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Re: Conflict between MIPS PLTS and abicalls stubs


From: Colin Burgess
Subject: Re: Conflict between MIPS PLTS and abicalls stubs
Date: Wed, 25 Mar 2009 22:46:26 -0400
User-agent: Thunderbird 2.0.0.21 (X11/20090318)

BTW - I'm not sure of the protocol - should this have been sent via the 
development list or entered into bugzilla?

Regards,

Colin

Colin Burgess wrote:
We have an issue where a nonPIC binary that is

* calling a function in a shared object
* calling another function in a shared object, which references the address of the first function, saving it as a function pointer. * later, calling yet another function (in a shared object) which invokes the function pointer.

Because the executable itself doesn't refer directly to the address of the function, an abicalls stub is generated. However, since the canonical address of the function is, as I understand it, the address of the stub in the executable's .MIPS.stubs section, when the function invocation is performed it will mess up because the $gp is pointing at the shared objects got, whereas the stub assumes that it points at the executables got.

If a the address of the function is taken in the executable, then all is well since this generates a PLT
entry with STO_MIPS_PLT.

Attached is an example application, which I've tried to comment as clearly as possible.

This is with binutils 2.19, under QNX 6.4.1

Regards,

Colin


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