Memory

Stack

Function Call

Function call convention determines how this works, in 2106:

1. Caller: pass parameters using registers or stack
2. Caller: save return PC on stack
3. Jump to callee (transfer control from caller to callee)
4. Callee: Save current value of the registers it intends to use on stack (spill the registers)
5. Callee: Save old frame pointer, stack pointer on stack
6. Callee: Allocate space for local variables on stack
7. Callee: Adjust FP to correct location, adjust SP to point to new stack top

Returning from Function

1. Callee: Place return result in register (if applicable)
2. Callee: Restore spilled registers
3. Callee: Restore saved FP & SP
4. Jump to return address (transfer control back to caller using saved PC)
5. Caller: Utilise return result in register (if applicable)
6. Caller: Continue execution

Frame Pointer

• To facilitate access of items in the stack frame
• SP can be difficult to use because it can change (when allocating more stuff etc)
• FP points to fixed location in stack frame, so we can easily access items relative to FP
• Usage of FP is platform dependent

Heap

• For dynamically allocated memory (c malloc, cpp new etc.)
• Allocated at runtime: Cannot place in data region
• Not deallocated with function: cannot place on stack
• Allocated in heap. Heap grows downward