1 /*
2 * Stack-less Just-In-Time compiler
3 *
4 * Copyright 2009-2012 Zoltan Herczeg (hzmester@freemail.hu). All rights reserved.
5 *
6 * Redistribution and use in source and binary forms, with or without modification, are
7 * permitted provided that the following conditions are met:
8 *
9 * 1. Redistributions of source code must retain the above copyright notice, this list of
10 * conditions and the following disclaimer.
11 *
12 * 2. Redistributions in binary form must reproduce the above copyright notice, this list
13 * of conditions and the following disclaimer in the documentation and/or other materials
14 * provided with the distribution.
15 *
16 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) AND CONTRIBUTORS ``AS IS'' AND ANY
17 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
18 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT
19 * SHALL THE COPYRIGHT HOLDER(S) OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
20 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED
21 * TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
22 * BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
23 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
24 * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
25 */
26
27 /*
28 This file contains a simple executable memory allocator
29
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
33 not suggested.
34
35 How does it work:
36 Memory is allocated in continuous memory areas called chunks by alloc_chunk()
37 Chunk format:
38 [ block ][ block ] ... [ block ][ block terminator ]
39
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.
43 Block size:
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.
47 Previous block size:
48 0 - This is the first block of the memory chunk.
49 n - The size of the previous block.
50
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
54 is called.
55
56 When a block is freed, the new free block is connected to its adjacent free
57 blocks if possible.
58
59 [ free block ][ used block ][ free block ]
60 and "used block" is freed, the three blocks are connected together:
61 [ one big free block ]
62 */
63
64 /* --------------------------------------------------------------------- */
65 /* System (OS) functions */
66 /* --------------------------------------------------------------------- */
67
68 /* 64 KByte. */
69 #define CHUNK_SIZE 0x10000
70
71 /*
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
80 */
81
82 #ifdef _WIN32
83
alloc_chunk(sljit_uw size)84 static SLJIT_INLINE void* alloc_chunk(sljit_uw size)
85 {
86 return VirtualAlloc(NULL, size, MEM_COMMIT | MEM_RESERVE, PAGE_EXECUTE_READWRITE);
87 }
88
free_chunk(void * chunk,sljit_uw size)89 static SLJIT_INLINE void free_chunk(void* chunk, sljit_uw size)
90 {
91 SLJIT_UNUSED_ARG(size);
92 VirtualFree(chunk, 0, MEM_RELEASE);
93 }
94
95 #else
96
alloc_chunk(sljit_uw size)97 static SLJIT_INLINE void* alloc_chunk(sljit_uw size)
98 {
99 void* retval;
100
101 #ifdef MAP_ANON
102 retval = mmap(NULL, size, PROT_READ | PROT_WRITE | PROT_EXEC, MAP_PRIVATE | MAP_ANON, -1, 0);
103 #else
104 if (dev_zero < 0) {
105 if (open_dev_zero())
106 return NULL;
107 }
108 retval = mmap(NULL, size, PROT_READ | PROT_WRITE | PROT_EXEC, MAP_PRIVATE, dev_zero, 0);
109 #endif
110
111 return (retval != MAP_FAILED) ? retval : NULL;
112 }
113
free_chunk(void * chunk,sljit_uw size)114 static SLJIT_INLINE void free_chunk(void* chunk, sljit_uw size)
115 {
116 munmap(chunk, size);
117 }
118
119 #endif
120
121 /* --------------------------------------------------------------------- */
122 /* Common functions */
123 /* --------------------------------------------------------------------- */
124
125 #define CHUNK_MASK (~(CHUNK_SIZE - 1))
126
127 struct block_header {
128 sljit_uw size;
129 sljit_uw prev_size;
130 };
131
132 struct free_block {
133 struct block_header header;
134 struct free_block *next;
135 struct free_block *prev;
136 sljit_uw size;
137 };
138
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)
145
146 static struct free_block* free_blocks;
147 static sljit_uw allocated_size;
148 static sljit_uw total_size;
149
sljit_insert_free_block(struct free_block * free_block,sljit_uw size)150 static SLJIT_INLINE void sljit_insert_free_block(struct free_block *free_block, sljit_uw size)
151 {
152 free_block->header.size = 0;
153 free_block->size = size;
154
155 free_block->next = free_blocks;
156 free_block->prev = 0;
157 if (free_blocks)
158 free_blocks->prev = free_block;
159 free_blocks = free_block;
160 }
161
sljit_remove_free_block(struct free_block * free_block)162 static SLJIT_INLINE void sljit_remove_free_block(struct free_block *free_block)
163 {
164 if (free_block->next)
165 free_block->next->prev = free_block->prev;
166
167 if (free_block->prev)
168 free_block->prev->next = free_block->next;
169 else {
170 SLJIT_ASSERT(free_blocks == free_block);
171 free_blocks = free_block->next;
172 }
173 }
174
sljit_malloc_exec(sljit_uw size)175 SLJIT_API_FUNC_ATTRIBUTE void* sljit_malloc_exec(sljit_uw size)
176 {
177 struct block_header *header;
178 struct block_header *next_header;
179 struct free_block *free_block;
180 sljit_uw chunk_size;
181
182 allocator_grab_lock();
183 if (size < sizeof(struct free_block))
184 size = sizeof(struct free_block);
185 size = ALIGN_SIZE(size);
186
187 free_block = free_blocks;
188 while (free_block) {
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. */
193 chunk_size -= size;
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;
198 }
199 else {
200 sljit_remove_free_block(free_block);
201 header = (struct block_header*)free_block;
202 size = chunk_size;
203 }
204 allocated_size += size;
205 header->size = size;
206 allocator_release_lock();
207 return MEM_START(header);
208 }
209 free_block = free_block->next;
210 }
211
212 chunk_size = (size + sizeof(struct block_header) + CHUNK_SIZE - 1) & CHUNK_MASK;
213 header = (struct block_header*)alloc_chunk(chunk_size);
214 if (!header) {
215 allocator_release_lock();
216 return NULL;
217 }
218
219 chunk_size -= sizeof(struct block_header);
220 total_size += chunk_size;
221
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;
226 header->size = size;
227 chunk_size -= size;
228
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);
233 }
234 else {
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);
239 }
240 next_header->size = 1;
241 next_header->prev_size = chunk_size;
242 allocator_release_lock();
243 return MEM_START(header);
244 }
245
sljit_free_exec(void * ptr)246 SLJIT_API_FUNC_ATTRIBUTE void sljit_free_exec(void* ptr)
247 {
248 struct block_header *header;
249 struct free_block* free_block;
250
251 allocator_grab_lock();
252 header = AS_BLOCK_HEADER(ptr, -(sljit_sw)sizeof(struct block_header));
253 allocated_size -= header->size;
254
255 /* Connecting free blocks together if possible. */
256
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;
264 }
265 else {
266 free_block = (struct free_block*)header;
267 sljit_insert_free_block(free_block, header->size);
268 }
269
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;
276 }
277
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));
285 }
286 }
287
288 allocator_release_lock();
289 }
290
sljit_free_unused_memory_exec(void)291 SLJIT_API_FUNC_ATTRIBUTE void sljit_free_unused_memory_exec(void)
292 {
293 struct free_block* free_block;
294 struct free_block* next_free_block;
295
296 allocator_grab_lock();
297
298 free_block = free_blocks;
299 while (free_block) {
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));
306 }
307 free_block = next_free_block;
308 }
309
310 SLJIT_ASSERT((total_size && free_blocks) || (!total_size && !free_blocks));
311 allocator_release_lock();
312 }
313