Re: gcc and -fPIC

[Gerhard Wiesinger <lists@wiesinger.com>]

On Fri, 15 Oct 2004, Jeffrey A Law wrote:

> 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.
>

OK, I got it now.

Thank you.

Ciao,
Gerhard