Re: AR/XM question

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#230

From: Jonathan Scott
Date: Tue, 25 Oct 2005 18:33

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From the example you give, it's not clear whether you've made
sure that AR4 is zero (to access primary) and that AR5 was zero
(before the LAM) so that the ALET constant was also loaded from
primary.  You should normally load them with LAM to make sure,
preferably before switching to AR mode.

If you access your client's address space using a secondary ALET
with SASN=OLD, your server needs AX authority to access the
client address space.  You can avoid this requirement by instead
using a home ALET (value 2), which does not require any special
authority (but of course means that you cannot support calls from
client code which is already running in cross-memory mode, as the
parameters are assumed to be in the home address space rather
than the calling address space).

I'd also like to comment that if something doesn't work in its
original key, switching to key 0 is rarely a good idea!

In most cases, cross-memory server code should run in supervisor
state but key 8, which allows it to access its own private
storage and that of a typical caller without any special key
processing, but means that it can use authorized operating system
services and switch to key 0 temporarily when necessary.

Jonathan Scott
IBM Hursley, UK

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From: Jonathan Scott <jonathan_scott@vnet.ibm.com>
Newsgroups: bit.listserv.asm370
Subject: Re: AR/XM question
Date: Tue, 25 Oct 2005 12:33:48 -0600
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