want to clarify powerpc assembly conventions in head.S and entry.S

[Chris Friesen]

I'm doing some work in head.S and entry.S, and I just wanted to make 
sure that I had the conventions down.

According to the docs I read, r0 and r3-12 are caller-saves.  They seem 
to be saved in EXCEPTION_PROLOG_2 (head.S) and restored in 
ret_from_except() (entry.S).  Thus, if I add code in entry.S I should be 
able to use any of those registers, without having to worry about 
restoring them myself--correct?

Also, I'm a bit confused about the three instances of the following line 
in entry.S:

	stwcx.	r0,0,r1			/* to clear the reservation */

I don't see the corresponding lwarx instruction.  What reservation is it 
referring to?

Thanks,

Chris
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