Xbox 360 Backward Compatibility
From xboxdevwiki
Xbox 360 Backward Compatibility is Microsofts original Xbox emulator for the Xbox 360.
The emulator binary is called xefu.xex. The first resource is xb1krnl which is a modified version of xboxkrnl.exe.
Modifications to xboxkrnl.exe
The IDEXPDTR section has been dropped, additionally the extra data from the MS-DOS header is gone.
Guest to host communication
The entrypoint of the kernel looks like:
80030878: 56 push %esi 80030879: 57 push %edi 8003087a: 8d 05 4c ac 02 80 lea 0x8002ac4c,%eax 80030880: 0f 3f (bad) 80030882: 04 20 80030884: 8d 05 6c ac 02 80 lea 0x8002ac6c,%eax 8003088a: 0f 3f (bad) 8003088c: 04 20 8003088e: 8d 05 8c ac 02 80 lea 0x8002ac8c,%eax 80030894: 0f 3f (bad) 80030896: 04 21 80030898: 8d 05 70 94 01 80 lea 0x80019470,%eax ...
According to this document by symantec (Page 5, Left-hand-side) the patterns 0F 3F x1 x2 and 0F C7 C8 y1 y2 are used for communication with the host.
| x1 | x2 | Notes |
|---|---|---|
| 0x04 | 0x20 | Seems to use eax (address) as parameter? eax points to a zero terminated list of pointers into the kernel memory [7 elements] |
| 0x04 | 0x21 | Seems to use eax (address) as parameter? " [4 elements] |
| 0x04 | 0x22 | Seems to use eax (address) as parameter? Seems to be some call to that address?! |
| 0x04 | 0x23 | Seems to use eax (address) as parameter? |
| 0x04 | 0x24 | Seems to use eax (address) as parameter? |
| 0x04 | 0x35 | Seems to use eax (address) as parameter? |
| 0x04 | 0x50 | Seems to use eax (address) as parameter? " [3 elements] |
| Cleaner list starts here [FIXME] | ||
| 0x04 | 0x20 | |
| 0x04 | 0x20 | |
| 0x04 | 0x21 | |
| 0x04 | 0x22 | |
| 0x04 | 0x23 | |
| 0x04 | 0x24 | |
| 0x04 | 0x35 | |
| 0x04 | 0x50 | |
| 0x06 | 0x00 | Seems to use eax (address) and ecx (size) as parameter? Memory is 0x00 filled before. location is 0x8002b420, size would be 0x3000 |
| 0x06 | 0x02 | |
| 0x06 | 0x20 | Some call or callback registration to the address pointed to by eax |
| 0x06 | 0x21 | |
| 0x06 | 0x22 | |
| 0x06 | 0x23 | Some call or callback registration to the address pointed to by eax |
| 0x06 | 0x24 | |
| 0x06 | 0x25 | |
| 0x06 | 0x26 | |
| 0x06 | 0x27 | |
| 0x06 | 0x28 | |
| 0x06 | 0x29 | |
| 0x06 | 0x40 | |
