/**************************************************************************** * mm/mm_heap/mm_memalign.c * * Copyright (C) 2007, 2009, 2011, 2013-2014 Gregory Nutt. All rights reserved. * Author: Gregory Nutt * * 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 ****************************************************************************/ #include #include #include /**************************************************************************** * Public Functions ****************************************************************************/ /**************************************************************************** * Name: mm_memalign * * Description: * memalign requests more than enough space from malloc, finds a region * within that chunk that meets the alignment request and then frees any * leading or trailing space. * * The alignment argument must be a power of two (not checked). 8-byte * alignment is guaranteed by normal malloc calls. * ****************************************************************************/ FAR void *mm_memalign(FAR struct mm_heap_s *heap, size_t alignment, size_t size) { FAR struct mm_allocnode_s *node; size_t rawchunk; size_t alignedchunk; size_t mask = (size_t)(alignment - 1); size_t allocsize; /* If this requested alinement's less than or equal to the natural alignment * of malloc, then just let malloc do the work. */ if (alignment <= MM_MIN_CHUNK) { return mm_malloc(heap, size); } /* Adjust the size to account for (1) the size of the allocated node, (2) * to make sure that it is an even multiple of our granule size, and to * include the alignment amount. * * Notice that we increase the allocation size by twice the requested * alignment. We do this so that there will be at least two valid * alignment points within the allocated memory. * * NOTE: These are sizes given to malloc and not chunk sizes. They do * not include SIZEOF_MM_ALLOCNODE. */ size = MM_ALIGN_UP(size); /* Make multiples of our granule size */ allocsize = size + 2*alignment; /* Add double full alignment size */ /* Then malloc that size */ rawchunk = (size_t)mm_malloc(heap, allocsize); if (rawchunk == 0) { return NULL; } /* We need to hold the MM semaphore while we muck with the chunks and * nodelist. */ mm_takesemaphore(heap); /* Get the node associated with the allocation and the next node after * the allocation. */ node = (FAR struct mm_allocnode_s *)(rawchunk - SIZEOF_MM_ALLOCNODE); /* Find the aligned subregion */ alignedchunk = (rawchunk + mask) & ~mask; /* Check if there is free space at the beginning of the aligned chunk */ if (alignedchunk != rawchunk) { FAR struct mm_allocnode_s *newnode; FAR struct mm_allocnode_s *next; size_t precedingsize; /* Get the node the next node after the allocation. */ next = (FAR struct mm_allocnode_s *)((FAR char *)node + node->size); /* Make sure that there is space to convert the preceding mm_allocnode_s * into an mm_freenode_s. I think that this should always be true */ DEBUGASSERT(alignedchunk >= rawchunk + 8); newnode = (FAR struct mm_allocnode_s *)(alignedchunk - SIZEOF_MM_ALLOCNODE); /* Preceding size is full size of the new 'node,' including * SIZEOF_MM_ALLOCNODE */ precedingsize = (size_t)newnode - (size_t)node; /* If we were unlucky, then the alignedchunk can lie in such a position * that precedingsize < SIZEOF_NODE_FREENODE. We can't let that happen * because we are going to cast 'node' to struct mm_freenode_s below. * This is why we allocated memory large enough to support two * alignment points. In this case, we will simply use the second * alignment point. */ if (precedingsize < SIZEOF_MM_FREENODE) { alignedchunk += alignment; newnode = (FAR struct mm_allocnode_s *)(alignedchunk - SIZEOF_MM_ALLOCNODE); precedingsize = (size_t)newnode - (size_t)node; } /* Set up the size of the new node */ newnode->size = (size_t)next - (size_t)newnode; newnode->preceding = precedingsize | MM_ALLOC_BIT; /* Reduce the size of the original chunk and mark it not allocated, */ node->size = precedingsize; node->preceding &= ~MM_ALLOC_BIT; /* Fix the preceding size of the next node */ next->preceding = newnode->size | (next->preceding & MM_ALLOC_BIT); /* Convert the newnode chunk size back into malloc-compatible size by * subtracting the header size SIZEOF_MM_ALLOCNODE. */ allocsize = newnode->size - SIZEOF_MM_ALLOCNODE; /* Add the original, newly freed node to the free nodelist */ mm_addfreechunk(heap, (FAR struct mm_freenode_s *)node); /* Replace the original node with the newlay realloaced, * aligned node */ node = newnode; } /* Check if there is free space at the end of the aligned chunk */ if (allocsize > size) { /* Shrink the chunk by that much -- remember, mm_shrinkchunk wants * internal chunk sizes that include SIZEOF_MM_ALLOCNODE, and not the * malloc-compatible sizes that we have. */ mm_shrinkchunk(heap, node, size + SIZEOF_MM_ALLOCNODE); } mm_givesemaphore(heap); return (FAR void *)alignedchunk; }