BPF Archive on lore.kernel.org
 help / color / Atom feed
From: "Eelco Chaudron" <echaudro@redhat.com>
To: "Yonghong Song" <yhs@fb.com>
Cc: "Alexei Starovoitov" <alexei.starovoitov@gmail.com>,
	Xdp <xdp-newbies@vger.kernel.org>, bpf <bpf@vger.kernel.org>
Subject: Re: Trying the bpf trace a bpf xdp program
Date: Wed, 04 Dec 2019 19:52:17 +0100
Message-ID: <E08A0006-E254-492C-92AB-408B58E456C0@redhat.com> (raw)
In-Reply-To: <b8d80047-3bc1-5393-76a1-7517cb2b7280@fb.com>



On 4 Dec 2019, at 19:01, Yonghong Song wrote:

<SNIP>

>>> I’ve put my code on GitHub, maybe it’s just something stupid…
>
> Thanks for the test case. This indeed a kernel bug.
> The following change fixed the issue:
>
>
> -bash-4.4$ git diff
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index a0482e1c4a77..034ef81f935b 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -9636,7 +9636,10 @@ static int check_attach_btf_id(struct
> bpf_verifier_env *env)
>                                  ret = -EINVAL;
>                                  goto out;
>                          }
> -                       addr = (long)
> tgt_prog->aux->func[subprog]->bpf_func;
> +                       if (subprog == 0)
> +                               addr = (long) tgt_prog->bpf_func;
> +                       else
> +                               addr = (long)
> tgt_prog->aux->func[subprog]->bpf_func;
>                  } else {
>                          addr = kallsyms_lookup_name(tname);
>                          if (!addr) {
> -bash-4.4$
>
> The reason is for a bpf program without any additional subprogram
> (callees), tgt_prog->aux->func is not populated and is a NULL pointer,
> so the access tgt_prog->aux->func[0]->bpf_func will segfault.
>
> With the above change, your test works properly.

Thanks for the quick response, and as you mention the test passes with 
the patch above.

I will continue my experiments later this week, and let you know if I 
run into any other problems.

Cheers,

Eelco



  reply index

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <E53E0693-1C3A-4B47-B205-DC8E5DAF3619@redhat.com>
2019-11-28 18:18 ` Alexei Starovoitov
2019-11-28 19:16   ` Eelco Chaudron
2019-11-28 19:47     ` Alexei Starovoitov
2019-11-29 16:30       ` Eelco Chaudron
2019-11-29 16:52         ` Yonghong Song
2019-12-02 16:34           ` Eelco Chaudron
2019-12-02 16:48             ` Yonghong Song
2019-12-04 13:19               ` Eelco Chaudron
2019-12-04 14:58                 ` Yonghong Song
2019-12-04 18:01                   ` Yonghong Song
2019-12-04 18:52                     ` Eelco Chaudron [this message]
2019-12-05 12:40                       ` Eelco Chaudron
2019-12-05 17:35                         ` Y Song
2019-12-06 13:04                           ` Eelco Chaudron
2019-12-07 16:51                             ` Alexei Starovoitov
2019-12-04 16:31                 ` Andrii Nakryiko
2019-12-04 18:03                   ` John Fastabend
2019-12-04 21:19                     ` Andrii Nakryiko

Reply instructions:

You may reply publically to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=E08A0006-E254-492C-92AB-408B58E456C0@redhat.com \
    --to=echaudro@redhat.com \
    --cc=alexei.starovoitov@gmail.com \
    --cc=bpf@vger.kernel.org \
    --cc=xdp-newbies@vger.kernel.org \
    --cc=yhs@fb.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

BPF Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/bpf/0 bpf/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 bpf bpf/ https://lore.kernel.org/bpf \
		bpf@vger.kernel.org
	public-inbox-index bpf

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.bpf


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git