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From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: Magnus Karlsson <magnus.karlsson@gmail.com>
Cc: "Toke Høiland-Jørgensen" <toke@redhat.com>,
	"Michal Swiatkowski" <michal.swiatkowski@linux.intel.com>,
	"Jakub Kicinski" <kuba@kernel.org>,
	"John Fastabend" <john.fastabend@gmail.com>,
	"Jesper Dangaard Brouer" <brouer@redhat.com>,
	"Andrii Nakryiko" <andrii.nakryiko@gmail.com>,
	BPF-dev-list <bpf@vger.kernel.org>,
	"William Tu" <u9012063@gmail.com>,
	xdp-hints@xdp-project.net
Subject: Re: XDP-hints: Howto support multiple BTF types per packet basis?
Date: Thu, 24 Jun 2021 07:58:55 -0700	[thread overview]
Message-ID: <CAADnVQKv5SLBfnBWnEBFqf0-DQv+NZuixGiCVx1hewfQFhHSKg@mail.gmail.com> (raw)
In-Reply-To: <CAJ8uoz2jgEJUb7Yj25HUrVX66PDde2o74GHsq21SdUtQESRkPw@mail.gmail.com>

On Thu, Jun 24, 2021 at 6:08 AM Magnus Karlsson
<magnus.karlsson@gmail.com> wrote:
> >
> > and libbpf could do relocations based on the different meta structs,
> > even removing the code for the ones that don't exist on the running
> > kernel.
>
> Just wondering how this will carry over to user-space and AF_XDP since
> it sees the same metadata area as XDP? AFAIK, dynamic linkers today
> cannot relocate structs or remove members, but I am not up-to-date
> with the latest here so might be completely wrong. And it would be
> good not to have to recompile a user-space binary just because a new
> NIC came out with a new BTF ID and layout, but with the same metadata
> member name and format as previous NICs/BTF IDs. But I do not know how
> to solve these things in user-space at the moment (except to have
> fixed locations for a common set of metadata, but that is what we are
> trying to avoid), so any hints and suggestions are highly appreciated.

CO-RE is not a kernel only feature.
The BTF tests in selftest/bpf exercise most of CO-RE purely in user space.
The libbpf needs to know the original BTF and the target BTF to
match one to another.
One option for AF_XDP would be to write a bpf program to be run in user space
and let libbpf handle relocations.
Another option is to teach llvm x86 backend to support
__attribute__((preserve_access_index)).
The work done by llvm BPF backend can be copy pasted to x86 backend.
Then standard x86 binaries will support dynamic struct layout.
imo CO-RE for x86 backend would be great to do regardless of xdp hints.
It's a straightforward copy-paste. Only need to convince x86 llvm maintainers.

  reply	other threads:[~2021-06-24 14:59 UTC|newest]

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20210526125848.1c7adbb0@carbon>
     [not found] ` <CAEf4BzYXUDyQaBjZmb_Q5-z3jw1-Uvdgxm+cfcQjSwb9oRoXnQ@mail.gmail.com>
     [not found]   ` <60aeb01ebcd10_fe49208b8@john-XPS-13-9370.notmuch>
     [not found]     ` <CAEf4Bza3m5dwZ_d0=zAWR+18f5RUjzv9=1NbhTKAO1uzWg_fzQ@mail.gmail.com>
     [not found]       ` <60aeeb5252147_19a622085a@john-XPS-13-9370.notmuch>
     [not found]         ` <CAEf4Bzb1OZHpHYagbVs7s9tMSk4wrbxzGeBCCBHQ-qCOgdu6EQ@mail.gmail.com>
     [not found]           ` <60b08442b18d5_1cf8208a0@john-XPS-13-9370.notmuch>
2021-05-28  9:16             ` Toke Høiland-Jørgensen
2021-05-28 10:38               ` Alexander Lobakin
2021-05-28 14:35               ` John Fastabend
2021-05-28 15:33                 ` Toke Høiland-Jørgensen
2021-05-28 16:02                 ` Jesper Dangaard Brouer
2021-05-28 17:29                   ` John Fastabend
2021-05-30  3:27                     ` Andrii Nakryiko
2021-05-31 11:03                     ` Toke Høiland-Jørgensen
2021-05-31 13:17                       ` Jesper Dangaard Brouer
2021-06-02  0:22                       ` John Fastabend
2021-06-02 16:18                         ` Jakub Kicinski
2021-06-22  7:44                           ` Michal Swiatkowski
2021-06-22 11:53                             ` Toke Høiland-Jørgensen
2021-06-23  8:32                               ` Michal Swiatkowski
2021-06-24 12:23                                 ` Toke Høiland-Jørgensen
2021-06-24 13:07                                   ` Magnus Karlsson
2021-06-24 14:58                                     ` Alexei Starovoitov [this message]
2021-06-24 15:11                                   ` Zvi Effron
2021-06-24 16:04                                     ` Toke Høiland-Jørgensen
2021-06-24 16:32                                       ` Zvi Effron
2021-06-24 16:45                                       ` Jesper Dangaard Brouer
2021-07-08  8:32                                   ` Michal Swiatkowski
2021-07-09 10:57                                     ` Toke Høiland-Jørgensen
2021-09-02  2:49                                       ` Michal Swiatkowski
2021-09-02  9:17                                         ` Jesper Dangaard Brouer
2021-09-07  6:27                                           ` Michal Swiatkowski
2021-09-08 13:28                                             ` Jesper Dangaard Brouer
2021-09-09 18:19                                               ` Andrii Nakryiko
2021-09-10 11:16                                                 ` Jesper Dangaard Brouer
     [not found]   ` <20210526222023.44f9b3c6@carbon>
     [not found]     ` <CAEf4BzZ+VSemxx7WFanw7DfLGN7w42G6ZC4dvOSB1zAsUgRQaw@mail.gmail.com>
2021-05-28 11:16       ` Jesper Dangaard Brouer
2021-05-30  3:24         ` Andrii Nakryiko

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