ovm/spec.org

VM Specification

• Data types
• Instructions
• Bytecode format
• Footnotes

Data types

There are 3 main data types of the virtual machine. They are all unsigned. There exist signed versions of these data types, though there is no difference in terms of bytecode between them. For an unsigned type <T> the signed version is simply S_<T>.

Name	Bits
Byte	8
HWord	32
Word	64

Instructions

An instruction for the virtual machine is composed of an opcode and, potentially, an operand. An opcode represents the behaviour of the instruction i.e. what is the instruction. The operand is a datum of one of the data types described previously.

Some instructions do have operands while others do not. The former type of instructions are called UNIT instructions while the latter type are called MULTI instructions¹.

All opcodes (with very few exceptions²) have two components: the root and the type specifier. The root represents the general behaviour of the instruction: PUSH, POP, MOV, etc. The type specifier specifies what data type it manipulates. A complete opcode will be a combination of these two e.g. PUSH_BYTE, POP_WORD, etc. Some opcodes may have more type specifiers than others.

Bytecode format

Bytecode files are byte sequence which encode instructions for the virtual machine. Any instruction (even with an operand) has one and only one byte sequence associated with it.

Footnotes

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¹

UNIT refers to the fact that the internal representation of these instructions are singular: two instances of the same UNIT instruction will be identical in terms of their binary. On the other hand, two instances of the same MULTI instruction may not be equivalent due to the operand they take. Crucially, most if not all MULTI instructions have different versions for each data type.

²

NOOP, HALT, MDELETE, MSIZE, JUMP_*