Edward Jaffe <[email protected]> wrote > On 4/10/2012 11:31 AM, McKown, John wrote: >> But that made me wonder why the z/Architecture does not specify that the >> contents of the AR register associated with the link register in any of >> the "branch and link" type instructions: BALR, BASR, BRAS, BRASL, and >> BASSM will be set to 0? >> >> Anybody have any idea why these type of instructions don't set the AR? > > Unnecessary. Instruction fetch is always from the primary address space.
No, in Home-space mode instructions are fetched from the HASN. Since you can't branch out of the current address space with any of the instructions you listed, there is no reason to test or manipulate the AR.
