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

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Date:   Mon, 9 Jan 2023 18:12:47 +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()

Hi Ingo, Happy New Year!

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>

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/ 



Thanks for reviewing!

- Sathvika