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From: Andrii Nakryiko <andrii.nakryiko@gmail.com>
To: Jiri Olsa <jolsa@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>, Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Andrii Nakryiko <andriin@fb.com>,
	Networking <netdev@vger.kernel.org>, bpf <bpf@vger.kernel.org>,
	Song Liu <songliubraving@fb.com>, Yonghong Song <yhs@fb.com>,
	Martin KaFai Lau <kafai@fb.com>, David Miller <davem@redhat.com>,
	John Fastabend <john.fastabend@gmail.com>,
	Wenbo Zhang <ethercflow@gmail.com>,
	KP Singh <kpsingh@chromium.org>,
	Brendan Gregg <bgregg@netflix.com>,
	Florent Revest <revest@chromium.org>,
	Al Viro <viro@zeniv.linux.org.uk>
Subject: Re: [PATCH v9 bpf-next 08/14] bpf: Add btf_struct_ids_match function
Date: Wed, 5 Aug 2020 14:57:10 -0700
Message-ID: <CAEf4Bza5H0+96Pgz1wmWJP=ABGikv3iEmMc9EMWMpZ0+c9Gpbg@mail.gmail.com> (raw)
In-Reply-To: <20200805213136.GG319954@krava>

On Wed, Aug 5, 2020 at 2:31 PM Jiri Olsa <jolsa@redhat.com> wrote:
>
> On Wed, Aug 05, 2020 at 07:56:51PM +0200, Jiri Olsa wrote:
> > On Tue, Aug 04, 2020 at 11:27:55PM -0700, Andrii Nakryiko wrote:
> >
> > SNIP
> >
> > > > diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
> > > > index 7bacc2f56061..ba05b15ad599 100644
> > > > --- a/kernel/bpf/btf.c
> > > > +++ b/kernel/bpf/btf.c
> > > > @@ -4160,6 +4160,37 @@ int btf_struct_access(struct bpf_verifier_log *log,
> > > >         return -EINVAL;
> > > >  }
> > > >
> > > > +bool btf_struct_ids_match(struct bpf_verifier_log *log,
> > > > +                         int off, u32 id, u32 need_type_id)
> > > > +{
> > > > +       const struct btf_type *type;
> > > > +       int err;
> > > > +
> > > > +       /* Are we already done? */
> > > > +       if (need_type_id == id && off == 0)
> > > > +               return true;
> > > > +
> > > > +again:
> > > > +       type = btf_type_by_id(btf_vmlinux, id);
> > > > +       if (!type)
> > > > +               return false;
> > > > +       err = btf_struct_walk(log, type, off, 1, &id);
> > >
> > > nit: this size=1 looks a bit artificial, seems like btf_struct_walk()
> > > will work with size==0 just as well, no?
> >
> > right, it will work the same for 0 ... not sure why I put
> > originaly 1 byte for size.. probably got mixed up by some
> > condition in btf_struct_walk that I thought 0 wouldn't pass,
> > but it should work, I'll change it, it's less tricky
>
> ok, I found why it's 1 ;-) it's this condition in btf_struct_walk:
>
>         for_each_member(i, t, member) {
>                 /* offset of the field in bytes */
>                 moff = btf_member_bit_offset(t, member) / 8;
>                 if (off + size <= moff)
>                         /* won't find anything, field is already too far */
>                         break;
>
> I originaly chose to use 'size = 1' not to medle with this (and probably causing
> other issues) and in any case we expect that anything we find have at least byte
> size, so it has some logic ;-)
>
> we could make 0 size a special case and don't break the loop for it,
> but I wonder there's already someone calling it with zero and is
> expecting it to fail
>

I see, ok, probably no need. Just let it be for now, I guess.

> jirka
>

  reply index

Thread overview: 38+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-08-01 17:03 [PATCH v9 bpf-next 00/14] bpf: Add d_path helper Jiri Olsa
2020-08-01 17:03 ` [PATCH v9 bpf-next 01/14] tools resolve_btfids: Add size check to get_id function Jiri Olsa
2020-08-05  6:00   ` Andrii Nakryiko
2020-08-01 17:03 ` [PATCH v9 bpf-next 02/14] tools resolve_btfids: Add support for set symbols Jiri Olsa
2020-08-05  6:04   ` Andrii Nakryiko
2020-08-01 17:03 ` [PATCH v9 bpf-next 03/14] bpf: Move btf_resolve_size into __btf_resolve_size Jiri Olsa
2020-08-01 17:03 ` [PATCH v9 bpf-next 04/14] bpf: Add elem_id pointer as argument to __btf_resolve_size Jiri Olsa
2020-08-01 17:03 ` [PATCH v9 bpf-next 05/14] bpf: Add type_id " Jiri Olsa
2020-08-05  6:05   ` Andrii Nakryiko
2020-08-01 17:03 ` [PATCH v9 bpf-next 06/14] bpf: Remove recursion call in btf_struct_access Jiri Olsa
2020-08-05  6:12   ` Andrii Nakryiko
2020-08-05 17:36     ` Jiri Olsa
2020-08-01 17:03 ` [PATCH v9 bpf-next 07/14] bpf: Factor btf_struct_access function Jiri Olsa
2020-08-05  6:18   ` Andrii Nakryiko
2020-08-01 17:03 ` [PATCH v9 bpf-next 08/14] bpf: Add btf_struct_ids_match function Jiri Olsa
2020-08-05  6:27   ` Andrii Nakryiko
2020-08-05 17:56     ` Jiri Olsa
2020-08-05 21:31       ` Jiri Olsa
2020-08-05 21:57         ` Andrii Nakryiko [this message]
2020-08-01 17:03 ` [PATCH v9 bpf-next 09/14] bpf: Add BTF_SET_START/END macros Jiri Olsa
2020-08-05  6:29   ` Andrii Nakryiko
2020-08-01 17:03 ` [PATCH v9 bpf-next 10/14] bpf: Add d_path helper Jiri Olsa
2020-08-02  3:13   ` Alexei Starovoitov
2020-08-02 18:26     ` Jiri Olsa
2020-08-05  6:35   ` Andrii Nakryiko
2020-08-05 17:58     ` Jiri Olsa
2020-08-05 21:01       ` Jiri Olsa
2020-08-05 21:09         ` Andrii Nakryiko
2020-08-07  0:31   ` KP Singh
2020-08-07  8:35     ` Jiri Olsa
2020-08-07  9:42       ` KP Singh
2020-08-01 17:03 ` [PATCH v9 bpf-next 11/14] bpf: Update .BTF_ids section in btf.rst with sets info Jiri Olsa
2020-08-01 17:03 ` [PATCH v9 bpf-next 12/14] selftests/bpf: Add verifier test for d_path helper Jiri Olsa
2020-08-01 17:03 ` [PATCH v9 bpf-next 13/14] selftests/bpf: Add " Jiri Olsa
2020-08-05  6:40   ` Andrii Nakryiko
2020-08-05 18:00     ` Jiri Olsa
2020-08-01 17:03 ` [PATCH v9 bpf-next 14/14] selftests/bpf: Add set test to resolve_btfids Jiri Olsa
2020-08-05  6:41   ` Andrii Nakryiko

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