0x10c Programming Notes

ABI

On April 5 2012, #0x10c-dev agreed to the following standard ABI:

- Registers A, B, C are clobberable across calls

- Registers I, J, X, Y, Z are preserved across calls

- Return in A

- J is used for base stack pointer (preserving the value of SP before allocating data for locals)

- Function local variables are kept on the stack

- Caller cleans stack

- First three arguments to A, B, C, remaining arguments pushed right-to-left onto stack

For example: myfunc(foo,bar,baz,flee,fuzz) A = foo, B = bar, C = baz, top of stack = flee, next on stack = fuzz

- No stupid tricks with the overflow flag

EXAMPLE FUNCTION CALL:

# func(1, 2, 3, 4, 5);

# first 3 arguments are passed via registers
SET A, 1
SET B, 2
SET C, 3
# 4 and 5 are pushed to stack in reverse order
SET PUSH, 5
SET PUSH, 4
JSR func
ADD SP, 2 # callers cleans up the stack (two passed words)

EXAMPLE FUNCTION PROLOGUE/EPILOGUE:

# Prologue:
SET PUSH, J
SET J, SP
SUB SP, 5 # Reserve 5 words for function locals

# Function body:
SET A, [J-1] # Access first local variable
SET B, [J+1] # Access 3rd function argument
SET C, [J+2] # Access 4th function argument

# etc ...

# Epilogue:
SET A, return_value
SET SP, J
SET J, POP
SET PC, POP # return

Last updated for DCPU16v11