q800: add alias for MacOS toolbox ROM at 0x40000000

According to the Apple Quadra 800 Developer Note document, the Quadra 800 ROM
consists of 2 ROM code sections based at offsets 0x0 and 0x800000. A/UX attempts
to access the toolbox ROM at the lower offset during startup, so provide a
memory alias to allow the access to succeed.

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Message-ID: <20231004083806.757242-20-mark.cave-ayland@ilande.co.uk>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>

hw/m68k/q800.c

@@ -660,6 +660,11 @@ static void q800_machine_init(MachineState *machine)
         filename = qemu_find_file(QEMU_FILE_TYPE_BIOS, bios_name);
         memory_region_add_subregion(get_system_memory(), MACROM_ADDR, &m->rom);
 
+        memory_region_init_alias(&m->rom_alias, NULL, "m68k_mac.rom-alias",
+                                 &m->rom, 0, MACROM_SIZE);
+        memory_region_add_subregion(get_system_memory(), 0x40000000,
+                                    &m->rom_alias);
+
         /* Load MacROM binary */
         if (filename) {
             bios_size = load_image_targphys(filename, MACROM_ADDR, MACROM_SIZE);

include/hw/m68k/q800.h

@@ -50,6 +50,7 @@ struct Q800MachineState {
     bool easc;
     M68kCPU cpu;
     MemoryRegion rom;
+    MemoryRegion rom_alias;
     GLUEState glue;
     MOS6522Q800VIA1State via1;
     MOS6522Q800VIA2State via2;