linux-kernel - Re: [PATCH bpf-next 1/2] bpf: Remove bpf_jit

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Message-ID: <CAADnVQJ2oHbYfgY9jqM_JMxUsoZxaNrxKSVFYfgCXuHVpDehpQ@mail.gmail.com>
Date:   Thu, 15 Apr 2021 16:49:36 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Quentin Monnet <quentin@...valent.com>
Cc:     Daniel Borkmann <daniel@...earbox.net>,
        Jianlin Lv <Jianlin.Lv@....com>, bpf <bpf@...r.kernel.org>,
        Jonathan Corbet <corbet@....net>,
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Subject: Re: [PATCH bpf-next 1/2] bpf: Remove bpf_jit_enable=2 debugging mode

On Thu, Apr 15, 2021 at 8:41 AM Quentin Monnet <quentin@...valent.com> wrote:
>
> 2021-04-15 16:37 UTC+0200 ~ Daniel Borkmann <daniel@...earbox.net>
> > On 4/15/21 11:32 AM, Jianlin Lv wrote:
> >> For debugging JITs, dumping the JITed image to kernel log is discouraged,
> >> "bpftool prog dump jited" is much better way to examine JITed dumps.
> >> This patch get rid of the code related to bpf_jit_enable=2 mode and
> >> update the proc handler of bpf_jit_enable, also added auxiliary
> >> information to explain how to use bpf_jit_disasm tool after this change.
> >>
> >> Signed-off-by: Jianlin Lv <Jianlin.Lv@....com>
>
> Hello,
>
> For what it's worth, I have already seen people dump the JIT image in
> kernel logs in Qemu VMs running with just a busybox, not for kernel
> development, but in a context where buiding/using bpftool was not
> possible.

If building/using bpftool is not possible then majority of selftests won't
be exercised. I don't think such environment is suitable for any kind
of bpf development. Much so for JIT debugging.
While bpf_jit_enable=2 is nothing but the debugging tool for JIT developers.
I'd rather nuke that code instead of carrying it from kernel to kernel.