netdev - Re: [PATCH bpf-next] tools/resolve_btfids: Fix sections with wrong alignment

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Date:   Wed, 19 Aug 2020 14:32:19 -0700
From:   Yonghong Song <yhs@...com>
To:     Jiri Olsa <jolsa@...nel.org>, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>
CC:     Mark Wielaard <mjw@...hat.com>, Nick Clifton <nickc@...hat.com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        <netdev@...r.kernel.org>, <bpf@...r.kernel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>,
        Andrii Nakryiko <andriin@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>
Subject: Re: [PATCH bpf-next] tools/resolve_btfids: Fix sections with wrong
 alignment



On 8/19/20 2:23 AM, Jiri Olsa wrote:
> The data of compressed section should be aligned to 4
> (for 32bit) or 8 (for 64 bit) bytes.
> 
> The binutils ld sets sh_addralign to 1, which makes libelf
> fail with misaligned section error during the update as
> reported by Jesper:
> 
>     FAILED elf_update(WRITE): invalid section alignment
> 
> While waiting for ld fix, we can fix compressed sections
> sh_addralign value manually.
> 
> Adding warning in -vv mode when the fix is triggered:
> 
>    $ ./tools/bpf/resolve_btfids/resolve_btfids -vv vmlinux
>    ...
>    section(36) .comment, size 44, link 0, flags 30, type=1
>    section(37) .debug_aranges, size 45684, link 0, flags 800, type=1
>     - fixing wrong alignment sh_addralign 16, expected 8
>    section(38) .debug_info, size 129104957, link 0, flags 800, type=1
>     - fixing wrong alignment sh_addralign 1, expected 8
>    section(39) .debug_abbrev, size 1152583, link 0, flags 800, type=1
>     - fixing wrong alignment sh_addralign 1, expected 8
>    section(40) .debug_line, size 7374522, link 0, flags 800, type=1
>     - fixing wrong alignment sh_addralign 1, expected 8
>    section(41) .debug_frame, size 702463, link 0, flags 800, type=1
>    section(42) .debug_str, size 1017571, link 0, flags 830, type=1
>     - fixing wrong alignment sh_addralign 1, expected 8
>    section(43) .debug_loc, size 3019453, link 0, flags 800, type=1
>     - fixing wrong alignment sh_addralign 1, expected 8
>    section(44) .debug_ranges, size 1744583, link 0, flags 800, type=1
>     - fixing wrong alignment sh_addralign 16, expected 8
>    section(45) .symtab, size 2955888, link 46, flags 0, type=2
>    section(46) .strtab, size 2613072, link 0, flags 0, type=3
>    ...
>    update ok for vmlinux
> 
> Another workaround is to disable compressed debug info data
> CONFIG_DEBUG_INFO_COMPRESSED kernel option.
> 
> Fixes: fbbb68de80a4 ("bpf: Add resolve_btfids tool to resolve BTF IDs in ELF object")
> Cc: Mark Wielaard <mjw@...hat.com>
> Cc: Nick Clifton <nickc@...hat.com>
> Reported-by: Jesper Dangaard Brouer <brouer@...hat.com>
> Signed-off-by: Jiri Olsa <jolsa@...nel.org>

Acked-by: Yonghong Song <yhs@...com>