hw/sun4m.c, line 154:
m48t59_write(nvram, i++, 0x80); /* Sun4m OBP */
This is not a machine type recognized by SunOS (and probably other
early versions of Solaris). According to idprom.h (some which is
quoted at http://www.sunmanagers.org/archives/1993/0050.html), the
only recognized sun4m IDs are:
#define IDM_SUN4M_690 0x71 /* SPARCsystem 600 series */
#define IDM_SUN4M_50 0x72 /* Campus 2 */
A SparcStation 10 is IDM_SUN4M_50. SunOS tries to print an error
message and panic() if the machine ID is neither 0x71 or 0x72. (It
fails with a data access exception because some of the devices haven't
been mapped yet.)
So this either needs to be changed to 0x72 or there needs to be some
way to configure qemu to specify the machine ID from the command line
(or config file).