libgloss/crx/sbrk.c

   1 /* sbrk.c -- Implementation of the low-level sbrk() routine
   2  *
   3  * Copyright (c) 2004 National Semiconductor Corporation
   4  *
   5  * The authors hereby grant permission to use, copy, modify, distribute,
   6  * and license this software and its documentation for any purpose, provided
   7  * that existing copyright notices are retained in all copies and that this
   8  * notice is included verbatim in any distributions. No written agreement,
   9  * license, or royalty fee is required for any of the authorized uses.
  10  * Modifications to this software may be copyrighted by their authors
  11  * and need not follow the licensing terms described here, provided that
  12  * the new terms are clearly indicated on the first page of each file where
  13  * they apply.
  14  */
  15
  16 #include <errno.h>
  17 #include <stddef.h> /* where ptrdiff_t is defined */
  18 #include <stdlib.h>
  19
  20 /* Extend heap space by size bytes.
  21    Return start of new space allocated, or -1 for errors
  22    Error cases:
  23     1. Allocation is not within heap range */
  24
  25 void * sbrk (ptrdiff_t size)
  26 {
  27   /*
  28   * The following two memory locations should be defined in the linker script file
  29   */
  30   extern const char _HEAP_START; /* start of heap */
  31   extern const char _HEAP_MAX;   /* end of heap (maximum value of heap_ptr) */
  32
  33   static const char * heap_ptr;  /* pointer to head of heap */
  34   const char * old_heap_ptr;
  35   static unsigned char init_sbrk = 0;
  36
  37   /* heap_ptr is initialized to HEAP_START */
  38   if (init_sbrk == 0)
  39   {
  40     heap_ptr = &_HEAP_START;
  41     init_sbrk = 1;
  42   }
  43
  44   old_heap_ptr = heap_ptr;
  45
  46   if ((heap_ptr + size) > &_HEAP_MAX)
  47   {
  48     /* top of heap is bigger than _HEAP_MAX */
  49     errno = ENOMEM;
  50     return (void *) -1;
  51   }
  52
  53   /* success: update heap_ptr and return previous value */
  54   heap_ptr += size;
  55   return (void *)old_heap_ptr;
  56 }