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From: shankar@hpclscu.HP.COM (Shankar Unni)
Newsgroups: comp.sys.hp
Subject: Re: HP PA assembly language question
Message-ID: <1340107@hpclscu.HP.COM>
Date: 6 Mar 90 20:37:47 GMT
References: <564@opus.NMSU.EDU>
Organization: Hewlett-Packard Calif. Language Lab
Lines: 35

> 	BL	target,rp			LDIL	L%target,rp
> 	BLE	R%target(GRr,rp)
> 	OR	GR31,0,rp

This seems to be a typo in the book. The April '89 copy has the following:

call:   BL    target,rp               or      LDIL   l%target,rp
                                              BLE    r%target(sr4,rp)
                                              OR     r31,r0,rp


return: BV    r0(rp)                  or      BE     0(sr0,rp)


This should be a little more clear. In each case, the first alternative is
pretty obvious. In the call case, the second case is a little more
complicated. The BLE instruction has a hardwired link register (r31). Since
the HP calling convention uses r2 as the return register ("rp" is an alias
for "r2"), there is an instruction in the shadow of the BLE to copy r31
into rp before entering the called function.

P.S. The OR r1,r0,rp convention to copy a register into another one is
reflected by the assembler pseudo-op COPY:

     COPY r1,r2  ==  OR r1,r0,r2

-----
Shankar Unni                                   E-Mail: 
Hewlett-Packard California Language Lab.     Internet: shankar@hpda.hp.com
Phone : (408) 447-5797                           UUCP: ...!hplabs!hpda!shankar

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