From: Stanislav Fomichev <sdf@fomichev.me>
To: Alexei Starovoitov <ast@kernel.org>
Cc: davem@davemloft.net, daniel@iogearbox.net,
netdev@vger.kernel.org, bpf@vger.kernel.org, kernel-team@fb.com
Subject: Re: [PATCH bpf-next 3/6] bpf: Introduce function-by-function verification
Date: Tue, 14 Jan 2020 15:39:04 -0800 [thread overview]
Message-ID: <20200114233904.GA2308546@mini-arch> (raw)
In-Reply-To: <20200108072538.3359838-4-ast@kernel.org>
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?
next prev parent reply other threads:[~2020-01-14 23:39 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 [this message]
2020-01-14 23:56 ` Andrii Nakryiko
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
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