MACH Virtual Machine

Mach is a very simple virtual machine. This project was written to teach myself about how virtual machines function, and how various factors can effect its speed and feature set. The binaries used by this virtual machine do not have separate .text and .data sections. Instead, data used by an instruction is written directly after its op code. This makes assembly and execution easier, but adds more complexity to jumps, and ensuring that data isn't read as an op code.

Writing Programs

Currently, programs for mach are written in a simplified assembly. Mach uses a simple, stack based assembly language.

Here's an example of a program that prints "Hello!" to the console. Notice that since we are using a stack, characters must be added in reverse in order for them to be emitted in the correct order.

pushc '\n'
pushc '!'
pushc 'o'
pushc 'l'
pushc 'l'
pushc 'e'
pushc 'h'
emitc 6
halt

Here's an example of a program that multiplies two numbers, then prints the result to the console.

pushn 166.5
pushn 15
multn
emitn 1

Compiling Programs

A few example programs can be found in the examples folder. To assemble a mach program, you can have two options:

Assemble using the assembly script:

./mass <yourassemblyfile>

Assemble with the assembler directly:

java -jar mass.jar <yourassemblyfile>

Currently all assembled programs will be written to out.m, but an option to specify the output will be added soon. The assembler will eventually be written in c.

Using Mach

To use the virtual machine, simply execute the mach binary and specify a path to a compiled mach program. ./mach coolprogram.m

Instruction Set

Instruction	Example	Parameter Bytes	Description	Layout
pushc	pushc '\s'	1	Pushes a given character onto the stack.	pushc <char>
emitc	emitc 1	4	Pops the given number of characters off of the stack and prints them to the console.	emitc <number>
printc	printc 1	4	Prints the given number of characters without popping them off of the stack.	printc <number>
pushn	pushn 0.75	8	Pushes the given number onto the stack.	pushn <number>
emitn	emitn 1	4	Pops the given number of numbers off of the stack and prints them to the console.	emitn <number>
printn	printn 1	4	Prints the given number of numbers without popping them off of the stack.	printn <number>
multn	multn	0	Pops 2 numbers off of the stack then pushes the product back onto the stack.	multn
addn	addn	0	Pops 2 numbers off of the stack then pushes the sum back onto the stack.	addn
subn	subn	0	Pops 2 numbers off of the stack then pushes the difference back onto the stack.	subn
divn	divn	0	Pops 2 numbers off of the stack then pushes the quotient back onto the stack.	divn
pop	pop	0	Pops an item off of the stack.	pop
grow	grow	0	Clones the item at the top of the stack.	grow
popt	popt 3	4	Pops an item off the stack and stores it at the given table index.	popt <number>
pullt	pullt 3	4	Pushes an item onto the stack from the given table index.	pullt <number>
jump	jump :somewhere	4	Jumps to the given label.	jump <label>
jumplt	jumplt 10 :somewhere	12	Jumps to the given label if the number on the top of the stack is less than the given number.	jumplt <number> <label>
jumpgt	jumpgt 0 :positive	12	Jumps to the given label if the number at the top of the stack is greater than the given number.	jumpgt <number> <label>
jumpe	jumpe 42 :theanswer	12	Jumps to the given label if the number at the top of the stack is equal to the given number.	jumpe <number> <label>
jumpne	jumpne 0 :nonzero	12	Jumps to the given label if the number at the top of the stack is not equal to the given number.	jumpne <number> <label>
jumplte	jumplte 100 :somewhere	12	Jumps to the given label if the number at the top of the stack is less than or equal to the given number.	jumplte <number> <label>
jumpgte	jumpgte 1000 :bignumber	12	Jumps to the given label if the number at the top of the stack is greater then or equal to the given number.	jumpgte <number> <label>
halt	halt	0	Halts execution.	halt
ptime	ptime	0	Pushes the current system time in nanoseconds onto the stack.	ptime