Awesome
This is a very simple architecture (and executable format) made for the purpose of teaching how to write Binja loaders and architectures.
My hope for this repo is that it can be a simple teaching resource for this topic. While it covers the basics, it leaves some important topics (like flags) uncovered. PRs welcome!
An example "firmware image" is included here
DUMB Architecture
Following is a description of the architecture. In this document, we use the following format to specify bitfields:
0:xxyy represents a single byte: 0 means that the first (upper) nibble of the byte is zero, while xxyy indicates two 2-bit fields making up the lower nibble of the byte.
Registers
sp(stack pointer)r0(GPR)r1(GPR)r2(GPR)r3(GPR)
Instructions
One Byte Instructions
| Format | Tokenization | Meaning |
|---|---|---|
0:xxyy | mov rx ry | Move the value in ry into rx |
1:xxyy | add rx ry | Add the values of ry and rx and store the result in rx |
2:xxyy | and rx ry | And the values of ry and rx and store the result in rx |
3:xxyy | or rx ry | Or the values of ry and rx and store the result in rx |
4:xxyy | xor rx ry | Xor the values of ry and rx and store the result in rx |
9:____ | ret | Return from the current function to the address stored on the stack. |
Five Byte Instructions
| Format | Tokenization | Meaning |
|---|---|---|
a0 XX XX XX XX | call XXXXXXXXX | Push addr + 5 onto the stack and transfer execution to XXXXXXXX (little endian dword) |
7:xxyy XX XX XX XX | jlt rx, ry, XXXXXXXX | If rx is less than ry, jump to XXXXXXXX, otherwise continue to next instr |
8:__rr XX XX XX XX | mov rr, XXXXXXXX | Move the immediate XXXXXXXX into rr |
DUMB Format
DUMB files are extremely simple, containing only magic, and metadata for a single section. The format is as follows:
| Offset | Length | Contents (if applicable) | Description |
|---|---|---|---|
| 0 | 4 | "DUMB" | Magic |
| 4 | 4 | N/A | Section length stored as little endian dword |
| 8 | 4 | N/A | Address to load section at, stored as little endian dword |