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From: David Ahern <dsahern@gmail.com>
To: Andrii Nakryiko <andrii.nakryiko@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 07:58:28 -0600	[thread overview]
Message-ID: <cce56767-efbe-e572-6290-111c6c845578@gmail.com> (raw)
In-Reply-To: <CAEf4Bza3gMzfSQcv_QDzVP=vsCzxy=8DHwU-EVqOt8XagK7OHw@mail.gmail.com>

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.

  reply	other threads:[~2021-07-26 13:58 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 [this message]
2021-07-26 15:13               ` Andrii Nakryiko
2021-07-27  2:51                 ` David Ahern
2021-07-27 19:05                   ` Andrii Nakryiko

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