Xref: utzoo comp.lang.c:12513 comp.arch:6310
Path: utzoo!attcan!uunet!mcvax!hp4nl!philmds!nlgvax!hans
From: hans@nlgvax.UUCP (Hans Zuidam)
Newsgroups: comp.lang.c,comp.arch
Subject: Re: HP/Rumors
Summary: HP9000/500 pointers
Message-ID: <243@nlgvax.UUCP>
Date: 9 Sep 88 07:54:08 GMT
References: <580@white.gcm> <2327@mhres.mh.nl> <2921@ttrdc.UUCP>
Reply-To: hans@nlgvax.UUCP (Hans Zuidam)
Followup-To: comp.arch
Organization: Philips Research Geldrop
Lines: 41

In article <2921@ttrdc.UUCP> levy@ttrdc.UUCP (Daniel R. Levy) writes:
>In article <2327@mhres.mh.nl>, jv@mhres.mh.nl (Johan Vromans) writes:
>> A quote from the file etc/MACHINES of the GNU 18.50 distribution:
>> 
>>   "The [HP9000] series 500 has a seriously incompatible memory architecture
>>   "which relocates data in memory during execution of a program,
>>   "and support for it would be difficult to implement.

(This is from memory)
When I worked at the Eindhoven University of Technology we had 4 HP9000/500s
and we ported emacs to it.

The real problem (with emacs 16.??) we had was that emacs assumed that a machine
with 32 bit words uses only 24 address bits. The upper 8 were assumed to be free
and available for type tags. In essence, it assumed that all machines have a VAX
like addressing scheme. The HP9000/500 uses all 32 bits. This same problem
occurred every time we tried to port a program which made any assumption on the
format of a pointer.

The "problem" is that the HP9000/500 has a segmented memory architecture. Each
pointer consists of a segment number and a segment offset and then some. At load
time the segments are assigned to the program and each pointer (identified as
such in the load file) is fixed up with the segment number of its associated data.
When you have emacs dump itself to create a faster loadable binary, you would
have to write every pointer back with no segment assigned. For arbitrary pointers
this is a hell of a job.

A colleague of mine succeeded in porting it but without the dump facility. If
you are interrested, you can contact him at the following address:

		Geert Leon Janssen
		Eindhoven University of Technology,
		Department of Electrical Engineering,
		P.O. Box 513,
		5600 MB Eindhoven, The Netherlands.
		(UUCP: ...!mcvax!euteal!geert)
-- 
Hans Zuidam                                    E-Mail: hans@nlgvax.UUCP
Philips Telecommunications and Data Systems,   Tel: +31 40 892288
Project Centre Geldrop, Building XR
Willem Alexanderlaan 7B, 5664 AN Geldrop       The Netherlands