VM.md

VM Architecture

The virtual machine is a simple stack-machine architecture with both a stack and heap for larger values. The VM is also known as the kernel (not to be confused with operating system kernels).

typedef struct VM
{
    size_t ip;          // instruction pointer
    int flag;           // set after comparison

    VMInstruction *code;
    int code_size;

    // Memory
    // Stack and a heap
    VMMem mem;
    
    // Statically allocated string table
    char** string_tbl;

    // GC implementation omitted for simplicity
} VM;

Instructions

Stack Manipulation:

pushi 123:                  Push an int to the stack
pushf 3.14:                 Push a float to the stack
popi:                       Pop an int value from the stack
popf:                       Pop a float value from the stack
pops:                       Pop a string value from the stack
stores <index>,<string>:    Store a string into the string table
loads <index>:              Load a string from the string table onto the stack

Comparison:

cmp:                        Pop two items off the stack, compare them, set flag
j <label|addr>:             Jump to a label/jump to a absolute/relative address
jeq <label|addr>:           Jump if equal (flag=1)
jne <label|addr>:           Jump if not equal (flag=0)

Math:

addi/subi/mul/div:          Integer addition/subtraction/multiplication/division
addf/subf:                  Floating point addition/subtraction

Functions:

call:                       Call a function defined, see below for specification
ret:                        Return from a function

Kernel Builtins

The kernel provides a set of built-in instructions and functions.

• Locals:

Local variables can be declared at the top of a function using the local instruction. They can be accessed using their name e.g $local1 and modified using set.

Locals can only be used in functions because they store variables within stack frames.

local $local1: int = 1
set $local1 123

• If:

If $local1 equals $local2, then jump to .success. Otherwise, the ip will increment past the if statement Valid operators are: eq, ne, lt, gt.

local $local1: int = 1
local $local2: int = 2
if $local1 eq $local2 .success
j .fail

• Functions:

Functions are defined using the func keyword. They cannot take any parameters, and must return a value upon exit using the ret instruction. They can only be called using call.

func do_nothing()
   local $local1: int = 0
   
   ret
end

call $do_nothing()

Bytecode format

The bytecode format is defined in src/runtime/bytecode.h