NAME
STACK —
stack macros
SYNOPSIS
#include
<sys/param.h>
type
STACK_ALLOC(sp,
size);
type
STACK_MAX(sp,
size);
type
STACK_ALIGN(sp,
bytes);
type
STACK_GROW(sp,
size);
type
STACK_SHRINK(sp,
size);
DESCRIPTION
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.