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Re: gcc and -fPIC
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