From: Milian Wolff <mail@milianw.de>
To: Mark Wielaard <mark@klomp.org>
Cc: elfutils-devel@sourceware.org
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_
Right?
> 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.
Cheers
--
Milian Wolff
mail@milianw.de
http://milianw.de
next prev parent 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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