EOF container assembler prototype

[gumb0]

This is a prototype for emitting EOF container bytecode from assembler.

The following syntax for defining EOF sections is proposed:

section .code
stop

section .code outputs=1
push0
retf

section .code inputs=1 outputs=nonret max_stack_height=2
pop
push0
push0
return

section .data
%include_hex("data.etk")

• EOF container is generated in case at least one section is defined, otherwise legacy code is generated.
• Code sections and data section are supported.
• Code sections may declare their number of inputs/outputs and max stack height (this data goes into EOF type section)
• Section attributes are optional and by default are inputs=0 outputs=nonret max_stack_height=0
• outputs=nonret means sections is non-returning.

TODO

• Each code section should be in a separate scope
• Test that sections get correct size when variable-size pushes are used
• max_stack_height may be automatically calculated within a forward pass during assembly

Known issues / limitations:

• Attributes are allowed for data sections too, but are ignored (probably shoud be disallowed)
• Attributes can be duplicated, only last mentioned value is used (better should not be allowed)
• No bounds checking for attribute values, panic when above the limit

Future work for EOF support

• Support new instructions (partially done in EIP-4200: EOF - Static relative jumps #128, EIP-663: Unlimited SWAP and DUP instructions #129, EIP-6206: EOF - JUMPF instruction #130, EIP-4750: EOF - Functions #131)
• Support nested containers (for this we'll probably need a directive for defining section end besides section start)
• Disallow banned instruction in EOF? e.g. dynamic jumps
• General question whether etk should allow generating invalid code, or should it be validated
• Support in disassembler?