mm/mm_malloc.c

/************************************************************
 * mm/mm_malloc.c
 *
 *   Copyright (C) 2007, 2009 Gregory Nutt. All rights reserved.
 *   Author: Gregory Nutt <spudmonkey@racsa.co.cr>
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 * 3. Neither the name NuttX nor the names of its contributors may be
 *    used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
 * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 *
 ************************************************************/

/************************************************************
 * Included Files
 ************************************************************/

/* Special definitions when we operate in the normal vs. the
 * host-pc test environement.
 */

#include <assert.h>
#include "mm_environment.h"
#include "mm_internal.h"

/************************************************************
 * Pre-processor Definitions
 ************************************************************/

#ifndef NULL
#  define NULL ((void*)0)
#endif

/************************************************************
 * Type Definitions
 ************************************************************/

/************************************************************
 * Private Data
 ************************************************************/

/************************************************************
 * Public Data
 ************************************************************/

/************************************************************
 * Private Functions
 ************************************************************/

/************************************************************
 * Public Functions
 ************************************************************/

/************************************************************
 * malloc
 *
 * Description:
 *  Find the smallest chunk that satisfies the request.
 *  Take the memory from that chunk, save the remaining,
 *  smaller chunk (if any).
 *
 *  8-byte alignment of the allocated data is assured.
 *
 ************************************************************/

FAR void *malloc(size_t size)
{
  FAR struct mm_freenode_s *node;
  void *ret = NULL;
  int ndx;

  /* Handle bad sizes */

  if (size <= 0)
    {
      return NULL;
    }

  /* Adjust the size to account for (1) the size of the allocated
   * node and (2) to make sure that it is an even multiple of
   * our granule size.
   */

  size = MM_ALIGN_UP(size + SIZEOF_MM_ALLOCNODE);

  /* We need to hold the MM semaphore while we muck with the
   * nodelist.
   */

  mm_takesemaphore();

  /* Get the location in the node list to start the search.
   * Special case really big alloctions
   */

  if (size >= MM_MAX_CHUNK)
    {
      ndx = MM_NNODES-1;
    }
  else
    {
      /* Convert the request size into a nodelist index */

      ndx = mm_size2ndx(size);
    }

  /* Search for a large enough chunk in the list of nodes.
   * This list is ordered by size, but will have occasional
   * zero sized nodes as we visit other g_nodelist[] entries.
   */

  for (node = g_nodelist[ndx].flink;
       node && node->size < size;
       node = node->flink);

  /* If we found a node with non-zero size, then this is one
   * to use. Since the list is ordered, we know that is must be
   * best fitting chunk available.
   */

  if (node)
    {
      FAR struct mm_freenode_s *remainder;
      FAR struct mm_freenode_s *next;
      size_t remaining;

      /* Remove the node.  There must be a predecessor, but there may
       * not be a successor node.
       */

      DEBUGASSERT(node->blink);
      node->blink->flink = node->flink;
      if (node->flink)
        {
          node->flink->blink = node->blink;
        }

      /* Check if we have to split the free node into one of the
       * allocated size and another smaller freenode.  In some
       * cases, the remaining bytes can be smaller (they may be
       * SIZEOF_MM_ALLOCNODE).  In that case, we will just carry
       * the few wasted bytes at the end of the allocation.
       */

      remaining = node->size - size;
      if (remaining >= SIZEOF_MM_FREENODE)
        {
          /* Get a pointer to the next node in physical memory */

          next = (FAR struct mm_freenode_s*)(((char*)node) + node->size);

          /* Create the remainder node */

          remainder = (FAR struct mm_freenode_s*)(((char*)node) + size);
          remainder->size = remaining;
          remainder->preceding = size;

          /* Adjust the size of the node under consideration */

          node->size = size;

          /* Adjust the 'preceding' size of the (old) next node,
           * preserving the allocated flag.
           */

          next->preceding = remaining | (next->preceding & MM_ALLOC_BIT);

          /* Add the remainder back into the nodelist */

          mm_addfreechunk(remainder);
        }

      /* Handle the case of an exact size match */

      node->preceding |= MM_ALLOC_BIT;
      ret = (void*)((char*)node + SIZEOF_MM_ALLOCNODE);
    }

  mm_givesemaphore();
  mvdbg("Allocated %p\n", ret);
  return ret;
}