debugging gcc-generated assembly

[Jason Spencer]

Hi, Gang. 
 
I'm trying to chase a nasty bug in code generated by
GCC 2.7.2 on a Motorola PowerPC 603 core.  I have to
understand the register usage conventions the compiler
uses, but I can't find that in any of the docs. 
Specifically, I'm interested in things like which
register is the "this" pointer, which are used for
parameters, return values, etc.  Is there an easily
accessible doc that goes through those details for my
architecture?
 
Thanks.