Address 0 is a legal fetch address. The question is can I get away with not worrying about what is in the source address register? What, for example, if it points to a non-address or to something that happens to be fetch-protected. (Code is 64-bit FWIW, but I doubt that matters, other than increasing the number of potential invalid addresses.)
Obviously not the world's biggest deal, of course. One LHI R2,0 every now and then is not going to kill me. Charles -----Original Message----- From: IBM Mainframe Assembler List [mailto:[email protected]] On Behalf Of Gary Freestone Sent: Thursday, August 17, 2017 10:07 AM To: [email protected] Subject: Re: Source address significance for clearing MVCL Yes, I do believe you are correct. Checked a bit of old code for clearing an area and both source addr and length are 0 Regards, Gary Freestone -----Original Message----- From: IBM Mainframe Assembler List [mailto:[email protected]] On Behalf Of Charles Mills Sent: Thursday, 17 August 2017 11:01 PM To: [email protected] Subject: Source address significance for clearing MVCL I don't see this explicitly in the PoOp. Is my recollection correct? That for a "pure clearing" MVCL (source length zero, destination length non-zero) the contents of source address register R2 are not significant, and a specification or access exception on the source address is not possible?
