linux-kernel - Re: [PATCH] objtool: continue if find_insn() fails in decode

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Date:   Mon, 9 Jan 2023 23:04:26 +0530
From:   Sathvika Vasireddy <sv@...ux.ibm.com>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        jpoimboe@...hat.com, peterz@...radead.org, aik@...abs.ru,
        mpe@...erman.id.au, mingo@...hat.com, christophe.leroy@...roup.eu,
        mbenes@...e.cz, npiggin@...il.com, chenzhongjin@...wei.com,
        sfr@...b.auug.org.au, naveen.n.rao@...ux.vnet.ibm.com,
        Sathvika Vasireddy <sv@...ux.ibm.com>
Subject: Re: [PATCH] objtool: continue if find_insn() fails in
 decode_instructions()


On 09/01/23 22:23, Ingo Molnar wrote:
> * Sathvika Vasireddy <sv@...ux.ibm.com> wrote:
>
>> Hi Ingo, Happy New Year!
> Happy New Year to you too! :-)
>
>> On 07/01/23 15:51, Ingo Molnar wrote:
>>> * Sathvika Vasireddy <sv@...ux.ibm.com> wrote:
>>>
>>>> Currently, decode_instructions() is failing if it is not able to find
>>>> instruction, and this is happening since commit dbcdbdfdf137b4
>>>> ("objtool: Rework instruction -> symbol mapping") because it is
>>>> expecting instruction for STT_NOTYPE symbols.
>>>>
>>>> Due to this, the following objtool warnings are seen:
>>>>    [1] arch/powerpc/kernel/optprobes_head.o: warning: objtool: optprobe_template_end(): can't find starting instruction
>>>>    [2] arch/powerpc/kernel/kvm_emul.o: warning: objtool: kvm_template_end(): can't find starting instruction
>>>>    [3] arch/powerpc/kernel/head_64.o: warning: objtool: end_first_256B(): can't find starting instruction
>>>>
>>>> The warnings are thrown because find_insn() is failing for symbols that
>>>> are at the end of the file, or at the end of the section. Given how
>>>> STT_NOTYPE symbols are currently handled in decode_instructions(),
>>>> continue if the instruction is not found, instead of throwing warning
>>>> and returning.
>>>>
>>>> Signed-off-by: Naveen N. Rao <naveen.n.rao@...ux.vnet.ibm.com>
>>>> Signed-off-by: Sathvika Vasireddy <sv@...ux.ibm.com>
>>> The SOB chain doesn't look valid: is Naveen N. Rao, the first SOB line, the
>>> author of the patch? If yes then a matching From: line is needed.
>>>
>>> Or if two people developed the patch, then Co-developed-by should be used:
>>>
>>>           Co-developed-by: First Co-Author <first@...uthor.example.org>
>>>           Signed-off-by: First Co-Author <first@...uthor.example.org>
>>>           Co-developed-by: Second Co-Author <second@...uthor.example.org>
>>>           Signed-off-by: Second Co-Author <second@...uthor.example.org>
>>>
>>> [ In this SOB sequence "Second Co-Author" is the one who submits the patch. ]
>>>
>>> [ Please only use Co-developed-by if actual lines of code were written by
>>>     the co-author that created copyrightable material - it's not a courtesy
>>>     tag. Reviewed-by/Acked-by/Tested-by can be used to credit non-code
>>>     contributions. ]
>> Thank you for the clarification, and for bringing these points to my
>> attention. I'll keep these things in mind. In this case, since both Naveen
>> N. Rao and I developed the patch, the below tags
>> are applicable.
>>
>>          Co-developed-by: First Co-Author <first@...uthor.example.org>
>>          Signed-off-by: First Co-Author <first@...uthor.example.org>
>>          Co-developed-by: Second Co-Author <second@...uthor.example.org>
>>          Signed-off-by: Second Co-Author <second@...uthor.example.org>
> ... while filling in your real names & email addresses I suppose. ;-)
Indeed :-)
>
>> However, I would be dropping this particular patch, since I think Nick's
>> patch [1] is better to fix the objtool issue.
>>
>> [1] - https://lore.kernel.org/linuxppc-dev/20221220101323.3119939-1-npiggin@gmail.com/
> Ok, I'll pick up Nick's fix, with these tags added for the PowerPC
> regression aspect and your review:
>
>    Reported-by: Naveen N. Rao <naveen.n.rao@...ux.vnet.ibm.com>
>    Reported-by: Sathvika Vasireddy <sv@...ux.ibm.com>
>    Acked-by: Sathvika Vasireddy <sv@...ux.ibm.com>
>
> To document & credit the efforts of your patch.

Sure, thank you!

- Sathvika