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From: Milian Wolff <>
To: Mark Wielaard <>
Subject: Re: dwfl_module_addrinfo and @plt entries
Date: Fri, 06 Jan 2017 10:28:00 -0000	[thread overview]
Message-ID: <4367790.cbajsgPFcv@milian-kdab2> (raw)
In-Reply-To: <20170104134223.GN2187@stream>

On Wednesday, January 4, 2017 2:42:23 PM CET Mark Wielaard wrote:
> On Wed, Jan 04, 2017 at 01:41:26AM +0100, Milian Wolff wrote:
> > how do I get symbol information for @plt entries?
> Short answer. You cannot with the dwfl_module_getsym/addr*
> functions. And we don't have accessors for "fake" symbols
> (yet). Sorry.

Thanks for the clarification Mark.

> Longer answer. An address pointing into the PLT does
> really point to an ELF symbol.

You mean: does _not_

> The PLT/GOT contains entries
> that are architecture specific "jump targets" that contain
> (self-modifying) code/data on first access. A PLT entry
> is code that sets up the correct (absolute) address of
> a function on first access. And on second access it fetches
> that function address and jumps to it. Since this is
> architecture specific we would need a backend function
> that translates an address pointing into the PLT into
> an actual function address. You would then be able to
> fetch the actual ELF symbol that address is associated
> with.
> If we have such a backend function then we could even
> do what BFD apparently does. Which is to then create a
> "fake" symbol with as name real_function@plt. But I am
> not sure such fake symbols are very useful (and will
> quickly become confusing since they aren't real ELF
> symbols).

So the objdump command I used is leveraging BFD internally to give me the @plt 
names? I noticed that I also see @plt in perf, which is also probably using 
BFD internally. That at least clarifies why it works in some tools but not in 
when using dwfl.

> Hope that helps. And maybe inspires someone (you?) to
> write up such a backend function and corresponding
> dwfl frontend function.

It does help, thanks. I'm interested in contributing such functionality, but, 
sadly, I'm not sure when I'll get the time to actually do it.


Milian Wolff

  reply	other threads:[~2017-01-06 10:28 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-01-04  0:41 Milian Wolff
2017-01-04 13:42 ` Mark Wielaard
2017-01-06 10:28   ` Milian Wolff [this message]
2017-01-06 19:17     ` Mark Wielaard
2017-07-05 13:34       ` Milian Wolff
2017-07-07 11:03         ` Mark Wielaard
2017-07-10 11:06           ` Milian Wolff
2017-08-28 14:28             ` Milian Wolff

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