[libunwind] How does libunwind find the PFS, the return address and the alloc instruction?

[Johan Walles]

When unwinding the stack on IA64, how does libunwind find the alloc instruction, 
the register in which the PFS is stored, and the register in which the return 
address is stored?

More specifically, regarding the dynamic unwinding, do I need to tell libunwind 
about these things, or does it figure them out by itself (by disassembling the 
function)?

  Cheers //Johan