PowerPC context switch question

[dufault at hda.com (Peter Dufault)]

What does the stwu/ldzu do for us in _CPU_Context_switch()?  I know  
what it's doing, I'm interested in knowing why.
I assume it's setting up for the upcoming dcbz, right?  Why do we do  
the dcbz there?  The next instruction won't start pulling that in  
anyway?  Are there alignment assumptions on the context area?

That sudden switch to "OFFSET-GP_18" had me puzzled for a while.

Peter