netdev - Re: [PATCH bpf-next] kbuild: add ability to generate BTF type info for vmlinux

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Date:   Wed, 3 Apr 2019 01:00:35 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     andrii.nakryiko@...il.com, bpf@...r.kernel.org,
        netdev@...r.kernel.org, kernel-team@...com
Cc:     Andrii Nakryiko <andriin@...com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Alexei Starovoitov <ast@...com>, Yonghong Song <yhs@...com>,
        Martin KaFai Lau <kafai@...com>
Subject: Re: [PATCH bpf-next] kbuild: add ability to generate BTF type info
 for vmlinux

On 04/02/2019 06:49 PM, andrii.nakryiko@...il.com wrote:
> From: Andrii Nakryiko <andriin@...com>
> 
> This patch adds new config option to trigger generation of BTF type
> information from DWARF debuginfo for vmlinux and kernel modules through
> pahole, which in turn relies on libbpf for btf_dedup() algorithm.
> 
> The intent is to record compact type information of all types used
> inside kernel, including all the structs/unions/typedefs/etc. This
> enables BPF's compile-once-run-everywhere ([0]) approach, in which
> tracing programs that are inspecting kernel's internal data (e.g.,
> struct task_struct) can be compiled on a system running some kernel
> version, but would be possible to run on other kernel versions (and
> configurations) without recompilation, even if the layout of structs
> changed and/or some of the fields were added, removed, or renamed.
> 
> This is only possible if BPF loader can get kernel type info to adjust
> all the offsets correctly. This patch is a first time in this direction,
> making sure that BTF type info is part of Linux kernel image in
> non-loadable ELF section.
> 
> BTF deduplication ([1]) algorithm typically provides 100x savings
> compared to DWARF data, so resulting .BTF section is not big as is
> typically about 2MB in size.
> 
> [0] http://vger.kernel.org/lpc-bpf2018.html#session-2
> [1] https://facebookmicrosites.github.io/bpf/blog/2018/11/14/btf-enhancement.html
> 
> Cc: Masahiro Yamada <yamada.masahiro@...ionext.com>
> Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
> Cc: Daniel Borkmann <daniel@...earbox.net>
> Cc: Alexei Starovoitov <ast@...com>
> Cc: Yonghong Song <yhs@...com>
> Cc: Martin KaFai Lau <kafai@...com>
> Signed-off-by: Andrii Nakryiko <andriin@...com>

LGTM! As subject is targetting bpf-next this time since this BPF-related patch
in this form has been sitting on the list for over 1.5months, I've taken it in
there now, thanks!