Re: [PATCH bpf-next 1/2] bpf: Remove bpf_jit_enable=2 debugging mode

From: Christophe Leroy <christophe.leroy@csgroup.eu>
To: Quentin Monnet <quentin@isovalent.com>,
	Alexei Starovoitov <alexei.starovoitov@gmail.com>
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Subject: Re: [PATCH bpf-next 1/2] bpf: Remove bpf_jit_enable=2 debugging mode
Date: Fri, 14 May 2021 08:34:07 +0200	[thread overview]
Message-ID: <52171382-1eca-58e2-b3d1-b2cc6b431e27@csgroup.eu> (raw)
In-Reply-To: <58296f87-ad00-a0f5-954b-2150aa84efc4@isovalent.com>

Le 23/04/2021 à 12:26, Quentin Monnet a écrit :
> 2021-04-23 09:19 UTC+0200 ~ Christophe Leroy <christophe.leroy@csgroup.eu>
> 
> [...]
> 
>> I finally managed to cross compile bpftool with libbpf, libopcodes,
>> readline, ncurses, libcap, libz and all needed stuff. Was not easy but I
>> made it.
> 
> Libcap is optional and bpftool does not use readline or ncurses. May I
> ask how you tried to build it?
> 
>>
>> Now, how do I use it ?
>>
>> Let say I want to dump the jitted code generated from a call to
>> 'tcpdump'. How do I do that with 'bpftool prog dump jited' ?
>>
>> I thought by calling this line I would then get programs dumped in a way
>> or another just like when setting 'bpf_jit_enable=2', but calling that
>> line just provides me some bpftool help text.
> 
> Well the purpose of this text is to help you find the way to call
> bpftool to do what you want :). For dumping your programs' instructions,
> you need to tell bpftool what program to dump: Bpftool isn't waiting
> until you load a program to dump it, instead you need to load your
> program first and then tell bpftool to retrieve the instructions from
> the kernel. To reference your program you could use a pinned path, or
> first list the programs on your system with "bpftool prog show":
> 
> 
>      # bpftool prog show
>      138: tracing  name foo  tag e54c922dfa54f65f  gpl
>              loaded_at 2021-02-25T01:32:30+0000  uid 0
>              xlated 256B  jited 154B  memlock 4096B  map_ids 64
>              btf_id 235

Got the following error:

root@vgoip:~# ./bpftool prog show
libbpf: elf: endianness mismatch in pid_iter_bpf.
libbpf: failed to initialize skeleton BPF object 'pid_iter_bpf': -4003
Error: failed to open PID iterator skeleton

Christophe