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From: Jiri Olsa <jolsa@redhat.com>
To: Andrii Nakryiko <andrii.nakryiko@gmail.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 06/14] bpf: Remove recursion call in btf_struct_access
Date: Wed, 5 Aug 2020 19:36:58 +0200
Message-ID: <20200805173658.GB319954@krava> (raw)
In-Reply-To: <CAEf4BzYtO+ELTpBVwWmWRkmgOCmCnCWU6iZzYjfNRHvb7rgEJg@mail.gmail.com>

On Tue, Aug 04, 2020 at 11:12:49PM -0700, Andrii Nakryiko wrote:
> On Sat, Aug 1, 2020 at 10:04 AM Jiri Olsa <jolsa@kernel.org> wrote:
> >
> > Andrii suggested we can simply jump to again label
> > instead of making recursion call.
> >
> > Suggested-by: Andrii Nakryiko <andriin@fb.com>
> > Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> > ---
> >  kernel/bpf/btf.c | 11 +++++------
> >  1 file changed, 5 insertions(+), 6 deletions(-)
> >
> > diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
> > index bc05a24f7361..0f995038b589 100644
> > --- a/kernel/bpf/btf.c
> > +++ b/kernel/bpf/btf.c
> > @@ -3931,14 +3931,13 @@ int btf_struct_access(struct bpf_verifier_log *log,
> >                 /* Only allow structure for now, can be relaxed for
> >                  * other types later.
> >                  */
> > -               elem_type = btf_type_skip_modifiers(btf_vmlinux,
> > -                                                   array_elem->type, NULL);
> > -               if (!btf_type_is_struct(elem_type))
> > +               t = btf_type_skip_modifiers(btf_vmlinux, array_elem->type,
> > +                                           NULL);
> > +               if (!btf_type_is_struct(t))
> >                         goto error;
> >
> > -               off = (off - moff) % elem_type->size;
> > -               return btf_struct_access(log, elem_type, off, size, atype,
> > -                                        next_btf_id);
> > +               off = (off - moff) % t->size;
> > +               goto again;
> 
> Transformation looks good, thanks. So:
> 
> Acked-by: Andrii Nakryiko <andriin@fb.com>
> 
> But this '% t->size' makes me wonder what will happen when we have an
> array of zero-sized structs or multi-dimensional arrays with
> dimensions of size 0... I.e.:
> 
> struct {} arr[123];
> 
> or
> 
> int arr[0][0]0];
> 
> We should probably be more careful with division here.

right, definitely..  I'll send follow up patch for that

thanks,
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 [this message]
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
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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