1 /* objalloc.c -- routines to allocate memory for objects
2 Copyright (C) 1997-2023 Free Software Foundation, Inc.
3 Written by Ian Lance Taylor, Cygnus Solutions.
4
5 This program is free software; you can redistribute it and/or modify it
6 under the terms of the GNU General Public License as published by the
7 Free Software Foundation; either version 2, or (at your option) any
8 later version.
9
10 This program is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13 GNU General Public License for more details.
14
15 You should have received a copy of the GNU General Public License
16 along with this program; if not, write to the Free Software
17 Foundation, 51 Franklin Street - Fifth Floor,
18 Boston, MA 02110-1301, USA. */
19
20 #include "config.h"
21 #include "ansidecl.h"
22
23 #include "objalloc.h"
24
25 /* Get a definition for NULL. */
26 #include <stdio.h>
27
28 #if VMS
29 #include <stdlib.h>
30 #include <unixlib.h>
31 #else
32
33 /* Get a definition for size_t. */
34 #include <stddef.h>
35
36 #ifdef HAVE_STDLIB_H
37 #include <stdlib.h>
38 #else
39 /* For systems with larger pointers than ints, this must be declared. */
40 extern void *malloc (size_t);
41 extern void free (void *);
42 #endif
43
44 #endif
45
46 /* These routines allocate space for an object. Freeing allocated
47 space may or may not free all more recently allocated space.
48
49 We handle large and small allocation requests differently. If we
50 don't have enough space in the current block, and the allocation
51 request is for more than 512 bytes, we simply pass it through to
52 malloc. */
53
54 /* The objalloc structure is defined in objalloc.h. */
55
56 /* This structure appears at the start of each chunk. */
57
58 struct objalloc_chunk
59 {
60 /* Next chunk. */
61 struct objalloc_chunk *next;
62 /* If this chunk contains large objects, this is the value of
63 current_ptr when this chunk was allocated. If this chunk
64 contains small objects, this is NULL. */
65 char *current_ptr;
66 };
67
68 /* The aligned size of objalloc_chunk. */
69
70 #define CHUNK_HEADER_SIZE \
71 ((sizeof (struct objalloc_chunk) + OBJALLOC_ALIGN - 1) \
72 &~ (OBJALLOC_ALIGN - 1))
73
74 /* We ask for this much memory each time we create a chunk which is to
75 hold small objects. */
76
77 #define CHUNK_SIZE (4096 - 32)
78
79 /* A request for this amount or more is just passed through to malloc. */
80
81 #define BIG_REQUEST (512)
82
83 /* Create an objalloc structure. */
84
85 struct objalloc *
86 objalloc_create (void)
87 {
88 struct objalloc *ret;
89 struct objalloc_chunk *chunk;
90
91 ret = (struct objalloc *) malloc (sizeof *ret);
92 if (ret == NULL)
93 return NULL;
94
95 ret->chunks = (void *) malloc (CHUNK_SIZE);
96 if (ret->chunks == NULL)
97 {
98 free (ret);
99 return NULL;
100 }
101
102 chunk = (struct objalloc_chunk *) ret->chunks;
103 chunk->next = NULL;
104 chunk->current_ptr = NULL;
105
106 ret->current_ptr = (char *) chunk + CHUNK_HEADER_SIZE;
107 ret->current_space = CHUNK_SIZE - CHUNK_HEADER_SIZE;
108
109 return ret;
110 }
111
112 /* Allocate space from an objalloc structure. */
113
114 void *
115 _objalloc_alloc (struct objalloc *o, unsigned long original_len)
116 {
117 unsigned long len = original_len;
118
119 /* We avoid confusion from zero sized objects by always allocating
120 at least 1 byte. */
121 if (len == 0)
122 len = 1;
123
124 len = (len + OBJALLOC_ALIGN - 1) &~ (OBJALLOC_ALIGN - 1);
125
126 /* Check for overflow in the alignment operation above and the
127 malloc argument below. */
128 if (len + CHUNK_HEADER_SIZE < original_len)
129 return NULL;
130
131 if (len <= o->current_space)
132 {
133 o->current_ptr += len;
134 o->current_space -= len;
135 return (void *) (o->current_ptr - len);
136 }
137
138 if (len >= BIG_REQUEST)
139 {
140 char *ret;
141 struct objalloc_chunk *chunk;
142
143 ret = (char *) malloc (CHUNK_HEADER_SIZE + len);
144 if (ret == NULL)
145 return NULL;
146
147 chunk = (struct objalloc_chunk *) ret;
148 chunk->next = (struct objalloc_chunk *) o->chunks;
149 chunk->current_ptr = o->current_ptr;
150
151 o->chunks = (void *) chunk;
152
153 return (void *) (ret + CHUNK_HEADER_SIZE);
154 }
155 else
156 {
157 struct objalloc_chunk *chunk;
158
159 chunk = (struct objalloc_chunk *) malloc (CHUNK_SIZE);
160 if (chunk == NULL)
161 return NULL;
162 chunk->next = (struct objalloc_chunk *) o->chunks;
163 chunk->current_ptr = NULL;
164
165 o->current_ptr = (char *) chunk + CHUNK_HEADER_SIZE;
166 o->current_space = CHUNK_SIZE - CHUNK_HEADER_SIZE;
167
168 o->chunks = (void *) chunk;
169
170 return objalloc_alloc (o, len);
171 }
172 }
173
174 /* Free an entire objalloc structure. */
175
176 void
177 objalloc_free (struct objalloc *o)
178 {
179 struct objalloc_chunk *l;
180
181 l = (struct objalloc_chunk *) o->chunks;
182 while (l != NULL)
183 {
184 struct objalloc_chunk *next;
185
186 next = l->next;
187 free (l);
188 l = next;
189 }
190
191 free (o);
192 }
193
194 /* Free a block from an objalloc structure. This also frees all more
195 recently allocated blocks. */
196
197 void
198 objalloc_free_block (struct objalloc *o, void *block)
199 {
200 struct objalloc_chunk *p, *small;
201 char *b = (char *) block;
202
203 /* First set P to the chunk which contains the block we are freeing,
204 and set Q to the last small object chunk we see before P. */
205 small = NULL;
206 for (p = (struct objalloc_chunk *) o->chunks; p != NULL; p = p->next)
207 {
208 if (p->current_ptr == NULL)
209 {
210 if (b > (char *) p && b < (char *) p + CHUNK_SIZE)
211 break;
212 small = p;
213 }
214 else
215 {
216 if (b == (char *) p + CHUNK_HEADER_SIZE)
217 break;
218 }
219 }
220
221 /* If we can't find the chunk, the caller has made a mistake. */
222 if (p == NULL)
223 abort ();
224
225 if (p->current_ptr == NULL)
226 {
227 struct objalloc_chunk *q;
228 struct objalloc_chunk *first;
229
230 /* The block is in a chunk containing small objects. We can
231 free every chunk through SMALL, because they have certainly
232 been allocated more recently. After SMALL, we will not see
233 any chunks containing small objects; we can free any big
234 chunk if the current_ptr is greater than or equal to B. We
235 can then reset the new current_ptr to B. */
236
237 first = NULL;
238 q = (struct objalloc_chunk *) o->chunks;
239 while (q != p)
240 {
241 struct objalloc_chunk *next;
242
243 next = q->next;
244 if (small != NULL)
245 {
246 if (small == q)
247 small = NULL;
248 free (q);
249 }
250 else if (q->current_ptr > b)
251 free (q);
252 else if (first == NULL)
253 first = q;
254
255 q = next;
256 }
257
258 if (first == NULL)
259 first = p;
260 o->chunks = (void *) first;
261
262 /* Now start allocating from this small block again. */
263 o->current_ptr = b;
264 o->current_space = ((char *) p + CHUNK_SIZE) - b;
265 }
266 else
267 {
268 struct objalloc_chunk *q;
269 char *current_ptr;
270
271 /* This block is in a large chunk by itself. We can free
272 everything on the list up to and including this block. We
273 then start allocating from the next chunk containing small
274 objects, setting current_ptr from the value stored with the
275 large chunk we are freeing. */
276
277 current_ptr = p->current_ptr;
278 p = p->next;
279
280 q = (struct objalloc_chunk *) o->chunks;
281 while (q != p)
282 {
283 struct objalloc_chunk *next;
284
285 next = q->next;
286 free (q);
287 q = next;
288 }
289
290 o->chunks = (void *) p;
291
292 while (p->current_ptr != NULL)
293 p = p->next;
294
295 o->current_ptr = current_ptr;
296 o->current_space = ((char *) p + CHUNK_SIZE) - current_ptr;
297 }
298 }