2 * Stack-less Just-In-Time compiler
4 * Copyright 2009-2012 Zoltan Herczeg (hzmester@freemail.hu). All rights reserved.
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7 * permitted provided that the following conditions are met:
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28 This file contains a simple executable memory allocator
30 It is assumed, that executable code blocks are usually medium (or sometimes
31 large) memory blocks, and the allocator is not too frequently called (less
32 optimized than other allocators). Thus, using it as a generic allocator is
36 Memory is allocated in continuous memory areas called chunks by alloc_chunk()
38 [ block ][ block ] ... [ block ][ block terminator ]
40 All blocks and the block terminator is started with block_header. The block
41 header contains the size of the previous and the next block. These sizes
42 can also contain special values.
44 0 - The block is a free_block, with a different size member.
45 1 - The block is a block terminator.
46 n - The block is used at the moment, and the value contains its size.
48 0 - This is the first block of the memory chunk.
49 n - The size of the previous block.
51 Using these size values we can go forward or backward on the block chain.
52 The unused blocks are stored in a chain list pointed by free_blocks. This
53 list is useful if we need to find a suitable memory area when the allocator
56 When a block is freed, the new free block is connected to its adjacent free
59 [ free block ][ used block ][ free block ]
60 and "used block" is freed, the three blocks are connected together:
61 [ one big free block ]
64 /* --------------------------------------------------------------------- */
65 /* System (OS) functions */
66 /* --------------------------------------------------------------------- */
69 #define CHUNK_SIZE 0x10000
72 alloc_chunk / free_chunk :
73 * allocate executable system memory chunks
74 * the size is always divisible by CHUNK_SIZE
75 allocator_grab_lock / allocator_release_lock :
76 * make the allocator thread safe
77 * can be empty if the OS (or the application) does not support threading
78 * only the allocator requires this lock, sljit is fully thread safe
79 as it only uses local variables
84 static SLJIT_INLINE void* alloc_chunk(sljit_uw size)
86 return VirtualAlloc(NULL, size, MEM_COMMIT | MEM_RESERVE, PAGE_EXECUTE_READWRITE);
89 static SLJIT_INLINE void free_chunk(void* chunk, sljit_uw size)
91 SLJIT_UNUSED_ARG(size);
92 VirtualFree(chunk, 0, MEM_RELEASE);
97 static SLJIT_INLINE void* alloc_chunk(sljit_uw size)
102 retval = mmap(NULL, size, PROT_READ | PROT_WRITE | PROT_EXEC, MAP_PRIVATE | MAP_ANON, -1, 0);
108 retval = mmap(NULL, size, PROT_READ | PROT_WRITE | PROT_EXEC, MAP_PRIVATE, dev_zero, 0);
111 return (retval != MAP_FAILED) ? retval : NULL;
114 static SLJIT_INLINE void free_chunk(void* chunk, sljit_uw size)
121 /* --------------------------------------------------------------------- */
122 /* Common functions */
123 /* --------------------------------------------------------------------- */
125 #define CHUNK_MASK (~(CHUNK_SIZE - 1))
127 struct block_header {
133 struct block_header header;
134 struct free_block *next;
135 struct free_block *prev;
139 #define AS_BLOCK_HEADER(base, offset) \
140 ((struct block_header*)(((sljit_ub*)base) + offset))
141 #define AS_FREE_BLOCK(base, offset) \
142 ((struct free_block*)(((sljit_ub*)base) + offset))
143 #define MEM_START(base) ((void*)(((sljit_ub*)base) + sizeof(struct block_header)))
144 #define ALIGN_SIZE(size) (((size) + sizeof(struct block_header) + 7) & ~7)
146 static struct free_block* free_blocks;
147 static sljit_uw allocated_size;
148 static sljit_uw total_size;
150 static SLJIT_INLINE void sljit_insert_free_block(struct free_block *free_block, sljit_uw size)
152 free_block->header.size = 0;
153 free_block->size = size;
155 free_block->next = free_blocks;
156 free_block->prev = 0;
158 free_blocks->prev = free_block;
159 free_blocks = free_block;
162 static SLJIT_INLINE void sljit_remove_free_block(struct free_block *free_block)
164 if (free_block->next)
165 free_block->next->prev = free_block->prev;
167 if (free_block->prev)
168 free_block->prev->next = free_block->next;
170 SLJIT_ASSERT(free_blocks == free_block);
171 free_blocks = free_block->next;
175 SLJIT_API_FUNC_ATTRIBUTE void* sljit_malloc_exec(sljit_uw size)
177 struct block_header *header;
178 struct block_header *next_header;
179 struct free_block *free_block;
182 allocator_grab_lock();
183 if (size < sizeof(struct free_block))
184 size = sizeof(struct free_block);
185 size = ALIGN_SIZE(size);
187 free_block = free_blocks;
189 if (free_block->size >= size) {
190 chunk_size = free_block->size;
191 if (chunk_size > size + 64) {
192 /* We just cut a block from the end of the free block. */
194 free_block->size = chunk_size;
195 header = AS_BLOCK_HEADER(free_block, chunk_size);
196 header->prev_size = chunk_size;
197 AS_BLOCK_HEADER(header, size)->prev_size = size;
200 sljit_remove_free_block(free_block);
201 header = (struct block_header*)free_block;
204 allocated_size += size;
206 allocator_release_lock();
207 return MEM_START(header);
209 free_block = free_block->next;
212 chunk_size = (size + sizeof(struct block_header) + CHUNK_SIZE - 1) & CHUNK_MASK;
213 header = (struct block_header*)alloc_chunk(chunk_size);
215 allocator_release_lock();
219 chunk_size -= sizeof(struct block_header);
220 total_size += chunk_size;
222 header->prev_size = 0;
223 if (chunk_size > size + 64) {
224 /* Cut the allocated space into a free and a used block. */
225 allocated_size += size;
229 free_block = AS_FREE_BLOCK(header, size);
230 free_block->header.prev_size = size;
231 sljit_insert_free_block(free_block, chunk_size);
232 next_header = AS_BLOCK_HEADER(free_block, chunk_size);
235 /* All space belongs to this allocation. */
236 allocated_size += chunk_size;
237 header->size = chunk_size;
238 next_header = AS_BLOCK_HEADER(header, chunk_size);
240 next_header->size = 1;
241 next_header->prev_size = chunk_size;
242 allocator_release_lock();
243 return MEM_START(header);
246 SLJIT_API_FUNC_ATTRIBUTE void sljit_free_exec(void* ptr)
248 struct block_header *header;
249 struct free_block* free_block;
251 allocator_grab_lock();
252 header = AS_BLOCK_HEADER(ptr, -(sljit_sw)sizeof(struct block_header));
253 allocated_size -= header->size;
255 /* Connecting free blocks together if possible. */
257 /* If header->prev_size == 0, free_block will equal to header.
258 In this case, free_block->header.size will be > 0. */
259 free_block = AS_FREE_BLOCK(header, -(sljit_sw)header->prev_size);
260 if (SLJIT_UNLIKELY(!free_block->header.size)) {
261 free_block->size += header->size;
262 header = AS_BLOCK_HEADER(free_block, free_block->size);
263 header->prev_size = free_block->size;
266 free_block = (struct free_block*)header;
267 sljit_insert_free_block(free_block, header->size);
270 header = AS_BLOCK_HEADER(free_block, free_block->size);
271 if (SLJIT_UNLIKELY(!header->size)) {
272 free_block->size += ((struct free_block*)header)->size;
273 sljit_remove_free_block((struct free_block*)header);
274 header = AS_BLOCK_HEADER(free_block, free_block->size);
275 header->prev_size = free_block->size;
278 /* The whole chunk is free. */
279 if (SLJIT_UNLIKELY(!free_block->header.prev_size && header->size == 1)) {
280 /* If this block is freed, we still have (allocated_size / 2) free space. */
281 if (total_size - free_block->size > (allocated_size * 3 / 2)) {
282 total_size -= free_block->size;
283 sljit_remove_free_block(free_block);
284 free_chunk(free_block, free_block->size + sizeof(struct block_header));
288 allocator_release_lock();
291 SLJIT_API_FUNC_ATTRIBUTE void sljit_free_unused_memory_exec(void)
293 struct free_block* free_block;
294 struct free_block* next_free_block;
296 allocator_grab_lock();
298 free_block = free_blocks;
300 next_free_block = free_block->next;
301 if (!free_block->header.prev_size &&
302 AS_BLOCK_HEADER(free_block, free_block->size)->size == 1) {
303 total_size -= free_block->size;
304 sljit_remove_free_block(free_block);
305 free_chunk(free_block, free_block->size + sizeof(struct block_header));
307 free_block = next_free_block;
310 SLJIT_ASSERT((total_size && free_blocks) || (!total_size && !free_blocks));
311 allocator_release_lock();