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From: mao@postgres.berkeley.edu (Mike Olson)
Newsgroups: comp.sys.dec
Subject: unaligned data access on DS3100's
Message-ID: <23185@pasteur.Berkeley.EDU>
Date: 17 Mar 90 23:45:49 GMT
Sender: news@pasteur.Berkeley.EDU
Reply-To: mao@eden.berkeley.edu (Mike Olson)
Distribution: usa
Organization: University of California, Berkeley
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we're running Ultrix Worksystem V2.0 (Rev. 7) on decstation 3100's here.
we're porting code developed on other systems, and have pretty consistent
problems with alignment assumptions that were made in the original code.
we want to fix those now.

when a program makes a misaligned memory reference, the kernel prints the
message

	Fixed up unaligned data access for pid XXXXX (...) at pc 0x40ae14

and permits the program to continue running.  there's clearly some sort of
exception handler taking care of this.  i'd like that exception handler to
behave differently.  rather than fixing the ref, i'd like it to dump core
and let me deal with the problem myself.

is this configurable?  i'm surprised that this behavior is the default; it
seems to me pretty easy to guess wrong when you're twiddling pointers on
behalf of a user program at runtime.  i know that i could fire up the
program under dec's dbx and use stopi, but that's pretty messy if the
alignment is only occasionally bad at a particular point in the code.

if anyone knows how to defeat this behavior, i would appreciate hearing about
it.
					mike olson
					postgres research group
					uc berkeley
					mao@postgres.Berkeley.EDU