ld gas Fake PLT entries and absolute address

["chrima.hercou" <chrima dot hercou at laposte dot net>]

Hi Gnu community !

I've got some questions dealing with particular uses of GAS and LD :
I'm working on a code, in assembly X86-64 which must contains absolute
address of PLT entry. The idea is having something like :

label:
.long functionCall@PLT

later, i will load this address in a register, for an absolute call.

My problems are :
* How can i obtained this address ? For now, i compile the code, look at .plt
section, put the address and recompile it.
* How can i create artificial PLT entry ? For now, i use a declaration like the
'label' one, and put the '--unresolved-symbols=ignore-in-object-files' flag.

So, why this ?
The aim is having instrumentations in the code that are only activated when a
LD_PRELOAD is made. Instrumentations's function reside in PLT entries and the
address for the call (absolute PLT address) resides in particular headers.
It would be nice if i could compile without having to give a fake shared object
for having my PLT entries (and it will not resolve the first problem).

Best regards,
Matth


Une messagerie gratuite, garantie à vie et des services en plus, Ãa vous tente ?
Je crÃe ma boÃte mail www.laposte.net