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.
v1 half baked version implemented in C
v2 reimplemntation in go.
v2.1 gomodules and new examples.
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
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
The module checks and runs an executable file.
go run ./main.go -v -i out/sample.yz
start : Start machine execution
end : End machine execution
set : Set register to register or immediate value
put : Push register or immediate value into the stack
get : Fetch value from the stack into register
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
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
| 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 |
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