source: trunk/binutils/libiberty/alloca.c@ 2446

/* alloca.c -- allocate automatically reclaimed memory
   (Mostly) portable public-domain implementation -- D A Gwyn

   This implementation of the PWB library alloca function,
   which is used to allocate space off the run-time stack so
   that it is automatically reclaimed upon procedure exit,
   was inspired by discussions with J. Q. Johnson of Cornell.
   J.Otto Tennant <[email protected]> contributed the Cray support.

   There are some preprocessor constants that can
   be defined when compiling for your specific system, for
   improved efficiency; however, the defaults should be okay.

   The general concept of this implementation is to keep
   track of all alloca-allocated blocks, and reclaim any
   that are found to be deeper in the stack than the current
   invocation.  This heuristic does not reclaim storage as
   soon as it becomes invalid, but it will do so eventually.

   As a special case, alloca(0) reclaims storage without
   allocating any.  It is a good idea to use alloca(0) in
   your main control loop, etc. to force garbage collection.  */

/*

@deftypefn Replacement void* alloca (size_t @var{size})

This function allocates memory which will be automatically reclaimed
after the procedure exits.  The @libib{} implementation does not free
the memory immediately but will do so eventually during subsequent
calls to this function.  Memory is allocated using @code{xmalloc} under
normal circumstances.

The header file @file{alloca-conf.h} can be used in conjunction with the
GNU Autoconf test @code{AC_FUNC_ALLOCA} to test for and properly make
available this function.  The @code{AC_FUNC_ALLOCA} test requires that
client code use a block of preprocessor code to be safe (see the Autoconf
manual for more); this header incorporates that logic and more, including
the possibility of a GCC built-in function.

@end deftypefn

*/

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#include <libiberty.h>

#ifdef HAVE_STRING_H
#include <string.h>
#endif
#ifdef HAVE_STDLIB_H
#include <stdlib.h>
#endif

/* These variables are used by the ASTRDUP implementation that relies
   on C_alloca.  */
const char *libiberty_optr;
char *libiberty_nptr;
unsigned long libiberty_len;

/* If your stack is a linked list of frames, you have to
   provide an "address metric" ADDRESS_FUNCTION macro.  */

#if defined (CRAY) && defined (CRAY_STACKSEG_END)
static long i00afunc ();
#define ADDRESS_FUNCTION(arg) (char *) i00afunc (&(arg))
#else
#define ADDRESS_FUNCTION(arg) &(arg)
#endif

#ifndef NULL
#define NULL    0
#endif

/* 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.  */