[releng_6 tinderbox] failure on sparc64/sparc64

[M. Warner Losh]

In message: <20060205220211.GA5151 at falcon.midgard.homeip.net>
            Erik Trulsson <ertr1013 at student.uu.se> writes:
: On Sun, Feb 05, 2006 at 04:45:34PM +0100, Dag-Erling Smørgrav wrote:
: > Stefan Farfeleder <stefanf at FreeBSD.org> writes:
: > > On Sat, Feb 04, 2006 at 03:58:56PM -0700, M. Warner Losh wrote:
: > > > This driver wants to access these structures as arrays of uint32_t.
: > > > It used to cast directly, but that isn't allowed.  So, I've passed
: > > > the cast through a (void *).  Is that allowed?  Eg:
: > > > 
: > > > 	struct foo foo;
: > > > 	((uint32_t *)(void *)&foo)[3] = 12;
: > > > 
: > > > is that OK?
: > > I'm afraid that only silences the warning without solving the underlying
: > > problem.  I don't think there's a Standard conforming way to treat a
: > > struct foo as an uint32_t array.
: > 
: > A union should do the trick.
: 
: No, it will not.  If you have a struct foo and try to access it as an array
: of int, the program will have unspecified (and maybe even undefined)
: behaviour.  It does not matter if you do it with a union or by casting
: pointers.
: 
: In general, if you have an object of type X, then the only ways it can be
: accessed is either as an object of type X, or as an array of [unsigned]
: char.  

So the proper fix for the above code is:

	struct foo foo;
	uint32_t value[sizeof(foo) / sizeof(uint32_t)];

	memcpy(value, &foo);
	// write out value one 32-bit word at a time

Is that right?  Or at least 'proper' here means defined.

Warner