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

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Date:   Wed, 19 Aug 2020 19:36:18 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Yonghong Song <yhs@...com>
Cc:     Jiri Olsa <jolsa@...nel.org>, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        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>,
        Nick Desaulniers <ndesaulniers@...gle.com>
Subject: Re: [PATCH bpf-next] tools/resolve_btfids: Fix sections with wrong
 alignment

On Wed, Aug 19, 2020 at 08:31:51AM -0700, Yonghong Song wrote:
> 
> 
> 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.
> 
> So CONFIG_DEBUG_INFO_COMPRESSED is required to reproduce the bug, right?

correct

> 
> I turned on CONFIG_DEBUG_INFO_COMPRESSED in my config and got a bunch of
> build failures.
> 
> ld: drivers/crypto/virtio/virtio_crypto_algs.o: unable to initialize
> decompress status for section .debug_info
> ld: drivers/crypto/virtio/virtio_crypto_algs.o: unable to initialize
> decompress status for section .debug_info
> ld: drivers/crypto/virtio/virtio_crypto_algs.o: unable to initialize
> decompress status for section .debug_info
> ld: drivers/crypto/virtio/virtio_crypto_algs.o: unable to initialize
> decompress status for section .debug_info
> drivers/crypto/virtio/virtio_crypto_algs.o: file not recognized: File format
> not recognized
> 
> ld: net/llc/llc_core.o: unable to initialize decompress status for section
> .debug_info
> ld: net/llc/llc_core.o: unable to initialize decompress status for section
> .debug_info
> ld: net/llc/llc_core.o: unable to initialize decompress status for section
> .debug_info
> ld: net/llc/llc_core.o: unable to initialize decompress status for section
> .debug_info
> net/llc/llc_core.o: file not recognized: File format not recognized
> 
> ...
> 
> The 'ld' in my system:
> 
> $ ld -V
> GNU ld version 2.30-74.el8
>   Supported emulations:
>    elf_x86_64
>    elf32_x86_64
>    elf_i386
>    elf_iamcu
>    i386linux
>    elf_l1om
>    elf_k1om
>    i386pep
>    i386pe
> $
> 
> Do you know what is the issue here?

mine's: GNU ld version 2.32-31.fc31

there's version info in commit:
  10e68b02c861 Makefile: support compressed debug info

  Compress the debug information using zlib.  Requires GCC 5.0+ or Clang
  5.0+, binutils 2.26+, and zlib.

cc-ing Nick Desaulniers, author of that patch.. any idea about the error above?

thanks,
jirka