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A simple stack-style machine language interpreter.

Project description

simple-stack-machine

A simple stack-style machine language interpreter.

Install

pip install simple-stack-machine

Usage

python3 -m simple_stack_machine <filepath.asm>
python3 -m simple_stack_machine --debug <filepath.asm>

Example Programs

See https://github.com/GGN-2015/simple-stack-machine/tree/main/sample_asm

Instructions and Data

You have a 64-bit address space where each position stores one byte. This space holds all program code and data.

All instructions (except PUSHIMM) are 1 byte long. The address of the currently executing instruction is stored in a 64-bit Program Counter (PC).

Register Set

  1. Program Counter: PC (64-bit)
  2. Stack Pointer: SP (64-bit)
  3. Address Pointer: AP (64-bit)

The position pointed to by SP is the address of the top stack element + 8 (the machine word size is 64 bits).

At program startup:

  • Initial PC is stored at: mem[8] ... mem[15]
  • Initial SP is stored at: mem[16] ... mem[23]
  • AP is initialized to 0

Calling Convention

Before calling a function, the caller is responsible for creating the parameter list:

stack: [..., arg_1, arg_2, ..., arg_n]

Then, the caller creates a storage location for the return value:

stack: [..., arg_1, arg_2, ..., arg_n, 0]

Next, push the return address (ret_addr) onto the stack and jump unconditionally to the target function entry. When the program reaches the function entry, the stack must be in this state:

stack: [..., arg_1, arg_2, ..., arg_n, 0, ret_addr]

Inside the target function:

  • You may copy and use arg_1, ..., arg_n as needed
  • You must assign the function’s return value to the position of the 0 (we mandate all return values are integers)
  • Avoid modifying ret_addr or any positions before it (except the return value storage location)

After the target function returns, the stack state becomes:

stack: [..., arg_1, arg_2, ..., arg_n, ret_ans]

Where ret_ans is the function’s computed result.

Instruction Set

0. Do Nothing: NOP

PC += 1;

1. Halt Instruction: HALT

SP -= 8;
exit(make_interger(mem, SP, SP + 8));

2. Discard Top Stack Element: POP

SP -= 8;
PC += 1;

3. Assign to Address Pointer: POPAP

{
    SP -= 8;
    AP = make_interger(mem, SP, SP + 8);
}
PC += 1;

4. Push Immediate Value to Stack: PUSHIMM

for(int i = 0; i < 8; i += 1) {
    mem[SP + i] = mem[PC + 1 + i];
}
SP += 8;
PC += 9; // Occupies 9 bytes in the program

5. Assign to Stack Pointer: POPSP

{
    SP -= 8;
    SP = make_interger(mem, SP, SP + 8);
}
PC += 1;

6. Push Stack Pointer Value to Stack: PUSHSP

save_interger(SP, mem, SP, SP + 8);
SP += 8;
PC += 1;

7. Push Program Counter Value to Stack: PUSHPC

save_interger(PC, mem, SP, SP + 8);
SP += 8;
PC += 1;

8. Function Call: CALL

{
    long long old_pc = PC;
    SP -= 8;
    PC = make_interger(mem, SP, SP + 8);
    save_interger(old_pc + 1, mem, SP, SP + 8)
    SP += 8;
}

9. Load Memory to Stack Top: LOAD

for(int i = 0; i < 8; i += 1) {
    mem[SP + i] = mem[AP + i];
}
SP += 8;
PC += 1;

10. Write Stack Top to Memory: SAVE

SP -= 8;
for(int i = 0; i < 8; i += 1) {
    mem[AP + i] = mem[SP + i];
}
PC += 1;

11. System Call: SYSCAL

mem[0] = 1; // Trigger system call
            // System call arguments are stored in mem[8] ~ mem[63]
            // After completion, mem[0] is cleared to 0
            // mem[8] ~ mem[63] may contain return results
PC += 1;

12. Signed Addition: ADD

{
    SP -= 8;
    long long val_2 = make_interger(mem, SP, SP + 8); // mem[SP] ... mem[SP + 7] form a 64-bit integer
    SP -= 8;
    long long val_1 = make_interger(mem, SP, SP + 8);
    
    long long ans = val_1 + val_2;
    save_interger(ans, mem, SP, SP + 8); // Store result back to stack top
    SP += 8;
}
PC += 1;

13. Signed Subtraction: SUB

{
    SP -= 8;
    long long val_2 = make_interger(mem, SP, SP + 8); // mem[SP] ... mem[SP + 7] form a 64-bit integer
    SP -= 8;
    long long val_1 = make_interger(mem, SP, SP + 8);
    
    long long ans = val_1 - val_2;
    save_interger(ans, mem, SP, SP + 8); // Store result back to stack top
    SP += 8;
}
PC += 1;

14. Signed Multiplication: MUL

{
    SP -= 8;
    long long val_2 = make_interger(mem, SP, SP + 8); // mem[SP] ... mem[SP + 7] form a 64-bit integer
    SP -= 8;
    long long val_1 = make_interger(mem, SP, SP + 8);
    
    long long ans = val_1 * val_2;
    save_interger(ans, mem, SP, SP + 8); // Store result back to stack top
    SP += 8;
}
PC += 1;

15. Signed Division: DIV

{
    SP -= 8;
    long long val_2 = make_interger(mem, SP, SP + 8); // mem[SP] ... mem[SP + 7] form a 64-bit integer
    SP -= 8;
    long long val_1 = make_interger(mem, SP, SP + 8);
    
    long long ans = val_1 / val_2;
    save_interger(ans, mem, SP, SP + 8); // Store result back to stack top
    SP += 8;
}
PC += 1;

16. Signed Modulo: MOD

{
    SP -= 8;
    long long val_2 = make_interger(mem, SP, SP + 8); // mem[SP] ... mem[SP + 7] form a 64-bit integer
    SP -= 8;
    long long val_1 = make_interger(mem, SP, SP + 8);
    
    long long ans = val_1 % val_2;
    save_interger(ans, mem, SP, SP + 8); // Store result back to stack top
    SP += 8;
}
PC += 1;

17. Negation: NEG

{
    SP -= 8;
    long long val = make_interger(mem, SP, SP + 8);
    
    long long ans = -val;
    save_interger(ans, mem, SP, SP + 8); // Store result back to stack top
    SP += 8;
}
PC += 1;

18. Logical NOT: NOT

{
    SP -= 8;
    long long val = make_interger(mem, SP, SP + 8);
    
    long long ans = (!val);
    save_interger(ans, mem, SP, SP + 8); // Store result back to stack top
    SP += 8;
}
PC += 1;

19. Bitwise AND: AND

{
    SP -= 8;
    long long val_2 = make_interger(mem, SP, SP + 8); // mem[SP] ... mem[SP + 7] form a 64-bit integer
    SP -= 8;
    long long val_1 = make_interger(mem, SP, SP + 8);
    
    long long ans = (val_1 & val_2);
    save_interger(ans, mem, SP, SP + 8); // Store result back to stack top
    SP += 8;
}
PC += 1;

20. Bitwise OR: OR

{
    SP -= 8;
    long long val_2 = make_interger(mem, SP, SP + 8); // mem[SP] ... mem[SP + 7] form a 64-bit integer
    SP -= 8;
    long long val_1 = make_interger(mem, SP, SP + 8);
    
    long long ans = (val_1 | val_2);
    save_interger(ans, mem, SP, SP + 8); // Store result back to stack top
    SP += 8;
}
PC += 1;

21. Bitwise XOR: XOR

{
    SP -= 8;
    long long val_2 = make_interger(mem, SP, SP + 8); // mem[SP] ... mem[SP + 7] form a 64-bit integer
    SP -= 8;
    long long val_1 = make_interger(mem, SP, SP + 8);
    
    long long ans = (val_1 ^ val_2);
    save_interger(ans, mem, SP, SP + 8); // Store result back to stack top
    SP += 8;
}
PC += 1;

22. Logical Right Shift: RSH

{
    SP -= 8;
    long long val_2 = make_interger(mem, SP, SP + 8); // mem[SP] ... mem[SP + 7] form a 64-bit integer
    SP -= 8;
    long long val_1 = make_interger(mem, SP, SP + 8);
    
    long long ans = (val_1 >> val_2);
    save_interger(ans, mem, SP, SP + 8); // Store result back to stack top
    SP += 8;
}
PC += 1;

23. Logical Left Shift: LSH

{
    SP -= 8;
    long long val_2 = make_interger(mem, SP, SP + 8); // mem[SP] ... mem[SP + 7] form a 64-bit integer
    SP -= 8;
    long long val_1 = make_interger(mem, SP, SP + 8);
    
    long long ans = (val_1 << val_2);
    save_interger(ans, mem, SP, SP + 8); // Store result back to stack top
    SP += 8;
}
PC += 1;

24. Unconditional Jump: JMP

SP -= 8;
PC = make_interger(mem, SP, SP + 8);

25. Conditional Jump: BR

{
    SP -= 8;
    long long val_2 = make_interger(mem, SP, SP + 8); // mem[SP] ... mem[SP + 7] form a 64-bit integer
    SP -= 8;
    long long val_1 = make_interger(mem, SP, SP + 8);
    
    if(val_1 != 0) {
        PC = val_2 - 1;
    }
}
PC += 1;

26. Less Than or Equal: LEQ

{
    SP -= 8;
    long long val_2 = make_interger(mem, SP, SP + 8); // mem[SP] ... mem[SP + 7] form a 64-bit integer
    SP -= 8;
    long long val_1 = make_interger(mem, SP, SP + 8);
    
    long long ans = (val_1 <= val_2);
    save_interger(ans, mem, SP, SP + 8); // Store result back to stack top
    SP += 8;
}
PC += 1;

27. Less Than: LT

{
    SP -= 8;
    long long val_2 = make_interger(mem, SP, SP + 8); // mem[SP] ... mem[SP + 7] form a 64-bit integer
    SP -= 8;
    long long val_1 = make_interger(mem, SP, SP + 8);
    
    long long ans = (val_1 < val_2);
    save_interger(ans, mem, SP, SP + 8); // Store result back to stack top
    SP += 8;
}
PC += 1;

28. Equal To: EQU

{
    SP -= 8;
    long long val_2 = make_interger(mem, SP, SP + 8); // mem[SP] ... mem[SP + 7] form a 64-bit integer
    SP -= 8;
    long long val_1 = make_interger(mem, SP, SP + 8);
    
    long long ans = (val_1 == val_2);
    save_interger(ans, mem, SP, SP + 8); // Store result back to stack top
    SP += 8;
}
PC += 1;

29. Duplicate Stack Element: DUP

{
    SP -= 8;
    long long offset = make_interger(mem, SP, SP + 8);

    for(int i = 0; i < 8; i += 1) {
        mem[SP + i] = mem[SP - 8 * offset - 8 + i];
    }
    SP += 8;
}
PC += 1;

30. Set Stack Element: POPS

{
    SP -= 8;
    long long offset = make_interger(mem, SP, SP + 8);

    SP -= 8;
    val_pos = SP;

    for(int i = 0; i < 8; i += 1) {
        mem[SP - 8 * offset - 8 + i] = mem[val_pos + i];
    }
}
PC += 1;

31. Swap Top Two Stack Elements: EXCH

{
    for(int i = 0; i < 8; i += 1) {
        unsigned char t = mem[SP - 16 + i];
        mem[SP - 16 + i] = mem[SP - 8 + i];
        mem[SP - 8 + i] = t;
    }
}
PC += 1;

System Calls

Only three system calls are supported:

  1. Read a character from standard input
  2. Output a null-terminated string (\0) to standard output
  3. Enable/disable debug mode

Read a Character from Standard Input

PUSHIMM 8 // Address 8 stores the system call type
POPAP
PUSHIMM 1 // System call 1 = read a character from stdin
SAVE
SYSCAL

// After execution, the character's ASCII code is stored in the 64-bit variable at address 8
PUSHIMM 8
POPAP
LOAD // Push this value onto the stack

Output a String

PUSHIMM 16 // Address 16 stores system call arguments
POPAP      
PUSHIMM str_ptr // Store the string's starting address here
SAVE

PUSHIMM 8 // Address 8 stores the system call type
POPAP
PUSHIMM 2 // System call 2 = output a string
SAVE
SYSCAL

// After execution, the number of successfully output characters is stored in the 64-bit variable at address 8
PUSHIMM 8
POPAP
LOAD // Push this value onto the stack

Enable/Disable Debug Mode

PUSHIMM 16 // Address 16 stores system call arguments
POPAP      
PUSHIMM 1 // Non-zero = enable debug mode; 0 = disable debug mode
SAVE

PUSHIMM 8 // Address 8 stores the system call type
POPAP
PUSHIMM 3 // System call 3 = toggle debug mode
SAVE
SYSCAL

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