=andrii@kernel.org \
--cc=ast@kernel.org \
--cc=bpf@vger.kernel.org \
--cc=brouer@redhat.com \
--cc=daniel@iogearbox.net \
--cc=dsahern@gmail.com \
--cc=haoluo@google.com \
--cc=john.fastabend@gmail.com \
--cc=jolsa@kernel.org \
--cc=kpsingh@kernel.org \
--cc=kuba@kernel.org \
--cc=magnus.karlsson@gmail.com \
--cc=martin.lau@linux.dev \
--cc=mtahhan@redhat.com \
--cc=netdev@vger.kernel.org \
--cc=song@kernel.org \
--cc=toke@redhat.com \
--cc=willemb@google.com \
--cc=xdp-hints@xdp-project.net \
--cc=yhs@fb.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox