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Date:   Fri, 30 Sep 2022 15:39:53 +0530
From:   "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>
Subject: Re: [PATCH] scripts/faddr2line: Fix regression in name resolution on
 ppc64le
To:     Thadeu Lima de Souza Cascardo <cascardo@canonical.com>,
        Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc:     Jiri Olsa <jolsa@kernel.org>, Josh Poimboeuf <jpoimboe@redhat.com>,
        LKML <linux-kernel@vger.kernel.org>,
        linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
        Peter Zijlstra <peterz@infradead.org>
References: <20220927075211.897152-1-srikar@linux.vnet.ibm.com>
        <YzLcPZYTWXfrU+K4@quatroqueijos.cascardo.eti.br>
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Thadeu Lima de Souza Cascardo wrote:
> On Tue, Sep 27, 2022 at 01:22:11PM +0530, Srikar Dronamraju wrote:
>> Commit 1d1a0e7c5100 ("scripts/faddr2line: Fix overlapping text section f=
ailures")
>> can cause scripts/faddr2line to fail on ppc64le machines on few
>> distributions, while working on other distributions. The failure can be
>> attributed to difference in readelf output on various distributions.
>>=20
>> $ ./scripts/faddr2line vmlinux find_busiest_group+0x00
>> no match for find_busiest_group+0x00
>>=20
>> Expected output was:
>> $ ./scripts/faddr2line vmlinux find_busiest_group+0x00
>> find_busiest_group+0x00/0x3d0:
>> find_busiest_group at kernel/sched/fair.c:9595
>>=20
>> On ppc64le, readelf adds localentry tag before the symbol name on few
>> distributions and adds the localentry tag after the symbol name on few
>> other distributions. This problem has been discussed in the reference
>> URL given below. This problem can be overcome by filtering out
>> localentry tags in readelf output. Similar fixes are already present in
>> kernel by way of commits:
>>=20
>> 1fd6cee127e2 ("libbpf: Fix VERSIONED_SYM_COUNT number parsing")
>> aa915931ac3e ("libbpf: Fix readelf output parsing for Fedora")
>>=20
>> Fixes: 1d1a0e7c5100 ("scripts/faddr2line: Fix overlapping text section f=
ailures")
>> Reference: https://lore.kernel.org/bpf/20191211160133.GB4580@calabresa/
>> Cc: "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>
>> Cc: Jiri Olsa <jolsa@kernel.org>
>> Cc: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
>=20
> Reviewed-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
>=20
> The other instances of readelf --wide on faddr2line use --section-headers=
 and
> should not required the same mangling.

There's one usage of readelf with --file-header in faddr2line which also=20
doesn't need this. The extra information being printed is from st_other=20
and is very specific to the symbol table.

Acked-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>


- Naveen