netdev - Re: [PATCHv4 0/2] libbpf: Add support to use optional extended section index table

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Date:   Wed, 27 Jan 2021 07:38:56 -0500
From:   Joe Lawrence <joe.lawrence@...hat.com>
To:     Jiri Olsa <jolsa@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andriin@...com>
Cc:     dwarves@...r.kernel.org, netdev@...r.kernel.org,
        bpf@...r.kernel.org, Yonghong Song <yhs@...com>,
        Hao Luo <haoluo@...gle.com>, Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>, Mark Wielaard <mjw@...hat.com>
Subject: Re: [PATCHv4 0/2] libbpf: Add support to use optional extended
 section index table

On 1/24/21 5:15 PM, Jiri Olsa wrote:
> hi,
> kpatch guys hit an issue with pahole over their vmlinux, which
> contains many (over 100000) sections, pahole crashes.
> 
> With so many sections, ELF is using extended section index table,
> which is used to hold values for some of the indexes and extra
> code is needed to retrieve them.
> 
> This patchset adds the support for pahole to properly read string
> table index and symbol's section index, which are used in btf_encoder.
> 
> This patchset also adds support for libbpf to properly parse .BTF
> section on such object.
> 
> This patchset is based on previously posted fix [1].
> 
> v4 changes:
>    - use size_t instead of Elf32_Word [Andrii]
>    - move elf_symtab__for_each_symbol_index and elf_sym__get
>      elf_symtab.h [Andrii]
>    - added ack for patch 1 [Andrii]
>    - changed elf_sym__get to be simpler [Andrii]
>    - changed elf_symtab__for_each_symbol_index to skip bad symbols
>    - use zalloc for struct elf_symtab allocation to get zero
>      initialized members
> 
> v3 changes:
>    - directly bail out for !str in elf_section_by_name [Andrii]
>    - use symbol index in collect_function [Andrii]
>    - use symbol index in collect_percpu_var
>    - change elf_symtab__for_each_symbol_index, move elf_sym__get
>      to for's condition part
>    - libbpf patch got merged
> 
> v2 changes:
>    - many variables renames [Andrii]
>    - use elf_getshdrstrndx() unconditionally [Andrii]
>    - add elf_symtab__for_each_symbol_index macro [Andrii]
>    - add more comments [Andrii]
>    - verify that extended symtab section type is SHT_SYMTAB_SHNDX [Andrii]
>    - fix Joe's crash in dwarves build, wrong sym.st_shndx assignment
> 
> thanks,
> jirka
> 
> 
> [1] https://lore.kernel.org/bpf/20210113102509.1338601-1-jolsa@kernel.org/
> ---
> Jiri Olsa (2):
>        elf_symtab: Add support for SHN_XINDEX index to elf_section_by_name
>        bpf_encoder: Translate SHN_XINDEX in symbol's st_shndx values
> 
>   btf_encoder.c | 33 +++++++++++++++++----------------
>   dutil.c       |  8 +++++++-
>   elf_symtab.c  | 41 +++++++++++++++++++++++++++++++++++++++--
>   elf_symtab.h  | 29 +++++++++++++++++++++++++++++
>   4 files changed, 92 insertions(+), 19 deletions(-)
> 

For v4 patchset:

Tested-by: Joe Lawrence <joe.lawrence@...hat.com>

Thanks Jiri!

-- Joe