netdev - Re: [PATCH bpf-next v2 00/13] bpf: add btf func info support

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Message-ID: <3e873133-bae5-416b-3e75-d4c0622398e6@fb.com>
Date:   Wed, 17 Oct 2018 16:13:08 +0000
From:   Yonghong Song <yhs@...com>
To:     Edward Cree <ecree@...arflare.com>,
        Alexei Starovoitov <ast@...com>, Martin Lau <kafai@...com>,
        "daniel@...earbox.net" <daniel@...earbox.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
CC:     Kernel Team <Kernel-team@...com>
Subject: Re: [PATCH bpf-next v2 00/13] bpf: add btf func info support



On 10/17/18 4:02 AM, Edward Cree wrote:
> I think the BTF work needs to be better documented; at the moment the only way
>   to determine how BTF sections are structured is to read through the headers,
>   and cross-reference with the DWARF spec to guess at the semantics of various
>   fields.  I've been working on adding BTF support to ebpf_asm, and finding
>   very frustrating the amount of guesswork required.
> Therefore please make sure that each patch extending the BTF format includes
>   documentation patches describing both the layout and the semantics of the new

Make sense. I will add some comments to describe the layout in patch #9.

>   extensions.  For example in patch #9 there is no explanation of
>   btf_ext_header.line_info_off and btf_ext_header.line_info_len (they're not
>   even used by the code, so one cannot reverse-engineer it); while it's fairly
>   clear that they indicate the bounds of the line_info subsection, there is no

The line_info field is added because it is implemented in llvm. I 
imported it to kernel tools directory to be compatible with what llvm 
generates although we did not process it yet. I will add a comment on this.

In the long term, I guess we should add description of format etc.
in Documentation/bpf directory like BTF.rst.

>   specification of what this subsection contains.
> 
> -Ed
>