From owner-freebsd-questions  Fri Sep 24 12:50:48 1999
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Date: Fri, 24 Sep 1999 13:07:30 -0700 (PDT)
From: Alfred Perlstein <bright@wintelcom.net>
To: Zhihui Zhang <zzhang@cs.binghamton.edu>
Cc: freebsd-questions@FreeBSD.ORG
Subject: Re: A program that causes "bus error"
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On Fri, 24 Sep 1999, Zhihui Zhang wrote:

> 
> The following program causes "bus error" on a Sun workstation whether I
> compile it with cc or gcc:
> 
> #include <stdio.h>
> main()
> {
> 	union { 
> 		char a[10]; int i;
> 	} u;
> 	int * p = (int *) &(u.a[1]);
> 	 * p = 17;
> 	printf("%d\n", *p);
> }

You are violating sparc's alignment restrictions by doing this,
a x86 machine will deal with the alignment issues in hardware however
a sparc will trap to the OS (SIGBUS) if non-aligned accesses are
attempted.

-Alfred



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