Reentrancy support for multiprocessor systems

[Likely, Grant]

I'm working on a SMP PowerPC board that has 2 8260s on the same address bus.
The application I'm writing has no OS, so it simply has a seperate thread of
execution running on each of the processors.

The question that I have is with regard to the concurrent support for
reentrancy.  As far as I understand, newlib is fully reentrant providing
that each process has a seperate reentrancy structure, and the pointer to
that structure is stored in _impure_ptr.  The problem lies in the fact that
because the processors are executing concurrently and they share an
identical address space, I need to choose a value for _impure_ptr based on
the processor the code is executing on.  I cannot use the reentrant versions
of the library functions because I'm using a pre-written application in my
threads that I cannot rewrite to use the _r functions.

Is it safe to modify the _impure_ptr pointer to be a macro that calls a
function and returns the correct pointer?  (just like the errno macro?)  Is
there a better way to do this?

Thanks,
g.