Calling conventions

The Lightfoot SDK supports applications that contain Java, C and assembler code. Java and C are high level languages that have specific calling conventions, while assembler can have any type of calling convention!

Java calling convention

Soft bytecodes used

Soft bytecode	Description
`Jivirt`	Invoke a virtual method
`Jiinterf`	Invoke an interface method
`Jistatic0`	Invoke a static method with zero parameters
`Jistatic`	Invoke a static method
`Jcscall0`	Call the C function on the stack with zero parameters.
`Jcscalln`	Call the C function on the stack with zero parameters.
`Jispec`	Invoke a special method, either private, a superclass method or a constructor
`Jxreturn`	Return from the method. Any value to return is on the stack.

Parameters/local variables

The first 4 parameters and local variables are stored in parameter registers P0-P3. The remaining parameters and local variables are stored in the paramter pool at entries 4 and above.

Stack frame

The stack frame for Java methods is as follows

`method pointer`
`stack counter`	`flags`
`previous ppp`
`return address`
`previous cpp`
`next ppp`

C calling convention

Soft bytecodes used

Soft bytecode	Description
`ccall0`	Call a named function with zero parameters
`ccalln`	Call a named function with the specified number of parameters
`cscall0`	Call the function on the stack with zero parameters
`cscalln`	Call the function on the stack with the specified number of parameters
`cret`	Return a value from the function. The value to return should be on the stack and will be stored in parameter register `P3`
`cret0`	Return no values from the function.

Parameters

All parameters are stored in the parameter pool starting at entry 0. Return values from functions are stored in parameter register P3.

Stack frame

The stack frame for C functions is as follows

`previous ppp`
`return address`
`previous cpp`
`next ppp`