From: Jeffrey A Law <law@redhat.com>
To: Gerhard Wiesinger <lists@wiesinger.com>
Cc: gcc-help@gcc.gnu.org
Subject: Re: gcc and -fPIC
Date: Fri, 15 Oct 2004 19:11:00 -0000 [thread overview]
Message-ID: <1097867494.4992.3.camel@localhost.localdomain> (raw)
In-Reply-To: <Pine.LNX.4.61.0410152045110.31053@bbs.intern>
On Fri, 2004-10-15 at 12:51, Gerhard Wiesinger wrote:
> On Fri, 15 Oct 2004 bserdar@nc.rr.com wrote:
>
> >
> >> 80485b3: e8 00 00 00 00 call 80485b8 <X::f()+0xc>
> >> 80485b8: 5b pop %ebx
> >> 80485b9: 81 c3 5c 12 00 00 add $0x125c,%ebx
> >
> > With pop ebx, it pops the eip at that instruction to ebx. I'm guessing it'll use ebx as a base pointer to data (or code?) from this point on. You can verify this guess by accessing some global variables from within X::f() and see whether it uses ebx-relative access.
> >
>
> OK, but why is the function call at 80485b3 to the next address at
> 80485b8?
Because it allows us to get the current PC's value in a position
independent way.
ie, the call pushes the return address onto the stack and we pop
that value into ebx.
jeff
next prev parent reply other threads:[~2004-10-15 19:11 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-10-15 18:26 bserdar
2004-10-15 18:46 ` Dave Korn
2004-10-15 18:51 ` Gerhard Wiesinger
2004-10-15 19:11 ` Jeffrey A Law [this message]
2004-10-15 19:16 ` Gerhard Wiesinger
-- strict thread matches above, loose matches on Subject: below --
2004-10-15 18:58 bserdar
2004-10-15 17:08 Gerhard Wiesinger
2004-10-15 17:54 ` Dave Korn
2004-10-15 19:55 ` Andreas Schwab
2004-10-16 6:06 ` Gerhard Wiesinger
2004-10-16 12:09 ` Andreas Schwab
2004-10-16 15:17 ` Daniel Jacobowitz
2004-10-17 18:57 ` Gerhard Wiesinger
2004-10-17 19:31 ` Daniel Jacobowitz
2004-10-18 5:17 ` Gerhard Wiesinger
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