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
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.
sp(stack pointer)r0(GPR)r1(GPR)r2(GPR)r3(GPR)
| 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. |
| 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 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 |
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