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Message-ID: <58296f87-ad00-a0f5-954b-2150aa84efc4@isovalent.com>
Date:   Fri, 23 Apr 2021 11:26:16 +0100
From:   Quentin Monnet <quentin@...valent.com>
To:     Christophe Leroy <christophe.leroy@...roup.eu>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     Ian Rogers <irogers@...gle.com>, Song Liu <songliubraving@...com>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        Zi Shen Lim <zlim.lnx@...il.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Andrii Nakryiko <andrii@...nel.org>,
        Paul Mackerras <paulus@...ba.org>,
        Sandipan Das <sandipan@...ux.ibm.com>,
        "H. Peter Anvin" <hpa@...or.com>, sparclinux@...r.kernel.org,
        Shubham Bansal <illusionist.neo@...il.com>,
        Mahesh Bandewar <maheshb@...gle.com>,
        Will Deacon <will@...nel.org>,
        Nicolas Dichtel <nicolas.dichtel@...nd.com>,
        linux-s390 <linux-s390@...r.kernel.org>,
        Ilya Leoshkevich <iii@...ux.ibm.com>, paulburton@...nel.org,
        Jonathan Corbet <corbet@....net>,
        Mauro Carvalho Chehab <mchehab+huawei@...nel.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        X86 ML <x86@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        Russell King <linux@...linux.org.uk>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Ingo Molnar <mingo@...hat.com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Catalin Marinas <catalin.marinas@....com>,
        "Naveen N . Rao" <naveen.n.rao@...ux.ibm.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Tobias Klauser <tklauser@...tanz.ch>,
        linux-mips@...r.kernel.org, grantseltzer@...il.com,
        Xi Wang <xi.wang@...il.com>, Albert Ou <aou@...s.berkeley.edu>,
        Kees Cook <keescook@...omium.org>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Luke Nelson <luke.r.nels@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Heiko Carstens <hca@...ux.ibm.com>,
        ppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        KP Singh <kpsingh@...nel.org>, iecedge@...il.com,
        Simon Horman <horms@...ge.net.au>,
        Borislav Petkov <bp@...en8.de>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Yonghong Song <yhs@...com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Dmitry Vyukov <dvyukov@...gle.com>, tsbogend@...ha.franken.de,
        Daniel Borkmann <daniel@...earbox.net>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Network Development <netdev@...r.kernel.org>,
        David Ahern <dsahern@...nel.org>,
        Wang YanQing <udknight@...il.com>,
        Martin KaFai Lau <kafai@...com>,
        Björn Töpel <bjorn@...nel.org>,
        Palmer Dabbelt <palmer@...belt.com>, bpf <bpf@...r.kernel.org>,
        Jianlin Lv <Jianlin.Lv@....com>,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH bpf-next 1/2] bpf: Remove bpf_jit_enable=2 debugging mode

2021-04-23 09:19 UTC+0200 ~ Christophe Leroy <christophe.leroy@...roup.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

Then you can use for example the program id displayed on the first line
to reference and dump your program:

    # bpftool prog dump jited id 138

You should find additional documentation under
tools/bpf/bpftool/Documentation.

> 
> By the way, I would be nice to have a kernel OPTION that selects all
> OPTIONS required for building bpftool. Because you discover them one by
> one at every build failure. I had to had CONFIG_IPV6, CONFIG_DEBUG_BTF,
> CONFIG_CGROUPS, ... If there could be an option like "Build a 'bpftool'
> ready kernel" that selected all those, it would be great.
> 
> Christophe

I do not believe any of these are required to build bpftool.

Quentin

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