BytecodeVM

A basic Virtual machine operating on bytecode.

It operates on a stack and shares memory for instructions and data (van neumann architecture).

It can compile to a binary file and run from a file, or compile and run directly from the assembly file.

Currently a command line program but I plan to integrate it into ETEngine as a visual node based programming language. Commands:

• compile [filename.bca] compiles a .bca assembly file to a binary .bce executable
• run [filename.bce] runs a bytecode executable file
• cRun [filename.bca] compiles and directly runs an assembly file without saving the executable

Instruction Set

Opcode	Description
LITERAL	Push next 4 bytes
LITERAL_ARRAY	Get x from next 4 bytes; Push x sets of 4 bytes - temporary
LOAD ; LOAD_ARG ; LOAD_LCL	Pop a; Push RAM[a]
STORE ; STORE_LCL	Pop b; Pop a; RAM[b] = a
ADD	Pop b; Pop a; Push a + b
SUB	Pop b; Pop a; Push a - b
LESS	Pop b; Pop a; Push a < b
GREATER	Pop b; Pop a; Push a > b
NOT	Pop a; Push !a
EQUALS	Pop b; Pop a; Push a == b
JMP	Pop a; goto a;
JMP_IF	Pop b; Pop a; if a goto b
CALL	put current state in a stack frame; store RTN; Pop a; goto a;
RETURN	Restore to previous stack frame; append working stack; goto RTN
PRINT	Pop x; for x Print Pop - temporary, will be a library function based on null terminated strings
PRINT_INT	Pop a; Print string of a
PRINT_ENDL	Start a new line in console

LOAD and STORE have segment modifiers that can be used as base addresses within functions

Segment	Description
LCL	pointer to first local variable
ARG	pointer to first argument

Variable Type	Description
static	a fixed address variable, referenced directly
argument	a variable that sits in the working stack of the previous function's frame
local	a local variable within the stack frame of the current function

There is no concept of scope so all variables should be unique Variables are declared implicitly upon their first occurance with the exception of arguments Variables declared before the first function are static, after the first function they are local

The assembler also features Symbols (variables and labels)

• Variables start with # and are statically allocated at compile time
• Jump labels start with @
• Subroutines start with $ and are followed by argument declarations

Planned

I plan to add:

• indexed library function support (executes function at pushed index)
• Dynamic memory allocation
• Support for standard types int float char bool (maybe short, long, double etc) unsigned or signed
• Built in support for variable length arrays, strings and vectors