The design of the Inferno virtual machine

Created: 2020-08-24T05:56:17.023567

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VM Design Document

Particulars about the VM

Instructions are of the form:

OP src1, src2, dst

• Opcodes work on memory addresses or offsets directly, not through registers.
• This is similar to an "infinite register" machine.

Types

• 32-bit signed word
• 64-bit signed big
• 8-bit unsigned byte
• 64-bit float real
• Platform dependent pointer

Memory segments

• Code segments are not addressible from the instruction set.
• Code segments may contain either VM opcodes, or compiled native code pages.

Memory management

• VM prefers automated reference counting (ARC) primarily
• A mark/sweep (or equivalent) garbage collector exists to collect cycles
• Pointers need special pointer operations to keep ARC/GC data up to date

Type descriptors

• Type descriptors consist of a word to identify the type, a word for the size of the type in bytes, and a pointer map.
• The pointer map is one or more bytes.
• Each bit in the pointer map indicates a pointer is stored at some word in the type.
• The most significant bit of the pointer map is the lowest address of the type.

Registers

• mp register: module pointer; points to memory for a given module
• fp register: frame pointer; poitns to memory for the current thread frame