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This is a version (aka dlmalloc) of malloc/free/realloc written by
Doug Lea and released to the public domain, as explained at Send questions,
comments, complaints, performance data, etc to
* Version 2.8.3 Thu Sep 22 11:16:15 2005 Doug Lea (dl at gee)
Note: There may be an updated version of this malloc obtainable at
Check before installing!
* Quickstart
This library is all in one file to simplify the most common usage:
ftp it, compile it (-O3), and link it into another program. All of
the compile-time options default to reasonable values for use on
most platforms. You might later want to step through various
compile-time and dynamic tuning options.
For convenience, an include file for code using this malloc is at:
You don't really need this .h file unless you call functions not
defined in your system include files. The .h file contains only the
excerpts from this file needed for using this malloc on ANSI C/C++
systems, so long as you haven't changed compile-time options about
naming and tuning parameters. If you do, then you can create your
own malloc.h that does include all settings by cutting at the point
indicated below. Note that you may already by default be using a C
library containing a malloc that is based on some version of this
malloc (for example in linux). You might still want to use the one
in this file to customize settings or to avoid overheads associated
with library versions.
* Vital statistics:
Supported pointer/size_t representation: 4 or 8 bytes
size_t MUST be an unsigned type of the same width as
pointers. (If you are using an ancient system that declares
size_t as a signed type, or need it to be a different width
than pointers, you can use a previous release of this malloc
(e.g. 2.7.2) supporting these.)
Alignment: 8 bytes (default)
This suffices for nearly all current machines and C compilers.
However, you can define MALLOC_ALIGNMENT to be wider than this
if necessary (up to 128bytes), at the expense of using more space.
Minimum overhead per allocated chunk: 4 or 8 bytes (if 4byte sizes)
8 or 16 bytes (if 8byte sizes)
Each malloced chunk has a hidden word of overhead holding size
and status information, and additional cross-check word
if FOOTERS is defined.
Minimum allocated size: 4-byte ptrs: 16 bytes (including overhead)
8-byte ptrs: 32 bytes (including overhead)
Even a request for zero bytes (i.e., malloc(0)) returns a
pointer to something of the minimum allocatable size.
The maximum overhead wastage (i.e., number of extra bytes
allocated than were requested in malloc) is less than or equal
to the minimum size, except for requests >= mmap_threshold that
are serviced via mmap(), where the worst case wastage is about
32 bytes plus the remainder from a system page (the minimal
mmap unit); typically 4096 or 8192 bytes.
Security: static-safe; optionally more or less
The "security" of malloc refers to the ability of malicious
code to accentuate the effects of errors (for example, freeing
space that is not currently malloc'ed or overwriting past the
ends of chunks) in code that calls malloc. This malloc
guarantees not to modify any memory locations below the base of
heap, i.e., static variables, even in the presence of usage
errors. The routines additionally detect most improper frees
and reallocs. All this holds as long as the static bookkeeping
for malloc itself is not corrupted by some other means. This
is only one aspect of security -- these checks do not, and
cannot, detect all possible programming errors.
If FOOTERS is defined nonzero, then each allocated chunk
carries an additional check word to verify that it was malloced
from its space. These check words are the same within each
execution of a program using malloc, but differ across
executions, so externally crafted fake chunks cannot be
freed. This improves security by rejecting frees/reallocs that
could corrupt heap memory, in addition to the checks preventing
writes to statics that are always on. This may further improve
security at the expense of time and space overhead. (Note that
FOOTERS may also be worth using with MSPACES.)
By default detected errors cause the program to abort (calling
"abort()"). You can override this to instead proceed past
errors by defining PROCEED_ON_ERROR. In this case, a bad free
has no effect, and a malloc that encounters a bad address
caused by user overwrites will ignore the bad address by
dropping pointers and indices to all known memory. This may
be appropriate for programs that should continue if at all
possible in the face of programming errors, although they may
run out of memory because dropped memory is never reclaimed.
If you don't like either of these options, you can define
else. And if if you are sure that your program using malloc has
no errors or vulnerabilities, you can define INSECURE to 1,
which might (or might not) provide a small performance improvement.
Thread-safety: NOT thread-safe unless USE_LOCKS defined
When USE_LOCKS is defined, each public call to malloc, free,
etc is surrounded with either a pthread mutex or a win32
spinlock (depending on WIN32). This is not especially fast, and
can be a major bottleneck. It is designed only to provide
minimal protection in concurrent environments, and to provide a
basis for extensions. If you are using malloc in a concurrent
program, consider instead using ptmalloc, which is derived from
a version of this malloc. (See
System requirements: Any combination of MORECORE and/or MMAP/MUNMAP
This malloc can use unix sbrk or any emulation (invoked using
the CALL_MORECORE macro) and/or mmap/munmap or any emulation
(invoked using CALL_MMAP/CALL_MUNMAP) to get and release system
memory. On most unix systems, it tends to work best if both
MORECORE and MMAP are enabled. On Win32, it uses emulations
based on VirtualAlloc. It also uses common C library functions
like memset.
Compliance: I believe it is compliant with the Single Unix Specification
(See Also SVID/XPG, ANSI C, and probably
others as well.
* Overview of algorithms
This is not the fastest, most space-conserving, most portable, or
most tunable malloc ever written. However it is among the fastest
while also being among the most space-conserving, portable and
tunable. Consistent balance across these factors results in a good
general-purpose allocator for malloc-intensive programs.
In most ways, this malloc is a best-fit allocator. Generally, it
chooses the best-fitting existing chunk for a request, with ties
broken in approximately least-recently-used order. (This strategy
normally maintains low fragmentation.) However, for requests less
than 256bytes, it deviates from best-fit when there is not an
exactly fitting available chunk by preferring to use space adjacent
to that used for the previous small request, as well as by breaking
ties in approximately most-recently-used order. (These enhance
locality of series of small allocations.) And for very large requests
(>= 256Kb by default), it relies on system memory mapping
facilities, if supported. (This helps avoid carrying around and
possibly fragmenting memory used only for large chunks.)
All operations (except malloc_stats and mallinfo) have execution
times that are bounded by a constant factor of the number of bits in
a size_t, not counting any clearing in calloc or copying in realloc,
or actions surrounding MORECORE and MMAP that have times
proportional to the number of non-contiguous regions returned by
system allocation routines, which is often just 1.
The implementation is not very modular and seriously overuses
macros. Perhaps someday all C compilers will do as good a job
inlining modular code as can now be done by brute-force expansion,
but now, enough of them seem not to.
Some compilers issue a lot of warnings about code that is
dead/unreachable only on some platforms, and also about intentional
uses of negation on unsigned types. All known cases of each can be
For a longer but out of date high-level description, see
If MSPACES is defined, then in addition to malloc, free, etc.,
this file also defines mspace_malloc, mspace_free, etc. These
are versions of malloc routines that take an "mspace" argument
obtained using create_mspace, to control all internal bookkeeping.
If ONLY_MSPACES is defined, only these versions are compiled.
So if you would like to use this allocator for only some allocations,
and your system malloc for others, you can compile with
ONLY_MSPACES and then do something like...
static mspace mymspace = create_mspace(0,0); // for example
#define mymalloc(bytes) mspace_malloc(mymspace, bytes)
(Note: If you only need one instance of an mspace, you can instead
use "USE_DL_PREFIX" to relabel the global malloc.)
You can similarly create thread-local allocators by storing
mspaces as thread-locals. For example:
static __thread mspace tlms = 0;
void* tlmalloc(size_t bytes) {
if (tlms == 0) tlms = create_mspace(0, 0);
return mspace_malloc(tlms, bytes);
void tlfree(void* mem) { mspace_free(tlms, mem); }
Unless FOOTERS is defined, each mspace is completely independent.
You cannot allocate from one and free to another (although
conformance is only weakly checked, so usage errors are not always
caught). If FOOTERS is defined, then each chunk carries around a tag
indicating its originating mspace, and frees are directed to their
originating spaces.
------------------------- Compile-time options ---------------------------
Be careful in setting #define values for numerical constants of type
size_t. On some systems, literal values are not automatically extended
to size_t precision unless they are explicitly casted.
WIN32 default: defined if _WIN32 defined
Defining WIN32 sets up defaults for MS environment and compilers.
Otherwise defaults are for unix.
MALLOC_ALIGNMENT default: (size_t)8
Controls the minimum alignment for malloc'ed chunks. It must be a
power of two and at least 8, even on machines for which smaller
alignments would suffice. It may be defined as larger than this
though. Note however that code and data structures are optimized for
the case of 8-byte alignment.
MSPACES default: 0 (false)
If true, compile in support for independent allocation spaces.
This is only supported if HAVE_MMAP is true.
ONLY_MSPACES default: 0 (false)
If true, only compile in mspace versions, not regular versions.
USE_LOCKS default: 0 (false)
Causes each call to each public routine to be surrounded with
pthread or WIN32 mutex lock/unlock. (If set true, this can be
overridden on a per-mspace basis for mspace versions.)
FOOTERS default: 0
If true, provide extra checking and dispatching by placing
information in the footers of allocated chunks. This adds
space and time overhead.
INSECURE default: 0
If true, omit checks for usage errors and heap space overwrites.
USE_DL_PREFIX default: NOT defined
Causes compiler to prefix all public routines with the string 'dl'.
This can be useful when you only want to use this malloc in one part
of a program, using your regular system malloc elsewhere.
ABORT default: defined as abort()
Defines how to abort on failed checks. On most systems, a failed
check cannot die with an "assert" or even print an informative
message, because the underlying print routines in turn call malloc,
which will fail again. Generally, the best policy is to simply call
abort(). It's not very useful to do more than this because many
errors due to overwriting will show up as address faults (null, odd
addresses etc) rather than malloc-triggered checks, so will also
abort. Also, most compilers know that abort() does not return, so
can better optimize code conditionally calling it.
PROCEED_ON_ERROR default: defined as 0 (false)
Controls whether detected bad addresses cause them to bypassed
rather than aborting. If set, detected bad arguments to free and
realloc are ignored. And all bookkeeping information is zeroed out
upon a detected overwrite of freed heap space, thus losing the
ability to ever return it from malloc again, but enabling the
application to proceed. If PROCEED_ON_ERROR is defined, the
static variable malloc_corruption_error_count is compiled in
and can be examined to see if errors have occurred. This option
generates slower code than the default abort policy.
DEBUG default: NOT defined
The DEBUG setting is mainly intended for people trying to modify
this code or diagnose problems when porting to new platforms.
However, it may also be able to better isolate user errors than just
using runtime checks. The assertions in the check routines spell
out in more detail the assumptions and invariants underlying the
algorithms. The checking is fairly extensive, and will slow down
execution noticeably. Calling malloc_stats or mallinfo with DEBUG
set will attempt to check every non-mmapped allocated and free chunk
in the course of computing the summaries.
ABORT_ON_ASSERT_FAILURE default: defined as 1 (true)
Debugging assertion failures can be nearly impossible if your
version of the assert macro causes malloc to be called, which will
lead to a cascade of further failures, blowing the runtime stack.
ABORT_ON_ASSERT_FAILURE cause assertions failures to call abort(),
which will usually make debugging easier.
MALLOC_FAILURE_ACTION default: sets errno to ENOMEM, or no-op on win32
The action to take before "return 0" when malloc fails to be able to
return memory because there is none available.
HAVE_MORECORE default: 1 (true) unless win32 or ONLY_MSPACES
True if this system supports sbrk or an emulation of it.
MORECORE default: sbrk
The name of the sbrk-style system routine to call to obtain more
memory. See below for guidance on writing custom MORECORE
functions. The type of the argument to sbrk/MORECORE varies across
systems. It cannot be size_t, because it supports negative
arguments, so it is normally the signed type of the same width as
size_t (sometimes declared as "intptr_t"). It doesn't much matter
though. Internally, we only call it with arguments less than half
the max value of a size_t, which should work across all reasonable
possibilities, although sometimes generating compiler warnings. See
near the end of this file for guidelines for creating a custom
version of MORECORE.
MORECORE_CONTIGUOUS default: 1 (true)
If true, take advantage of fact that consecutive calls to MORECORE
with positive arguments always return contiguous increasing
addresses. This is true of unix sbrk. It does not hurt too much to
set it true anyway, since malloc copes with non-contiguities.
Setting it false when definitely non-contiguous saves time
and possibly wasted space it would take to discover this though.
True if MORECORE cannot release space back to the system when given
negative arguments. This is generally necessary only if you are
using a hand-crafted MORECORE function that cannot handle negative
HAVE_MMAP default: 1 (true)
True if this system supports mmap or an emulation of it. If so, and
HAVE_MORECORE is not true, MMAP is used for all system
allocation. If set and HAVE_MORECORE is true as well, MMAP is
primarily used to directly allocate very large blocks. It is also
used as a backup strategy in cases where MORECORE fails to provide
space from system. Note: A single call to MUNMAP is assumed to be
able to unmap memory that may have be allocated using multiple calls
to MMAP, so long as they are adjacent.
HAVE_MREMAP default: 1 on linux, else 0
If true realloc() uses mremap() to re-allocate large blocks and
extend or shrink allocation spaces.
MMAP_CLEARS default: 1 on unix
True if mmap clears memory so calloc doesn't need to. This is true
for standard unix mmap using /dev/zero.
USE_BUILTIN_FFS default: 0 (i.e., not used)
Causes malloc to use the builtin ffs() function to compute indices.
Some compilers may recognize and intrinsify ffs to be faster than the
supplied C version. Also, the case of x86 using gcc is special-cased
to an asm instruction, so is already as fast as it can be, and so
this setting has no effect. (On most x86s, the asm version is only
slightly faster than the C version.)
malloc_getpagesize default: derive from system includes, or 4096.
The system page size. To the extent possible, this malloc manages
memory from the system in page-size units. This may be (and
usually is) a function rather than a constant. This is ignored
if WIN32, where page size is determined using getSystemInfo during
USE_DEV_RANDOM default: 0 (i.e., not used)
Causes malloc to use /dev/random to initialize secure magic seed for
stamping footers. Otherwise, the current time is used.
NO_MALLINFO default: 0
If defined, don't compile "mallinfo". This can be a simple way
of dealing with mismatches between system declarations and
those in this file.
MALLINFO_FIELD_TYPE default: size_t
The type of the fields in the mallinfo struct. This was originally
defined as "int" in SVID etc, but is more usefully defined as
size_t. The value is used only if HAVE_USR_INCLUDE_MALLOC_H is not set
REALLOC_ZERO_BYTES_FREES default: not defined
This should be set if a call to realloc with zero bytes should
be the same as a call to free. Some people think it should. Otherwise,
since this malloc returns a unique pointer for malloc(0), so does
realloc(p, 0).
LACKS_STDLIB_H default: NOT defined unless on WIN32
Define these if your system does not have these header files.
You might need to manually insert some of the declarations they provide.
system_info.dwAllocationGranularity in WIN32,
otherwise 64K.
Also settable using mallopt(M_GRANULARITY, x)
The unit for allocating and deallocating memory from the system. On
most systems with contiguous MORECORE, there is no reason to
make this more than a page. However, systems with MMAP tend to
either require or encourage larger granularities. You can increase
this value to prevent system allocation functions to be called so
often, especially if they are slow. The value must be at least one
page and must be a power of two. Setting to 0 causes initialization
to either page size or win32 region size. (Note: In previous
versions of malloc, the equivalent of this option was called
Also settable using mallopt(M_TRIM_THRESHOLD, x)
The maximum amount of unused top-most memory to keep before
releasing via malloc_trim in free(). Automatic trimming is mainly
useful in long-lived programs using contiguous MORECORE. Because
trimming via sbrk can be slow on some systems, and can sometimes be
wasteful (in cases where programs immediately afterward allocate
more large chunks) the value should be high enough so that your
overall system performance would improve by releasing this much
memory. As a rough guide, you might set to a value close to the
average size of a process (program) running on your system.
Releasing this much memory would allow such a process to run in
memory. Generally, it is worth tuning trim thresholds when a
program undergoes phases where several large chunks are allocated
and released in ways that can reuse each other's storage, perhaps
mixed with phases where there are no such chunks at all. The trim
value must be greater than page size to have any useful effect. To
disable trimming completely, you can set to MAX_SIZE_T. Note that the trick
some people use of mallocing a huge space and then freeing it at
program startup, in an attempt to reserve system memory, doesn't
have the intended effect under automatic trimming, since that memory
will immediately be returned to the system.
Also settable using mallopt(M_MMAP_THRESHOLD, x)
The request size threshold for using MMAP to directly service a
request. Requests of at least this size that cannot be allocated
using already-existing space will be serviced via mmap. (If enough
normal freed space already exists it is used instead.) Using mmap
segregates relatively large chunks of memory so that they can be
individually obtained and released from the host system. A request
serviced through mmap is never reused by any other request (at least
not directly; the system may just so happen to remap successive
requests to the same locations). Segregating space in this way has
the benefits that: Mmapped space can always be individually released
back to the system, which helps keep the system level memory demands
of a long-lived program low. Also, mapped memory doesn't become
`locked' between other chunks, as can happen with normally allocated
chunks, which means that even trimming via malloc_trim would not
release them. However, it has the disadvantage that the space
cannot be reclaimed, consolidated, and then used to service later
requests, as happens with normal chunks. The advantages of mmap
nearly always outweigh disadvantages for "large" chunks, but the
value of "large" may vary across systems. The default is an
empirically derived value that works well in most systems. You can
disable mmap by setting to MAX_SIZE_T.
#ifndef WIN32
#ifdef _WIN32
#define WIN32 1
#endif /* _WIN32 */
#endif /* WIN32 */
#ifdef WIN32
#include <windows.h>
#define HAVE_MMAP 1
#define MMAP_CLEARS 0 /* WINCE and some others apparently don't clear */
#endif /* WIN32 */
#ifdef __OS2__
#define INCL_DOS
#include <os2.h>
#define HAVE_MMAP 1
#endif /* __OS2__ */
#if defined(DARWIN) || defined(_DARWIN)
/* Mac OSX docs advise not to use sbrk; it seems better to use mmap */
#define HAVE_MMAP 1
#endif /* HAVE_MORECORE */
#endif /* DARWIN */
#include <sys/types.h> /* For size_t */
#endif /* LACKS_SYS_TYPES_H */
/* The maximum possible size_t value has all bits set */
#define MAX_SIZE_T (~(size_t)0)
#define ONLY_MSPACES 0
#endif /* ONLY_MSPACES */
#ifndef MSPACES
#define MSPACES 1
#else /* ONLY_MSPACES */
#define MSPACES 0
#endif /* ONLY_MSPACES */
#endif /* MSPACES */
#define MALLOC_ALIGNMENT ((size_t)8U)
#ifndef FOOTERS
#define FOOTERS 0
#endif /* FOOTERS */
#ifndef ABORT
#define ABORT abort()
#endif /* ABORT */
#endif /* PROCEED_ON_ERROR */
#ifndef USE_LOCKS
#define USE_LOCKS 0
#endif /* USE_LOCKS */
#ifndef INSECURE
#define INSECURE 0
#endif /* INSECURE */
#ifndef HAVE_MMAP
#define HAVE_MMAP 1
#endif /* HAVE_MMAP */
#define MMAP_CLEARS 1
#endif /* MMAP_CLEARS */
#ifdef linux
#define HAVE_MREMAP 1
#else /* linux */
#define HAVE_MREMAP 0
#endif /* linux */
#endif /* HAVE_MREMAP */
#else /* ONLY_MSPACES */
#endif /* ONLY_MSPACES */
#endif /* HAVE_MORECORE */
#else /* !HAVE_MORECORE */
#ifndef MORECORE
#define MORECORE sbrk
#endif /* MORECORE */
#endif /* HAVE_MORECORE */
#define DEFAULT_GRANULARITY (0) /* 0 means to compute in init_mparams */
#define DEFAULT_GRANULARITY ((size_t)64U * (size_t)1024U)
#define DEFAULT_TRIM_THRESHOLD ((size_t)2U * (size_t)1024U * (size_t)1024U)
#define DEFAULT_MMAP_THRESHOLD ((size_t)256U * (size_t)1024U)
#else /* HAVE_MMAP */
#endif /* HAVE_MMAP */
#endif /* USE_BUILTIN_FFS */
#define USE_DEV_RANDOM 0
#endif /* USE_DEV_RANDOM */
#define NO_MALLINFO 0
#endif /* NO_MALLINFO */
#define MALLINFO_FIELD_TYPE size_t
mallopt tuning options. SVID/XPG defines four standard parameter
numbers for mallopt, normally defined in malloc.h. None of these
are used in this malloc, so setting them has no effect. But this
malloc does support the following options.
#define M_TRIM_THRESHOLD (-1)
#define M_GRANULARITY (-2)
#define M_MMAP_THRESHOLD (-3)
/* ------------------------ Mallinfo declarations ------------------------ */
This version of malloc supports the standard SVID/XPG mallinfo
routine that returns a struct containing usage properties and
statistics. It should work on any system that has a
/usr/include/malloc.h defining struct mallinfo. The main
declaration needed is the mallinfo struct that is returned (by-copy)
by mallinfo(). The malloinfo struct contains a bunch of fields that
are not even meaningful in this version of malloc. These fields are
are instead filled by mallinfo() with other numbers that might be of
HAVE_USR_INCLUDE_MALLOC_H should be set if you have a
/usr/include/malloc.h file that includes a declaration of struct
mallinfo. If so, it is included; else a compliant version is
declared below. These must be precisely the same for mallinfo() to
work. The original SVID version of this struct, defined on most
systems with mallinfo, declares all fields as ints. But some others
define as unsigned long. If your system defines the fields using a
type of different width than listed here, you MUST #include your
system version and #define HAVE_USR_INCLUDE_MALLOC_H.
#include "/usr/include/malloc.h"
/* HP-UX's stdlib.h redefines mallinfo unless _STRUCT_MALLINFO is defined */
struct mallinfo {
MALLINFO_FIELD_TYPE arena; /* non-mmapped space allocated from system */
MALLINFO_FIELD_TYPE ordblks; /* number of free chunks */
MALLINFO_FIELD_TYPE smblks; /* always 0 */
MALLINFO_FIELD_TYPE hblks; /* always 0 */
MALLINFO_FIELD_TYPE hblkhd; /* space in mmapped regions */
MALLINFO_FIELD_TYPE usmblks; /* maximum total allocated space */
MALLINFO_FIELD_TYPE fsmblks; /* always 0 */
MALLINFO_FIELD_TYPE uordblks; /* total allocated space */
MALLINFO_FIELD_TYPE fordblks; /* total free space */
MALLINFO_FIELD_TYPE keepcost; /* releasable (via malloc_trim) space */
#endif /* NO_MALLINFO */
#ifdef __cplusplus
extern "C" {
#endif /* __cplusplus */
/* ------------------- Declarations of public routines ------------------- */
#define dlcalloc calloc
#define dlfree free
#define dlmalloc malloc
#define dlmemalign memalign
#define dlrealloc realloc
#define dlvalloc valloc
#define dlpvalloc pvalloc
#define dlmallinfo mallinfo
#define dlmallopt mallopt
#define dlmalloc_trim malloc_trim
#define dlmalloc_stats malloc_stats
#define dlmalloc_usable_size malloc_usable_size
#define dlmalloc_footprint malloc_footprint
#define dlmalloc_max_footprint malloc_max_footprint
#define dlindependent_calloc independent_calloc
#define dlindependent_comalloc independent_comalloc
#endif /* USE_DL_PREFIX */
malloc(size_t n)
Returns a pointer to a newly allocated chunk of at least n bytes, or
null if no space is available, in which case errno is set to ENOMEM
on ANSI C systems.
If n is zero, malloc returns a minimum-sized chunk. (The minimum
size is 16 bytes on most 32bit systems, and 32 bytes on 64bit
systems.) Note that size_t is an unsigned type, so calls with
arguments that would be negative if signed are interpreted as
requests for huge amounts of space, which will often fail. The
maximum supported value of n differs across systems, but is in all
cases less than the maximum representable value of a size_t.
void* dlmalloc(size_t);
free(void* p)
Releases the chunk of memory pointed to by p, that had been previously
allocated using malloc or a related routine such as realloc.
It has no effect if p is null. If p was not malloced or already
freed, free(p) will by default cause the current program to abort.
void dlfree(void*);
calloc(size_t n_elements, size_t element_size);
Returns a pointer to n_elements * element_size bytes, with all locations
set to zero.
void* dlcalloc(size_t, size_t);
realloc(void* p, size_t n)
Returns a pointer to a chunk of size n that contains the same data
as does chunk p up to the minimum of (n, p's size) bytes, or null
if no space is available.
The returned pointer may or may not be the same as p. The algorithm
prefers extending p in most cases when possible, otherwise it
employs the equivalent of a malloc-copy-free sequence.
If p is null, realloc is equivalent to malloc.
If space is not available, realloc returns null, errno is set (if on
ANSI) and p is NOT freed.
if n is for fewer bytes than already held by p, the newly unused
space is lopped off and freed if possible. realloc with a size
argument of zero (re)allocates a minimum-sized chunk.
The old unix realloc convention of allowing the last-free'd chunk
to be used as an argument to realloc is not supported.
void* dlrealloc(void*, size_t);
memalign(size_t alignment, size_t n);
Returns a pointer to a newly allocated chunk of n bytes, aligned
in accord with the alignment argument.
The alignment argument should be a power of two. If the argument is
not a power of two, the nearest greater power is used.
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.
void* dlmemalign(size_t, size_t);
valloc(size_t n);
Equivalent to memalign(pagesize, n), where pagesize is the page
size of the system. If the pagesize is unknown, 4096 is used.
void* dlvalloc(size_t);
mallopt(int parameter_number, int parameter_value)
Sets 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. SVID/XPG/ANSI defines four standard param numbers for mallopt,
normally defined in malloc.h. None of these are use in this malloc,
so setting them has no effect. But this malloc also supports other
options in mallopt. See below for details. Briefly, supported
parameters are as follows (listed defaults are for "typical"
Symbol param # default allowed param values
M_TRIM_THRESHOLD -1 2*1024*1024 any (MAX_SIZE_T disables)
M_GRANULARITY -2 page size any power of 2 >= page size
M_MMAP_THRESHOLD -3 256*1024 any (or 0 if no MMAP support)
int dlmallopt(int, int);
Returns the number of bytes obtained from the system. The total
number of bytes allocated by malloc, realloc etc., is less than this
value. Unlike mallinfo, this function returns only a precomputed
result, so can be called frequently to monitor memory consumption.
Even if locks are otherwise defined, this function does not use them,
so results might not be up to date.
size_t dlmalloc_footprint(void);
Returns the maximum number of bytes obtained from the system. This
value will be greater than current footprint if deallocated space
has been reclaimed by the system. The peak number of bytes allocated
by malloc, realloc etc., is less than this value. Unlike mallinfo,
this function returns only a precomputed result, so can be called
frequently to monitor memory consumption. Even if locks are
otherwise defined, this function does not use them, so results might
not be up to date.
size_t dlmalloc_max_footprint(void);
Returns (by copy) a struct containing various summary statistics:
arena: current total non-mmapped bytes allocated from system
ordblks: the number of free chunks
smblks: always zero.
hblks: current number of mmapped regions
hblkhd: total bytes held in mmapped regions
usmblks: the maximum total allocated space. This will be greater
than current total if trimming has occurred.
fsmblks: always zero
uordblks: current total allocated space (normal or mmapped)
fordblks: total free space
keepcost: the maximum number of bytes that could ideally be released
back to system via malloc_trim. ("ideally" means that
it ignores page restrictions etc.)
Because these fields are ints, but internal bookkeeping may
be kept as longs, the reported values may wrap around zero and
thus be inaccurate.
struct mallinfo dlmallinfo(void);
#endif /* NO_MALLINFO */
independent_calloc(size_t n_elements, size_t element_size, void* chunks[]);
independent_calloc is similar to calloc, but instead of returning a
single cleared space, it returns an array of pointers to n_elements
independent elements that can hold contents of size elem_size, each
of which starts out cleared, and can be independently freed,
realloc'ed etc. The elements are guaranteed to be adjacently
allocated (this is not guaranteed to occur with multiple callocs or
mallocs), which may also improve cache locality in some
The "chunks" argument is optional (i.e., may be null, which is
probably the most typical usage). If it is null, the returned array
is itself dynamically allocated and should also be freed when it is
no longer needed. Otherwise, the chunks array must be of at least
n_elements in length. It is filled in with the pointers to the
In either case, independent_calloc returns this pointer array, or
null if the allocation failed. If n_elements is zero and "chunks"
is null, it returns a chunk representing an array with zero elements
(which should be freed if not wanted).
Each element must be individually freed when it is no longer
needed. If you'd like to instead be able to free all at once, you
should instead use regular calloc and assign pointers into this
space to represent elements. (In this case though, you cannot
independently free elements.)
independent_calloc simplifies and speeds up implementations of many
kinds of pools. It may also be useful when constructing large data
structures that initially have a fixed number of fixed-sized nodes,
but the number is not known at compile time, and some of the nodes
may later need to be freed. For example:
struct Node { int item; struct Node* next; };
struct Node* build_list() {
struct Node** pool;
int n = read_number_of_nodes_needed();
if (n <= 0) return 0;
pool = (struct Node**)(independent_calloc(n, sizeof(struct Node), 0);
if (pool == 0) die();
// organize into a linked list...
struct Node* first = pool[0];
for (i = 0; i < n-1; ++i)
pool[i]->next = pool[i+1];
free(pool); // Can now free the array (or not, if it is needed later)
return first;
void** dlindependent_calloc(size_t, size_t, void**);
independent_comalloc(size_t n_elements, size_t sizes[], void* chunks[]);
independent_comalloc allocates, all at once, a set of n_elements
chunks with sizes indicated in the "sizes" array. It returns
an array of pointers to these elements, each of which can be
independently freed, realloc'ed etc. The elements are guaranteed to
be adjacently allocated (this is not guaranteed to occur with
multiple callocs or mallocs), which may also improve cache locality
in some applications.
The "chunks" argument is optional (i.e., may be null). If it is null
the returned array is itself dynamically allocated and should also
be freed when it is no longer needed. Otherwise, the chunks array
must be of at least n_elements in length. It is filled in with the
pointers to the chunks.
In either case, independent_comalloc returns this pointer array, or
null if the allocation failed. If n_elements is zero and chunks is
null, it returns a chunk representing an array with zero elements
(which should be freed if not wanted).
Each element must be individually freed when it is no longer
needed. If you'd like to instead be able to free all at once, you
should instead use a single regular malloc, and assign pointers at
particular offsets in the aggregate space. (In this case though, you
cannot independently free elements.)
independent_comallac differs from independent_calloc in that each
element may have a different size, and also that it does not
automatically clear elements.
independent_comalloc can be used to speed up allocation in cases
where several structs or objects must always be allocated at the
same time. For example:
struct Head { ... }
struct Foot { ... }
void send_message(char* msg) {
int msglen = strlen(msg);
size_t sizes[3] = { sizeof(struct Head), msglen, sizeof(struct Foot) };
void* chunks[3];
if (independent_comalloc(3, sizes, chunks) == 0)
struct Head* head = (struct Head*)(chunks[0]);
char* body = (char*)(chunks[1]);
struct Foot* foot = (struct Foot*)(chunks[2]);
// ...
In general though, independent_comalloc is worth using only for
larger values of n_elements. For small values, you probably won't
detect enough difference from series of malloc calls to bother.
Overuse of independent_comalloc can increase overall memory usage,
since it cannot reuse existing noncontiguous small chunks that
might be available for some of the elements.
void** dlindependent_comalloc(size_t, size_t*, void**);
pvalloc(size_t n);
Equivalent to valloc(minimum-page-that-holds(n)), that is,
round up n to nearest pagesize.
void* dlpvalloc(size_t);
malloc_trim(size_t pad);
If possible, gives memory back to the system (via negative arguments
to sbrk) if there is unused memory at the `high' end of the malloc
pool or in unused MMAP segments. 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. 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.
int dlmalloc_trim(size_t);
malloc_usable_size(void* p);
Returns the number of bytes you can actually use in
an allocated chunk, which may be more than you requested (although
often not) due to alignment and minimum size constraints.
You can use this many bytes without worrying about
overwriting other allocated objects. This is not a particularly great
programming practice. malloc_usable_size can be more useful in
debugging and assertions, for example:
p = malloc(n);
assert(malloc_usable_size(p) >= 256);
size_t dlmalloc_usable_size(void*);
Prints on stderr the amount of space obtained 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), 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. Because it includes
alignment wastage as being in use, this figure may be greater than
zero even when no user-level chunks are allocated.
The reported current and maximum system memory can be inaccurate if
a program makes other calls to system memory allocation functions
(normally sbrk) outside of malloc.
malloc_stats prints only the most commonly interesting statistics.
More information can be obtained by calling mallinfo.
void dlmalloc_stats(void);
#endif /* ONLY_MSPACES */
mspace is an opaque type representing an independent
region of space that supports mspace_malloc, etc.
typedef void* mspace;
create_mspace creates and returns a new independent space with the
given initial capacity, or, if 0, the default granularity size. It
returns null if there is no system memory available to create the
space. If argument locked is non-zero, the space uses a separate
lock to control access. The capacity of the space will grow
dynamically as needed to service mspace_malloc requests. You can
control the sizes of incremental increases of this space by
compiling with a different DEFAULT_GRANULARITY or dynamically
setting with mallopt(M_GRANULARITY, value).
mspace create_mspace(size_t capacity, int locked);
destroy_mspace destroys the given space, and attempts to return all
of its memory back to the system, returning the total number of
bytes freed. After destruction, the results of access to all memory
used by the space become undefined.
size_t destroy_mspace(mspace msp);
create_mspace_with_base uses the memory supplied as the initial base
of a new mspace. Part (less than 128*sizeof(size_t) bytes) of this
space is used for bookkeeping, so the capacity must be at least this
large. (Otherwise 0 is returned.) When this initial space is
exhausted, additional memory will be obtained from the system.
Destroying this space will deallocate all additionally allocated
space (if possible) but not the initial base.
mspace create_mspace_with_base(void* base, size_t capacity, int locked);
mspace_malloc behaves as malloc, but operates within
the given space.
void* mspace_malloc(mspace msp, size_t bytes);
mspace_free behaves as free, but operates within
the given space.
If compiled with FOOTERS==1, mspace_free is not actually needed.
free may be called instead of mspace_free because freed chunks from
any space are handled by their originating spaces.
void mspace_free(mspace msp, void* mem);
mspace_realloc behaves as realloc, but operates within
the given space.
If compiled with FOOTERS==1, mspace_realloc is not actually
needed. realloc may be called instead of mspace_realloc because
realloced chunks from any space are handled by their originating
void* mspace_realloc(mspace msp, void* mem, size_t newsize);
mspace_calloc behaves as calloc, but operates within
the given space.
void* mspace_calloc(mspace msp, size_t n_elements, size_t elem_size);
mspace_memalign behaves as memalign, but operates within
the given space.
void* mspace_memalign(mspace msp, size_t alignment, size_t bytes);
mspace_independent_calloc behaves as independent_calloc, but
operates within the given space.
void** mspace_independent_calloc(mspace msp, size_t n_elements,
size_t elem_size, void* chunks[]);
mspace_independent_comalloc behaves as independent_comalloc, but
operates within the given space.
void** mspace_independent_comalloc(mspace msp, size_t n_elements,
size_t sizes[], void* chunks[]);
mspace_footprint() returns the number of bytes obtained from the
system for this space.
size_t mspace_footprint(mspace msp);
mspace_max_footprint() returns the peak number of bytes obtained from the
system for this space.
size_t mspace_max_footprint(mspace msp);
mspace_mallinfo behaves as mallinfo, but reports properties of
the given space.
struct mallinfo mspace_mallinfo(mspace msp);
#endif /* NO_MALLINFO */
mspace_malloc_stats behaves as malloc_stats, but reports
properties of the given space.
void mspace_malloc_stats(mspace msp);
mspace_trim behaves as malloc_trim, but
operates within the given space.
int mspace_trim(mspace msp, size_t pad);
An alias for mallopt.
int mspace_mallopt(int, int);
#endif /* MSPACES */
#ifdef __cplusplus
}; /* end of extern "C" */
#endif /* __cplusplus */
To make a fully customizable malloc.h header file, cut everything
above this line, put into file malloc.h, edit to suit, and #include it
on the next line, as well as in programs that use this malloc.
/* #include "malloc.h" */
/*------------------------------ internal #includes ---------------------- */
#ifdef _MSC_VER
#pragma warning( disable : 4146 ) /* no "unsigned" warnings */
#endif /* _MSC_VER */
#include <stdio.h> /* for printing in malloc_stats */
#include <errno.h> /* for MALLOC_FAILURE_ACTION */
#endif /* LACKS_ERRNO_H */
#include <time.h> /* for magic initialization */
#endif /* FOOTERS */
#include <stdlib.h> /* for abort() */
#endif /* LACKS_STDLIB_H */
#ifdef DEBUG
#define assert(x) if(!(x)) ABORT
#include <assert.h>
#else /* DEBUG */
#define assert(x)
#endif /* DEBUG */
#include <string.h> /* for memset etc */
#endif /* LACKS_STRING_H */
#include <strings.h> /* for ffs */
#endif /* LACKS_STRINGS_H */
#endif /* USE_BUILTIN_FFS */
#include <sys/mman.h> /* for mmap */
#endif /* LACKS_SYS_MMAN_H */
#include <fcntl.h>
#endif /* LACKS_FCNTL_H */
#endif /* HAVE_MMAP */
#include <unistd.h> /* for sbrk */
#else /* LACKS_UNISTD_H */
#if !defined(__FreeBSD__) && !defined(__OpenBSD__) && !defined(__NetBSD__)
extern void* sbrk(ptrdiff_t);
#endif /* FreeBSD etc */
#endif /* LACKS_UNISTD_H */
#endif /* HAVE_MMAP */
#ifndef WIN32
#ifndef malloc_getpagesize
# ifdef _SC_PAGESIZE /* some SVR4 systems omit an underscore */
# ifndef _SC_PAGE_SIZE
# endif
# endif
# ifdef _SC_PAGE_SIZE
# define malloc_getpagesize sysconf(_SC_PAGE_SIZE)
# else
# if defined(BSD) || defined(DGUX) || defined(HAVE_GETPAGESIZE)
extern size_t getpagesize();
# define malloc_getpagesize getpagesize()
# else
# ifdef WIN32 /* use supplied emulation of getpagesize */
# define malloc_getpagesize getpagesize()
# else
# include <sys/param.h>
# endif
# define malloc_getpagesize EXEC_PAGESIZE
# else
# ifdef NBPG
# ifndef CLSIZE
# define malloc_getpagesize NBPG
# else
# define malloc_getpagesize (NBPG * CLSIZE)
# endif
# else
# ifdef NBPC
# define malloc_getpagesize NBPC
# else
# ifdef PAGESIZE
# define malloc_getpagesize PAGESIZE
# else /* just guess */
# define malloc_getpagesize ((size_t)4096U)
# endif
# endif
# endif
# endif
# endif
# endif
# endif
/* ------------------- size_t and alignment properties -------------------- */
/* The byte and bit size of a size_t */
#define SIZE_T_SIZE (sizeof(size_t))
#define SIZE_T_BITSIZE (sizeof(size_t) << 3)
/* Some constants coerced to size_t */
/* Annoying but necessary to avoid errors on some platforms */
#define SIZE_T_ZERO ((size_t)0)
#define SIZE_T_ONE ((size_t)1)
#define SIZE_T_TWO ((size_t)2)
/* The bit mask value corresponding to MALLOC_ALIGNMENT */
/* True if address a has acceptable alignment */
#define is_aligned(A) (((size_t)((A)) & (CHUNK_ALIGN_MASK)) == 0)
/* the number of bytes to offset an address to align it */
#define align_offset(A)\
((((size_t)(A) & CHUNK_ALIGN_MASK) == 0)? 0 :\
/* -------------------------- MMAP preliminaries ------------------------- */
If HAVE_MORECORE or HAVE_MMAP are false, we just define calls and
checks to fail so compiler optimizer can delete code rather than
using so many "#if"s.
/* MORECORE and MMAP must return MFAIL on failure */
#define MFAIL ((void*)(MAX_SIZE_T))
#define CMFAIL ((char*)(MFAIL)) /* defined for convenience */
#define CALL_MMAP(s) MFAIL
#define CALL_MUNMAP(a, s) (-1)
#else /* HAVE_MMAP */
#if !defined(WIN32) && !defined (__OS2__)
#define CALL_MUNMAP(a, s) munmap((a), (s))
#if !defined(MAP_ANONYMOUS) && defined(MAP_ANON)
#endif /* MAP_ANON */
#define CALL_MMAP(s) mmap(0, (s), MMAP_PROT, MMAP_FLAGS, -1, 0)
#else /* MAP_ANONYMOUS */
Nearly all versions of mmap support MAP_ANONYMOUS, so the following
is unlikely to be needed, but is supplied just in case.
static int dev_zero_fd = -1; /* Cached file descriptor for /dev/zero. */
#define CALL_MMAP(s) ((dev_zero_fd < 0) ? \
(dev_zero_fd = open("/dev/zero", O_RDWR), \
mmap(0, (s), MMAP_PROT, MMAP_FLAGS, dev_zero_fd, 0)) : \
mmap(0, (s), MMAP_PROT, MMAP_FLAGS, dev_zero_fd, 0))
#endif /* MAP_ANONYMOUS */
#elif defined(__OS2__)
/* OS/2 MMAP via DosAllocMem */
static void* os2mmap(size_t size) {
void* ptr;
if (DosAllocMem(&ptr, size, OBJ_ANY|PAG_COMMIT|PAG_READ|PAG_WRITE) &&
DosAllocMem(&ptr, size, PAG_COMMIT|PAG_READ|PAG_WRITE))
return MFAIL;
return ptr;
#define os2direct_mmap(n) os2mmap(n)
/* This function supports releasing coalesed segments */
static int os2munmap(void* ptr, size_t size) {
while (size) {
ULONG ulSize = size;
ULONG ulFlags = 0;
if (DosQueryMem(ptr, &ulSize, &ulFlags) != 0)
return -1;
if ((ulFlags & PAG_BASE) == 0 ||(ulFlags & PAG_COMMIT) == 0 ||
ulSize > size)
return -1;
if (DosFreeMem(ptr) != 0)
return -1;
ptr = ( void * ) ( ( char * ) ptr + ulSize );
size -= ulSize;
return 0;
#define CALL_MMAP(s) os2mmap(s)
#define CALL_MUNMAP(a, s) os2munmap((a), (s))
#define DIRECT_MMAP(s) os2direct_mmap(s)
#else /* WIN32 */
/* Win32 MMAP via VirtualAlloc */
static void* win32mmap(size_t size) {
void* ptr = VirtualAlloc(0, size, MEM_RESERVE|MEM_COMMIT, PAGE_EXECUTE_READWRITE);
return (ptr != 0)? ptr: MFAIL;
/* For direct MMAP, use MEM_TOP_DOWN to minimize interference */
static void* win32direct_mmap(size_t size) {
void* ptr = VirtualAlloc(0, size, MEM_RESERVE|MEM_COMMIT|MEM_TOP_DOWN,
return (ptr != 0)? ptr: MFAIL;
/* This function supports releasing coalesed segments */
static int win32munmap(void* ptr, size_t size) {
char* cptr = ptr;
while (size) {
if (VirtualQuery(cptr, &minfo, sizeof(minfo)) == 0)
return -1;
if (minfo.BaseAddress != cptr || minfo.AllocationBase != cptr ||
minfo.State != MEM_COMMIT || minfo.RegionSize > size)
return -1;
if (VirtualFree(cptr, 0, MEM_RELEASE) == 0)
return -1;
cptr += minfo.RegionSize;
size -= minfo.RegionSize;
return 0;
#define CALL_MMAP(s) win32mmap(s)
#define CALL_MUNMAP(a, s) win32munmap((a), (s))
#define DIRECT_MMAP(s) win32direct_mmap(s)
#endif /* WIN32 */
#endif /* HAVE_MMAP */
#define CALL_MREMAP(addr, osz, nsz, mv) mremap((addr), (osz), (nsz), (mv))
#else /* HAVE_MMAP && HAVE_MREMAP */
#define CALL_MREMAP(addr, osz, nsz, mv) MFAIL
#endif /* HAVE_MMAP && HAVE_MREMAP */
#else /* HAVE_MORECORE */
#endif /* HAVE_MORECORE */
/* mstate bit set if contiguous morecore disabled or failed */
/* segment bit set in create_mspace_with_base */
#define EXTERN_BIT (8U)
/* --------------------------- Lock preliminaries ------------------------ */
When locks are defined, there are up to two global locks:
* If HAVE_MORECORE, morecore_mutex protects sequences of calls to
MORECORE. In many cases sys_alloc requires two calls, that should
not be interleaved with calls by other threads. This does not
protect against direct calls to MORECORE by other threads not
using this lock, so there is still code to cope the best we can on
* magic_init_mutex ensures that mparams.magic and other
unique mparams values are initialized only once.
#if !defined(WIN32) && !defined(__OS2__)
/* By default use posix locks */
#include <pthread.h>
#define MLOCK_T pthread_mutex_t
#define INITIAL_LOCK(l) pthread_mutex_init(l, NULL)
#define ACQUIRE_LOCK(l) pthread_mutex_lock(l)
#define RELEASE_LOCK(l) pthread_mutex_unlock(l)
static MLOCK_T morecore_mutex = PTHREAD_MUTEX_INITIALIZER;
#endif /* HAVE_MORECORE */
static MLOCK_T magic_init_mutex = PTHREAD_MUTEX_INITIALIZER;
#elif defined(__OS2__)
#define MLOCK_T HMTX
#define INITIAL_LOCK(l) DosCreateMutexSem(0, l, 0, FALSE)
#define ACQUIRE_LOCK(l) DosRequestMutexSem(*l, SEM_INDEFINITE_WAIT)
#define RELEASE_LOCK(l) DosReleaseMutexSem(*l)
static MLOCK_T morecore_mutex;
#endif /* HAVE_MORECORE */
static MLOCK_T magic_init_mutex;
#else /* WIN32 */
Because lock-protected regions have bounded times, and there
are no recursive lock calls, we can use simple spinlocks.
#define MLOCK_T long
static int win32_acquire_lock (MLOCK_T *sl) {
for (;;) {
#ifdef InterlockedCompareExchangePointer
if (!InterlockedCompareExchange(sl, 1, 0))
return 0;
#else /* Use older void* version */
if (!InterlockedCompareExchange((void**)sl, (void*)1, (void*)0))
return 0;
#endif /* InterlockedCompareExchangePointer */
Sleep (0);
static void win32_release_lock (MLOCK_T *sl) {
InterlockedExchange (sl, 0);
#define INITIAL_LOCK(l) *(l)=0
#define ACQUIRE_LOCK(l) win32_acquire_lock(l)
#define RELEASE_LOCK(l) win32_release_lock(l)
static MLOCK_T morecore_mutex;
#endif /* HAVE_MORECORE */
static MLOCK_T magic_init_mutex;
#endif /* WIN32 */
#define USE_LOCK_BIT (2U)
#else /* USE_LOCKS */
#define USE_LOCK_BIT (0U)
#define INITIAL_LOCK(l)
#endif /* USE_LOCKS */
#define ACQUIRE_MORECORE_LOCK() ACQUIRE_LOCK(&morecore_mutex);
#define RELEASE_MORECORE_LOCK() RELEASE_LOCK(&morecore_mutex);
#define ACQUIRE_MAGIC_INIT_LOCK() ACQUIRE_LOCK(&magic_init_mutex);
#define RELEASE_MAGIC_INIT_LOCK() RELEASE_LOCK(&magic_init_mutex);
#else /* USE_LOCKS */
#endif /* USE_LOCKS */
/* ----------------------- Chunk representations ------------------------ */
(The following includes lightly edited explanations by Colin Plumb.)
The malloc_chunk declaration below is misleading (but accurate and
necessary). It declares a "view" into memory allowing access to
necessary fields at known offsets from a given base.
Chunks of memory are maintained using a `boundary tag' method as
originally described by Knuth. (See the paper by Paul Wilson 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 fast. The head fields also hold bits
representing whether chunks are free or in use.
Here are some pictures to make it clearer. They are "exploded" to
show that the state of a chunk can be thought of as extending from
the high 31 bits of the head field of its header through the
prev_foot and PINUSE_BIT bit of the following chunk header.
A chunk that's in use looks like:
chunk-> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Size of previous chunk (if P = 1) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |P|
| Size of this chunk 1| +-+
mem-> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+- -+
| |
+- -+
| :
+- size - sizeof(size_t) available payload bytes -+
: |
chunk-> +- -+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |1|
| Size of next chunk (may or may not be in use) | +-+
mem-> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
And if it's free, it looks like this:
chunk-> +- -+
| User payload (must be in use, or we would have merged!) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |P|
| Size of this chunk 0| +-+
mem-> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next pointer |
| Prev pointer |
| :
+- size - sizeof(struct chunk) unused bytes -+
: |
chunk-> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Size of this chunk |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |0|
| Size of next chunk (must be in use, or we would have merged)| +-+
mem-> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| :
+- User payload -+
: |
Note that since we always merge adjacent free chunks, the chunks
adjacent to a free chunk must be in use.
Given a pointer to a chunk (which can be derived trivially from the
payload pointer) we can, in O(1) time, find out whether the adjacent
chunks are free, and if so, unlink them from the lists that they
are on and merge them with the current chunk.
Chunks always begin on even word boundaries, so the mem portion
(which is returned to the user) is also on an even word boundary, and
thus at least double-word aligned.
The P (PINUSE_BIT) 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. If pinuse is set for
any given chunk, then you CANNOT determine the size of the
previous chunk, and might even get a memory addressing fault when
trying to do so.
The C (CINUSE_BIT) bit, stored in the unused second-lowest bit of
the chunk size redundantly records whether the current chunk is
inuse. This redundancy enables usage checks within free and realloc,
and reduces indirection when freeing and consolidating chunks.
Each freshly allocated chunk must have both cinuse and pinuse set.
That is, each allocated chunk borders either a previously allocated
and still in-use chunk, or the base of its memory arena. This is
ensured by making all allocations from the the `lowest' part of any
found chunk. Further, no free chunk physically borders another one,
so each free chunk is known to be preceded and followed by either
inuse chunks or the ends of memory.
Note that the `foot' of the current chunk is actually represented
as the prev_foot of the NEXT chunk. This makes it easier to
deal with alignments etc but can be very confusing when trying
to extend or adapt this code.
The exceptions to all this are
1. The special chunk `top' is the top-most available chunk (i.e.,
the one bordering the end of available memory). It is treated
specially. Top 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). In effect,
the top chunk is treated as larger (and thus less well
fitting) than any other available chunk. The top chunk
doesn't update its trailing size field since there is no next
contiguous chunk that would have to index off it. However,
space is still allocated for it (TOP_FOOT_SIZE) to enable
separation or merging when space is extended.
3. Chunks allocated via mmap, which have the lowest-order bit
(IS_MMAPPED_BIT) set in their prev_foot fields, and do not set
PINUSE_BIT in their head fields. Because they are allocated
one-by-one, each must carry its own prev_foot field, which is
also used to hold the offset this chunk has within its mmapped
region, which is needed to preserve alignment. Each mmapped
chunk is trailed by the first two fields of a fake next-chunk
for sake of usage checks.
struct malloc_chunk {
size_t prev_foot; /* Size of previous chunk (if free). */
size_t head; /* Size and inuse bits. */
struct malloc_chunk* fd; /* double links -- used only if free. */
struct malloc_chunk* bk;
typedef struct malloc_chunk mchunk;
typedef struct malloc_chunk* mchunkptr;
typedef struct malloc_chunk* sbinptr; /* The type of bins of chunks */
typedef size_t bindex_t; /* Described below */
typedef unsigned int binmap_t; /* Described below */
typedef unsigned int flag_t; /* The type of various bit flag sets */
/* ------------------- Chunks sizes and alignments ----------------------- */
#define MCHUNK_SIZE (sizeof(mchunk))
#else /* FOOTERS */
#endif /* FOOTERS */
/* MMapped chunks need a second word of overhead ... */
/* ... and additional padding for fake next-chunk at foot */
/* The smallest size we can malloc is an aligned minimal chunk */
/* conversion from malloc headers to user pointers, and back */
#define chunk2mem(p) ((void*)((char*)(p) + TWO_SIZE_T_SIZES))
#define mem2chunk(mem) ((mchunkptr)((char*)(mem) - TWO_SIZE_T_SIZES))
/* chunk associated with aligned address A */
#define align_as_chunk(A) (mchunkptr)((A) + align_offset(chunk2mem(A)))
/* Bounds on request (not chunk) sizes. */
#define MAX_REQUEST ((-MIN_CHUNK_SIZE) << 2)
/* pad request bytes into a usable size */
#define pad_request(req) \
/* pad request, checking for minimum (but not maximum) */
#define request2size(req) \
(((req) < MIN_REQUEST)? MIN_CHUNK_SIZE : pad_request(req))
/* ------------------ Operations on head and foot fields ----------------- */
The head field of a chunk is or'ed with PINUSE_BIT when previous
adjacent chunk in use, and or'ed with CINUSE_BIT if this chunk is in
use. If the chunk was obtained with mmap, the prev_foot field has
IS_MMAPPED_BIT set, otherwise holding the offset of the base of the
mmapped region to the base of the chunk.
/* Head value for fenceposts */
/* extraction of fields from head words */
#define cinuse(p) ((p)->head & CINUSE_BIT)
#define pinuse(p) ((p)->head & PINUSE_BIT)
#define chunksize(p) ((p)->head & ~(INUSE_BITS))
#define clear_pinuse(p) ((p)->head &= ~PINUSE_BIT)
#define clear_cinuse(p) ((p)->head &= ~CINUSE_BIT)
/* Treat space at ptr +/- offset as a chunk */
#define chunk_plus_offset(p, s) ((mchunkptr)(((char*)(p)) + (s)))
#define chunk_minus_offset(p, s) ((mchunkptr)(((char*)(p)) - (s)))
/* Ptr to next or previous physical malloc_chunk. */
#define next_chunk(p) ((mchunkptr)( ((char*)(p)) + ((p)->head & ~INUSE_BITS)))
#define prev_chunk(p) ((mchunkptr)( ((char*)(p)) - ((p)->prev_foot) ))
/* extract next chunk's pinuse bit */
#define next_pinuse(p) ((next_chunk(p)->head) & PINUSE_BIT)
/* Get/set size at footer */
#define get_foot(p, s) (((mchunkptr)((char*)(p) + (s)))->prev_foot)
#define set_foot(p, s) (((mchunkptr)((char*)(p) + (s)))->prev_foot = (s))
/* Set size, pinuse bit, and foot */
#define set_size_and_pinuse_of_free_chunk(p, s)\
((p)->head = (s|PINUSE_BIT), set_foot(p, s))
/* Set size, pinuse bit, foot, and clear next pinuse */
#define set_free_with_pinuse(p, s, n)\
(clear_pinuse(n), set_size_and_pinuse_of_free_chunk(p, s))
#define is_mmapped(p)\
(!((p)->head & PINUSE_BIT) && ((p)->prev_foot & IS_MMAPPED_BIT))
/* Get the internal overhead associated with chunk p */
#define overhead_for(p)\
/* Return true if malloced space is not necessarily cleared */
#define calloc_must_clear(p) (!is_mmapped(p))
#else /* MMAP_CLEARS */
#define calloc_must_clear(p) (1)
#endif /* MMAP_CLEARS */
/* ---------------------- Overlaid data structures ----------------------- */
When chunks are not in use, they are treated as nodes of either
lists or trees.
"Small" 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 |
Larger chunks are kept in a form of bitwise digital trees (aka
tries) keyed on chunksizes. Because malloc_tree_chunks are only for
free chunks greater than 256 bytes, their size doesn't impose any
constraints on user chunk sizes. Each node looks like:
chunk-> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Size of previous chunk |
`head:' | Size of chunk, in bytes |P|
mem-> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Forward pointer to next chunk of same size |
| Back pointer to previous chunk of same size |
| Pointer to left child (child[0]) |
| Pointer to right child (child[1]) |
| Pointer to parent |
| bin index of this chunk |
| Unused space .
. |
nextchunk-> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
`foot:' | Size of chunk, in bytes |
Each tree holding treenodes is a tree of unique chunk sizes. Chunks
of the same size are arranged in a circularly-linked list, with only
the oldest chunk (the next to be used, in our FIFO ordering)
actually in the tree. (Tree members are distinguished by a non-null
parent pointer.) If a chunk with the same size an an existing node
is inserted, it is linked off the existing node using pointers that
work in the same way as fd/bk pointers of small chunks.
Each tree contains a power of 2 sized range of chunk sizes (the
smallest is 0x100 <= x < 0x180), which is is divided in half at each
tree level, with the chunks in the smaller half of the range (0x100
<= x < 0x140 for the top nose) in the left subtree and the larger
half (0x140 <= x < 0x180) in the right subtree. This is, of course,
done by inspecting individual bits.
Using these rules, each node's left subtree contains all smaller
sizes than its right subtree. However, the node at the root of each
subtree has no particular ordering relationship to either. (The
dividing line between the subtree sizes is based on trie relation.)
If we remove the last chunk of a given size from the interior of the
tree, we need to replace it with a leaf node. The tree ordering
rules permit a node to be replaced by any leaf below it.
The smallest chunk in a tree (a common operation in a best-fit
allocator) can be found by walking a path to the leftmost leaf in
the tree. Unlike a usual binary tree, where we follow left child
pointers until we reach a null, here we follow the right child
pointer any time the left one is null, until we reach a leaf with
both child pointers null. The smallest chunk in the tree will be
somewhere along that path.
The worst case number of steps to add, find, or remove a node is
bounded by the number of bits differentiating chunks within
bins. Under current bin calculations, this ranges from 6 up to 21
(for 32 bit sizes) or up to 53 (for 64 bit sizes). The typical case
is of course much better.
struct malloc_tree_chunk {
/* The first four fields must be compatible with malloc_chunk */
size_t prev_foot;
size_t head;
struct malloc_tree_chunk* fd;
struct malloc_tree_chunk* bk;
struct malloc_tree_chunk* child[2];
struct malloc_tree_chunk* parent;
bindex_t index;
typedef struct malloc_tree_chunk tchunk;
typedef struct malloc_tree_chunk* tchunkptr;
typedef struct malloc_tree_chunk* tbinptr; /* The type of bins of trees */
/* A little helper macro for trees */
#define leftmost_child(t) ((t)->child[0] != 0? (t)->child[0] : (t)->child[1])
/* ----------------------------- Segments -------------------------------- */
Each malloc space may include non-contiguous segments, held in a
list headed by an embedded malloc_segment record representing the
top-most space. Segments also include flags holding properties of
the space. Large chunks that are directly allocated by mmap are not
included in this list. They are instead independently created and
destroyed without otherwise keeping track of them.
Segment management mainly comes into play for spaces allocated by
MMAP. Any call to MMAP might or might not return memory that is
adjacent to an existing segment. MORECORE normally contiguously
extends the current space, so this space is almost always adjacent,
which is simpler and faster to deal with. (This is why MORECORE is
used preferentially to MMAP when both are available -- see
sys_alloc.) When allocating using MMAP, we don't use any of the
hinting mechanisms (inconsistently) supported in various
implementations of unix mmap, or distinguish reserving from
committing memory. Instead, we just ask for space, and exploit
contiguity when we get it. It is probably possible to do
better than this on some systems, but no general scheme seems
to be significantly better.
Management entails a simpler variant of the consolidation scheme
used for chunks to reduce fragmentation -- new adjacent memory is
normally prepended or appended to an existing segment. However,
there are limitations compared to chunk consolidation that mostly
reflect the fact that segment processing is relatively infrequent
(occurring only when getting memory from system) and that we
don't expect to have huge numbers of segments:
* Segments are not indexed, so traversal requires linear scans. (It
would be possible to index these, but is not worth the extra
overhead and complexity for most programs on most platforms.)
* New segments are only appended to old ones when holding top-most
memory; if they cannot be prepended to others, they are held in
different segments.
Except for the top-most segment of an mstate, each segment record
is kept at the tail of its segment. Segments are added by pushing
segment records onto the list headed by &mstate.seg for the
containing mstate.
Segment flags control allocation/merge/deallocation policies:
* If EXTERN_BIT set, then we did not allocate this segment,
and so should not try to deallocate or merge with others.
(This currently holds only for the initial segment passed
into create_mspace_with_base.)
* If IS_MMAPPED_BIT set, the segment may be merged with
other surrounding mmapped segments and trimmed/de-allocated
using munmap.
* If neither bit is set, then the segment was obtained using
MORECORE so can be merged with surrounding MORECORE'd segments
and deallocated/trimmed using MORECORE with negative arguments.
struct malloc_segment {
char* base; /* base address */
size_t size; /* allocated size */
struct malloc_segment* next; /* ptr to next segment */
/* The mmap magic is supposed to store the address of the executable
segment at the very end of the requested block. */
# define mmap_exec_offset(b,s) (*(ptrdiff_t*)((b)+(s)-sizeof(ptrdiff_t)))
/* We can only merge segments if their corresponding executable
segments are at identical offsets. */
# define check_segment_merge(S,b,s) \
(mmap_exec_offset((b),(s)) == (S)->exec_offset)
# define add_segment_exec_offset(p,S) ((char*)(p) + (S)->exec_offset)
# define sub_segment_exec_offset(p,S) ((char*)(p) - (S)->exec_offset)
/* The removal of sflags only works with HAVE_MORECORE == 0. */
# define get_segment_flags(S) (IS_MMAPPED_BIT)
# define set_segment_flags(S,v) \
(((v) != IS_MMAPPED_BIT) ? (ABORT, (v)) : \
(((S)->exec_offset = \
mmap_exec_offset((S)->base, (S)->size)), \
(mmap_exec_offset((S)->base + (S)->exec_offset, (S)->size) != \
(S)->exec_offset) ? (ABORT, (v)) : \
(mmap_exec_offset((S)->base, (S)->size) = 0), (v)))
/* We use an offset here, instead of a pointer, because then, when
base changes, we don't have to modify this. On architectures
with segmented addresses, this might not work. */
ptrdiff_t exec_offset;
# define get_segment_flags(S) ((S)->sflags)
# define set_segment_flags(S,v) ((S)->sflags = (v))
# define check_segment_merge(S,b,s) (1)
flag_t sflags; /* mmap and extern flag */
#define is_mmapped_segment(S) (get_segment_flags(S) & IS_MMAPPED_BIT)
#define is_extern_segment(S) (get_segment_flags(S) & EXTERN_BIT)
typedef struct malloc_segment msegment;
typedef struct malloc_segment* msegmentptr;
/* ---------------------------- malloc_state ----------------------------- */
A malloc_state holds all of the bookkeeping for a space.
The main fields are:
The topmost chunk of the currently active segment. Its size is
cached in topsize. The actual size of topmost space is
topsize+TOP_FOOT_SIZE, which includes space reserved for adding
fenceposts and segment records if necessary when getting more
space from the system. The size at which to autotrim top is
cached from mparams in trim_check, except that it is disabled if
an autotrim fails.
Designated victim (dv)
This is the preferred chunk for servicing small requests that
don't have exact fits. It is normally the chunk split off most
recently to service another small request. Its size is cached in
dvsize. The link fields of this chunk are not maintained since it
is not kept in a bin.
An array of bin headers for free chunks. These bins hold chunks
with sizes less than MIN_LARGE_SIZE bytes. Each bin contains
chunks of all the same size, spaced 8 bytes apart. To simplify
use in double-linked lists, each bin header acts as a malloc_chunk
pointing to the real first node, if it exists (else pointing to
itself). This avoids special-casing for headers. But to avoid
waste, we allocate only the fd/bk pointers of bins, and then use
repositioning tricks to treat these as the fields of a chunk.
Treebins are pointers to the roots of trees holding a range of
sizes. There are 2 equally spaced treebins for each power of two
from TREE_SHIFT to TREE_SHIFT+16. The last bin holds anything
Bin maps
There is one bit map for small bins ("smallmap") and one for
treebins ("treemap). Each bin sets its bit when non-empty, and
clears the bit when empty. Bit operations are then used to avoid
bin-by-bin searching -- nearly all "search" is done without ever
looking at bins that won't be selected. The bit maps
conservatively use 32 bits per map word, even if on 64bit system.
For a good description of some of the bit-based techniques used
here, see Henry S. Warren Jr's book "Hacker's Delight" (and
supplement at Many of these are
intended to reduce the branchiness of paths through malloc etc, as
well as to reduce the number of memory locations read or written.
A list of segments headed by an embedded malloc_segment record
representing the initial space.
Address check support
The least_addr field is the least address ever obtained from
MORECORE or MMAP. Attempted frees and reallocs of any address less
than this are trapped (unless INSECURE is defined).
Magic tag
A cross-check field that should always hold same value as mparams.magic.
Bits recording whether to use MMAP, locks, or contiguous MORECORE
Each space keeps track of current and maximum system memory
obtained via MORECORE or MMAP.
If USE_LOCKS is defined, the "mutex" lock is acquired and released
around every public call using this mspace.
/* Bin types, widths and sizes */
#define NSMALLBINS (32U)
#define NTREEBINS (32U)
#define TREEBIN_SHIFT (8U)
struct malloc_state {
binmap_t smallmap;
binmap_t treemap;
size_t dvsize;
size_t topsize;
char* least_addr;
mchunkptr dv;
mchunkptr top;
size_t trim_check;
size_t magic;
mchunkptr smallbins[(NSMALLBINS+1)*2];
tbinptr treebins[NTREEBINS];
size_t footprint;
size_t max_footprint;
flag_t mflags;
MLOCK_T mutex; /* locate lock among fields that rarely change */
#endif /* USE_LOCKS */
msegment seg;
typedef struct malloc_state* mstate;
/* ------------- Global malloc_state and malloc_params ------------------- */
malloc_params holds global properties, including those that can be
dynamically set using mallopt. There is a single instance, mparams,
initialized in init_mparams.
struct malloc_params {
size_t magic;
size_t page_size;
size_t granularity;
size_t mmap_threshold;
size_t trim_threshold;
flag_t default_mflags;
static struct malloc_params mparams;
/* The global malloc_state used for all non-"mspace" calls */
static struct malloc_state _gm_;
#define gm (&_gm_)
#define is_global(M) ((M) == &_gm_)
#define is_initialized(M) ((M)->top != 0)
/* -------------------------- system alloc setup ------------------------- */
/* Operations on mflags */
#define use_lock(M) ((M)->mflags & USE_LOCK_BIT)
#define enable_lock(M) ((M)->mflags |= USE_LOCK_BIT)
#define disable_lock(M) ((M)->mflags &= ~USE_LOCK_BIT)
#define use_mmap(M) ((M)->mflags & USE_MMAP_BIT)
#define enable_mmap(M) ((M)->mflags |= USE_MMAP_BIT)
#define disable_mmap(M) ((M)->mflags &= ~USE_MMAP_BIT)
#define use_noncontiguous(M) ((M)->mflags & USE_NONCONTIGUOUS_BIT)
#define disable_contiguous(M) ((M)->mflags |= USE_NONCONTIGUOUS_BIT)
#define set_lock(M,L)\
((M)->mflags = (L)?\
((M)->mflags | USE_LOCK_BIT) :\
((M)->mflags & ~USE_LOCK_BIT))
/* page-align a size */
#define page_align(S)\
(((S) + (mparams.page_size)) & ~(mparams.page_size - SIZE_T_ONE))
/* granularity-align a size */
#define granularity_align(S)\
(((S) + (mparams.granularity)) & ~(mparams.granularity - SIZE_T_ONE))
#define is_page_aligned(S)\
(((size_t)(S) & (mparams.page_size - SIZE_T_ONE)) == 0)
#define is_granularity_aligned(S)\
(((size_t)(S) & (mparams.granularity - SIZE_T_ONE)) == 0)
/* True if segment S holds address A */
#define segment_holds(S, A)\
((char*)(A) >= S->base && (char*)(A) < S->base + S->size)
/* Return segment holding given address */
static msegmentptr segment_holding(mstate m, char* addr) {
msegmentptr sp = &m->seg;
for (;;) {
if (addr >= sp->base && addr < sp->base + sp->size)
return sp;
if ((sp = sp->next) == 0)
return 0;
/* Return true if segment contains a segment link */
static int has_segment_link(mstate m, msegmentptr ss) {
msegmentptr sp = &m->seg;
for (;;) {
if ((char*)sp >= ss->base && (char*)sp < ss->base + ss->size)
return 1;
if ((sp = sp->next) == 0)
return 0;
#define should_trim(M,s) ((s) > (M)->trim_check)
#define should_trim(M,s) (0)
TOP_FOOT_SIZE is padding at the end of a segment, including space
that may be needed to place segment records and fenceposts when new
noncontiguous segments are added.
#define TOP_FOOT_SIZE\
(align_offset(chunk2mem(0))+pad_request(sizeof(struct malloc_segment))+MIN_CHUNK_SIZE)
/* ------------------------------- Hooks -------------------------------- */
PREACTION should be defined to return 0 on success, and nonzero on
failure. If you are not using locking, you can redefine these to do
anything you like.
/* Ensure locks are initialized */
#define GLOBALLY_INITIALIZE() (mparams.page_size == 0 && init_mparams())
#define PREACTION(M) ((GLOBALLY_INITIALIZE() || use_lock(M))? ACQUIRE_LOCK(&(M)->mutex) : 0)
#define POSTACTION(M) { if (use_lock(M)) RELEASE_LOCK(&(M)->mutex); }
#else /* USE_LOCKS */
#define PREACTION(M) (0)
#endif /* PREACTION */
#endif /* POSTACTION */
#endif /* USE_LOCKS */
CORRUPTION_ERROR_ACTION is triggered upon detected bad addresses.
USAGE_ERROR_ACTION is triggered on detected bad frees and
reallocs. The argument p is an address that might have triggered the
fault. It is ignored by the two predefined actions, but might be
useful in custom actions that try to help diagnose errors.
/* A count of the number of corruption errors causing resets */
int malloc_corruption_error_count;
/* default corruption action */
static void reset_on_error(mstate m);
#define CORRUPTION_ERROR_ACTION(m) reset_on_error(m)
#define USAGE_ERROR_ACTION(m, p)
#else /* PROCEED_ON_ERROR */
#endif /* PROCEED_ON_ERROR */
/* -------------------------- Debugging setup ---------------------------- */
#if ! DEBUG
#define check_free_chunk(M,P)
#define check_inuse_chunk(M,P)
#define check_malloced_chunk(M,P,N)
#define check_mmapped_chunk(M,P)
#define check_malloc_state(M)
#define check_top_chunk(M,P)
#else /* DEBUG */
#define check_free_chunk(M,P) do_check_free_chunk(M,P)
#define check_inuse_chunk(M,P) do_check_inuse_chunk(M,P)
#define check_top_chunk(M,P) do_check_top_chunk(M,P)
#define check_malloced_chunk(M,P,N) do_check_malloced_chunk(M,P,N)
#define check_mmapped_chunk(M,P) do_check_mmapped_chunk(M,P)
#define check_malloc_state(M) do_check_malloc_state(M)
static void do_check_any_chunk(mstate m, mchunkptr p);
static void do_check_top_chunk(mstate m, mchunkptr p);
static void do_check_mmapped_chunk(mstate m, mchunkptr p);
static void do_check_inuse_chunk(mstate m, mchunkptr p);
static void do_check_free_chunk(mstate m, mchunkptr p);
static void do_check_malloced_chunk(mstate m, void* mem, size_t s);
static void do_check_tree(mstate m, tchunkptr t);
static void do_check_treebin(mstate m, bindex_t i);
static void do_check_smallbin(mstate m, bindex_t i);
static void do_check_malloc_state(mstate m);
static int bin_find(mstate m, mchunkptr x);
static size_t traverse_and_check(mstate m);
#endif /* DEBUG */
/* ---------------------------- Indexing Bins ---------------------------- */
#define is_small(s) (((s) >> SMALLBIN_SHIFT) < NSMALLBINS)
#define small_index(s) ((s) >> SMALLBIN_SHIFT)
#define small_index2size(i) ((i) << SMALLBIN_SHIFT)
#define MIN_SMALL_INDEX (small_index(MIN_CHUNK_SIZE))
/* addressing by index. See above about smallbin repositioning */
#define smallbin_at(M, i) ((sbinptr)((char*)&((M)->smallbins[(i)<<1])))
#define treebin_at(M,i) (&((M)->treebins[i]))
/* assign tree index for size S to variable I */
#if defined(__GNUC__) && defined(__i386__)
#define compute_tree_index(S, I)\
size_t X = S >> TREEBIN_SHIFT;\
if (X == 0)\
I = 0;\
else if (X > 0xFFFF)\
else {\
unsigned int K;\
__asm__("bsrl %1,%0\n\t" : "=r" (K) : "rm" (X));\
I = (bindex_t)((K << 1) + ((S >> (K + (TREEBIN_SHIFT-1)) & 1)));\
#else /* GNUC */
#define compute_tree_index(S, I)\
size_t X = S >> TREEBIN_SHIFT;\
if (X == 0)\
I = 0;\
else if (X > 0xFFFF)\
else {\
unsigned int Y = (unsigned int)X;\
unsigned int N = ((Y - 0x100) >> 16) & 8;\
unsigned int K = (((Y <<= N) - 0x1000) >> 16) & 4;\
N += K;\
N += K = (((Y <<= K) - 0x4000) >> 16) & 2;\
K = 14 - N + ((Y <<= K) >> 15);\
I = (K << 1) + ((S >> (K + (TREEBIN_SHIFT-1)) & 1));\
#endif /* GNUC */
/* Bit representing maximum resolved size in a treebin at i */
#define bit_for_tree_index(i) \
(i == NTREEBINS-1)? (SIZE_T_BITSIZE-1) : (((i) >> 1) + TREEBIN_SHIFT - 2)
/* Shift placing maximum resolved bit in a treebin at i as sign bit */
#define leftshift_for_tree_index(i) \
((i == NTREEBINS-1)? 0 : \
((SIZE_T_BITSIZE-SIZE_T_ONE) - (((i) >> 1) + TREEBIN_SHIFT - 2)))
/* The size of the smallest chunk held in bin with index i */
#define minsize_for_tree_index(i) \
((SIZE_T_ONE << (((i) >> 1) + TREEBIN_SHIFT)) | \
(((size_t)((i) & SIZE_T_ONE)) << (((i) >> 1) + TREEBIN_SHIFT - 1)))
/* ------------------------ Operations on bin maps ----------------------- */
/* bit corresponding to given index */
#define idx2bit(i) ((binmap_t)(1) << (i))
/* Mark/Clear bits with given index */
#define mark_smallmap(M,i) ((M)->smallmap |= idx2bit(i))
#define clear_smallmap(M,i) ((M)->smallmap &= ~idx2bit(i))
#define smallmap_is_marked(M,i) ((M)->smallmap & idx2bit(i))
#define mark_treemap(M,i) ((M)->treemap |= idx2bit(i))
#define clear_treemap(M,i) ((M)->treemap &= ~idx2bit(i))
#define treemap_is_marked(M,i) ((M)->treemap & idx2bit(i))
/* index corresponding to given bit */
#if defined(__GNUC__) && defined(__i386__)
#define compute_bit2idx(X, I)\
unsigned int J;\
__asm__("bsfl %1,%0\n\t" : "=r" (J) : "rm" (X));\
I = (bindex_t)J;\
#else /* GNUC */
#define compute_bit2idx(X, I) I = ffs(X)-1
#else /* USE_BUILTIN_FFS */
#define compute_bit2idx(X, I)\
unsigned int Y = X - 1;\
unsigned int K = Y >> (16-4) & 16;\
unsigned int N = K; Y >>= K;\
N += K = Y >> (8-3) & 8; Y >>= K;\
N += K = Y >> (4-2) & 4; Y >>= K;\
N += K = Y >> (2-1) & 2; Y >>= K;\
N += K = Y >> (1-0) & 1; Y >>= K;\
I = (bindex_t)(N + Y);\
#endif /* USE_BUILTIN_FFS */
#endif /* GNUC */
/* isolate the least set bit of a bitmap */
#define least_bit(x) ((x) & -(x))
/* mask with all bits to left of least bit of x on */
#define left_bits(x) ((x<<1) | -(x<<1))
/* mask with all bits to left of or equal to least bit of x on */
#define same_or_left_bits(x) ((x) | -(x))
/* ----------------------- Runtime Check Support ------------------------- */
For security, the main invariant is that malloc/free/etc never
writes to a static address other than malloc_state, unless static
malloc_state itself has been corrupted, which cannot occur via
malloc (because of these checks). In essence this means that we
believe all pointers, sizes, maps etc held in malloc_state, but
check all of those linked or offsetted from other embedded data
structures. These checks are interspersed with main code in a way
that tends to minimize their run-time cost.
When FOOTERS is defined, in addition to range checking, we also
verify footer fields of inuse chunks, which can be used guarantee
that the mstate controlling malloc/free is intact. This is a
streamlined version of the approach described by William Robertson
et al in "Run-time Detection of Heap-based Overflows" LISA'03 The footer
of an inuse chunk holds the xor of its mstate and a random seed,
that is checked upon calls to free() and realloc(). This is
(probablistically) unguessable from outside the program, but can be
computed by any code successfully malloc'ing any chunk, so does not
itself provide protection against code that has already broken
security through some other means. Unlike Robertson et al, we
always dynamically check addresses of all offset chunks (previous,
next, etc). This turns out to be cheaper than relying on hashes.
/* Check if address a is at least as high as any from MORECORE or MMAP */
#define ok_address(M, a) ((char*)(a) >= (M)->least_addr)
/* Check if address of next chunk n is higher than base chunk p */
#define ok_next(p, n) ((char*)(p) < (char*)(n))
/* Check if p has its cinuse bit on */
#define ok_cinuse(p) cinuse(p)
/* Check if p has its pinuse bit on */
#define ok_pinuse(p) pinuse(p)
#else /* !INSECURE */
#define ok_address(M, a) (1)
#define ok_next(b, n) (1)
#define ok_cinuse(p) (1)
#define ok_pinuse(p) (1)
#endif /* !INSECURE */
/* Check if (alleged) mstate m has expected magic field */
#define ok_magic(M) ((M)->magic == mparams.magic)
#else /* (FOOTERS && !INSECURE) */
#define ok_magic(M) (1)
#endif /* (FOOTERS && !INSECURE) */
/* In gcc, use __builtin_expect to minimize impact of checks */
#if defined(__GNUC__) && __GNUC__ >= 3
#define RTCHECK(e) __builtin_expect(e, 1)
#else /* GNUC */
#define RTCHECK(e) (e)
#endif /* GNUC */
#else /* !INSECURE */
#define RTCHECK(e) (1)
#endif /* !INSECURE */
/* macros to set up inuse chunks with or without footers */
#define mark_inuse_foot(M,p,s)
/* Set cinuse bit and pinuse bit of next chunk */
#define set_inuse(M,p,s)\
((p)->head = (((p)->head & PINUSE_BIT)|s|CINUSE_BIT),\
((mchunkptr)(((char*)(p)) + (s)))->head |= PINUSE_BIT)
/* Set cinuse and pinuse of this chunk and pinuse of next chunk */
#define set_inuse_and_pinuse(M,p,s)\
((p)->head = (s|PINUSE_BIT|CINUSE_BIT),\
((mchunkptr)(((char*)(p)) + (s)))->head |= PINUSE_BIT)
/* Set size, cinuse and pinuse bit of this chunk */
#define set_size_and_pinuse_of_inuse_chunk(M, p, s)\
((p)->head = (s|PINUSE_BIT|CINUSE_BIT))
#else /* FOOTERS */
/* Set foot of inuse chunk to be xor of mstate and seed */
#define mark_inuse_foot(M,p,s)\
(((mchunkptr)((char*)(p) + (s)))->prev_foot = ((size_t)(M) ^ mparams.magic))
#define get_mstate_for(p)\
((mstate)(((mchunkptr)((char*)(p) +\
(chunksize(p))))->prev_foot ^ mparams.magic))
#define set_inuse(M,p,s)\
((p)->head = (((p)->head & PINUSE_BIT)|s|CINUSE_BIT),\
(((mchunkptr)(((char*)(p)) + (s)))->head |= PINUSE_BIT), \
#define set_inuse_and_pinuse(M,p,s)\
((p)->head = (s|PINUSE_BIT|CINUSE_BIT),\
(((mchunkptr)(((char*)(p)) + (s)))->head |= PINUSE_BIT),\
#define set_size_and_pinuse_of_inuse_chunk(M, p, s)\
((p)->head = (s|PINUSE_BIT|CINUSE_BIT),\
mark_inuse_foot(M, p, s))
#endif /* !FOOTERS */
/* ---------------------------- setting mparams -------------------------- */
/* Initialize mparams */
static int init_mparams(void) {
if (mparams.page_size == 0) {
size_t s;
mparams.mmap_threshold = DEFAULT_MMAP_THRESHOLD;
mparams.trim_threshold = DEFAULT_TRIM_THRESHOLD;
mparams.default_mflags = USE_LOCK_BIT|USE_MMAP_BIT;
int fd;
unsigned char buf[sizeof(size_t)];
/* Try to use /dev/urandom, else fall back on using time */
if ((fd = open("/dev/urandom", O_RDONLY)) >= 0 &&
read(fd, buf, sizeof(buf)) == sizeof(buf)) {
s = *((size_t *) buf);
#endif /* USE_DEV_RANDOM */
s = (size_t)(time(0) ^ (size_t)0x55555555U);
s |= (size_t)8U; /* ensure nonzero */
s &= ~(size_t)7U; /* improve chances of fault for bad values */
#else /* (FOOTERS && !INSECURE) */
s = (size_t)0x58585858U;
#endif /* (FOOTERS && !INSECURE) */
if (mparams.magic == 0) {
mparams.magic = s;
/* Set up lock for main malloc area */
gm->mflags = mparams.default_mflags;
#if !defined(WIN32) && !defined(__OS2__)
mparams.page_size = malloc_getpagesize;
mparams.granularity = ((DEFAULT_GRANULARITY != 0)?
DEFAULT_GRANULARITY : mparams.page_size);
#elif defined (__OS2__)
/* if low-memory is used, os2munmap() would break
if it were anything other than 64k */
mparams.page_size = 4096u;
mparams.granularity = 65536u;
#else /* WIN32 */
SYSTEM_INFO system_info;
mparams.page_size = system_info.dwPageSize;
mparams.granularity = system_info.dwAllocationGranularity;
#endif /* WIN32 */
/* Sanity-check configuration:
size_t must be unsigned and as wide as pointer type.
ints must be at least 4 bytes.
alignment must be at least 8.
Alignment, min chunk size, and page size must all be powers of 2.
if ((sizeof(size_t) != sizeof(char*)) ||
(sizeof(int) < 4) ||
(MALLOC_ALIGNMENT < (size_t)8U) ||
((mparams.granularity & (mparams.granularity-SIZE_T_ONE)) != 0) ||
((mparams.page_size & (mparams.page_size-SIZE_T_ONE)) != 0))
return 0;
/* support for mallopt */
static int change_mparam(int param_number, int value) {
size_t val = (size_t)value;
switch(param_number) {
mparams.trim_threshold = val;
return 1;
if (val >= mparams.page_size && ((val & (val-1)) == 0)) {
mparams.granularity = val;
return 1;
return 0;
mparams.mmap_threshold = val;
return 1;
return 0;
/* ------------------------- Debugging Support --------------------------- */
/* Check properties of any chunk, whether free, inuse, mmapped etc */
static void do_check_any_chunk(mstate m, mchunkptr p) {
assert((is_aligned(chunk2mem(p))) || (p->head == FENCEPOST_HEAD));
assert(ok_address(m, p));
/* Check properties of top chunk */
static void do_check_top_chunk(mstate m, mchunkptr p) {
msegmentptr sp = segment_holding(m, (char*)p);
size_t sz = chunksize(p);
assert(sp != 0);
assert((is_aligned(chunk2mem(p))) || (p->head == FENCEPOST_HEAD));
assert(ok_address(m, p));
assert(sz == m->topsize);
assert(sz > 0);
assert(sz == ((sp->base + sp->size) - (char*)p) - TOP_FOOT_SIZE);
/* Check properties of (inuse) mmapped chunks */
static void do_check_mmapped_chunk(mstate m, mchunkptr p) {
size_t sz = chunksize(p);
size_t len = (sz + (p->prev_foot & ~IS_MMAPPED_BIT) + MMAP_FOOT_PAD);
assert((is_aligned(chunk2mem(p))) || (p->head == FENCEPOST_HEAD));
assert(ok_address(m, p));
assert((len & (mparams.page_size-SIZE_T_ONE)) == 0);
assert(chunk_plus_offset(p, sz)->head == FENCEPOST_HEAD);
assert(chunk_plus_offset(p, sz+SIZE_T_SIZE)->head == 0);
/* Check properties of inuse chunks */
static void do_check_inuse_chunk(mstate m, mchunkptr p) {
do_check_any_chunk(m, p);
/* If not pinuse and not mmapped, previous chunk has OK offset */
assert(is_mmapped(p) || pinuse(p) || next_chunk(prev_chunk(p)) == p);
if (is_mmapped(p))
do_check_mmapped_chunk(m, p);
/* Check properties of free chunks */
static void do_check_free_chunk(mstate m, mchunkptr p) {
size_t sz = p->head & ~(PINUSE_BIT|CINUSE_BIT);
mchunkptr next = chunk_plus_offset(p, sz);
do_check_any_chunk(m, p);
assert (!is_mmapped(p));
if (p != m->dv && p != m->top) {
if (sz >= MIN_CHUNK_SIZE) {
assert((sz & CHUNK_ALIGN_MASK) == 0);
assert(next->prev_foot == sz);
assert (next == m->top || cinuse(next));
assert(p->fd->bk == p);
assert(p->bk->fd == p);
else /* markers are always of size SIZE_T_SIZE */
assert(sz == SIZE_T_SIZE);
/* Check properties of malloced chunks at the point they are malloced */
static void do_check_malloced_chunk(mstate m, void* mem, size_t s) {
if (mem != 0) {
mchunkptr p = mem2chunk(mem);
size_t sz = p->head & ~(PINUSE_BIT|CINUSE_BIT);
do_check_inuse_chunk(m, p);
assert((sz & CHUNK_ALIGN_MASK) == 0);
assert(sz >= MIN_CHUNK_SIZE);
assert(sz >= s);
/* unless mmapped, size is less than MIN_CHUNK_SIZE more than request */
assert(is_mmapped(p) || sz < (s + MIN_CHUNK_SIZE));
/* Check a tree and its subtrees. */
static void do_check_tree(mstate m, tchunkptr t) {
tchunkptr head = 0;
tchunkptr u = t;
bindex_t tindex = t->index;
size_t tsize = chunksize(t);
bindex_t idx;
compute_tree_index(tsize, idx);
assert(tindex == idx);
assert(tsize >= MIN_LARGE_SIZE);
assert(tsize >= minsize_for_tree_index(idx));
assert((idx == NTREEBINS-1) || (tsize < minsize_for_tree_index((idx+1))));
do { /* traverse through chain of same-sized nodes */
do_check_any_chunk(m, ((mchunkptr)u));
assert(u->index == tindex);
assert(chunksize(u) == tsize);
assert(u->fd->bk == u);
assert(u->bk->fd == u);
if (u->parent == 0) {
assert(u->child[0] == 0);
assert(u->child[1] == 0);
else {
assert(head == 0); /* only one node on chain has parent */
head = u;
assert(u->parent != u);
assert (u->parent->child[0] == u ||
u->parent->child[1] == u ||
*((tbinptr*)(u->parent)) == u);
if (u->child[0] != 0) {
assert(u->child[0]->parent == u);
assert(u->child[0] != u);
do_check_tree(m, u->child[0]);
if (u->child[1] != 0) {
assert(u->child[1]->parent == u);
assert(u->child[1] != u);
do_check_tree(m, u->child[1]);
if (u->child[0] != 0 && u->child[1] != 0) {
assert(chunksize(u->child[0]) < chunksize(u->child[1]));
u = u->fd;
} while (u != t);
assert(head != 0);
/* Check all the chunks in a treebin. */
static void do_check_treebin(mstate m, bindex_t i) {
tbinptr* tb = treebin_at(m, i);
tchunkptr t = *tb;
int empty = (m->treemap & (1U << i)) == 0;
if (t == 0)
if (!empty)
do_check_tree(m, t);
/* Check all the chunks in a smallbin. */
static void do_check_smallbin(mstate m, bindex_t i) {
sbinptr b = smallbin_at(m, i);
mchunkptr p = b->bk;
unsigned int empty = (m->smallmap & (1U << i)) == 0;
if (p == b)
if (!empty) {
for (; p != b; p = p->bk) {
size_t size = chunksize(p);
mchunkptr q;
/* each chunk claims to be free */
do_check_free_chunk(m, p);
/* chunk belongs in bin */
assert(small_index(size) == i);
assert(p->bk == b || chunksize(p->bk) == chunksize(p));
/* chunk is followed by an inuse chunk */
q = next_chunk(p);
if (q->head != FENCEPOST_HEAD)
do_check_inuse_chunk(m, q);
/* Find x in a bin. Used in other check functions. */
static int bin_find(mstate m, mchunkptr x) {
size_t size = chunksize(x);
if (is_small(size)) {
bindex_t sidx = small_index(size);
sbinptr b = smallbin_at(m, sidx);
if (smallmap_is_marked(m, sidx)) {
mchunkptr p = b;
do {
if (p == x)
return 1;
} while ((p = p->fd) != b);
else {
bindex_t tidx;
compute_tree_index(size, tidx);
if (treemap_is_marked(m, tidx)) {
tchunkptr t = *treebin_at(m, tidx);
size_t sizebits = size << leftshift_for_tree_index(tidx);
while (t != 0 && chunksize(t) != size) {
t = t->child[(sizebits >> (SIZE_T_BITSIZE-SIZE_T_ONE)) & 1];
sizebits <<= 1;
if (t != 0) {
tchunkptr u = t;
do {
if (u == (tchunkptr)x)
return 1;
} while ((u = u->fd) != t);
return 0;
/* Traverse each chunk and check it; return total */
static size_t traverse_and_check(mstate m) {
size_t sum = 0;
if (is_initialized(m)) {
msegmentptr s = &m->seg;
sum += m->topsize + TOP_FOOT_SIZE;
while (s != 0) {
mchunkptr q = align_as_chunk(s->base);
mchunkptr lastq = 0;
while (segment_holds(s, q) &&
q != m->top && q->head != FENCEPOST_HEAD) {
sum += chunksize(q);
if (cinuse(q)) {
assert(!bin_find(m, q));
do_check_inuse_chunk(m, q);
else {
assert(q == m->dv || bin_find(m, q));
assert(lastq == 0 || cinuse(lastq)); /* Not 2 consecutive free */
do_check_free_chunk(m, q);
lastq = q;
q = next_chunk(q);
s = s->next;
return sum;
/* Check all properties of malloc_state. */
static void do_check_malloc_state(mstate m) {
bindex_t i;
size_t total;
/* check bins */
for (i = 0; i < NSMALLBINS; ++i)
do_check_smallbin(m, i);
for (i = 0; i < NTREEBINS; ++i)
do_check_treebin(m, i);
if (m->dvsize != 0) { /* check dv chunk */
do_check_any_chunk(m, m->dv);
assert(m->dvsize == chunksize(m->dv));
assert(m->dvsize >= MIN_CHUNK_SIZE);
assert(bin_find(m, m->dv) == 0);
if (m->top != 0) { /* check top chunk */
do_check_top_chunk(m, m->top);
assert(m->topsize == chunksize(m->top));
assert(m->topsize > 0);
assert(bin_find(m, m->top) == 0);
total = traverse_and_check(m);
assert(total <= m->footprint);
assert(m->footprint <= m->max_footprint);
#endif /* DEBUG */
/* ----------------------------- statistics ------------------------------ */
static struct mallinfo internal_mallinfo(mstate m) {
struct mallinfo nm = { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 };
if (!PREACTION(m)) {
if (is_initialized(m)) {
size_t nfree = SIZE_T_ONE; /* top always free */
size_t mfree = m->topsize + TOP_FOOT_SIZE;
size_t sum = mfree;
msegmentptr s = &m->seg;
while (s != 0) {
mchunkptr q = align_as_chunk(s->base);
while (segment_holds(s, q) &&
q != m->top && q->head != FENCEPOST_HEAD) {
size_t sz = chunksize(q);
sum += sz;
if (!cinuse(q)) {
mfree += sz;
q = next_chunk(q);
s = s->next;
nm.arena = sum;
nm.ordblks = nfree;
nm.hblkhd = m->footprint - sum;
nm.usmblks = m->max_footprint;
nm.uordblks = m->footprint - mfree;
nm.fordblks = mfree;
nm.keepcost = m->topsize;
return nm;
#endif /* !NO_MALLINFO */
static void internal_malloc_stats(mstate m) {
if (!PREACTION(m)) {
size_t maxfp = 0;
size_t fp = 0;
size_t used = 0;
if (is_initialized(m)) {
msegmentptr s = &m->seg;
maxfp = m->max_footprint;
fp = m->footprint;
used = fp - (m->topsize + TOP_FOOT_SIZE);
while (s != 0) {
mchunkptr q = align_as_chunk(s->base);
while (segment_holds(s, q) &&
q != m->top && q->head != FENCEPOST_HEAD) {
if (!cinuse(q))
used -= chunksize(q);
q = next_chunk(q);
s = s->next;
fprintf(stderr, "max system bytes = %10lu\n", (unsigned long)(maxfp));
fprintf(stderr, "system bytes = %10lu\n", (unsigned long)(fp));
fprintf(stderr, "in use bytes = %10lu\n", (unsigned long)(used));
/* ----------------------- Operations on smallbins ----------------------- */
Various forms of linking and unlinking are defined as macros. Even
the ones for trees, which are very long but have very short typical
paths. This is ugly but reduces reliance on inlining support of
/* Link a free chunk into a smallbin */
#define insert_small_chunk(M, P, S) {\
bindex_t I = small_index(S);\
mchunkptr B = smallbin_at(M, I);\
mchunkptr F = B;\
assert(S >= MIN_CHUNK_SIZE);\
if (!smallmap_is_marked(M, I))\
mark_smallmap(M, I);\
else if (RTCHECK(ok_address(M, B->fd)))\
F = B->fd;\
else {\
B->fd = P;\
F->bk = P;\
P->fd = F;\
P->bk = B;\
/* Unlink a chunk from a smallbin */
#define unlink_small_chunk(M, P, S) {\
mchunkptr F = P->fd;\
mchunkptr B = P->bk;\
bindex_t I = small_index(S);\
assert(P != B);\
assert(P != F);\
assert(chunksize(P) == small_index2size(I));\
if (F == B)\
clear_smallmap(M, I);\
else if (RTCHECK((F == smallbin_at(M,I) || ok_address(M, F)) &&\
(B == smallbin_at(M,I) || ok_address(M, B)))) {\
F->bk = B;\
B->fd = F;\
else {\
/* Unlink the first chunk from a smallbin */
#define unlink_first_small_chunk(M, B, P, I) {\
mchunkptr F = P->fd;\
assert(P != B);\
assert(P != F);\
assert(chunksize(P) == small_index2size(I));\
if (B == F)\
clear_smallmap(M, I);\
else if (RTCHECK(ok_address(M, F))) {\
B->fd = F;\
F->bk = B;\
else {\
/* Replace dv node, binning the old one */
/* Used only when dvsize known to be small */
#define replace_dv(M, P, S) {\
size_t DVS = M->dvsize;\
if (DVS != 0) {\
mchunkptr DV = M->dv;\
insert_small_chunk(M, DV, DVS);\
M->dvsize = S;\
M->dv = P;\
/* ------------------------- Operations on trees ------------------------- */
/* Insert chunk into tree */
#define insert_large_chunk(M, X, S) {\
tbinptr* H;\
bindex_t I;\
compute_tree_index(S, I);\
H = treebin_at(M, I);\
X->index = I;\
X->child[0] = X->child[1] = 0;\
if (!treemap_is_marked(M, I)) {\
mark_treemap(M, I);\
*H = X;\
X->parent = (tchunkptr)H;\
X->fd = X->bk = X;\
else {\
tchunkptr T = *H;\
size_t K = S << leftshift_for_tree_index(I);\
for (;;) {\
if (chunksize(T) != S) {\
tchunkptr* C = &(T->child[(K >> (SIZE_T_BITSIZE-SIZE_T_ONE)) & 1]);\
K <<= 1;\
if (*C != 0)\
T = *C;\
else if (RTCHECK(ok_address(M, C))) {\
*C = X;\
X->parent = T;\
X->fd = X->bk = X;\
else {\
else {\
tchunkptr F = T->fd;\
if (RTCHECK(ok_address(M, T) && ok_address(M, F))) {\
T->fd = F->bk = X;\
X->fd = F;\
X->bk = T;\
X->parent = 0;\
else {\
Unlink steps:
1. If x is a chained node, unlink it from its same-sized fd/bk links
and choose its bk node as its replacement.
2. If x was the last node of its size, but not a leaf node, it must
be replaced with a leaf node (not merely one with an open left or
right), to make sure that lefts and rights of descendants
correspond properly to bit masks. We use the rightmost descendant
of x. We could use any other leaf, but this is easy to locate and
tends to counteract removal of leftmosts elsewhere, and so keeps
paths shorter than minimally guaranteed. This doesn't loop much
because on average a node in a tree is near the bottom.
3. If x is the base of a chain (i.e., has parent links) relink
x's parent and children to x's replacement (or null if none).
#define unlink_large_chunk(M, X) {\
tchunkptr XP = X->parent;\
tchunkptr R;\
if (X->bk != X) {\
tchunkptr F = X->fd;\
R = X->bk;\
if (RTCHECK(ok_address(M, F))) {\
F->bk = R;\
R->fd = F;\
else {\
else {\
tchunkptr* RP;\
if (((R = *(RP = &(X->child[1]))) != 0) ||\
((R = *(RP = &(X->child[0]))) != 0)) {\
tchunkptr* CP;\
while ((*(CP = &(R->child[1])) != 0) ||\
(*(CP = &(R->child[0])) != 0)) {\
R = *(RP = CP);\
if (RTCHECK(ok_address(M, RP)))\
*RP = 0;\
else {\
if (XP != 0) {\
tbinptr* H = treebin_at(M, X->index);\
if (X == *H) {\
if ((*H = R) == 0) \
clear_treemap(M, X->index);\
else if (RTCHECK(ok_address(M, XP))) {\
if (XP->child[0] == X) \
XP->child[0] = R;\
else \
XP->child[1] = R;\
if (R != 0) {\
if (RTCHECK(ok_address(M, R))) {\
tchunkptr C0, C1;\
R->parent = XP;\
if ((C0 = X->child[0]) != 0) {\
if (RTCHECK(ok_address(M, C0))) {\
R->child[0] = C0;\
C0->parent = R;\
if ((C1 = X->child[1]) != 0) {\
if (RTCHECK(ok_address(M, C1))) {\
R->child[1] = C1;\
C1->parent = R;\
/* Relays to large vs small bin operations */
#define insert_chunk(M, P, S)\
if (is_small(S)) insert_small_chunk(M, P, S)\
else { tchunkptr TP = (tchunkptr)(P); insert_large_chunk(M, TP, S); }
#define unlink_chunk(M, P, S)\
if (is_small(S)) unlink_small_chunk(M, P, S)\
else { tchunkptr TP = (tchunkptr)(P); unlink_large_chunk(M, TP); }
/* Relays to internal calls to malloc/free from realloc, memalign etc */
#define internal_malloc(m, b) mspace_malloc(m, b)
#define internal_free(m, mem) mspace_free(m,mem);
#else /* ONLY_MSPACES */
#define internal_malloc(m, b)\
(m == gm)? dlmalloc(b) : mspace_malloc(m, b)
#define internal_free(m, mem)\
if (m == gm) dlfree(mem); else mspace_free(m,mem);
#else /* MSPACES */
#define internal_malloc(m, b) dlmalloc(b)
#define internal_free(m, mem) dlfree(mem)
#endif /* MSPACES */
#endif /* ONLY_MSPACES */
/* ----------------------- Direct-mmapping chunks ----------------------- */
Directly mmapped chunks are set up with an offset to the start of
the mmapped region stored in the prev_foot field of the chunk. This
allows reconstruction of the required argument to MUNMAP when freed,
and also allows adjustment of the returned chunk to meet alignment
requirements (especially in memalign). There is also enough space
allocated to hold a fake next chunk of size SIZE_T_SIZE to maintain
the PINUSE bit so frees can be checked.
/* Malloc using mmap */
static void* mmap_alloc(mstate m, size_t nb) {
size_t mmsize = granularity_align(nb + SIX_SIZE_T_SIZES + CHUNK_ALIGN_MASK);
if (mmsize > nb) { /* Check for wrap around 0 */
char* mm = (char*)(DIRECT_MMAP(mmsize));
if (mm != CMFAIL) {
size_t offset = align_offset(chunk2mem(mm));
size_t psize = mmsize - offset - MMAP_FOOT_PAD;
mchunkptr p = (mchunkptr)(mm + offset);
p->prev_foot = offset | IS_MMAPPED_BIT;
(p)->head = (psize|CINUSE_BIT);
mark_inuse_foot(m, p, psize);
chunk_plus_offset(p, psize)->head = FENCEPOST_HEAD;
chunk_plus_offset(p, psize+SIZE_T_SIZE)->head = 0;
if (mm < m->least_addr)
m->least_addr = mm;
if ((m->footprint += mmsize) > m->max_footprint)
m->max_footprint = m->footprint;
check_mmapped_chunk(m, p);
return chunk2mem(p);
return 0;
/* Realloc using mmap */
static mchunkptr mmap_resize(mstate m, mchunkptr oldp, size_t nb) {
size_t oldsize = chunksize(oldp);
if (is_small(nb)) /* Can't shrink mmap regions below small size */
return 0;
/* Keep old chunk if big enough but not too big */
if (oldsize >= nb + SIZE_T_SIZE &&
(oldsize - nb) <= (mparams.granularity << 1))
return oldp;
else {
size_t offset = oldp->prev_foot & ~IS_MMAPPED_BIT;
size_t oldmmsize = oldsize + offset + MMAP_FOOT_PAD;
size_t newmmsize = granularity_align(nb + SIX_SIZE_T_SIZES +
char* cp = (char*)CALL_MREMAP((char*)oldp - offset,
oldmmsize, newmmsize, 1);
if (cp != CMFAIL) {
mchunkptr newp = (mchunkptr)(cp + offset);
size_t psize = newmmsize - offset - MMAP_FOOT_PAD;
newp->head = (psize|CINUSE_BIT);
mark_inuse_foot(m, newp, psize);
chunk_plus_offset(newp, psize)->head = FENCEPOST_HEAD;
chunk_plus_offset(newp, psize+SIZE_T_SIZE)->head = 0;
if (cp < m->least_addr)
m->least_addr = cp;
if ((m->footprint += newmmsize - oldmmsize) > m->max_footprint)
m->max_footprint = m->footprint;
check_mmapped_chunk(m, newp);
return newp;
return 0;