2 * libc/stdlib/malloc/malloc.h -- small malloc implementation
4 * Copyright (C) 2002 NEC Corporation
5 * Copyright (C) 2002 Miles Bader <miles@gnu.org>
7 * This file is subject to the terms and conditions of the GNU Lesser
8 * General Public License. See the file COPYING.LIB in the main
9 * directory of this archive for more details.
11 * Written by Miles Bader <miles@gnu.org>
14 /* The alignment we guarantee for malloc return values. */
15 #define MALLOC_ALIGNMENT (sizeof (double))
17 /* The system pagesize we assume; we really ought to get it with
18 getpagesize, but gee, how annoying. */
19 #define MALLOC_PAGE_SIZE 4096
21 /* The minimum size of block we request from the the system to extend the
22 heap for small allocations (we may request a bigger block if necessary to
23 satisfy a particularly big request). */
24 #define MALLOC_HEAP_EXTEND_SIZE MALLOC_PAGE_SIZE
26 /* When a heap free-area grows above this size, try to unmap it, releasing
27 the memory back to the system. */
28 #define MALLOC_UNMAP_THRESHOLD (8*MALLOC_PAGE_SIZE)
29 /* When unmapping a free-area, retain this many bytes if it's the only one,
30 to avoid completely emptying the heap. This is only a heuristic -- the
31 existance of another free area, even if it's smaller than
32 MALLOC_MIN_SIZE, will cause us not to reserve anything. */
33 #define MALLOC_MIN_SIZE (2*MALLOC_PAGE_SIZE)
36 /* For systems with an MMU, use sbrk to map/unmap memory for the malloc
37 heap, instead of mmap/munmap. This is a tradeoff -- sbrk is faster than
38 mmap/munmap, and guarantees contiguous allocation, but is also less
39 flexible, and causes the heap to only be shrinkable from the end. */
40 #ifdef __UCLIBC_HAS_MMU__
41 # define MALLOC_USE_SBRK
45 /* The size of a malloc allocation is stored in a size_t word
46 MALLOC_ALIGNMENT bytes prior to the start address of the allocation:
48 +--------+---------+-------------------+
49 | SIZE |(unused) | allocation ... |
50 +--------+---------+-------------------+
55 /* Return base-address of a malloc allocation, given the user address. */
56 #define MALLOC_BASE(addr) ((void *)((char *)addr - MALLOC_ALIGNMENT))
57 /* Return the size of a malloc allocation, given the user address. */
58 #define MALLOC_SIZE(addr) (*(size_t *)MALLOC_BASE(addr))
59 /* Sets the size of a malloc allocation, given the user address. */
60 #define MALLOC_SET_SIZE(addr, size) (*(size_t *)MALLOC_BASE(addr) = (size))
62 /* Return the user address of a malloc allocation, given the base address. */
63 #define MALLOC_ADDR(base) ((void *)((char *)base + MALLOC_ALIGNMENT))
66 #ifdef __UCLIBC_HAS_THREADS__
70 # define MALLOC_USE_LOCKING
72 typedef pthread_mutex_t malloc_mutex_t;
73 # define MALLOC_MUTEX_INIT PTHREAD_MUTEX_INITIALIZER
75 /* The main malloc lock. This must be hold while accessing __malloc_heap,
76 and in order to gain __malloc_sbrk_lock. */
77 extern malloc_mutex_t __malloc_lock;
78 # define __malloc_lock() pthread_mutex_lock (&__malloc_lock)
79 # define __malloc_unlock() pthread_mutex_unlock (&__malloc_lock)
81 # ifdef MALLOC_USE_SBRK
82 /* This lock is used to serialize uses of the `sbrk' function (in both
83 malloc and free, sbrk may be used several times in succession, and
84 things will break if these multiple calls are interleaved with another
85 thread's use of sbrk!). */
86 extern malloc_mutex_t __malloc_sbrk_lock;
87 # define __malloc_lock_sbrk() pthread_mutex_lock (&__malloc_sbrk_lock)
88 # define __malloc_unlock_sbrk() pthread_mutex_unlock (&__malloc_sbrk_lock)
89 # endif /* MALLOC_USE_SBRK */
91 #else /* !__UCLIBC_HAS_THREADS__ */
93 /* Without threads, mutex operations are a nop. */
94 # define __malloc_lock() (void)0
95 # define __malloc_unlock() (void)0
96 # define __malloc_lock_sbrk() (void)0
97 # define __malloc_unlock_sbrk() (void)0
99 #endif /* __UCLIBC_HAS_THREADS__ */
102 /* Change this to `#if 1' to cause malloc to emit debugging info to stderr. */
105 #define MALLOC_DEBUG(fmt, args...) fprintf (stderr, fmt , ##args)
107 #define MALLOC_DEBUG(fmt, args...) (void)0
111 /* Return SZ rounded down to POWER_OF_2_SIZE (which must be power of 2). */
112 #define MALLOC_ROUND_DOWN(sz, power_of_2_size) \
113 ((sz) & ~(power_of_2_size - 1))
114 /* Return SZ rounded to POWER_OF_2_SIZE (which must be power of 2). */
115 #define MALLOC_ROUND_UP(sz, power_of_2_size) \
116 MALLOC_ROUND_DOWN ((sz) + (power_of_2_size - 1), (power_of_2_size))
118 /* Return SZ rounded down to a multiple MALLOC_PAGE_SIZE. */
119 #define MALLOC_ROUND_DOWN_TO_PAGE_SIZE(sz) \
120 MALLOC_ROUND_DOWN (sz, MALLOC_PAGE_SIZE)
121 /* Return SZ rounded up to a multiple MALLOC_PAGE_SIZE. */
122 #define MALLOC_ROUND_UP_TO_PAGE_SIZE(sz) \
123 MALLOC_ROUND_UP (sz, MALLOC_PAGE_SIZE)
126 /* The malloc heap. */
127 extern struct heap __malloc_heap;