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

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Message-ID: <Y7xGas4FAHFUtEJE@gmail.com>
Date:   Mon, 9 Jan 2023 17:53:04 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Sathvika Vasireddy <sv@...ux.ibm.com>
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
Subject: Re: [PATCH] objtool: continue if find_insn() fails in
 decode_instructions()


* 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. ;-)

> 
> 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.

Thanks,

	Ingo