#include <common.h>
#if defined(CONFIG_UNIT_TEST)
#define DEBUG
#endif
#include <malloc.h>
#include <asm/io.h>
#ifdef DEBUG
#if __STD_C
static void malloc_update_mallinfo (void);
void malloc_stats (void);
#else
static void malloc_update_mallinfo ();
void malloc_stats();
#endif
#endif /* DEBUG */
DECLARE_GLOBAL_DATA_PTR;
/*
Emulation of sbrk for WIN32
All code within the ifdef WIN32 is untested by me.
Thanks to Martin Fong and others for supplying this.
*/
#ifdef WIN32
#define AlignPage(add) (((add) + (malloc_getpagesize-1)) & \
~(malloc_getpagesize-1))
#define AlignPage64K(add) (((add) + (0x10000 - 1)) & ~(0x10000 - 1))
/* resrve 64MB to insure large contiguous space */
#define RESERVED_SIZE (1024*1024*64)
#define NEXT_SIZE (2048*1024)
#define TOP_MEMORY ((unsigned long)2*1024*1024*1024)
struct GmListElement;
typedef struct GmListElement GmListElement;
struct GmListElement
{
GmListElement* next;
void* base;
};
static GmListElement* head = 0;
static unsigned int gNextAddress = 0;
static unsigned int gAddressBase = 0;
static unsigned int gAllocatedSize = 0;
static
GmListElement* makeGmListElement (void* bas)
{
GmListElement* this;
this = (GmListElement*)(void*)LocalAlloc (0, sizeof (GmListElement));
assert (this);
if (this)
{
this->base = bas;
this->next = head;
head = this;
}
return this;
}
void gcleanup ()
{
BOOL rval;
assert ( (head == NULL) || (head->base == (void*)gAddressBase));
if (gAddressBase && (gNextAddress - gAddressBase))
{
rval = VirtualFree ((void*)gAddressBase,
gNextAddress - gAddressBase,
MEM_DECOMMIT);
assert (rval);
}
while (head)
{
GmListElement* next = head->next;
rval = VirtualFree (head->base, 0, MEM_RELEASE);
assert (rval);
LocalFree (head);
head = next;
}
}
static
void* findRegion (void* start_address, unsigned long size)
{
MEMORY_BASIC_INFORMATION info;
if (size >= TOP_MEMORY) return NULL;
while ((unsigned long)start_address + size < TOP_MEMORY)
{
VirtualQuery (start_address, &info, sizeof (info));
if ((info.State == MEM_FREE) && (info.RegionSize >= size))
return start_address;
else
{
/* Requested region is not available so see if the */
/* next region is available. Set 'start_address' */
/* to the next region and call 'VirtualQuery()' */
/* again. */
start_address = (char*)info.BaseAddress + info.RegionSize;
/* Make sure we start looking for the next region */
/* on the *next* 64K boundary. Otherwise, even if */
/* the new region is free according to */
/* 'VirtualQuery()', the subsequent call to */
/* 'VirtualAlloc()' (which follows the call to */
/* this routine in 'wsbrk()') will round *down* */
/* the requested address to a 64K boundary which */
/* we already know is an address in the */
/* unavailable region. Thus, the subsequent call */
/* to 'VirtualAlloc()' will fail and bring us back */
/* here, causing us to go into an infinite loop. */
start_address =
(void *) AlignPage64K((unsigned long) start_address);
}
}
return NULL;
}
void* wsbrk (long size)
{
void* tmp;
if (size > 0)
{
if (gAddressBase == 0)
{
gAllocatedSize = max (RESERVED_SIZE, AlignPage (size));
gNextAddress = gAddressBase =
(unsigned int)VirtualAlloc (NULL, gAllocatedSize,
MEM_RESERVE, PAGE_NOACCESS);
} else if (AlignPage (gNextAddress + size) > (gAddressBase +
gAllocatedSize))
{
long new_size = max (NEXT_SIZE, AlignPage (size));
void* new_address = (void*)(gAddressBase+gAllocatedSize);
do
{
new_address = findRegion (new_address, new_size);
if (!new_address)
return (void*)-1;
gAddressBase = gNextAddress =
(unsigned int)VirtualAlloc (new_address, new_size,
MEM_RESERVE, PAGE_NOACCESS);
/* repeat in case of race condition */
/* The region that we found has been snagged */
/* by another thread */
}
while (gAddressBase == 0);
assert (new_address == (void*)gAddressBase);
gAllocatedSize = new_size;
if (!makeGmListElement ((void*)gAddressBase))
return (void*)-1;
}
if ((size + gNextAddress) > AlignPage (gNextAddress))
{
void* res;
res = VirtualAlloc ((void*)AlignPage (gNextAddress),
(size + gNextAddress -
AlignPage (gNextAddress)),
MEM_COMMIT, PAGE_READWRITE);
if (!res)
return (void*)-1;
}
tmp = (void*)gNextAddress;
gNextAddress = (unsigned int)tmp + size;
return tmp;
}
else if (size < 0)
{
unsigned int alignedGoal = AlignPage (gNextAddress + size);
/* Trim by releasing the virtual memory */
if (alignedGoal >= gAddressBase)
{
VirtualFree ((void*)alignedGoal, gNextAddress - alignedGoal,
MEM_DECOMMIT);
gNextAddress = gNextAddress + size;
return (void*)gNextAddress;
}
else
{
VirtualFree ((void*)gAddressBase, gNextAddress - gAddressBase,
MEM_DECOMMIT);
gNextAddress = gAddressBase;
return (void*)-1;
}
}
else
{
return (void*)gNextAddress;
}
}
#endif
/*
Type declarations
*/
struct malloc_chunk
{
INTERNAL_SIZE_T prev_size; /* Size of previous chunk (if free). */
INTERNAL_SIZE_T size; /* Size in bytes, including overhead. */
struct malloc_chunk* fd; /* double links -- used only if free. */
struct malloc_chunk* bk;
} __attribute__((__may_alias__)) ;
typedef struct malloc_chunk* mchunkptr;
/*
malloc_chunk details:
(The following includes lightly edited explanations by Colin Plumb.)
Chunks of memory are maintained using a `boundary tag' method as
described in e.g., Knuth or Standish. (See the paper by Paul
Wilson ftp://ftp.cs.utexas.edu/pub/garbage/allocsrv.ps for a
survey of such techniques.) Sizes of free chunks are stored both
in the front of each chunk and at the end. This makes
consolidating fragmented chunks into bigger chunks very fast. The
size fields also hold bits representing whether chunks are free or
in use.
An allocated chunk looks like this:
chunk-> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Size of previous chunk, if allocated | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Size of chunk, in bytes |P|
mem-> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| User data starts here... .
. .
. (malloc_usable_space() bytes) .
. |
nextchunk-> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Size of chunk |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where "chunk" is the front of the chunk for the purpose of most of
the malloc code, but "mem" is the pointer that is returned to the
user. "Nextchunk" is the beginning of the next contiguous chunk.
Chunks always begin on even word boundries, so the mem portion
(which is returned to the user) is also on an even word boundary, and
thus double-word aligned.
Free chunks are stored in circular doubly-linked lists, and look like this:
chunk-> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Size of previous chunk |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
`head:' | Size of chunk, in bytes |P|
mem-> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Forward pointer to next chunk in list |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Back pointer to previous chunk in list |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Unused space (may be 0 bytes long) .
. .
. |
nextchunk-> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
`foot:' | Size of chunk, in bytes |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The P (PREV_INUSE) bit, stored in the unused low-order bit of the
chunk size (which is always a multiple of two words), is an in-use
bit for the *previous* chunk. If that bit is *clear*, then the
word before the current chunk size contains the previous chunk
size, and can be used to find the front of the previous chunk.
(The very first chunk allocated always has this bit set,
preventing access to non-existent (or non-owned) memory.)
Note that the `foot' of the current chunk is actually represented
as the prev_size of the NEXT chunk. (This makes it easier to
deal with alignments etc).
The two exceptions to all this are
1. The special chunk `top', which doesn't bother using the
trailing size field since there is no
next contiguous chunk that would have to index off it. (After
initialization, `top' is forced to always exist. If it would
become less than MINSIZE bytes long, it is replenished via
malloc_extend_top.)
2. Chunks allocated via mmap, which have the second-lowest-order
bit (IS_MMAPPED) set in their size fields. Because they are
never merged or traversed from any other chunk, they have no
foot size or inuse information.
Available chunks are kept in any of several places (all declared below):
* `av': An array of chunks serving as bin headers for consolidated
chunks. Each bin is doubly linked. The bins are approximately
proportionally (log) spaced. There are a lot of these bins
(128). This may look excessive, but works very well in
practice. All procedures maintain the invariant that no
consolidated chunk physically borders another one. Chunks in
bins are kept in size order, with ties going to the
approximately least recently used chunk.
The chunks in each bin are maintained in decreasing sorted order by
size. This is irrelevant for the small bins, which all contain
the same-sized chunks, but facilitates best-fit allocation for
larger chunks. (These lists are just sequential. Keeping them in
order almost never requires enough traversal to warrant using
fancier ordered data structures.) Chunks of the same size are
linked with the most recently freed at the front, and allocations
are taken from the back. This results in LRU or FIFO allocation
order, which tends to give each chunk an equal opportunity to be
consolidated with adjacent freed chunks, resulting in larger free
chunks and less fragmentation.
* `top': The top-most available chunk (i.e., the one bordering the
end of available memory) is treated specially. It is never
included in any bin, is used only if no other chunk is
available, and is released back to the system if it is very
large (see M_TRIM_THRESHOLD).
* `last_remainder': A bin holding only the remainder of the
most recently split (non-top) chunk. This bin is checked
before other non-fitting chunks, so as to provide better
locality for runs of sequentially allocated chunks.
* Implicitly, through the host system's memory mapping tables.
If supported, requests greater than a threshold are usually
serviced via calls to mmap, and then later released via munmap.
*/
/* sizes, alignments */
#define SIZE_SZ (sizeof(INTERNAL_SIZE_T))
#define MALLOC_ALIGNMENT (SIZE_SZ + SIZE_SZ)
#define MALLOC_ALIGN_MASK (MALLOC_ALIGNMENT - 1)
#define MINSIZE (sizeof(struct malloc_chunk))
/* conversion from malloc headers to user pointers, and back */
#define chunk2mem(p) ((Void_t*)((char*)(p) + 2*SIZE_SZ))
#define mem2chunk(mem) ((mchunkptr)((char*)(mem) - 2*SIZE_SZ))
/* pad request bytes into a usable size */
#define request2size(req) \
(((long)((req) + (SIZE_SZ + MALLOC_ALIGN_MASK)) < \
(long)(MINSIZE + MALLOC_ALIGN_MASK)) ? MINSIZE : \
(((req) + (SIZE_SZ + MALLOC_ALIGN_MASK)) & ~(MALLOC_ALIGN_MASK)))
/* Check if m has acceptable alignment */
#define aligned_OK(m) (((unsigned long)((m)) & (MALLOC_ALIGN_MASK)) == 0)
/*
Physical chunk operations
*/
/* size field is or'ed with PREV_INUSE when previous adjacent chunk in use */
#define PREV_INUSE 0x1
/* size field is or'ed with IS_MMAPPED if the chunk was obtained with mmap() */
#define IS_MMAPPED 0x2
/* Bits to mask off when extracting size */
#define SIZE_BITS (PREV_INUSE|IS_MMAPPED)
/* Ptr to next physical malloc_chunk. */
#define next_chunk(p) ((mchunkptr)( ((char*)(p)) + ((p)->size & ~PREV_INUSE) ))
/* Ptr to previous physical malloc_chunk */
#define prev_chunk(p)\
((mchunkptr)( ((char*)(p)) - ((p)->prev_size) ))
/* Treat space at ptr + offset as a chunk */
#define chunk_at_offset(p, s) ((mchunkptr)(((char*)(p)) + (s)))
/*
Dealing with use bits
*/
/* extract p's inuse bit */
#define inuse(p)\
((((mchunkptr)(((char*)(p))+((p)->size & ~PREV_INUSE)))->size) & PREV_INUSE)
/* extract inuse bit of previous chunk */
#define prev_inuse(p) ((p)->size & PREV_INUSE)
/* check for mmap()'ed chunk */
#define chunk_is_mmapped(p) ((p)->size & IS_MMAPPED)
/* set/clear chunk as in use without otherwise disturbing */
#define set_inuse(p)\
((mchunkptr)(((char*)(p)) + ((p)->size & ~PREV_INUSE)))->size |= PREV_INUSE
#define clear_inuse(p)\
((mchunkptr)(((char*)(p)) + ((p)->size & ~PREV_INUSE)))->size &= ~(PREV_INUSE)
/* check/set/clear inuse bits in known places */
#define inuse_bit_at_offset(p, s)\
(((mchunkptr)(((char*)(p)) + (s)))->size & PREV_INUSE)
#define set_inuse_bit_at_offset(p, s)\
(((mchunkptr)(((char*)(p)) + (s)))->size |= PREV_INUSE)
#define clear_inuse_bit_at_offset(p, s)\
(((mchunkptr)(((char*)(p)) + (s)))->size &= ~(PREV_INUSE))
/*
Dealing with size fields
*/
/* Get size, ignoring use bits */
#define chunksize(p) ((p)->size & ~(SIZE_BITS))
/* Set size at head, without disturbing its use bit */
#define set_head_size(p, s) ((p)->size = (((p)->size & PREV_INUSE) | (s)))
/* Set size/use ignoring previous bits in header */
#define set_head(p, s) ((p)->size = (s))
/* Set size at footer (only when chunk is not in use) */
#define set_foot(p, s) (((mchunkptr)((char*)(p) + (s)))->prev_size = (s))
/*
Bins
The bins, `av_' are an array of pairs of pointers serving as the
heads of (initially empty) doubly-linked lists of chunks, laid out
in a way so that each pair can be treated as if it were in a
malloc_chunk. (This way, the fd/bk offsets for linking bin heads
and chunks are the same).
Bins for sizes < 512 bytes contain chunks of all the same size, spaced
8 bytes apart. Larger bins are approximately logarithmically
spaced. (See the table below.) The `av_' array is never mentioned
directly in the code, but instead via bin access macros.
Bin layout:
64 bins of size 8
32 bins of size 64
16 bins of size 512
8 bins of size 4096
4 bins of size 32768
2 bins of size 262144
1 bin of size what's left
There is actually a little bit of slop in the numbers in bin_index
for the sake of speed. This makes no difference elsewhere.
The special chunks `top' and `last_remainder' get their own bins,
(this is implemented via yet more trickery with the av_ array),
although `top' is never properly linked to its bin since it is
always handled specially.
*/
#define NAV 128 /* number of bins */
typedef struct malloc_chunk* mbinptr;
/* access macros */
#define bin_at(i) ((mbinptr)((char*)&(av_[2*(i) + 2]) - 2*SIZE_SZ))
#define next_bin(b) ((mbinptr)((char*)(b) + 2 * sizeof(mbinptr)))
#define prev_bin(b) ((mbinptr)((char*)(b) - 2 * sizeof(mbinptr)))
/*
The first 2 bins are never indexed. The corresponding av_ cells are instead
used for bookkeeping. This is not to save space, but to simplify
indexing, maintain locality, and avoid some initialization tests.
*/
#define top (av_[2]) /* The topmost chunk */
#define last_remainder (bin_at(1)) /* remainder from last split */
/*
Because top initially points to its own bin with initial
zero size, thus forcing extension on the first malloc request,
we avoid having any special code in malloc to check whether
it even exists yet. But we still need to in malloc_extend_top.
*/
#define initial_top ((mchunkptr)(bin_at(0)))
/* Helper macro to initialize bins */
#define IAV(i) bin_at(i), bin_at(i)
static mbinptr av_[NAV * 2 + 2] = {
NULL, NULL,
IAV(0), IAV(1), IAV(2), IAV(3), IAV(4), IAV(5), IAV(6), IAV(7),
IAV(8), IAV(9), IAV(10), IAV(11), IAV(12), IAV(13), IAV(14), IAV(15),
IAV(16), IAV(17), IAV(18), IAV(19), IAV(20), IAV(21), IAV(22), IAV(23),
IAV(24), IAV(25), IAV(26), IAV(27), IAV(28), IAV(29), IAV(30), IAV(31),
IAV(32), IAV(33), IAV(34), IAV(35), IAV(36), IAV(37), IAV(38), IAV(39),
IAV(40), IAV(41), IAV(42), IAV(43), IAV(44), IAV(45), IAV(46), IAV(47),
IAV(48), IAV(49), IAV(50), IAV(51), IAV(52), IAV(53), IAV(54), IAV(55),
IAV(56), IAV(57), IAV(58), IAV(59), IAV(60), IAV(61), IAV(62), IAV(63),
IAV(64), IAV(65), IAV(66), IAV(67), IAV(68), IAV(69), IAV(70), IAV(71),
IAV(72), IAV(73), IAV(74), IAV(75), IAV(76), IAV(77), IAV(78), IAV(79),
IAV(80), IAV(81), IAV(82), IAV(83), IAV(84), IAV(85), IAV(86), IAV(87),
IAV(88), IAV(89), IAV(90), IAV(91), IAV(92), IAV(93), IAV(94), IAV(95),
IAV(96), IAV(97), IAV(98), IAV(99), IAV(100), IAV(101), IAV(102), IAV(103),
IAV(104), IAV(105), IAV(106), IAV(107), IAV(108), IAV(109), IAV(110), IAV(111),
IAV(112), IAV(113), IAV(114), IAV(115), IAV(116), IAV(117), IAV(118), IAV(119),
IAV(120), IAV(121), IAV(122), IAV(123), IAV(124), IAV(125), IAV(126), IAV(127)
};
#ifdef CONFIG_NEEDS_MANUAL_RELOC
static void malloc_bin_reloc(void)
{
mbinptr *p = &av_[2];
size_t i;
for (i = 2; i < ARRAY_SIZE(av_); ++i, ++p)
*p = (mbinptr)((ulong)*p + gd->reloc_off);
}
#else
static inline void malloc_bin_reloc(void) {}
#endif
ulong mem_malloc_start = 0;
ulong mem_malloc_end = 0;
ulong mem_malloc_brk = 0;
void *sbrk(ptrdiff_t increment)
{
ulong old = mem_malloc_brk;
ulong new = old + increment;
/*
* if we are giving memory back make sure we clear it out since
* we set MORECORE_CLEARS to 1
*/
if (increment < 0)
memset((void *)new, 0, -increment);
if ((new < mem_malloc_start) || (new > mem_malloc_end))
return (void *)MORECORE_FAILURE;
mem_malloc_brk = new;
return (void *)old;
}
void mem_malloc_init(ulong start, ulong size)
{
mem_malloc_start = start;
mem_malloc_end = start + size;
mem_malloc_brk = start;
debug("using memory %#lx-%#lx for malloc()\n", mem_malloc_start,
mem_malloc_end);
#ifdef CONFIG_SYS_MALLOC_CLEAR_ON_INIT
memset((void *)mem_malloc_start, 0x0, size);
#endif
malloc_bin_reloc();
}
/* field-extraction macros */
#define first(b) ((b)->fd)
#define last(b) ((b)->bk)
/*
Indexing into bins
*/
#define bin_index(sz) \
(((((unsigned long)(sz)) >> 9) == 0) ? (((unsigned long)(sz)) >> 3): \
((((unsigned long)(sz)) >> 9) <= 4) ? 56 + (((unsigned long)(sz)) >> 6): \
((((unsigned long)(sz)) >> 9) <= 20) ? 91 + (((unsigned long)(sz)) >> 9): \
((((unsigned long)(sz)) >> 9) <= 84) ? 110 + (((unsigned long)(sz)) >> 12): \
((((unsigned long)(sz)) >> 9) <= 340) ? 119 + (((unsigned long)(sz)) >> 15): \
((((unsigned long)(sz)) >> 9) <= 1364) ? 124 + (((unsigned long)(sz)) >> 18): \
126)
/*
bins for chunks < 512 are all spaced 8 bytes apart, and hold
identically sized chunks. This is exploited in malloc.
*/
#define MAX_SMALLBIN 63
#define MAX_SMALLBIN_SIZE 512
#define SMALLBIN_WIDTH 8
#define smallbin_index(sz) (((unsigned long)(sz)) >> 3)
/*
Requests are `small' if both the corresponding and the next bin are small
*/
#define is_small_request(nb) (nb < MAX_SMALLBIN_SIZE - SMALLBIN_WIDTH)
/*
To help compensate for the large number of bins, a one-level index
structure is used for bin-by-bin searching. `binblocks' is a
one-word bitvector recording whether groups of BINBLOCKWIDTH bins
have any (possibly) non-empty bins, so they can be skipped over
all at once during during traversals. The bits are NOT always
cleared as soon as all bins in a block are empty, but instead only
when all are noticed to be empty during traversal in malloc.
*/
#define BINBLOCKWIDTH 4 /* bins per block */
#define binblocks_r ((INTERNAL_SIZE_T)av_[1]) /* bitvector of nonempty blocks */
#define binblocks_w (av_[1])
/* bin<->block macros */
#define idx2binblock(ix) ((unsigned)1 << (ix / BINBLOCKWIDTH))
#define mark_binblock(ii) (binblocks_w = (mbinptr)(binblocks_r | idx2binblock(ii)))
#define clear_binblock(ii) (binblocks_w = (mbinptr)(binblocks_r & ~(idx2binblock(ii))))
/* Other static bookkeeping data */
/* variables holding tunable values */
static unsigned long trim_threshold = DEFAULT_TRIM_THRESHOLD;
static unsigned long top_pad = DEFAULT_TOP_PAD;
static unsigned int n_mmaps_max = DEFAULT_MMAP_MAX;
static unsigned long mmap_threshold = DEFAULT_MMAP_THRESHOLD;
/* The first value returned from sbrk */
static char* sbrk_base = (char*)(-1);
/* The maximum memory obtained from system via sbrk */
static unsigned long max_sbrked_mem = 0;
/* The maximum via either sbrk or mmap */
static unsigned long max_total_mem = 0;
/* internal working copy of mallinfo */
static struct mallinfo current_mallinfo = { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 };
/* The total memory obtained from system via sbrk */
#define sbrked_mem (current_mallinfo.arena)
/* Tracking mmaps */
#ifdef DEBUG
static unsigned int n_mmaps = 0;
#endif /* DEBUG */
static unsigned long mmapped_mem = 0;
#if HAVE_MMAP
static unsigned int max_n_mmaps = 0;
static unsigned long max_mmapped_mem = 0;
#endif
/*
Debugging support
*/
#ifdef DEBUG
/*
These routines make a number of assertions about the states
of data structures that should be true at all times. If any
are not true, it's very likely that a user program has somehow
trashed memory. (It's also possible that there is a coding error
in malloc. In which case, please report it!)
*/
#if __STD_C
static void do_check_chunk(mchunkptr p)
#else
static void do_check_chunk(p) mchunkptr p;
#endif
{
INTERNAL_SIZE_T sz = p->size & ~PREV_INUSE;
/* No checkable chunk is mmapped */
assert(!chunk_is_mmapped(p));
/* Check for legal address ... */
assert((char*)p >= sbrk_base);
if (p != top)
assert((char*)p + sz <= (char*)top);
else
assert((char*)p + sz <= sbrk_base + sbrked_mem);
}
#if __STD_C
static void do_check_free_chunk(mchunkptr p)
#else
static void do_check_free_chunk(p) mchunkptr p;
#endif
{
INTERNAL_SIZE_T sz = p->size & ~PREV_INUSE;
mchunkptr next = chunk_at_offset(p, sz);
do_check_chunk(p);
/* Check whether it claims to be free ... */
assert(!inuse(p));
/* Unless a special marker, must have OK fields */
if ((long)sz >= (long)MINSIZE)
{
assert((sz & MALLOC_ALIGN_MASK) == 0);
assert(aligned_OK(chunk2mem(p)));
/* ... matching footer field */
assert(next->prev_size == sz);
/* ... and is fully consolidated */
assert(prev_inuse(p));
assert (next == top || inuse(next));
/* ... and has minimally sane links */
assert(p->fd->bk == p);
assert(p->bk->fd == p);
}
else /* markers are always of size SIZE_SZ */
assert(sz == SIZE_SZ);
}
#if __STD_C
static void do_check_inuse_chunk(mchunkptr p)
#else
static void do_check_inuse_chunk(p) mchunkptr p;
#endif
{
mchunkptr next = next_chunk(p);
do_check_chunk(p);
/* Check whether it claims to be in use ... */
assert(inuse(p));
/* ... and is surrounded by OK chunks.
Since more things can be checked with free chunks than inuse ones,
if an inuse chunk borders them and debug is on, it's worth doing them.
*/
if (!prev_inuse(p))
{
mchunkptr prv = prev_chunk(p);
assert(next_chunk(prv) == p);
do_check_free_chunk(prv);
}
if (next == top)
{
assert(prev_inuse(next));
assert(chunksize(next) >= MINSIZE);
}
else if (!inuse(next))
do_check_free_chunk(next);
}
#if __STD_C
static void do_check_malloced_chunk(mchunkptr p, INTERNAL_SIZE_T s)
#else
static void do_check_malloced_chunk(p, s) mchunkptr p; INTERNAL_SIZE_T s;
#endif
{
INTERNAL_SIZE_T sz = p->size & ~PREV_INUSE;
long room = sz - s;
do_check_inuse_chunk(p);
/* Legal size ... */
assert((long)sz >= (long)MINSIZE);
assert((sz & MALLOC_ALIGN_MASK) == 0);
assert(room >= 0);
assert(room < (long)MINSIZE);
/* ... and alignment */
assert(aligned_OK(chunk2mem(p)));
/* ... and was allocated at front of an available chunk */
assert(prev_inuse(p));
}
#define check_free_chunk(P) do_check_free_chunk(P)
#define check_inuse_chunk(P) do_check_inuse_chunk(P)
#define check_chunk(P) do_check_chunk(P)
#define check_malloced_chunk(P,N) do_check_malloced_chunk(P,N)
#else
#define check_free_chunk(P)
#define check_inuse_chunk(P)
#define check_chunk(P)
#define check_malloced_chunk(P,N)
#endif
/*
Macro-based internal utilities
*/
/*
Linking chunks in bin lists.
Call these only with variables, not arbitrary expressions, as arguments.
*/
/*
Place chunk p of size s in its bin, in size order,
putting it ahead of others of same size.
*/
#define frontlink(P, S, IDX, BK, FD) \
{ \
if (S < MAX_SMALLBIN_SIZE) \
{ \
IDX = smallbin_index(S); \
mark_binblock(IDX); \
BK = bin_at(IDX); \
FD = BK->fd; \
P->bk = BK; \
P->fd = FD; \
FD->bk = BK->fd = P; \
} \
else \
{ \
IDX = bin_index(S); \
BK = bin_at(IDX); \
FD = BK->fd; \
if (FD == BK) mark_binblock(IDX); \
else \
{ \
while (FD != BK && S < chunksize(FD)) FD = FD->fd; \
BK = FD->bk; \
} \
P->bk = BK; \
P->fd = FD; \
FD->bk = BK->fd = P; \
} \
}
/* take a chunk off a list */
#define unlink(P, BK, FD) \
{ \
BK = P->bk; \
FD = P->fd; \
FD->bk = BK; \
BK->fd = FD; \
} \
/* Place p as the last remainder */
#define link_last_remainder(P) \
{ \
last_remainder->fd = last_remainder->bk = P; \
P->fd = P->bk = last_remainder; \
}
/* Clear the last_remainder bin */
#define clear_last_remainder \
(last_remainder->fd = last_remainder->bk = last_remainder)
/* Routines dealing with mmap(). */
#if HAVE_MMAP
#if __STD_C
static mchunkptr mmap_chunk(size_t size)
#else
static mchunkptr mmap_chunk(size) size_t size;
#endif
{
size_t page_mask = malloc_getpagesize - 1;
mchunkptr p;
#ifndef MAP_ANONYMOUS
static int fd = -1;
#endif
if(n_mmaps >= n_mmaps_max) return 0; /* too many regions */
/* For mmapped chunks, the overhead is one SIZE_SZ unit larger, because
* there is no following chunk whose prev_size field could be used.
*/
size = (size + SIZE_SZ + page_mask) & ~page_mask;
#ifdef MAP_ANONYMOUS
p = (mchunkptr)mmap(0, size, PROT_READ|PROT_WRITE,
MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
#else /* !MAP_ANONYMOUS */
if (fd < 0)
{
fd = open("/dev/zero", O_RDWR);
if(fd < 0) return 0;
}
p = (mchunkptr)mmap(0, size, PROT_READ|PROT_WRITE, MAP_PRIVATE, fd, 0);
#endif
if(p == (mchunkptr)-1) return 0;
n_mmaps++;
if (n_mmaps > max_n_mmaps) max_n_mmaps = n_mmaps;
/* We demand that eight bytes into a page must be 8-byte aligned. */
assert(aligned_OK(chunk2mem(p)));
/* The offset to the start of the mmapped region is stored
* in the prev_size field of the chunk; normally it is zero,
* but that can be changed in memalign().
*/
p->prev_size = 0;
set_head(p, size|IS_MMAPPED);
mmapped_mem += size;
if ((unsigned long)mmapped_mem > (unsigned long)max_mmapped_mem)
max_mmapped_mem = mmapped_mem;
if ((unsigned long)(mmapped_mem + sbrked_mem) > (unsigned long)max_total_mem)
max_total_mem = mmapped_mem + sbrked_mem;
return p;
}
#if __STD_C
static void munmap_chunk(mchunkptr p)
#else
static void munmap_chunk(p) mchunkptr p;
#endif
{
INTERNAL_SIZE_T size = chunksize(p);
int ret;
assert (chunk_is_mmapped(p));
assert(! ((char*)p >= sbrk_base && (char*)p < sbrk_base + sbrked_mem));
assert((n_mmaps > 0));
assert(((p->prev_size + size) & (malloc_getpagesize-1)) == 0);
n_mmaps--;
mmapped_mem -= (size + p->prev_size);
ret = munmap((char *)p - p->prev_size, size + p->prev_size);
/* munmap returns non-zero on failure */
assert(ret == 0);
}
#if HAVE_MREMAP
#if __STD_C
static mchunkptr mremap_chunk(mchunkptr p, size_t new_size)
#else
static mchunkptr mremap_chunk(p, new_size) mchunkptr p; size_t new_size;
#endif
{
size_t page_mask = malloc_getpagesize - 1;
INTERNAL_SIZE_T offset = p->prev_size;
INTERNAL_SIZE_T size = chunksize(p);
char *cp;
assert (chunk_is_mmapped(p));
assert(! ((char*)p >= sbrk_base && (char*)p < sbrk_base + sbrked_mem));
assert((n_mmaps > 0));
assert(((size + offset) & (malloc_getpagesize-1)) == 0);
/* Note the extra SIZE_SZ overhead as in mmap_chunk(). */
new_size = (new_size + offset + SIZE_SZ + page_mask) & ~page_mask;
cp = (char *)mremap((char *)p - offset, size + offset, new_size, 1);
if (cp == (char *)-1) return 0;
p = (mchunkptr)(cp + offset);
assert(aligned_OK(chunk2mem(p)));
assert((p->prev_size == offset));
set_head(p, (new_size - offset)|IS_MMAPPED);
mmapped_mem -= size + offset;
mmapped_mem += new_size;
if ((unsigned long)mmapped_mem > (unsigned long)max_mmapped_mem)
max_mmapped_mem = mmapped_mem;
if ((unsigned long)(mmapped_mem + sbrked_mem) > (unsigned long)max_total_mem)
max_total_mem = mmapped_mem + sbrked_mem;
return p;
}
#endif /* HAVE_MREMAP */
#endif /* HAVE_MMAP */
/*
Extend the top-most chunk by obtaining memory from system.
Main interface to sbrk (but see also malloc_trim).
*/
#if __STD_C
static void malloc_extend_top(INTERNAL_SIZE_T nb)
#else
static void malloc_extend_top(nb) INTERNAL_SIZE_T nb;
#endif
{
char* brk; /* return value from sbrk */
INTERNAL_SIZE_T front_misalign; /* unusable bytes at front of sbrked space */
INTERNAL_SIZE_T correction; /* bytes for 2nd sbrk call */
char* new_brk; /* return of 2nd sbrk call */
INTERNAL_SIZE_T top_size; /* new size of top chunk */
mchunkptr old_top = top; /* Record state of old top */
INTERNAL_SIZE_T old_top_size = chunksize(old_top);
char* old_end = (char*)(chunk_at_offset(old_top, old_top_size));
/* Pad request with top_pad plus minimal overhead */
INTERNAL_SIZE_T sbrk_size = nb + top_pad + MINSIZE;
unsigned long pagesz = malloc_getpagesize;
/* If not the first time through, round to preserve page boundary */
/* Otherwise, we need to correct to a page size below anyway. */
/* (We also correct below if an intervening foreign sbrk call.) */
if (sbrk_base != (char*)(-1))
sbrk_size = (sbrk_size + (pagesz - 1)) & ~(pagesz - 1);
brk = (char*)(MORECORE (sbrk_size));
/* Fail if sbrk failed or if a foreign sbrk call killed our space */
if (brk == (char*)(MORECORE_FAILURE) ||
(brk < old_end && old_top != initial_top))
return;
sbrked_mem += sbrk_size;
if (brk == old_end) /* can just add bytes to current top */
{
top_size = sbrk_size + old_top_size;
set_head(top, top_size | PREV_INUSE);
}
else
{
if (sbrk_base == (char*)(-1)) /* First time through. Record base */
sbrk_base = brk;
else /* Someone else called sbrk(). Count those bytes as sbrked_mem. */
sbrked_mem += brk - (char*)old_end;
/* Guarantee alignment of first new chunk made from this space */
front_misalign = (unsigned long)chunk2mem(brk) & MALLOC_ALIGN_MASK;
if (front_misalign > 0)
{
correction = (MALLOC_ALIGNMENT) - front_misalign;
brk += correction;
}
else
correction = 0;
/* Guarantee the next brk will be at a page boundary */
correction += ((((unsigned long)(brk + sbrk_size))+(pagesz-1)) &
~(pagesz - 1)) - ((unsigned long)(brk + sbrk_size));
/* Allocate correction */
new_brk = (char*)(MORECORE (correction));
if (new_brk == (char*)(MORECORE_FAILURE)) return;
sbrked_mem += correction;
top = (mchunkptr)brk;
top_size = new_brk - brk + correction;
set_head(top, top_size | PREV_INUSE);
if (old_top != initial_top)
{
/* There must have been an intervening foreign sbrk call. */
/* A double fencepost is necessary to prevent consolidation */
/* If not enough space to do this, then user did something very wrong */
if (old_top_size < MINSIZE)
{
set_head(top, PREV_INUSE); /* will force null return from malloc */
return;
}
/* Also keep size a multiple of MALLOC_ALIGNMENT */
old_top_size = (old_top_size - 3*SIZE_SZ) & ~MALLOC_ALIGN_MASK;
set_head_size(old_top, old_top_size);
chunk_at_offset(old_top, old_top_size )->size =
SIZE_SZ|PREV_INUSE;
chunk_at_offset(old_top, old_top_size + SIZE_SZ)->size =
SIZE_SZ|PREV_INUSE;
/* If possible, release the rest. */
if (old_top_size >= MINSIZE)
fREe(chunk2mem(old_top));
}
}
if ((unsigned long)sbrked_mem > (unsigned long)max_sbrked_mem)
max_sbrked_mem = sbrked_mem;
if ((unsigned long)(mmapped_mem + sbrked_mem) > (unsigned long)max_total_mem)
max_total_mem = mmapped_mem + sbrked_mem;
/* We always land on a page boundary */
assert(((unsigned long)((char*)top + top_size) & (pagesz - 1)) == 0);
}
/* Main public routines */
/*
Malloc Algorthim:
The requested size is first converted into a usable form, `nb'.
This currently means to add 4 bytes overhead plus possibly more to
obtain 8-byte alignment and/or to obtain a size of at least
MINSIZE (currently 16 bytes), the smallest allocatable size.
(All fits are considered `exact' if they are within MINSIZE bytes.)
From there, the first successful of the following steps is taken:
1. The bin corresponding to the request size is scanned, and if
a chunk of exactly the right size is found, it is taken.
2. The most recently remaindered chunk is used if it is big
enough. This is a form of (roving) first fit, used only in
the absence of exact fits. Runs of consecutive requests use
the remainder of the chunk used for the previous such request
whenever possible. This limited use of a first-fit style
allocation strategy tends to give contiguous chunks
coextensive lifetimes, which improves locality and can reduce
fragmentation in the long run.
3. Other bins are scanned in increasing size order, using a
chunk big enough to fulfill the request, and splitting off
any remainder. This search is strictly by best-fit; i.e.,
the smallest (with ties going to approximately the least
recently used) chunk that fits is selected.
4. If large enough, the chunk bordering the end of memory
(`top') is split off. (This use of `top' is in accord with
the best-fit search rule. In effect, `top' is treated as
larger (and thus less well fitting) than any other available
chunk since it can be extended to be as large as necessary
(up to system limitations).
5. If the request size meets the mmap threshold and the
system supports mmap, and there are few enough currently
allocated mmapped regions, and a call to mmap succeeds,
the request is allocated via direct memory mapping.
6. Otherwise, the top of memory is extended by
obtaining more space from the system (normally using sbrk,
but definable to anything else via the MORECORE macro).
Memory is gathered from the system (in system page-sized
units) in a way that allows chunks obtained across different
sbrk calls to be consolidated, but does not require
contiguous memory. Thus, it should be safe to intersperse
mallocs with other sbrk calls.
All allocations are made from the the `lowest' part of any found
chunk. (The implementation invariant is that prev_inuse is
always true of any allocated chunk; i.e., that each allocated
chunk borders either a previously allocated and still in-use chunk,
or the base of its memory arena.)
*/
#if __STD_C
Void_t* mALLOc(size_t bytes)
#else
Void_t* mALLOc(bytes) size_t bytes;
#endif
{
mchunkptr victim; /* inspected/selected chunk */
INTERNAL_SIZE_T victim_size; /* its size */
int idx; /* index for bin traversal */
mbinptr bin; /* associated bin */
mchunkptr remainder; /* remainder from a split */
long remainder_size; /* its size */
int remainder_index; /* its bin index */
unsigned long block; /* block traverser bit */
int startidx; /* first bin of a traversed block */
mchunkptr fwd; /* misc temp for linking */
mchunkptr bck; /* misc temp for linking */
mbinptr q; /* misc temp */
INTERNAL_SIZE_T nb;
#if CONFIG_VAL(SYS_MALLOC_F_LEN)
if (!(gd->flags & GD_FLG_FULL_MALLOC_INIT))
return malloc_simple(bytes);
#endif
/* check if mem_malloc_init() was run */
if ((mem_malloc_start == 0) && (mem_malloc_end == 0)) {
/* not initialized yet */
return NULL;
}
if ((long)bytes < 0) return NULL;
nb = request2size(bytes); /* padded request size; */
/* Check for exact match in a bin */
if (is_small_request(nb)) /* Faster version for small requests */
{
idx = smallbin_index(nb);
/* No traversal or size check necessary for small bins. */
q = bin_at(idx);
victim = last(q);
/* Also scan the next one, since it would have a remainder < MINSIZE */
if (victim == q)
{
q = next_bin(q);
victim = last(q);
}
if (victim != q)
{
victim_size = chunksize(victim);
unlink(victim, bck, fwd);
set_inuse_bit_at_offset(victim, victim_size);
check_malloced_chunk(victim, nb);
return chunk2mem(victim);
}
idx += 2; /* Set for bin scan below. We've already scanned 2 bins. */
}
else
{
idx = bin_index(nb);
bin = bin_at(idx);
for (victim = last(bin); victim != bin; victim = victim->bk)
{
victim_size = chunksize(victim);
remainder_size = victim_size - nb;
if (remainder_size >= (long)MINSIZE) /* too big */
{
--idx; /* adjust to rescan below after checking last remainder */
break;
}
else if (remainder_size >= 0) /* exact fit */
{
unlink(victim, bck, fwd);
set_inuse_bit_at_offset(victim, victim_size);
check_malloced_chunk(victim, nb);
return chunk2mem(victim);
}
}
++idx;
}
/* Try to use the last split-off remainder */
if ( (victim = last_remainder->fd) != last_remainder)
{
victim_size = chunksize(victim);
remainder_size = victim_size - nb;
if (remainder_size >= (long)MINSIZE) /* re-split */
{
remainder = chunk_at_offset(victim, nb);
set_head(victim, nb | PREV_INUSE);
link_last_remainder(remainder);
set_head(remainder, remainder_size | PREV_INUSE);
set_foot(remainder, remainder_size);
check_malloced_chunk(victim, nb);
return chunk2mem(victim);
}
clear_last_remainder;
if (remainder_size >= 0) /* exhaust */
{
set_inuse_bit_at_offset(victim, victim_size);
check_malloced_chunk(victim, nb);
return chunk2mem(victim);
}
/* Else place in bin */
frontlink(victim, victim_size, remainder_index, bck, fwd);
}
/*
If there are any possibly nonempty big-enough blocks,
search for best fitting chunk by scanning bins in blockwidth units.
*/
if ( (block = idx2binblock(idx)) <= binblocks_r)
{
/* Get to the first marked block */
if ( (block & binblocks_r) == 0)
{
/* force to an even block boundary */
idx = (idx & ~(BINBLOCKWIDTH - 1)) + BINBLOCKWIDTH;
block <<= 1;
while ((block & binblocks_r) == 0)
{
idx += BINBLOCKWIDTH;
block <<= 1;
}
}
/* For each possibly nonempty block ... */
for (;;)
{
startidx = idx; /* (track incomplete blocks) */
q = bin = bin_at(idx);
/* For each bin in this block ... */
do
{
/* Find and use first big enough chunk ... */
for (victim = last(bin); victim != bin; victim = victim->bk)
{
victim_size = chunksize(victim);
remainder_size = victim_size - nb;
if (remainder_size >= (long)MINSIZE) /* split */
{
remainder = chunk_at_offset(victim, nb);
set_head(victim, nb | PREV_INUSE);
unlink(victim, bck, fwd);
link_last_remainder(remainder);
set_head(remainder, remainder_size | PREV_INUSE);
set_foot(remainder, remainder_size);
check_malloced_chunk(victim, nb);
return chunk2mem(victim);
}
else if (remainder_size >= 0) /* take */
{
set_inuse_bit_at_offset(victim, victim_size);
unlink(victim, bck, fwd);
check_malloced_chunk(victim, nb);
return chunk2mem(victim);
}
}
bin = next_bin(bin);
} while ((++idx & (BINBLOCKWIDTH - 1)) != 0);
/* Clear out the block bit. */
do /* Possibly backtrack to try to clear a partial block */
{
if ((startidx & (BINBLOCKWIDTH - 1)) == 0)
{
av_[1] = (mbinptr)(binblocks_r & ~block);
break;
}
--startidx;
q = prev_bin(q);
} while (first(q) == q);
/* Get to the next possibly nonempty block */
if ( (block <<= 1) <= binblocks_r && (block != 0) )
{
while ((block & binblocks_r) == 0)
{
idx += BINBLOCKWIDTH;
block <<= 1;
}
}
else
break;
}
}
/* Try to use top chunk */
/* Require that there be a remainder, ensuring top always exists */
if ( (remainder_size = chunksize(top) - nb) < (long)MINSIZE)
{
#if HAVE_MMAP
/* If big and would otherwise need to extend, try to use mmap instead */
if ((unsigned long)nb >= (unsigned long)mmap_threshold &&
(victim = mmap_chunk(nb)))
return chunk2mem(victim);
#endif
/* Try to extend */
malloc_extend_top(nb);
if ( (remainder_size = chunksize(top) - nb) < (long)MINSIZE)
return NULL; /* propagate failure */
}
victim = top;
set_head(victim, nb | PREV_INUSE);
top = chunk_at_offset(victim, nb);
set_head(top, remainder_size | PREV_INUSE);
check_malloced_chunk(victim, nb);
return chunk2mem(victim);
}
/*
free() algorithm :
cases:
1. free(0) has no effect.
2. If the chunk was allocated via mmap, it is release via munmap().
3. If a returned chunk borders the current high end of memory,
it is consolidated into the top, and if the total unused
topmost memory exceeds the trim threshold, malloc_trim is
called.
4. Other chunks are consolidated as they arrive, and
placed in corresponding bins. (This includes the case of
consolidating with the current `last_remainder').
*/
#if __STD_C
void fREe(Void_t* mem)
#else
void fREe(mem) Void_t* mem;
#endif
{
mchunkptr p; /* chunk corresponding to mem */
INTERNAL_SIZE_T hd; /* its head field */
INTERNAL_SIZE_T sz; /* its size */
int idx; /* its bin index */
mchunkptr next; /* next contiguous chunk */
INTERNAL_SIZE_T nextsz; /* its size */
INTERNAL_SIZE_T prevsz; /* size of previous contiguous chunk */
mchunkptr bck; /* misc temp for linking */
mchunkptr fwd; /* misc temp for linking */
int islr; /* track whether merging with last_remainder */
#if CONFIG_VAL(SYS_MALLOC_F_LEN)
/* free() is a no-op - all the memory will be freed on relocation */
if (!(gd->flags & GD_FLG_FULL_MALLOC_INIT))
return;
#endif
if (mem == NULL) /* free(0) has no effect */
return;
p = mem2chunk(mem);
hd = p->size;
#if HAVE_MMAP
if (hd & IS_MMAPPED) /* release mmapped memory. */
{
munmap_chunk(p);
return;
}
#endif
check_inuse_chunk(p);
sz = hd & ~PREV_INUSE;
next = chunk_at_offset(p, sz);
nextsz = chunksize(next);
if (next == top) /* merge with top */
{
sz += nextsz;
if (!(hd & PREV_INUSE)) /* consolidate backward */
{
prevsz = p->prev_size;
p = chunk_at_offset(p, -((long) prevsz));
sz += prevsz;
unlink(p, bck, fwd);
}
set_head(p, sz | PREV_INUSE);
top = p;
if ((unsigned long)(sz) >= (unsigned long)trim_threshold)
malloc_trim(top_pad);
return;
}
set_head(next, nextsz); /* clear inuse bit */
islr = 0;
if (!(hd & PREV_INUSE)) /* consolidate backward */
{
prevsz = p->prev_size;
p = chunk_at_offset(p, -((long) prevsz));
sz += prevsz;
if (p->fd == last_remainder) /* keep as last_remainder */
islr = 1;
else
unlink(p, bck, fwd);
}
if (!(inuse_bit_at_offset(next, nextsz))) /* consolidate forward */
{
sz += nextsz;
if (!islr && next->fd == last_remainder) /* re-insert last_remainder */
{
islr = 1;
link_last_remainder(p);
}
else
unlink(next, bck, fwd);
}
set_head(p, sz | PREV_INUSE);
set_foot(p, sz);
if (!islr)
frontlink(p, sz, idx, bck, fwd);
}
/*
Realloc algorithm:
Chunks that were obtained via mmap cannot be extended or shrunk
unless HAVE_MREMAP is defined, in which case mremap is used.
Otherwise, if their reallocation is for additional space, they are
copied. If for less, they are just left alone.
Otherwise, if the reallocation is for additional space, and the
chunk can be extended, it is, else a malloc-copy-free sequence is
taken. There are several different ways that a chunk could be
extended. All are tried:
* Extending forward into following adjacent free chunk.
* Shifting backwards, joining preceding adjacent space
* Both shifting backwards and extending forward.
* Extending into newly sbrked space
Unless the #define REALLOC_ZERO_BYTES_FREES is set, realloc with a
size argument of zero (re)allocates a minimum-sized chunk.
If the reallocation is for less space, and the new request is for
a `small' (<512 bytes) size, then the newly unused space is lopped
off and freed.
The old unix realloc convention of allowing the last-free'd chunk
to be used as an argument to realloc is no longer supported.
I don't know of any programs still relying on this feature,
and allowing it would also allow too many other incorrect
usages of realloc to be sensible.
*/
#if __STD_C
Void_t* rEALLOc(Void_t* oldmem, size_t bytes)
#else
Void_t* rEALLOc(oldmem, bytes) Void_t* oldmem; size_t bytes;
#endif
{
INTERNAL_SIZE_T nb; /* padded request size */
mchunkptr oldp; /* chunk corresponding to oldmem */
INTERNAL_SIZE_T oldsize; /* its size */
mchunkptr newp; /* chunk to return */
INTERNAL_SIZE_T newsize; /* its size */
Void_t* newmem; /* corresponding user mem */
mchunkptr next; /* next contiguous chunk after oldp */
INTERNAL_SIZE_T nextsize; /* its size */
mchunkptr prev; /* previous contiguous chunk before oldp */
INTERNAL_SIZE_T prevsize; /* its size */
mchunkptr remainder; /* holds split off extra space from newp */
INTERNAL_SIZE_T remainder_size; /* its size */
mchunkptr bck; /* misc temp for linking */
mchunkptr fwd; /* misc temp for linking */
#ifdef REALLOC_ZERO_BYTES_FREES
if (!bytes) {
fREe(oldmem);
return NULL;
}
#endif
if ((long)bytes < 0) return NULL;
/* realloc of null is supposed to be same as malloc */
if (oldmem == NULL) return mALLOc(bytes);
#if CONFIG_VAL(SYS_MALLOC_F_LEN)
if (!(gd->flags & GD_FLG_FULL_MALLOC_INIT)) {
/* This is harder to support and should not be needed */
panic("pre-reloc realloc() is not supported");
}
#endif
newp = oldp = mem2chunk(oldmem);
newsize = oldsize = chunksize(oldp);
nb = request2size(bytes);
#if HAVE_MMAP
if (chunk_is_mmapped(oldp))
{
#if HAVE_MREMAP
newp = mremap_chunk(oldp, nb);
if(newp) return chunk2mem(newp);
#endif
/* Note the extra SIZE_SZ overhead. */
if(oldsize - SIZE_SZ >= nb) return oldmem; /* do nothing */
/* Must alloc, copy, free. */
newmem = mALLOc(bytes);
if (!newmem)
return NULL; /* propagate failure */
MALLOC_COPY(newmem, oldmem, oldsize - 2*SIZE_SZ);
munmap_chunk(oldp);
return newmem;
}
#endif
check_inuse_chunk(oldp);
if ((long)(oldsize) < (long)(nb))
{
/* Try expanding forward */
next = chunk_at_offset(oldp, oldsize);
if (next == top || !inuse(next))
{
nextsize = chunksize(next);
/* Forward into top only if a remainder */
if (next == top)
{
if ((long)(nextsize + newsize) >= (long)(nb + MINSIZE))
{
newsize += nextsize;
top = chunk_at_offset(oldp, nb);
set_head(top, (newsize - nb) | PREV_INUSE);
set_head_size(oldp, nb);
return chunk2mem(oldp);
}
}
/* Forward into next chunk */
else if (((long)(nextsize + newsize) >= (long)(nb)))
{
unlink(next, bck, fwd);
newsize += nextsize;
goto split;
}
}
else
{
next = NULL;
nextsize = 0;
}
/* Try shifting backwards. */
if (!prev_inuse(oldp))
{
prev = prev_chunk(oldp);
prevsize = chunksize(prev);
/* try forward + backward first to save a later consolidation */
if (next != NULL)
{
/* into top */
if (next == top)
{
if ((long)(nextsize + prevsize + newsize) >= (long)(nb + MINSIZE))
{
unlink(prev, bck, fwd);
newp = prev;
newsize += prevsize + nextsize;
newmem = chunk2mem(newp);
MALLOC_COPY(newmem, oldmem, oldsize - SIZE_SZ);
top = chunk_at_offset(newp, nb);
set_head(top, (newsize - nb) | PREV_INUSE);
set_head_size(newp, nb);
return newmem;
}
}
/* into next chunk */
else if (((long)(nextsize + prevsize + newsize) >= (long)(nb)))
{
unlink(next, bck, fwd);
unlink(prev, bck, fwd);
newp = prev;
newsize += nextsize + prevsize;
newmem = chunk2mem(newp);
MALLOC_COPY(newmem, oldmem, oldsize - SIZE_SZ);
goto split;
}
}
/* backward only */
if (prev != NULL && (long)(prevsize + newsize) >= (long)nb)
{
unlink(prev, bck, fwd);
newp = prev;
newsize += prevsize;
newmem = chunk2mem(newp);
MALLOC_COPY(newmem, oldmem, oldsize - SIZE_SZ);
goto split;
}
}
/* Must allocate */
newmem = mALLOc (bytes);
if (newmem == NULL) /* propagate failure */
return NULL;
/* Avoid copy if newp is next chunk after oldp. */
/* (This can only happen when new chunk is sbrk'ed.) */
if ( (newp = mem2chunk(newmem)) == next_chunk(oldp))
{
newsize += chunksize(newp);
newp = oldp;
goto split;
}
/* Otherwise copy, free, and exit */
MALLOC_COPY(newmem, oldmem, oldsize - SIZE_SZ);
fREe(oldmem);
return newmem;
}
split: /* split off extra room in old or expanded chunk */
if (newsize - nb >= MINSIZE) /* split off remainder */
{
remainder = chunk_at_offset(newp, nb);
remainder_size = newsize - nb;
set_head_size(newp, nb);
set_head(remainder, remainder_size | PREV_INUSE);
set_inuse_bit_at_offset(remainder, remainder_size);
fREe(chunk2mem(remainder)); /* let free() deal with it */
}
else
{
set_head_size(newp, newsize);
set_inuse_bit_at_offset(newp, newsize);
}
check_inuse_chunk(newp);
return chunk2mem(newp);
}
/*
memalign algorithm:
memalign requests more than enough space from malloc, finds a spot
within that chunk that meets the alignment request, and then
possibly frees the leading and trailing space.
The alignment argument must be a power of two. This property is not
checked by memalign, so misuse may result in random runtime errors.
8-byte alignment is guaranteed by normal malloc calls, so don't
bother calling memalign with an argument of 8 or less.
Overreliance on memalign is a sure way to fragment space.
*/
#if __STD_C
Void_t* mEMALIGn(size_t alignment, size_t bytes)
#else
Void_t* mEMALIGn(alignment, bytes) size_t alignment; size_t bytes;
#endif
{
INTERNAL_SIZE_T nb; /* padded request size */
char* m; /* memory returned by malloc call */
mchunkptr p; /* corresponding chunk */
char* brk; /* alignment point within p */
mchunkptr newp; /* chunk to return */
INTERNAL_SIZE_T newsize; /* its size */
INTERNAL_SIZE_T leadsize; /* leading space befor alignment point */
mchunkptr remainder; /* spare room at end to split off */
long remainder_size; /* its size */
if ((long)bytes < 0) return NULL;
#if CONFIG_VAL(SYS_MALLOC_F_LEN)
if (!(gd->flags & GD_FLG_FULL_MALLOC_INIT)) {
nb = roundup(bytes, alignment);
return malloc_simple(nb);
}
#endif
/* If need less alignment than we give anyway, just relay to malloc */
if (alignment <= MALLOC_ALIGNMENT) return mALLOc(bytes);
/* Otherwise, ensure that it is at least a minimum chunk size */
if (alignment < MINSIZE) alignment = MINSIZE;
/* Call malloc with worst case padding to hit alignment. */
nb = request2size(bytes);
m = (char*)(mALLOc(nb + alignment + MINSIZE));
/*
* The attempt to over-allocate (with a size large enough to guarantee the
* ability to find an aligned region within allocated memory) failed.
*
* Try again, this time only allocating exactly the size the user wants. If
* the allocation now succeeds and just happens to be aligned, we can still
* fulfill the user's request.
*/
if (m == NULL) {
size_t extra, extra2;
/*
* Use bytes not nb, since mALLOc internally calls request2size too, and
* each call increases the size to allocate, to account for the header.
*/
m = (char*)(mALLOc(bytes));
/* Aligned -> return it */
if ((((unsigned long)(m)) % alignment) == 0)
return m;
/*
* Otherwise, try again, requesting enough extra space to be able to
* acquire alignment.
*/
fREe(m);
/* Add in extra bytes to match misalignment of unexpanded allocation */
extra = alignment - (((unsigned long)(m)) % alignment);
m = (char*)(mALLOc(bytes + extra));
/*
* m might not be the same as before. Validate that the previous value of
* extra still works for the current value of m.
* If (!m), extra2=alignment so
*/
if (m) {
extra2 = alignment - (((unsigned long)(m)) % alignment);
if (extra2 > extra) {
fREe(m);
m = NULL;
}
}
/* Fall through to original NULL check and chunk splitting logic */
}
if (m == NULL) return NULL; /* propagate failure */
p = mem2chunk(m);
if ((((unsigned long)(m)) % alignment) == 0) /* aligned */
{
#if HAVE_MMAP
if(chunk_is_mmapped(p))
return chunk2mem(p); /* nothing more to do */
#endif
}
else /* misaligned */
{
/*
Find an aligned spot inside chunk.
Since we need to give back leading space in a chunk of at
least MINSIZE, if the first calculation places us at
a spot with less than MINSIZE leader, we can move to the
next aligned spot -- we've allocated enough total room so that
this is always possible.
*/
brk = (char*)mem2chunk(((unsigned long)(m + alignment - 1)) & -((signed) alignment));
if ((long)(brk - (char*)(p)) < MINSIZE) brk = brk + alignment;
newp = (mchunkptr)brk;
leadsize = brk - (char*)(p);
newsize = chunksize(p) - leadsize;
#if HAVE_MMAP
if(chunk_is_mmapped(p))
{
newp->prev_size = p->prev_size + leadsize;
set_head(newp, newsize|IS_MMAPPED);
return chunk2mem(newp);
}
#endif
/* give back leader, use the rest */
set_head(newp, newsize | PREV_INUSE);
set_inuse_bit_at_offset(newp, newsize);
set_head_size(p, leadsize);
fREe(chunk2mem(p));
p = newp;
assert (newsize >= nb && (((unsigned long)(chunk2mem(p))) % alignment) == 0);
}
/* Also give back spare room at the end */
remainder_size = chunksize(p) - nb;
if (remainder_size >= (long)MINSIZE)
{
remainder = chunk_at_offset(p, nb);
set_head(remainder, remainder_size | PREV_INUSE);
set_head_size(p, nb);
fREe(chunk2mem(remainder));
}
check_inuse_chunk(p);
return chunk2mem(p);
}
/*
valloc just invokes memalign with alignment argument equal
to the page size of the system (or as near to this as can
be figured out from all the includes/defines above.)
*/
#if __STD_C
Void_t* vALLOc(size_t bytes)
#else
Void_t* vALLOc(bytes) size_t bytes;
#endif
{
return mEMALIGn (malloc_getpagesize, bytes);
}
/*
pvalloc just invokes valloc for the nearest pagesize
that will accommodate request
*/
#if __STD_C
Void_t* pvALLOc(size_t bytes)
#else
Void_t* pvALLOc(bytes) size_t bytes;
#endif
{
size_t pagesize = malloc_getpagesize;
return mEMALIGn (pagesize, (bytes + pagesize - 1) & ~(pagesize - 1));
}
/*
calloc calls malloc, then zeroes out the allocated chunk.
*/
#if __STD_C
Void_t* cALLOc(size_t n, size_t elem_size)
#else
Void_t* cALLOc(n, elem_size) size_t n; size_t elem_size;
#endif
{
mchunkptr p;
INTERNAL_SIZE_T csz;
INTERNAL_SIZE_T sz = n * elem_size;
/* check if expand_top called, in which case don't need to clear */
#ifdef CONFIG_SYS_MALLOC_CLEAR_ON_INIT
#if MORECORE_CLEARS
mchunkptr oldtop = top;
INTERNAL_SIZE_T oldtopsize = chunksize(top);
#endif
#endif
Void_t* mem = mALLOc (sz);
if ((long)n < 0) return NULL;
if (mem == NULL)
return NULL;
else
{
#if CONFIG_VAL(SYS_MALLOC_F_LEN)
if (!(gd->flags & GD_FLG_FULL_MALLOC_INIT)) {
MALLOC_ZERO(mem, sz);
return mem;
}
#endif
p = mem2chunk(mem);
/* Two optional cases in which clearing not necessary */
#if HAVE_MMAP
if (chunk_is_mmapped(p)) return mem;
#endif
csz = chunksize(p);
#ifdef CONFIG_SYS_MALLOC_CLEAR_ON_INIT
#if MORECORE_CLEARS
if (p == oldtop && csz > oldtopsize)
{
/* clear only the bytes from non-freshly-sbrked memory */
csz = oldtopsize;
}
#endif
#endif
MALLOC_ZERO(mem, csz - SIZE_SZ);
return mem;
}
}
/*
cfree just calls free. It is needed/defined on some systems
that pair it with calloc, presumably for odd historical reasons.
*/
#if !defined(INTERNAL_LINUX_C_LIB) || !defined(__ELF__)
#if __STD_C
void cfree(Void_t *mem)
#else
void cfree(mem) Void_t *mem;
#endif
{
fREe(mem);
}
#endif
/*
Malloc_trim gives memory back to the system (via negative
arguments to sbrk) if there is unused memory at the `high' end of
the malloc pool. You can call this after freeing large blocks of
memory to potentially reduce the system-level memory requirements
of a program. However, it cannot guarantee to reduce memory. Under
some allocation patterns, some large free blocks of memory will be
locked between two used chunks, so they cannot be given back to
the system.
The `pad' argument to malloc_trim represents the amount of free
trailing space to leave untrimmed. If this argument is zero,
only the minimum amount of memory to maintain internal data
structures will be left (one page or less). Non-zero arguments
can be supplied to maintain enough trailing space to service
future expected allocations without having to re-obtain memory
from the system.
Malloc_trim returns 1 if it actually released any memory, else 0.
*/
#if __STD_C
int malloc_trim(size_t pad)
#else
int malloc_trim(pad) size_t pad;
#endif
{
long top_size; /* Amount of top-most memory */
long extra; /* Amount to release */
char* current_brk; /* address returned by pre-check sbrk call */
char* new_brk; /* address returned by negative sbrk call */
unsigned long pagesz = malloc_getpagesize;
top_size = chunksize(top);
extra = ((top_size - pad - MINSIZE + (pagesz-1)) / pagesz - 1) * pagesz;
if (extra < (long)pagesz) /* Not enough memory to release */
return 0;
else
{
/* Test to make sure no one else called sbrk */
current_brk = (char*)(MORECORE (0));
if (current_brk != (char*)(top) + top_size)
return 0; /* Apparently we don't own memory; must fail */
else
{
new_brk = (char*)(MORECORE (-extra));
if (new_brk == (char*)(MORECORE_FAILURE)) /* sbrk failed? */
{
/* Try to figure out what we have */
current_brk = (char*)(MORECORE (0));
top_size = current_brk - (char*)top;
if (top_size >= (long)MINSIZE) /* if not, we are very very dead! */
{
sbrked_mem = current_brk - sbrk_base;
set_head(top, top_size | PREV_INUSE);
}
check_chunk(top);
return 0;
}
else
{
/* Success. Adjust top accordingly. */
set_head(top, (top_size - extra) | PREV_INUSE);
sbrked_mem -= extra;
check_chunk(top);
return 1;
}
}
}
}
/*
malloc_usable_size:
This routine tells you how many bytes you can actually use in an
allocated chunk, which may be more than you requested (although
often not). You can use this many bytes without worrying about
overwriting other allocated objects. Not a particularly great
programming practice, but still sometimes useful.
*/
#if __STD_C
size_t malloc_usable_size(Void_t* mem)
#else
size_t malloc_usable_size(mem) Void_t* mem;
#endif
{
mchunkptr p;
if (mem == NULL)
return 0;
else
{
p = mem2chunk(mem);
if(!chunk_is_mmapped(p))
{
if (!inuse(p)) return 0;
check_inuse_chunk(p);
return chunksize(p) - SIZE_SZ;
}
return chunksize(p) - 2*SIZE_SZ;
}
}
/* Utility to update current_mallinfo for malloc_stats and mallinfo() */
#ifdef DEBUG
static void malloc_update_mallinfo()
{
int i;
mbinptr b;
mchunkptr p;
#ifdef DEBUG
mchunkptr q;
#endif
INTERNAL_SIZE_T avail = chunksize(top);
int navail = ((long)(avail) >= (long)MINSIZE)? 1 : 0;
for (i = 1; i < NAV; ++i)
{
b = bin_at(i);
for (p = last(b); p != b; p = p->bk)
{
#ifdef DEBUG
check_free_chunk(p);
for (q = next_chunk(p);
q < top && inuse(q) && (long)(chunksize(q)) >= (long)MINSIZE;
q = next_chunk(q))
check_inuse_chunk(q);
#endif
avail += chunksize(p);
navail++;
}
}
current_mallinfo.ordblks = navail;
current_mallinfo.uordblks = sbrked_mem - avail;
current_mallinfo.fordblks = avail;
current_mallinfo.hblks = n_mmaps;
current_mallinfo.hblkhd = mmapped_mem;
current_mallinfo.keepcost = chunksize(top);
}
#endif /* DEBUG */
/*
malloc_stats:
Prints on the amount of space obtain from the system (both
via sbrk and mmap), the maximum amount (which may be more than
current if malloc_trim and/or munmap got called), the maximum
number of simultaneous mmap regions used, and the current number
of bytes allocated via malloc (or realloc, etc) but not yet
freed. (Note that this is the number of bytes allocated, not the
number requested. It will be larger than the number requested
because of alignment and bookkeeping overhead.)
*/
#ifdef DEBUG
void malloc_stats()
{
malloc_update_mallinfo();
printf("max system bytes = %10u\n",
(unsigned int)(max_total_mem));
printf("system bytes = %10u\n",
(unsigned int)(sbrked_mem + mmapped_mem));
printf("in use bytes = %10u\n",
(unsigned int)(current_mallinfo.uordblks + mmapped_mem));
#if HAVE_MMAP
printf("max mmap regions = %10u\n",
(unsigned int)max_n_mmaps);
#endif
}
#endif /* DEBUG */
/*
mallinfo returns a copy of updated current mallinfo.
*/
#ifdef DEBUG
struct mallinfo mALLINFo()
{
malloc_update_mallinfo();
return current_mallinfo;
}
#endif /* DEBUG */
/*
mallopt:
mallopt is the general SVID/XPG interface to tunable parameters.
The format is to provide a (parameter-number, parameter-value) pair.
mallopt then sets the corresponding parameter to the argument
value if it can (i.e., so long as the value is meaningful),
and returns 1 if successful else 0.
See descriptions of tunable parameters above.
*/
#if __STD_C
int mALLOPt(int param_number, int value)
#else
int mALLOPt(param_number, value) int param_number; int value;
#endif
{
switch(param_number)
{
case M_TRIM_THRESHOLD:
trim_threshold = value; return 1;
case M_TOP_PAD:
top_pad = value; return 1;
case M_MMAP_THRESHOLD:
mmap_threshold = value; return 1;
case M_MMAP_MAX:
#if HAVE_MMAP
n_mmaps_max = value; return 1;
#else
if (value != 0) return 0; else n_mmaps_max = value; return 1;
#endif
default:
return 0;
}
}
int initf_malloc(void)
{
#if CONFIG_VAL(SYS_MALLOC_F_LEN)
assert(gd->malloc_base); /* Set up by crt0.S */
gd->malloc_limit = CONFIG_VAL(SYS_MALLOC_F_LEN);
gd->malloc_ptr = 0;
#endif
return 0;
}
/*
History:
V2.6.6 Sun Dec 5 07:42:19 1999 Doug Lea (dl at gee)
* return null for negative arguments
* Added Several WIN32 cleanups from Martin C. Fong <mcfong@yahoo.com>
* Add 'LACKS_SYS_PARAM_H' for those systems without 'sys/param.h'
(e.g. WIN32 platforms)
* Cleanup up header file inclusion for WIN32 platforms
* Cleanup code to avoid Microsoft Visual C++ compiler complaints
* Add 'USE_DL_PREFIX' to quickly allow co-existence with existing
memory allocation routines
* Set 'malloc_getpagesize' for WIN32 platforms (needs more work)
* Use 'assert' rather than 'ASSERT' in WIN32 code to conform to
usage of 'assert' in non-WIN32 code
* Improve WIN32 'sbrk()' emulation's 'findRegion()' routine to
avoid infinite loop
* Always call 'fREe()' rather than 'free()'
V2.6.5 Wed Jun 17 15:57:31 1998 Doug Lea (dl at gee)
* Fixed ordering problem with boundary-stamping
V2.6.3 Sun May 19 08:17:58 1996 Doug Lea (dl at gee)
* Added pvalloc, as recommended by H.J. Liu
* Added 64bit pointer support mainly from Wolfram Gloger
* Added anonymously donated WIN32 sbrk emulation
* Malloc, calloc, getpagesize: add optimizations from Raymond Nijssen
* malloc_extend_top: fix mask error that caused wastage after
foreign sbrks
* Add linux mremap support code from HJ Liu
V2.6.2 Tue Dec 5 06:52:55 1995 Doug Lea (dl at gee)
* Integrated most documentation with the code.
* Add support for mmap, with help from
Wolfram Gloger (Gloger@lrz.uni-muenchen.de).
* Use last_remainder in more cases.
* Pack bins using idea from colin@nyx10.cs.du.edu
* Use ordered bins instead of best-fit threshhold
* Eliminate block-local decls to simplify tracing and debugging.
* Support another case of realloc via move into top
* Fix error occuring when initial sbrk_base not word-aligned.
* Rely on page size for units instead of SBRK_UNIT to
avoid surprises about sbrk alignment conventions.
* Add mallinfo, mallopt. Thanks to Raymond Nijssen
(raymond@es.ele.tue.nl) for the suggestion.
* Add `pad' argument to malloc_trim and top_pad mallopt parameter.
* More precautions for cases where other routines call sbrk,
courtesy of Wolfram Gloger (Gloger@lrz.uni-muenchen.de).
* Added macros etc., allowing use in linux libc from
H.J. Lu (hjl@gnu.ai.mit.edu)
* Inverted this history list
V2.6.1 Sat Dec 2 14:10:57 1995 Doug Lea (dl at gee)
* Re-tuned and fixed to behave more nicely with V2.6.0 changes.
* Removed all preallocation code since under current scheme
the work required to undo bad preallocations exceeds
the work saved in good cases for most test programs.
* No longer use return list or unconsolidated bins since
no scheme using them consistently outperforms those that don't
given above changes.
* Use best fit for very large chunks to prevent some worst-cases.
* Added some support for debugging
V2.6.0 Sat Nov 4 07:05:23 1995 Doug Lea (dl at gee)
* Removed footers when chunks are in use. Thanks to
Paul Wilson (wilson@cs.texas.edu) for the suggestion.
V2.5.4 Wed Nov 1 07:54:51 1995 Doug Lea (dl at gee)
* Added malloc_trim, with help from Wolfram Gloger
(wmglo@Dent.MED.Uni-Muenchen.DE).
V2.5.3 Tue Apr 26 10:16:01 1994 Doug Lea (dl at g)
V2.5.2 Tue Apr 5 16:20:40 1994 Doug Lea (dl at g)
* realloc: try to expand in both directions
* malloc: swap order of clean-bin strategy;
* realloc: only conditionally expand backwards
* Try not to scavenge used bins
* Use bin counts as a guide to preallocation
* Occasionally bin return list chunks in first scan
* Add a few optimizations from colin@nyx10.cs.du.edu
V2.5.1 Sat Aug 14 15:40:43 1993 Doug Lea (dl at g)
* faster bin computation & slightly different binning
* merged all consolidations to one part of malloc proper
(eliminating old malloc_find_space & malloc_clean_bin)
* Scan 2 returns chunks (not just 1)
* Propagate failure in realloc if malloc returns 0
* Add stuff to allow compilation on non-ANSI compilers
from kpv@research.att.com
V2.5 Sat Aug 7 07:41:59 1993 Doug Lea (dl at g.oswego.edu)
* removed potential for odd address access in prev_chunk
* removed dependency on getpagesize.h
* misc cosmetics and a bit more internal documentation
* anticosmetics: mangled names in macros to evade debugger strangeness
* tested on sparc, hp-700, dec-mips, rs6000
with gcc & native cc (hp, dec only) allowing
Detlefs & Zorn comparison study (in SIGPLAN Notices.)
Trial version Fri Aug 28 13:14:29 1992 Doug Lea (dl at g.oswego.edu)
* Based loosely on libg++-1.2X malloc. (It retains some of the overall
structure of old version, but most details differ.)
*/