Calling Convention

Step	Responsibility	Action	Description
0	Caller	Save Current State	Ensure that any registers with important data in are pushed to the stack so that they can be restored later.
1	Caller	Push arguments	Push exactly n arguments to the stack (in order, last argument pushed first)
2	Caller	Call function	Execute `call namespace::function` this automatically pushes the return address (pcx) and jumps to the function
3	Function	Set up stack frame	Execute `push bpr; mov spr, bpr` to establish new stack frame
4	Function	Access arguments	Read arguments starting at `spr+8` (first 3 args at offsets 8, 12, 16)
5	Function	Execute function	Perform the function's operations using the arguments
6	Function	Store return value	Write return value (if any) to `spr+8`
7	Function	Restore stack frame	Execute `mov bpr, spr; pop bpr` to restore previous stack frame
8	Function	Return	Execute `return` pseudo-instruction to return to caller
9	Caller	Clean up stack	Pop exactly n arguments from the stack to clean up
10	Caller	Handle unused values	Use `pop zero` to discard any unused stack values if needed
11	Caller	Restore State	Pop any registers that were pushed in step 0 (or `pop zero` if no longer needed)

Notes:

The namespace in step 2 is the name assigned in the include statement
The call pseudo-instruction automatically handles return address management so long as the callee does not mess with the stack
Arguments are accessed by the callee using offsets from the base pointer (bpr)

Function Control

Mnemonic	Operands	Description
CALL	`namespace::function`	Call a function with automatic return address management
RETURN	-	Return from a function to the caller

Examples:

call-local.dsa

// ensure the stack is set up first!

caller:
    push rg0    
    push rg1

    call callee  // make call to a local function
    pop rg0     // put result in rg0
    pop zero    // void second return val

callee:
    // setup new stack frame
    push bpr
    mov spr, bpr

    // function body

    // restore the stack frame
    mov bpr, spr
    pop bpr
    return              ; Return from the current function

call-external.dsa

include external "./external.dsa"

// ensure the stack is set up first!
db string: "Hello, world!"
caller:
    // push args
    lwi string, rg0
    push rg0
    call external::callee // do something with the string
    pop zero

external.dsa

callee:
    // set up the stack
    push bpr
    mov spr, bpr

    // function body

    // restore the stack frame
    mov bpr, spr
    pop bpr
    return              ; Return from the current function

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Calling Convention

Calling Convention

Function Control