avm/todo.org

TODOs

• WIP Write a label/jump system
• WIP Allow relative addresses in jumps
• Calling and returning control flow :VM:

WIP Write a label/jump system   ASM

Essentially a user should be able to write arbitrary labels (maybe through label x or x: syntax) which can be referred to by jump.

It'll purely be on the assembler side as a processing step, where the emitted bytecode purely refers to absolute addresses; the VM should just be dealing with absolute addresses here.

WIP Allow relative addresses in jumps   ASM

As requested, a special syntax for relative address jumps. Sometimes it's a bit nicer than a label.

TODO Calling and returning control flow :VM:   ASM

When writing library code we won't know the addresses of where callers are jumping from. However, most library functions want to return control flow back to where the user had called them: we want the code to act almost like an inline function.

There are two ways I can think of achieving this:

• Some extra syntax around labels (something like @inline <label>:) which tells the assembly processor to inline the label when a "jump" to that label is given

  • This requires no changes to the VM, which keeps it simple, but a major change to the assembler to be able to inline code. However, the work on writing a label system and relative addresses should provide some insight into how this could be possible.

• A call stack and two new syntactic constructs call and ret which work like so:

  • When call <label> is encountered, the next program address is pushed onto the call stack and control flow is set to the label
  • During execution of the <label>, when a ret is encountered, pop an address off the call stack and set control flow to that address
  • This simulates the notion of "calling" and "returning from" a function in classical languages, but requires more machinery on the VM side.