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Re: Uncovered NOP runs
- From: Ulrich Drepper <drepper at redhat dot com>
- To: elfutils-devel at lists dot fedorahosted dot org
- Date: Wed, 04 Feb 2009 08:24:16 -0800
- Subject: Re: Uncovered NOP runs
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Petr Machata wrote:
> First, is it
> OK for the producer to leave NOP runs alone?
Yes.
> If yes, dwarflint
> shouldn't warn about it, but then there is a problem of how to detect this.
These areas are not covered by any symbol. In correctly written code
the size associated with a symbol extends to just past the last
instruction. In asm code this is done using the .size pseudo-op. Take
a look at what the compiler generates.
> 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).
Actually, the NOPs are not emitted literally. They are the result of an
.align pseudo-op in asm code and aligning of sections in the linker.
> 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?
Actually, I think we'll have to do this work before stripping. The
reason is simple: the stripping has to be reversable. That's not
possible after the compression.
- --
➧ Ulrich Drepper ➧ Red Hat, Inc. ➧ 444 Castro St ➧ Mountain View, CA ❖
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