Basically, there are two types of functions:

Frame function

A function that requires a stack frame. A frame function allocates stack space, calls other functions, saves nonvolatile registers, or uses exception handling. It also requires a function table entry. A frame function requires prolog and epilog code. A frame function can dynamically allocate stack space and can employ a frame pointer. A frame function has the full capabilities of this calling standard at its disposal.

If a frame function does not call another function, then it is not required to align the stack. For more information, see Stack Allocation.

Leaf function

A function that does not require a stack frame. A leaf function does not require a function table entry. It cannot call any functions, allocate space, or save any nonvolatile registers. It can leave the stack unaligned while it executes.