A stack is an area of memory with a fixed origin but with a variable size. A stack pointer points to the most recently referenced location on the stack. Initially, when the stack has a size of zero, the stack pointer points to the origin of the stack. When data items are added to the stack, the stack pointer moves away from the origin.
The
STACK_ALLOC() macro returns a pointer to allocated stack space of some
size. Given the returned pointer
sp and
size,
STACK_MAX() returns the maximum stack address of the allocated stack space. The
STACK_ALIGN() macro can be used to align the stack pointer
sp by the specified amount of
bytes.
Two basic operations are common to all stacks: a data item is added (“push”) to the location pointed by
sp or a data item is removed (“pop”) from the stack. The stack pointer must be subsequently adjusted by the size of the data item. The
STACK_GROW() and
STACK_SHRINK() macros adjust the stack pointer
sp by given
size.
A stack may grow either up or down. The described macros take this into account by using the
__MACHINE_STACK_GROWS_UP preprocessor define.