判断堆栈增长方向

判断堆栈增长方向

说明：今天看到alloca.c中find_stack_direction函数，用来判断堆栈的增长方向，记录下来。

#define ADDRESS_FUNCTION(arg) &(arg)

/* Define STACK_DIRECTION if you know the direction of stack
growth for your system; otherwise it will be automatically
deduced at run-time.

STACK_DIRECTION > 0 => grows toward higher addresses
STACK_DIRECTION < 0 => grows toward lower addresses
STACK_DIRECTION = 0 => direction of growth unknown */

#ifndef STACK_DIRECTION
#define STACK_DIRECTION 0 /* Direction unknown. */
#endif

#if STACK_DIRECTION != 0

#define STACK_DIR STACK_DIRECTION /* Known at compile-time. */

#else /* STACK_DIRECTION == 0; need run-time code. */

static int stack_dir; /* 1 or -1 once known. */
#define STACK_DIR stack_dir

static void
find_stack_direction ()
{
static char *addr = NULL; /* Address of first `dummy', once known. */
auto char dummy; /* To get stack address. */

if (addr == NULL)
{ /* Initial entry. */
addr = ADDRESS_FUNCTION (dummy);

find_stack_direction (); /* Recurse once. */
}
else
{
/* Second entry. */
if (ADDRESS_FUNCTION (dummy) > addr)
stack_dir = 1; /* Stack grew upward. */
else
stack_dir = -1; /* Stack grew downward. */
}
}

#endif /* STACK_DIRECTION == 0 */