Re: [musl] Potential bug in __res_msend_rc() wrt to union initialization.

[Thorsten Glaser <tg@mirbsd.de>]

Jₑₙₛ Gustedt dixit:

>As soon as you store
>to any member, padding bytes may change to arbitrary values.

Yes, but where is that a problem?

Something like:

union foo {
	struct bar {
		char *s;
		size_t z;
	} a;
	struct baz {
		size_t z;
		char *s;
	} b;
};

int
somefunc(int mode, char *buf, size_t len, …)
{
	union foo u;

	memset(u, '\0', sizeof(u));
	/* … */
	if (mode) {
		/* from here on, u is decided to be a */
		u.a.s = NULL;
	} else {
		/* from here on, u is decided to be b */
		u.b.s = NULL;
	}
	/* … some other processing … */
	if (mode) {
		u.a.s = buf;
		u.a.z = len;
	} else {
		u.b.s = buf;
		u.b.z = len;
	}
	return (someotherfunc(&u, mode, …));
}