Re: [PATCH v4 00/28] objtool: Function validation tracing

[Alexandre Chartre]

On 11/17/25 13:37, David Laight wrote:
> On Mon, 17 Nov 2025 10:47:06 +0100
> Alexandre Chartre <alexandre.chartre@xxxxxxxxxx> wrote:
>
> > On 11/17/25 10:42, David Laight wrote:
> ...
> > > Although I think there ought to be some indication of the 31 NOP bytes
> > > at the end of the middle alternative.
> >
> > I am now compacting the code by removing all trailing NOPs. I should probably
> > improve that with printing the actual number of NOPs, for example NOP31 (or nop31)
>
> That is the sort of thing I was thinking of.
> Perhaps the actual opcodes on one line - eg: NOP5; NOP5; NOP5; NOP1

That might not always be very compact. For example __switch_to_asm() has 41 NOP1.
I will use NOP<n> for now, and we can improve later.

 
> > > I'd also decode those callq as 'callq .+6' - not sure what other people think?
> > > It is rather specific to that code.
> >
> > This is done by libopcodes. I will need to check if there is an option to display
> > the branch distance instead of the branch target.
>
> The 'problem' is that mostly you want the branch target - except when it is small.
> Then you don't need both 'address' and 'symbol+offset', and it is quicker to find
> the target by looking at the branch distance.
> I'm not sure how you'd please everyone :-)
>
> I'm sure one of the disassemblers ends up giving you the target address in a form
> that isn't on the instruction line!
> I've definitely counted opcode bytes to find the target.

I will investigate this for a later patch. Maybe have both the distance and the
destination (could be an option?).

Thanks,

alex.