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/*
* libc/stdlib/malloc/malloc.c -- malloc function
*
* Copyright (C) 2002 NEC Corporation
* Copyright (C) 2002 Miles Bader <miles@gnu.org>
*
* This file is subject to the terms and conditions of the GNU Lesser
* General Public License. See the file COPYING.LIB in the main
* directory of this archive for more details.
*
* Written by Miles Bader <miles@gnu.org>
*/
#include <stdlib.h>
#include <sys/mman.h>
#include "malloc.h"
#include "heap.h"
/* When we give memory to the heap, start this many bytes after the
beginning of the mmaped block. This is because we must ensure that
malloc return values are aligned to MALLOC_ALIGNMENT, but since we need
to use one word _before_ the beginning of that, we actually want the heap
to return values that are MALLOC_ALIGNMENT aligned - sizeof (size_t).
Since the heap always allocates in multiples of HEAP_GRANULARITY, we can
do this by (1) ensuring that HEAP_GRANULARITY is a multiple of
MALLOC_ALIGNMENT, and (2) making sure that the heap's free areas start
sizeof(size_t) bytes before our required alignment. */
#define MALLOC_HEAP_BLOCK_SHIM (MALLOC_ALIGNMENT - sizeof (size_t))
/* The heap used for small allocations. */
struct heap __malloc_heap = HEAP_INIT;
void *malloc (size_t size)
{
void *mem;
MALLOC_DEBUG ("malloc: %d bytes\n", size);
/* Include an extra word to record the size of the allocated block. */
size += sizeof (size_t);
if (size >= MALLOC_MMAP_THRESHOLD)
/* Use mmap for large allocations. */
{
/* Make sure we request enough memory to align the result correctly,
and that SIZE reflects that mmap hands back whole pages. */
size += MALLOC_ROUND_UP_TO_PAGE_SIZE (MALLOC_ALIGNMENT - sizeof(size_t));
mem = mmap (0, size, PROT_READ | PROT_WRITE,
MAP_SHARED | MAP_ANONYMOUS, 0, 0);
if (mem == MAP_FAILED)
return 0;
}
else
/* Use the heap for small allocations. */
{
mem = __heap_alloc (&__malloc_heap, &size);
if (! mem)
/* We couldn't allocate from the heap, so get some more memory
from the system, add it to the heap, and try again. */
{
/* If we're trying to allocate a block bigger than the default
MALLOC_HEAP_EXTEND_SIZE, make sure we get enough to hold it. */
size_t block_size = (size < MALLOC_HEAP_EXTEND_SIZE
? MALLOC_HEAP_EXTEND_SIZE
: MALLOC_ROUND_UP_TO_PAGE_SIZE (size));
/* Allocate the new heap block. */
void *block = mmap (0, block_size,
PROT_READ | PROT_WRITE,
MAP_SHARED | MAP_ANONYMOUS, 0, 0);
if (block != MAP_FAILED)
{
/* Put BLOCK into the heap. We first try to append BLOCK to
an existing free area, which is more efficient because it
doesn't require using a `shim' at the beginning (which
would prevent merging free-areas); since mmap often returns
contiguous areas, this is worth it. */
if (! __heap_append_free (&__malloc_heap, block, block_size))
/* Couldn't append, just add BLOCK as a new free-area. */
__heap_free (&__malloc_heap,
block + MALLOC_HEAP_BLOCK_SHIM,
block_size - MALLOC_HEAP_BLOCK_SHIM);
/* Try again to allocate. */
mem = __heap_alloc (&__malloc_heap, &size);
}
}
}
if (mem)
/* Record the size of this block just before the returned address. */
{
*(size_t *)mem = size;
mem = (size_t *)mem + 1;
MALLOC_DEBUG (" malloc: returning 0x%lx (base:0x%lx, total_size:%d)\n",
(long)mem, (long)mem - sizeof (size_t), size);
}
return mem;
}
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