linux-kernel - Re: [PATCH v2] powerpc: Do not consider weak unresolved symbol relocations as bad

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Date:   Fri, 31 Jan 2020 20:18:25 +1100
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Alex Ghiti <alex@...ti.fr>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Alexei Starovoitov <ast@...nel.org>,
        linux-next@...r.kernel.org, Zong Li <zong.li@...ive.com>,
        Palmer Dabbelt <palmerdabbelt@...gle.com>
Subject: Re: [PATCH v2] powerpc: Do not consider weak unresolved symbol relocations as bad

Alex Ghiti <alex@...ti.fr> writes:
> On 1/18/20 12:03 PM, Alexandre Ghiti wrote:
>> Commit 8580ac9404f6 ("bpf: Process in-kernel BTF") introduced two weak
>> symbols that may be unresolved at link time which result in an absolute
>> relocation to 0. relocs_check.sh emits the following warning:
>>
>> "WARNING: 2 bad relocations
>> c000000001a41478 R_PPC64_ADDR64    _binary__btf_vmlinux_bin_start
>> c000000001a41480 R_PPC64_ADDR64    _binary__btf_vmlinux_bin_end"
>>
>> whereas those relocations are legitimate even for a relocatable kernel
>> compiled with -pie option.
>>
>> relocs_check.sh already excluded some weak unresolved symbols explicitly:
>> remove those hardcoded symbols and add some logic that parses the symbols
>> using nm, retrieves all the weak unresolved symbols and excludes those from
>> the list of the potential bad relocations.
>>
>> Reported-by: Stephen Rothwell <sfr@...b.auug.org.au>
>> Signed-off-by: Alexandre Ghiti <alex@...ti.fr>
>> ---
>>
>> Changes in v2:
>> - Follow Stephen advice of using grep -F instead of looping over weak symbols
>>    using read, patch is way smaller and cleaner.
>> - Add missing nm in comment
>>
>>   arch/powerpc/Makefile.postlink     |  4 ++--
>>   arch/powerpc/tools/relocs_check.sh | 20 ++++++++++++--------
>>   2 files changed, 14 insertions(+), 10 deletions(-)
>>
...
>
> Hi guys,
>
>
> Any thought about that ?
>
> I do think this patch makes the whole check about absolute relocations 
> clearer.
> And in the future, it will avoid anyone to spend some time on those 
> "bad" relocations
> which actually aren't.

Sorry I missed the v2. Will pick it up.

cheers