On Mon, 17 Oct 2016 10:08:50 -0700, Ed Jaffe wrote:
>>
>> Hmmm... What happens if AMODE 31 code issues LRA and the real address
>> is above the bar?  Program check?  Or does LRA simply (always?) load a
>> 64-bit register?  Is there an LRAG instruction?
>
>Why not take at least a cursory glance at Principles of Operation before
>asking such questions publicly?
> 
You're right; thanks.  GIMF.  (Oops; the Urban Dictionary says that doesn't
mean what I expected.)  I find:
    z/OS 2.2.0
    z/OS MVS
    z/OS MVS Programming: Assembler Services Guide
    Understanding 31-bit addressing
    Understanding the use of central storage
    Central storage considerations for user programs
    Load real address (LRA) instruction

Woe be unto anyone who did LRA; LA in AMODE 24  (But why?.  And it
doesn't discuss AR mode.  Perhaps elsewhere, but my curiosity is exhausted.

Which leaves a historical question.  Was AMODE 31 antedated by the
availability of real storage >16 MiB, or was AMODE 64 antedated by
the availability of real storage >2GiB?  How did LRA(G) operate in
those eras?

And in a virtual guest with shadow page tables, does LRA return the
real real address or a virtual real address?  I suppose it's all emulated
by CP anyway, so it depends.  Or maybe SIE.  My head hurts.

Thanks,
gil

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