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From: Andrii Nakryiko <andrii.nakryiko@gmail.com>
To: David Ahern <dsahern@gmail.com>
Cc: Hangbin Liu <haliu@redhat.com>, Martynas Pumputis <m@lambda.lt>,
	Networking <netdev@vger.kernel.org>,
	Stephen Hemminger <stephen@networkplumber.org>,
	Daniel Borkmann <daniel@iogearbox.net>
Subject: Re: [PATCH iproute2] libbpf: fix attach of prog with multiple sections
Date: Mon, 26 Jul 2021 08:13:39 -0700	[thread overview]
Message-ID: <CAEf4BzZHTuq8FhxyoQ-gksXspUqmocsEGyU2D5r6pFibOSSVMw@mail.gmail.com> (raw)
In-Reply-To: <cce56767-efbe-e572-6290-111c6c845578@gmail.com>

On Mon, Jul 26, 2021 at 6:58 AM David Ahern <dsahern@gmail.com> wrote:
>
> On 7/23/21 6:25 PM, Andrii Nakryiko wrote:
> >>>>>> This is still problematic, because one section can have multiple BPF
> >>>>>> programs. I.e., it's possible two define two or more XDP BPF programs
> >>>>>> all with SEC("xdp") and libbpf works just fine with that. I suggest
> >>>>>> moving users to specify the program name (i.e., C function name
> >>>>>> representing the BPF program). All the xdp_mycustom_suffix namings are
> >>>>>> a hack and will be rejected by libbpf 1.0, so it would be great to get
> >>>>>> a head start on fixing this early on.
> >>>>>
> >>>>> Thanks for bringing this up. Currently, there is no way to specify a
> >>>>> function name with "tc exec bpf" (only a section name via the "sec" arg). So
> >>>>> probably, we should just add another arg to specify the function name.
> >>>>
> >>>> How about add a "prog" arg to load specified program name and mark
> >>>> "sec" as not recommended? To keep backwards compatibility we just load the
> >>>> first program in the section.
> >>>
> >>> Why not error out if there is more than one program with the same
> >>> section name? if there is just one (and thus section name is still
> >>> unique) -- then proceed. It seems much less confusing, IMO.
> >>>
> >>
> >> Let' see if I understand this correctly: libbpf 1.0 is not going to
> >> allow SEC("xdp_foo") or SEC("xdp_bar") kind of section names - which is
> >> the hint for libbpf to know program type. Instead only SEC("xdp") is
> >> allowed.
> >
> > Right.
> >
> >>
> >> Further, a single object file is not going to be allowed to have
> >> multiple SEC("xdp") instances for each program name.
> >
> > On the contrary. Libbpf already allows (and will keep allowing)
> > multiple BPF programs with SEC("xdp") in a single object file. Which
> > is why section_name is not a unique program identifier.
> >
>
> Does that require BTF? My attempts at loading an object file with 2
> SEC("xdp") programs failed. This is using bpftool from top of tree and
> loadall.

You mean kernel BTF? Not if XDP programs themselves were built
requiring CO-RE. So if those programs use #include "vmlinux.h", or
there is BPF_CORE_READ() use somewhere in the code, or explicit
__attribute__((preserve_access_index)) is used on some of the used
structs, then yes, vmlinux BTF will be needed. But otherwise no. Do
you have verbose error logs? I think with bpftool you can get them
with -d argument.

  reply	other threads:[~2021-07-26 15:16 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-05 12:43 Martynas Pumputis
2021-07-06  2:44 ` Hangbin Liu
2021-07-20 20:27 ` Andrii Nakryiko
2021-07-21 14:47   ` Martynas Pumputis
2021-07-21 14:59     ` David Ahern
2021-07-21 15:27       ` Martynas Pumputis
2021-07-23  4:01         ` Andrii Nakryiko
2021-07-23  4:41     ` Hangbin Liu
2021-07-23  4:51       ` Andrii Nakryiko
2021-07-23  7:55         ` Hangbin Liu
2021-07-23 16:09           ` Andrii Nakryiko
2021-07-24  8:12             ` Hangbin Liu
2021-07-24  0:12         ` David Ahern
2021-07-24  0:25           ` Andrii Nakryiko
2021-07-26 13:58             ` David Ahern
2021-07-26 15:13               ` Andrii Nakryiko [this message]
2021-07-27  2:51                 ` David Ahern
2021-07-27 19:05                   ` Andrii Nakryiko

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