Re: Uncovered NOP runs

[Roland McGrath <roland at redhat dot com>]

> .debug_arange analysis shows that there's a lot of holes in .text. 
> Turns out these are NOP runs (for alignment purposes, I guess).  First, 
> is it OK for the producer to leave NOP runs alone?  If yes, dwarflint 
> shouldn't warn about it, but then there is a problem of how to detect this.

Like I just posted: don't try anyway.

> I think we can assume that the compiler actually emits literal "NOP" 
> instructions for padding purposes (i.e. not one of these contraptions 
> that look like they do something).  

Nope.  The assembler or linker decides what to fill with, and they can be
clever with fancy multi-byte nop instructions on x86.

> But most of the time, we won't even see contents of .text, will we?  We
> are dealing with stripped debuginfo-only files.  Or are we going to do
> our debuginfo transformation business on full files?

It can be done both ways.  In the rpm build process as eventually revamped,
I think it will be rolled in with the stripping step, so will have full
originals at hand.  But dwarflint should not depend on looking at code
sections at all, I think.


Thanks,
Roland