Choi VM

Choivm is a virtual machine with a goal of being small and portable. It has its own assembly language called casm (choi assembly, a interface with pratically no abstraction for its bytecode)

Building:

Compile cbone.c and execute.

$ cc -o cbone cbone.c && ./cbone

Executing cbone will generate these following 3 executables:

choivm: the virtual machine bytecode interpreter.

choiasm: the assembly compiler.

choi_disasm: the disassembler.

Syntax:

choi_assembly:

@proc main
  @mem R1 "Hello, choi!"
  write R1

quickstart

Operands

push

push a value to a register.

  push R1 69

mov

move values between registers.

  mov R1 R2

add

sum two registers as integers.

  add R1 R2

sub

subtract two registers as integers

  sub R1 R2

div

divide two registers as integers.

  div R1 R2

mul

multiply two registers as integers.

  mul R1 R2

dump

dump a register to stdout as integer

  dump R1

jmp

Change the instruction pointer to a certain location.

  jmp hello-procedure

jz

Change the instruction pointer to a certain location if the last element in the stack is zero.

  jz hello-procedure

jnz

Change the instruction pointer to a certain location if the last element in the stack is not zero.

  jnz hello-procedure

call

Call a procedure, operand call makes the use of ret instruction possible by pushing the current address in the program.

  call hello-procedure

drop

set a register to zero

  drop R1

write

writes N bytes of an certain address in the constant pool

  write R1

syscall

looks up at the registers and execute a special function based on the R1 register.

  push R1 1
  push R2 0
  @mem R3 "Hello, world!"
  syscall

halt

stop execution and ends the program.

  halt

cmp

subtract two registers and push result to the stack

  cmp R1 R2

inc

increment a register by one

  inc R3

Special operands (operate stack, pool and procedures)

@proc

declares a procedure, while not visible at bytecode itself, it can be useful for cross referencing blocks

  @proc hello-procedure

@mem

push pointer/string to constant pool and its length to a register.

  @mem R1 "Hello, world"

@pop

pops an element of the stack to a register

  @pop R1

@push

push a value to the stack

  @push 69

confusion

operators preceded with '@' are different.

push is not the same as @push

push will push a value to a register

@push will push a value to the stack

Todos

• meta programming features to the assembly.

• handle strings like a sane person.

• a debugger for the bytecode.