209 lines
7.1 KiB
C
209 lines
7.1 KiB
C
/****************************************************************************
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* mm/mm_memalign.c
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*
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* Copyright (C) 2007, 2009, 2011 Gregory Nutt. All rights reserved.
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* Author: Gregory Nutt <gnutt@nuttx.org>
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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*
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in
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* the documentation and/or other materials provided with the
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* distribution.
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* 3. Neither the name NuttX nor the names of its contributors may be
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* used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
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* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
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* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
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* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
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* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
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* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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* POSSIBILITY OF SUCH DAMAGE.
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*
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****************************************************************************/
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/****************************************************************************
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* Included Files
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****************************************************************************/
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#include <assert.h>
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#include "mm_environment.h"
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#include "mm_internal.h"
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/****************************************************************************
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* Pre-processor Definitions
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****************************************************************************/
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/****************************************************************************
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* Global Functions
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****************************************************************************/
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/****************************************************************************
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* Name: memalign
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*
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* Description:
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* memalign requests more than enough space from malloc, finds a region
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* within that chunk that meets the alignment request and then frees any
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* leading or trailing space.
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*
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* The alignment argument must be a power of two (not checked). 8-byte
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* alignment is guaranteed by normal malloc calls.
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*
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****************************************************************************/
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FAR void *memalign(size_t alignment, size_t size)
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{
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FAR struct mm_allocnode_s *node;
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size_t rawchunk;
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size_t alignedchunk;
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size_t mask = (size_t)(alignment - 1);
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size_t allocsize;
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/* If this requested alignement less than or equal to the natural alignment
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* of malloc, then just let malloc do the work.
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*/
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if (alignment <= MM_MIN_CHUNK)
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{
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return malloc(size);
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}
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/* Adjust the size to account for (1) the size of the allocated node, (2)
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* to make sure that it is an even multiple of our granule size, and to
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* include the alignment amount.
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*
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* Notice that we increase the allocation size by twice the requested
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* alignment. We do this so that there will be at least two valid
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* alignment points within the allocated memory.
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*
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* NOTE: These are sizes given to malloc and not chunk sizes. They do
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* not include SIZEOF_MM_ALLOCNODE.
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*/
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size = MM_ALIGN_UP(size); /* Make multiples of our granule size */
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allocsize = size + 2*alignment; /* Add double full alignment size */
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/* Then malloc that size */
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rawchunk = (size_t)malloc(allocsize);
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if (rawchunk == 0)
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{
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return NULL;
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}
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/* We need to hold the MM semaphore while we muck with the chunks and
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* nodelist.
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*/
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mm_takesemaphore();
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/* Get the node associated with the allocation and the next node after
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* the allocation.
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*/
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node = (FAR struct mm_allocnode_s*)(rawchunk - SIZEOF_MM_ALLOCNODE);
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/* Find the aligned subregion */
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alignedchunk = (rawchunk + mask) & ~mask;
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/* Check if there is free space at the beginning of the aligned chunk */
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if (alignedchunk != rawchunk)
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{
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FAR struct mm_allocnode_s *newnode;
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FAR struct mm_allocnode_s *next;
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size_t precedingsize;
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/* Get the node the next node after the allocation. */
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next = (FAR struct mm_allocnode_s*)((char*)node + node->size);
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/* Make sure that there is space to convert the preceding mm_allocnode_s
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* into an mm_freenode_s. I think that this should always be true
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*/
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DEBUGASSERT(alignedchunk >= rawchunk + 8);
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newnode = (FAR struct mm_allocnode_s*)(alignedchunk - SIZEOF_MM_ALLOCNODE);
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/* Preceding size is full size of the new 'node,' including
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* SIZEOF_MM_ALLOCNODE
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*/
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precedingsize = (size_t)newnode - (size_t)node;
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/* If we were unlucky, then the alignedchunk can lie in such a position
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* that precedingsize < SIZEOF_NODE_FREENODE. We can't let that happen
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* because we are going to cast 'node' to struct mm_freenode_s below.
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* This is why we allocated memory large enough to support two
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* alignment points. In this case, we will simply use the second
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* alignment point.
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*/
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if (precedingsize < SIZEOF_MM_FREENODE)
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{
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alignedchunk += alignment;
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newnode = (FAR struct mm_allocnode_s*)(alignedchunk - SIZEOF_MM_ALLOCNODE);
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precedingsize = (size_t)newnode - (size_t)node;
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}
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/* Set up the size of the new node */
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newnode->size = (size_t)next - (size_t)newnode;
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newnode->preceding = precedingsize | MM_ALLOC_BIT;
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/* Reduce the size of the original chunk and mark it not allocated, */
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node->size = precedingsize;
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node->preceding &= ~MM_ALLOC_BIT;
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/* Fix the preceding size of the next node */
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next->preceding = newnode->size | (next->preceding & MM_ALLOC_BIT);
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/* Convert the newnode chunk size back into malloc-compatible size by
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* subtracting the header size SIZEOF_MM_ALLOCNODE.
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*/
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allocsize = newnode->size - SIZEOF_MM_ALLOCNODE;
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/* Add the original, newly freed node to the free nodelist */
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mm_addfreechunk((FAR struct mm_freenode_s *)node);
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/* Replace the original node with the newlay realloaced,
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* aligned node
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*/
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node = newnode;
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}
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/* Check if there is free space at the end of the aligned chunk */
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if (allocsize > size)
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{
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/* Shrink the chunk by that much -- remember, mm_shrinkchunk wants
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* internal chunk sizes that include SIZEOF_MM_ALLOCNODE, and not the
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* malloc-compatible sizes that we have.
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*/
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mm_shrinkchunk(node, size + SIZEOF_MM_ALLOCNODE);
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}
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mm_givesemaphore();
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return (FAR void*)alignedchunk;
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}
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