Please forgive me if I'm wrong (and please tell me in that case why it 
does work the way it works).

Full listing: 
http://cvsweb.netbsd.org/bsdweb.cgi/src/sys/arch/macppc/stand/ofwboot/ofdev.c?rev=1.15&content-type=text/x-cvsweb-markup

static char *
filename(char *str, char *ppart)
{
[...]
	for (cp = str; *cp; lp = cp) {
		/* For each component of the path name... */
		while (*++cp && *cp != '/')
			;
		savec = *cp;
		*cp = 0;
		/* ...look whether there is a device with this name */

[NEXT LINE: SHOULD IT NOT BE cp INSTEAD OF str?  Why else would you save cp in savec?]

		dhandle = OF_finddevice(str);
		*cp = savec;
[...]
	}
	return 0;
}