netdev - Re: [PATCH] libbpf: fix readelf output parsing on powerpc with recent binutils

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Date:   Tue, 10 Dec 2019 19:25:53 -0300
From:   Thadeu Lima de Souza Cascardo <cascardo@...onical.com>
To:     Justin Forbes <jmforbes@...uxtx.org>
Cc:     Daniel Borkmann <daniel@...earbox.net>,
        Song Liu <songliubraving@...com>,
        Andrii Nakryiko <andriin@...com>,
        Alexei Starovoitov <ast@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "open list:BPF (Safe dynamic programs and tools)" 
        <netdev@...r.kernel.org>, Yonghong Song <yhs@...com>,
        "open list:BPF (Safe dynamic programs and tools)" 
        <bpf@...r.kernel.org>, linuxppc-dev@...ts.ozlabs.org,
        Martin KaFai Lau <kafai@...com>,
        Aurelien Jarno <aurelien@...el32.net>,
        debian-kernel@...ts.debian.org
Subject: Re: [PATCH] libbpf: fix readelf output parsing on powerpc with
 recent binutils

On Tue, Dec 10, 2019 at 12:58:33PM -0600, Justin Forbes wrote:
> On Mon, Dec 2, 2019 at 3:37 AM Daniel Borkmann <daniel@...earbox.net> wrote:
> >
> > On Mon, Dec 02, 2019 at 04:53:26PM +1100, Michael Ellerman wrote:
> > > Aurelien Jarno <aurelien@...el32.net> writes:
> > > > On powerpc with recent versions of binutils, readelf outputs an extra
> > > > field when dumping the symbols of an object file. For example:
> > > >
> > > >     35: 0000000000000838    96 FUNC    LOCAL  DEFAULT [<localentry>: 8]     1 btf_is_struct
> > > >
> > > > The extra "[<localentry>: 8]" prevents the GLOBAL_SYM_COUNT variable to
> > > > be computed correctly and causes the checkabi target to fail.
> > > >
> > > > Fix that by looking for the symbol name in the last field instead of the
> > > > 8th one. This way it should also cope with future extra fields.
> > > >
> > > > Signed-off-by: Aurelien Jarno <aurelien@...el32.net>
> > > > ---
> > > >  tools/lib/bpf/Makefile | 4 ++--
> > > >  1 file changed, 2 insertions(+), 2 deletions(-)
> > >
> > > Thanks for fixing that, it's been on my very long list of test failures
> > > for a while.
> > >
> > > Tested-by: Michael Ellerman <mpe@...erman.id.au>
> >
> > Looks good & also continues to work on x86. Applied, thanks!
> 
> This actually seems to break horribly on PPC64le with binutils 2.33.1
> resulting in:
> Warning: Num of global symbols in sharedobjs/libbpf-in.o (32) does NOT
> match with num of versioned symbols in libbpf.so (184). Please make
> sure all LIBBPF_API symbols are versioned in libbpf.map.
> 
> This is the only arch that fails, with x86/arm/aarch64/s390 all
> building fine.  Reverting this patch allows successful build across
> all arches.
> 
> Justin

Well, I ended up debugging this same issue and had the same fix as Jarno's when
I noticed his fix was already applied.

I just installed a system with the latest binutils, 2.33.1, and it still breaks
without such fix. Can you tell what is the output of the following command on
your system?

readelf -s --wide tools/lib/bpf/sharedobjs/libbpf-in.o | cut -d "@" -f1 | sed 's/_v[0-9]_[0-9]_[0-9].*//' | awk '/GLOBAL/ && /DEFAULT/ && !/UND/ {print $0}' 

Cascardo.