From:	SMTP%"RELAY-INFO-VAX@CRVAX.SRI.COM" 20-OCT-1993 08:20:57.49
To:	EVERHART
CC:	
Subj:	Re: AXP special kernel ASTs

X-Newsgroups: comp.os.vms
From: dipirro@star.enet.dec.com (Steve DiPirro)
Subject: Re: AXP special kernel ASTs
Message-ID: <1993Oct19.175312.4706@nntpd.lkg.dec.com>
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Organization: Digital Equipment Corporation
Date: Tue, 19 Oct 1993 17:52:30 GMT
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To: Info-VAX@CRVAX.SRI.COM
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In article <931018163520.60@arisia.gce.com>, EVERHART@arisia.gce.com writes...
>It is still perfectly feasible to send special kernel ASTs on AXP;
>they work much the same as on VAX. What is NOT feasible without
>significant macro-64 hooks is grabbing a chunk of pool, copying code
>into it, and firing off ASTs into it and getting the code to do the
>same to get back...

While everything he said is true, I thought I'd point out a couple
of other differences. First, on AXP in the release following V1.5,
special kernel mode AST routines can be standard calls as well as the
older-style JSB interfaces. So you can use a C routine without any
special routine linkage as a special kernel mode AST.

Also, in *most* instances, people used the technique described above
(allocating pool, copying code into it, firing it off as an AST to
another process) to read and/or write memory (P0/P1 space) in the
context of another process. If that's all you need to do (and you
obviously have the privileges, etc. to run in kernel mode to start
with), there are new exec routines which do precisely that. They do
the work for you in order to read and write memory in the context of
another process. In fact, they'll do registers (GPRs) too. The routines
are called EXE$READ_PROCESS and EXE$WRITE_PROCESS and must be called
from kernel mode at IPL 0 to work. Linking /SYSEXE will resolve them.
The interfaces can be found in the PROC_READ_WRITE module in SYS for
those of you with listing/source kits.

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Steve DiPirro        dipirro@star.enet.dec.com

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