From: Andrii Nakryiko <andrii.nakryiko@gmail.com>
To: Stanislav Fomichev <sdf@fomichev.me>
Cc: Alexei Starovoitov <ast@kernel.org>,
"David S. Miller" <davem@davemloft.net>,
Daniel Borkmann <daniel@iogearbox.net>,
Networking <netdev@vger.kernel.org>, bpf <bpf@vger.kernel.org>,
Kernel Team <kernel-team@fb.com>
Subject: Re: [PATCH bpf-next 3/6] bpf: Introduce function-by-function verification
Date: Tue, 14 Jan 2020 15:56:24 -0800 [thread overview]
Message-ID: <CAEf4BzZUNKAT87UUQ9DKe8TvGG54PPDV-jPuK-J+Jx46Tm1oUA@mail.gmail.com> (raw)
In-Reply-To: <20200114233904.GA2308546@mini-arch>
On Tue, Jan 14, 2020 at 3:39 PM Stanislav Fomichev <sdf@fomichev.me> wrote:
>
> On 01/07, Alexei Starovoitov wrote:
> > New llvm and old llvm with libbpf help produce BTF that distinguish global and
> > static functions. Unlike arguments of static function the arguments of global
> > functions cannot be removed or optimized away by llvm. The compiler has to use
> > exactly the arguments specified in a function prototype. The argument type
> > information allows the verifier validate each global function independently.
> > For now only supported argument types are pointer to context and scalars. In
> > the future pointers to structures, sizes, pointer to packet data can be
> > supported as well. Consider the following example:
> > --- a/kernel/bpf/btf.c
> > +++ b/kernel/bpf/btf.c
> > @@ -2621,8 +2621,8 @@ static s32 btf_func_check_meta(struct btf_verifier_env *env,
> > return -EINVAL;
> > }
> >
> > - if (btf_type_vlen(t)) {
> > - btf_verifier_log_type(env, t, "vlen != 0");
> > + if (btf_type_vlen(t) > BTF_FUNC_EXTERN) {
> > + btf_verifier_log_type(env, t, "invalid func linkage");
> > return -EINVAL;
> Sorry for bringing it up after the review:
>
> This effectively teaches kernel about BTF_KIND_FUNC scope argument,
> right? Which means, if I take clang from the tip
> (https://github.com/llvm/llvm-project/commit/fbb64aa69835c8e3e9efe0afc8a73058b5a0fb3c#diff-f191c05d1eb0a6ca0e89d7e7938d73d4)
> and take 5.4 kernel, it will reject BTF because it now has a
> BTF_KIND_FUNC with global scope (any 'main' function is global and has
> non-zero vlen).
>
> What's the general guidance on the situation where clang starts
> spitting out some BTF and released kernels reject it? Is there some list of
> flags I can pass to clang to not emit some of the BTF features?
> Or am I missing something?
Isn't that the issue that 2d3eb67f64ec ("libbpf: Sanitize global
functions") addresses by sanitizing those BTF_KIND_FUNC as static
functions (with vlen=0)?
The general guidance is to have libbpf sanitize such BTF to make it
compatible with old kernels.
next prev parent reply other threads:[~2020-01-14 23:56 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-08 7:25 [PATCH bpf-next 0/6] bpf: Introduce global functions Alexei Starovoitov
2020-01-08 7:25 ` [PATCH bpf-next 1/6] libbpf: Sanitize BTF_KIND_FUNC linkage Alexei Starovoitov
2020-01-08 17:35 ` Song Liu
2020-01-08 18:57 ` Yonghong Song
2020-01-08 20:12 ` Alexei Starovoitov
2020-01-08 7:25 ` [PATCH bpf-next 2/6] libbpf: Collect static vs global info about functions Alexei Starovoitov
2020-01-08 10:25 ` Toke Høiland-Jørgensen
2020-01-08 16:25 ` Yonghong Song
2020-01-09 8:50 ` Toke Høiland-Jørgensen
2020-01-08 17:57 ` Song Liu
2020-01-08 20:10 ` Alexei Starovoitov
2020-01-08 7:25 ` [PATCH bpf-next 3/6] bpf: Introduce function-by-function verification Alexei Starovoitov
2020-01-08 10:28 ` Toke Høiland-Jørgensen
2020-01-08 20:06 ` Alexei Starovoitov
2020-01-09 8:57 ` Toke Høiland-Jørgensen
2020-01-09 23:03 ` Alexei Starovoitov
2020-01-10 10:08 ` Toke Høiland-Jørgensen
2020-01-08 19:10 ` Song Liu
2020-01-08 20:20 ` Alexei Starovoitov
2020-01-08 21:24 ` Song Liu
2020-01-08 23:05 ` Alexei Starovoitov
2020-01-14 23:39 ` Stanislav Fomichev
2020-01-14 23:56 ` Andrii Nakryiko [this message]
2020-01-15 0:44 ` Stanislav Fomichev
2020-01-08 7:25 ` [PATCH bpf-next 4/6] selftests/bpf: Add fexit-to-skb test for global funcs Alexei Starovoitov
2020-01-08 19:15 ` Song Liu
2020-01-08 7:25 ` [PATCH bpf-next 5/6] selftests/bpf: Add a test for a large global function Alexei Starovoitov
2020-01-08 19:16 ` Song Liu
2020-01-08 19:17 ` Song Liu
2020-01-08 7:25 ` [PATCH bpf-next 6/6] selftests/bpf: Modify a test to check global functions Alexei Starovoitov
2020-01-08 19:18 ` Song Liu
Reply instructions:
You may reply publicly 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=CAEf4BzZUNKAT87UUQ9DKe8TvGG54PPDV-jPuK-J+Jx46Tm1oUA@mail.gmail.com \
--to=andrii.nakryiko@gmail.com \
--cc=ast@kernel.org \
--cc=bpf@vger.kernel.org \
--cc=daniel@iogearbox.net \
--cc=davem@davemloft.net \
--cc=kernel-team@fb.com \
--cc=netdev@vger.kernel.org \
--cc=sdf@fomichev.me \
/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
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).