From: "Jose E. Marchesi" <jose.marchesi@oracle.com>
To: Yonghong Song <yhs@fb.com>
Cc: <bpf@vger.kernel.org>, Alexei Starovoitov <ast@kernel.org>,
Andrii Nakryiko <andrii@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>, <kernel-team@fb.com>,
david.faust@oracle.com
Subject: Re: [PATCH bpf-next 0/9] bpf: add support for new btf kind BTF_KIND_TAG
Date: Fri, 10 Sep 2021 00:45:44 +0200 [thread overview]
Message-ID: <87a6kl8j1j.fsf@oracle.com> (raw)
In-Reply-To: <20210907230050.1957493-1-yhs@fb.com> (Yonghong Song's message of "Tue, 7 Sep 2021 16:00:49 -0700")
Hi Yonghong.
> LLVM14 added support for a new C attribute ([1])
> __attribute__((btf_tag("arbitrary_str")))
> This attribute will be emitted to dwarf ([2]) and pahole
> will convert it to BTF. Or for bpf target, this
> attribute will be emitted to BTF directly ([3]).
> The attribute is intended to provide additional
> information for
> - struct/union type or struct/union member
> - static/global variables
> - static/global function or function parameter.
>
> This new attribute can be used to add attributes
> to kernel codes, e.g., pre- or post- conditions,
> allow/deny info, or any other info in which only
> the kernel is interested. Such attributes will
> be processed by clang frontend and emitted to
> dwarf, converting to BTF by pahole. Ultimiately
> the verifier can use these information for
> verification purpose.
>
> The new attribute can also be used for bpf
> programs, e.g., tagging with __user attributes
> for function parameters, specifying global
> function preconditions, etc. Such information
> may help verifier to detect user program
> bugs.
>
> After this series, pahole dwarf->btf converter
> will be enhanced to support new llvm tag
> for btf_tag attribute. With pahole support,
> we will then try to add a few real use case,
> e.g., __user/__rcu tagging, allow/deny list,
> some kernel function precondition, etc,
> in the kernel.
We are looking into implementing this in the GCC BPF port.
Supporting the new C attribute in BPF programs as a target-specific
attribute, and the new BTF kind, is straightforward enough.
However, I am afraid it will be difficult to upstream to GCC support for
a target-independent C attribute called `btf_tag' that emits a
LLVM-specific DWARF tag. Even if we proposed to use a GCC-specific
DWARF tag like DW_TAG_GNU_annotation using the same number, or better a
compiler neutral tag like DW_TAG_annotation or DW_TAG_BPF_annotation,
adding such an attribute for all targets would still likely to be much
controversial...
Would you be open to explore other, more generic, ways to convey these
annotations to pahole, something that could be easily supported by GCC,
and potentially other C compilers?
next prev parent reply other threads:[~2021-09-09 22:46 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-07 23:00 [PATCH bpf-next 0/9] bpf: add support for new btf kind BTF_KIND_TAG Yonghong Song
2021-09-07 23:00 ` [PATCH bpf-next 1/9] bpf: " Yonghong Song
2021-09-09 5:09 ` Andrii Nakryiko
2021-09-10 15:55 ` Yonghong Song
2021-09-07 23:01 ` [PATCH bpf-next 2/9] libbpf: rename btf_{hash,equal}_int to btf_{hash,equal}_int_tag Yonghong Song
2021-09-09 5:10 ` Andrii Nakryiko
2021-09-07 23:01 ` [PATCH bpf-next 3/9] libbpf: add support for BTF_KIND_TAG Yonghong Song
2021-09-09 5:26 ` Andrii Nakryiko
2021-09-10 16:04 ` Yonghong Song
2021-09-07 23:01 ` [PATCH bpf-next 4/9] bpftool: " Yonghong Song
2021-09-09 5:28 ` Andrii Nakryiko
2021-09-09 5:33 ` Andrii Nakryiko
2021-09-10 16:38 ` Yonghong Song
2021-09-10 18:05 ` Andrii Nakryiko
2021-09-10 16:04 ` Yonghong Song
2021-09-07 23:01 ` [PATCH bpf-next 5/9] selftests/bpf: test libbpf API function btf__add_tag() Yonghong Song
2021-09-09 5:35 ` Andrii Nakryiko
2021-09-10 16:39 ` Yonghong Song
2021-09-07 23:01 ` [PATCH bpf-next 6/9] selftests/bpf: add BTF_KIND_TAG unit tests Yonghong Song
2021-09-07 23:01 ` [PATCH bpf-next 7/9] selftests/bpf: test BTF_KIND_TAG for deduplication Yonghong Song
2021-09-07 23:01 ` [PATCH bpf-next 8/9] selftests/bpf: add a test with a bpf program with btf_tag attributes Yonghong Song
2021-09-09 5:39 ` Andrii Nakryiko
2021-09-07 23:01 ` [PATCH bpf-next 9/9] docs/bpf: add documentation for BTF_KIND_TAG Yonghong Song
2021-09-09 5:42 ` Andrii Nakryiko
2021-09-10 16:40 ` Yonghong Song
2021-09-10 18:05 ` Andrii Nakryiko
2021-09-09 22:45 ` Jose E. Marchesi [this message]
2021-09-09 23:30 ` [PATCH bpf-next 0/9] bpf: add support for new btf kind BTF_KIND_TAG Yonghong Song
2021-09-10 2:19 ` Jose E. Marchesi
2021-09-10 7:04 ` Yonghong Song
2021-09-10 8:31 ` Jose E. Marchesi
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