1/* mmap.c -- Memory allocation with mmap.
2 Copyright (C) 2012-2025 Free Software Foundation, Inc.
3 Written by Ian Lance Taylor, Google.
4
5Redistribution and use in source and binary forms, with or without
6modification, are permitted provided that the following conditions are
7met:
8
9 (1) Redistributions of source code must retain the above copyright
10 notice, this list of conditions and the following disclaimer.
11
12 (2) Redistributions in binary form must reproduce the above copyright
13 notice, this list of conditions and the following disclaimer in
14 the documentation and/or other materials provided with the
15 distribution.
16
17 (3) The name of the author may not be used to
18 endorse or promote products derived from this software without
19 specific prior written permission.
20
21THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
22IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
23WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
24DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT,
25INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
26(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
27SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
28HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
29STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
30IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
31POSSIBILITY OF SUCH DAMAGE. */
32
33#include "config.h"
34
35#include <errno.h>
36#include <string.h>
37#include <stdlib.h>
38#include <unistd.h>
39#include <sys/types.h>
40#include <sys/mman.h>
41
42#include "backtrace.h"
43#include "internal.h"
44
45#ifndef HAVE_DECL_GETPAGESIZE
46extern int getpagesize (void);
47#endif
48
49/* Memory allocation on systems that provide anonymous mmap. This
50 permits the backtrace functions to be invoked from a signal
51 handler, assuming that mmap is async-signal safe. */
52
53#ifndef MAP_ANONYMOUS
54#define MAP_ANONYMOUS MAP_ANON
55#endif
56
57#ifndef MAP_FAILED
58#define MAP_FAILED ((void *)-1)
59#endif
60
61/* A list of free memory blocks. */
62
63struct backtrace_freelist_struct
64{
65 /* Next on list. */
66 struct backtrace_freelist_struct *next;
67 /* Size of this block, including this structure. */
68 size_t size;
69};
70
71/* Free memory allocated by backtrace_alloc. */
72
73static void
74backtrace_free_locked (struct backtrace_state *state, void *addr, size_t size)
75{
76 /* Just leak small blocks. We don't have to be perfect. Don't put
77 more than 16 entries on the free list, to avoid wasting time
78 searching when allocating a block. If we have more than 16
79 entries, leak the smallest entry. */
80
81 if (size >= sizeof (struct backtrace_freelist_struct))
82 {
83 size_t c;
84 struct backtrace_freelist_struct **ppsmall;
85 struct backtrace_freelist_struct **pp;
86 struct backtrace_freelist_struct *p;
87
88 c = 0;
89 ppsmall = NULL;
90 for (pp = &state->freelist; *pp != NULL; pp = &(*pp)->next)
91 {
92 if (ppsmall == NULL || (*pp)->size < (*ppsmall)->size)
93 ppsmall = pp;
94 ++c;
95 }
96 if (c >= 16)
97 {
98 if (size <= (*ppsmall)->size)
99 return;
100 *ppsmall = (*ppsmall)->next;
101 }
102
103 p = (struct backtrace_freelist_struct *) addr;
104 p->next = state->freelist;
105 p->size = size;
106 state->freelist = p;
107 }
108}
109
110/* Allocate memory like malloc. If ERROR_CALLBACK is NULL, don't
111 report an error. */
112
113void *
114backtrace_alloc (struct backtrace_state *state,
115 size_t size, backtrace_error_callback error_callback,
116 void *data)
117{
118 void *ret;
119 int locked;
120 struct backtrace_freelist_struct **pp;
121 size_t pagesize;
122 size_t asksize;
123 void *page;
124
125 ret = NULL;
126
127 /* If we can acquire the lock, then see if there is space on the
128 free list. If we can't acquire the lock, drop straight into
129 using mmap. __sync_lock_test_and_set returns the old state of
130 the lock, so we have acquired it if it returns 0. */
131
132 if (!state->threaded)
133 locked = 1;
134 else
135 locked = __sync_lock_test_and_set (&state->lock_alloc, 1) == 0;
136
137 if (locked)
138 {
139 for (pp = &state->freelist; *pp != NULL; pp = &(*pp)->next)
140 {
141 if ((*pp)->size >= size)
142 {
143 struct backtrace_freelist_struct *p;
144
145 p = *pp;
146 *pp = p->next;
147
148 /* Round for alignment; we assume that no type we care about
149 is more than 8 bytes. */
150 size = (size + 7) & ~ (size_t) 7;
151 if (size < p->size)
152 backtrace_free_locked (state, addr: (char *) p + size,
153 size: p->size - size);
154
155 ret = (void *) p;
156
157 break;
158 }
159 }
160
161 if (state->threaded)
162 __sync_lock_release (&state->lock_alloc);
163 }
164
165 if (ret == NULL)
166 {
167 /* Allocate a new page. */
168
169 pagesize = getpagesize ();
170 asksize = (size + pagesize - 1) & ~ (pagesize - 1);
171 page = mmap (NULL, len: asksize, PROT_READ | PROT_WRITE,
172 MAP_PRIVATE | MAP_ANONYMOUS, fd: -1, offset: 0);
173 if (page == MAP_FAILED)
174 {
175 if (error_callback)
176 error_callback (data, "mmap", errno);
177 }
178 else
179 {
180 size = (size + 7) & ~ (size_t) 7;
181 if (size < asksize)
182 backtrace_free (state, mem: (char *) page + size, size: asksize - size,
183 error_callback, data);
184
185 ret = page;
186 }
187 }
188
189 return ret;
190}
191
192/* Free memory allocated by backtrace_alloc. */
193
194void
195backtrace_free (struct backtrace_state *state, void *addr, size_t size,
196 backtrace_error_callback error_callback ATTRIBUTE_UNUSED,
197 void *data ATTRIBUTE_UNUSED)
198{
199 int locked;
200
201 /* If we are freeing a large aligned block, just release it back to
202 the system. This case arises when growing a vector for a large
203 binary with lots of debug info. Calling munmap here may cause us
204 to call mmap again if there is also a large shared library; we
205 just live with that. */
206 if (size >= 16 * 4096)
207 {
208 size_t pagesize;
209
210 pagesize = getpagesize ();
211 if (((uintptr_t) addr & (pagesize - 1)) == 0
212 && (size & (pagesize - 1)) == 0)
213 {
214 /* If munmap fails for some reason, just add the block to
215 the freelist. */
216 if (munmap (addr: addr, len: size) == 0)
217 return;
218 }
219 }
220
221 /* If we can acquire the lock, add the new space to the free list.
222 If we can't acquire the lock, just leak the memory.
223 __sync_lock_test_and_set returns the old state of the lock, so we
224 have acquired it if it returns 0. */
225
226 if (!state->threaded)
227 locked = 1;
228 else
229 locked = __sync_lock_test_and_set (&state->lock_alloc, 1) == 0;
230
231 if (locked)
232 {
233 backtrace_free_locked (state, addr, size);
234
235 if (state->threaded)
236 __sync_lock_release (&state->lock_alloc);
237 }
238}
239
240/* Grow VEC by SIZE bytes. */
241
242void *
243backtrace_vector_grow (struct backtrace_state *state,size_t size,
244 backtrace_error_callback error_callback,
245 void *data, struct backtrace_vector *vec)
246{
247 void *ret;
248
249 if (size > vec->alc)
250 {
251 size_t pagesize;
252 size_t alc;
253 void *base;
254
255 pagesize = getpagesize ();
256 alc = vec->size + size;
257 if (vec->size == 0)
258 alc = 16 * size;
259 else if (alc < pagesize)
260 {
261 alc *= 2;
262 if (alc > pagesize)
263 alc = pagesize;
264 }
265 else
266 {
267 alc *= 2;
268 alc = (alc + pagesize - 1) & ~ (pagesize - 1);
269 }
270 base = backtrace_alloc (state, size: alc, error_callback, data);
271 if (base == NULL)
272 return NULL;
273 if (vec->base != NULL)
274 {
275 memcpy (dest: base, src: vec->base, n: vec->size);
276 backtrace_free (state, addr: vec->base, size: vec->size + vec->alc,
277 error_callback, data);
278 }
279 vec->base = base;
280 vec->alc = alc - vec->size;
281 }
282
283 ret = (char *) vec->base + vec->size;
284 vec->size += size;
285 vec->alc -= size;
286 return ret;
287}
288
289/* Finish the current allocation on VEC. */
290
291void *
292backtrace_vector_finish (
293 struct backtrace_state *state ATTRIBUTE_UNUSED,
294 struct backtrace_vector *vec,
295 backtrace_error_callback error_callback ATTRIBUTE_UNUSED,
296 void *data ATTRIBUTE_UNUSED)
297{
298 void *ret;
299
300 ret = vec->base;
301 vec->base = (char *) vec->base + vec->size;
302 vec->size = 0;
303 return ret;
304}
305
306/* Release any extra space allocated for VEC. */
307
308int
309backtrace_vector_release (struct backtrace_state *state,
310 struct backtrace_vector *vec,
311 backtrace_error_callback error_callback,
312 void *data)
313{
314 size_t size;
315 size_t alc;
316 size_t aligned;
317
318 /* Make sure that the block that we free is aligned on an 8-byte
319 boundary. */
320 size = vec->size;
321 alc = vec->alc;
322 aligned = (size + 7) & ~ (size_t) 7;
323 alc -= aligned - size;
324
325 backtrace_free (state, addr: (char *) vec->base + aligned, size: alc,
326 error_callback, data);
327 vec->alc = 0;
328 if (vec->size == 0)
329 vec->base = NULL;
330 return 1;
331}
332

source code of libbacktrace/mmap.c