From mboxrd@z Thu Jan  1 00:00:00 1970
Message-ID: <805e42c0155b88900921831b032c748e@terzarima.net>
From: Charles Forsyth <forsyth@terzarima.net>
Date: Wed, 15 Sep 2010 09:37:50 +0100
To: 9fans@9fans.net
In-Reply-To: <2947a8c22b8274d84c68f633ae888de7@plan9.bell-labs.com>
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Subject: Re: [9fans] c compiler bug
Topicbox-Message-UUID: 5758f198-ead6-11e9-9d60-3106f5b1d025

actually, it gets worse. i looked up the stuff for ARM, and it was much
as i expected, but they also pointed out another problem, obvious in retrospect.
you say you want structure assignments to work, or at least not
fail. fair enough, but what about this:

	S s;
	int *p = &s.c;
	*p = 1;
	int x = *p;

the point is that in general given an int*, there's no way to know that
the target is misaligned. ARM thoughtfully provides a __packed attribute,
as in
	__packed int *p;
and then an appropriate sequence of byte-by-byte loads (or stores) will be
used to access it, but a normal int* will produce an alignment trap.