On Tue, 4 Nov 2014 20:27:09 -0700 Paul Gilmartin <[email protected]> wrote:
:>On 2014-11-04, at 19:25, Chuck Arney wrote: :>> A 64-bit address is only ambiguous when the high word is zero and the high bit of the low word is on. When the high word is non-zero all 32 bits of the low word can address storage locations without ambiguity. :>I'm not sure why you're even discussing 64 bit addresses when in :>in AMODE 31. Isn't that a contradiction in terms? :>How do VM and Linux, which I understand to not block that range of :>addresses deal with the problem? :>Isn't there a bit in the old PSW that distinguishes between :>AMODE 31 and AMODE 64? :>Give me more context. Where might I encounter a 64-bit address :>such as 0000 0000 8000 1000 and be uncertain whether it was to :>be interpreted in AMODE 31 or AMODE 64? Never. The issue is addresses accesses via L when in 64-bit mode. There are various conventions where setting the high order bit is meaningful such as the end of a parmlist or indicating that the routine expects to be called in 31 bit mode. Until the code is changed to use LLGT(r) to clean the high order bit, it was felt that it was better to force an abend (by not allowing virtual addresses in that range to be assigned) rather than allow erroneous access to the wrong storage.. -- Binyamin Dissen <[email protected]> http://www.dissensoftware.com Director, Dissen Software, Bar & Grill - Israel Should you use the mailblocks package and expect a response from me, you should preauthorize the dissensoftware.com domain. I very rarely bother responding to challenge/response systems, especially those from irresponsible companies.
