alanvivona / simple-vm

An emulator for a fantasy architecture

Simple VM in Golang

I wanted to write a really simple vm just to get an idea of the inner workings of one.
Ended up with a fake arch, isa, assembler, dissasembler, executable file format and of course, the VM.

Changelog

v1 half baked version implemented in C
v2 reimplemntation in go.
v2.1 gomodules and new examples.

Usage

Assembler Module

go run ./asm/main.go -h

The module takes input from stdin and outputs the binary to a file.

cat examples/sample2.asm | go run ./asm/main.go -o out/sample.bin -v
cat out/sample.bin | xxd

Linker Module

go run ./link/main.go -h

The module takes a path to a raw binary file and saves an executable.
Executable files have a header and a checksum.

go run ./link/main.go -v -i sample.bin -o sample.yz
cat sample.bin | xxd
cat sample.yz | xxd

Virtual Machine Module

The module checks and runs an executable file.

go run ./main.go -v -i out/sample.yz

Instrution Set

Setup

start : Start machine execution
end : End machine execution

Set registers

set : Set register to register or immediate value

Stack

put : Push register or immediate value into the stack
get : Fetch value from the stack into register

Arithmetic

add : Add register or immediate value to register
sub : Substract register or immediate value to register
dec : Decrement register value by one
inc : Increment register value by one

Logic

not : Negate register value
neg : One's complement of register value
and : Logic AND between regiter or immediate value and target register
or : Logic OR between regiter or immediate value and target register
xor : Logic XOR between regiter or immediate value and target register

The YZ File format

Section	Subsection	Description
Header		Describes file structure
	Magic Number / File Signature	Two bytes signature. Value: 0x5959 ("YY")
	Checksum	Sha512 of the code section
	Size field	64 integer indicating next's section size
	Next section header	Label. Next section's name. Value: "code"
	Section delimiter	Indicates section end. Value: 0x6060 ("ZZ")
Code		Raw binary

Demo

Assemble + Create executable + Run inside the VM

Reset the output folder:

rm -rf ./out; mkdir out

Create a binary file by running the source code through the assembler:

cat ./examples/sample2.asm | go run ./asm/main.go -v -o test.bin

Create an executable by using the linker:

go run ./link/main.go -v -i test.bin -o test.yz

Notice the difference between raw binary and executable:

cat test.bin | xxd
cat test.yz | xxd

You should see a checksum, magic number and header end were added to the executable.

Run the executable in the virtual machine:

go run ./vm/main.go -v -i test.yz