1/* mmap.c -- Memory allocation with mmap.
2 Copyright (C) 2012-2017 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/* Memory allocation on systems that provide anonymous mmap. This
46 permits the backtrace functions to be invoked from a signal
47 handler, assuming that mmap is async-signal safe. */
48
49#ifndef MAP_ANONYMOUS
50#define MAP_ANONYMOUS MAP_ANON
51#endif
52
53#ifndef MAP_FAILED
54#define MAP_FAILED ((void *)-1)
55#endif
56
57/* A list of free memory blocks. */
58
59struct backtrace_freelist_struct
60{
61 /* Next on list. */
62 struct backtrace_freelist_struct *next;
63 /* Size of this block, including this structure. */
64 size_t size;
65};
66
67/* Free memory allocated by backtrace_alloc. */
68
69static void
70backtrace_free_locked (struct backtrace_state *state, void *addr, size_t size)
71{
72 /* Just leak small blocks. We don't have to be perfect. */
73 if (size >= sizeof (struct backtrace_freelist_struct))
74 {
75 struct backtrace_freelist_struct *p;
76
77 p = (struct backtrace_freelist_struct *) addr;
78 p->next = state->freelist;
79 p->size = size;
80 state->freelist = p;
81 }
82}
83
84/* Allocate memory like malloc. If ERROR_CALLBACK is NULL, don't
85 report an error. */
86
87void *
88backtrace_alloc (struct backtrace_state *state,
89 size_t size, backtrace_error_callback error_callback,
90 void *data)
91{
92 void *ret;
93 int locked;
94 struct backtrace_freelist_struct **pp;
95 size_t pagesize;
96 size_t asksize;
97 void *page;
98
99 ret = NULL;
100
101 /* If we can acquire the lock, then see if there is space on the
102 free list. If we can't acquire the lock, drop straight into
103 using mmap. __sync_lock_test_and_set returns the old state of
104 the lock, so we have acquired it if it returns 0. */
105
106 if (!state->threaded)
107 locked = 1;
108 else
109 locked = __sync_lock_test_and_set (&state->lock_alloc, 1) == 0;
110
111 if (locked)
112 {
113 for (pp = &state->freelist; *pp != NULL; pp = &(*pp)->next)
114 {
115 if ((*pp)->size >= size)
116 {
117 struct backtrace_freelist_struct *p;
118
119 p = *pp;
120 *pp = p->next;
121
122 /* Round for alignment; we assume that no type we care about
123 is more than 8 bytes. */
124 size = (size + 7) & ~ (size_t) 7;
125 if (size < p->size)
126 backtrace_free_locked (state, (char *) p + size,
127 p->size - size);
128
129 ret = (void *) p;
130
131 break;
132 }
133 }
134
135 if (state->threaded)
136 __sync_lock_release (&state->lock_alloc);
137 }
138
139 if (ret == NULL)
140 {
141 /* Allocate a new page. */
142
143 pagesize = getpagesize ();
144 asksize = (size + pagesize - 1) & ~ (pagesize - 1);
145 page = mmap (NULL, asksize, PROT_READ | PROT_WRITE,
146 MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
147 if (page == MAP_FAILED)
148 {
149 if (error_callback)
150 error_callback (data, "mmap", errno);
151 }
152 else
153 {
154 size = (size + 7) & ~ (size_t) 7;
155 if (size < asksize)
156 backtrace_free (state, (char *) page + size, asksize - size,
157 error_callback, data);
158
159 ret = page;
160 }
161 }
162
163 return ret;
164}
165
166/* Free memory allocated by backtrace_alloc. */
167
168void
169backtrace_free (struct backtrace_state *state, void *addr, size_t size,
170 backtrace_error_callback error_callback ATTRIBUTE_UNUSED,
171 void *data ATTRIBUTE_UNUSED)
172{
173 int locked;
174
175 /* If we are freeing a large aligned block, just release it back to
176 the system. This case arises when growing a vector for a large
177 binary with lots of debug info. Calling munmap here may cause us
178 to call mmap again if there is also a large shared library; we
179 just live with that. */
180 if (size >= 16 * 4096)
181 {
182 size_t pagesize;
183
184 pagesize = getpagesize ();
185 if (((uintptr_t) addr & (pagesize - 1)) == 0
186 && (size & (pagesize - 1)) == 0)
187 {
188 /* If munmap fails for some reason, just add the block to
189 the freelist. */
190 if (munmap (addr, size) == 0)
191 return;
192 }
193 }
194
195 /* If we can acquire the lock, add the new space to the free list.
196 If we can't acquire the lock, just leak the memory.
197 __sync_lock_test_and_set returns the old state of the lock, so we
198 have acquired it if it returns 0. */
199
200 if (!state->threaded)
201 locked = 1;
202 else
203 locked = __sync_lock_test_and_set (&state->lock_alloc, 1) == 0;
204
205 if (locked)
206 {
207 backtrace_free_locked (state, addr, size);
208
209 if (state->threaded)
210 __sync_lock_release (&state->lock_alloc);
211 }
212}
213
214/* Grow VEC by SIZE bytes. */
215
216void *
217backtrace_vector_grow (struct backtrace_state *state,size_t size,
218 backtrace_error_callback error_callback,
219 void *data, struct backtrace_vector *vec)
220{
221 void *ret;
222
223 if (size > vec->alc)
224 {
225 size_t pagesize;
226 size_t alc;
227 void *base;
228
229 pagesize = getpagesize ();
230 alc = vec->size + size;
231 if (vec->size == 0)
232 alc = 16 * size;
233 else if (alc < pagesize)
234 {
235 alc *= 2;
236 if (alc > pagesize)
237 alc = pagesize;
238 }
239 else
240 {
241 alc *= 2;
242 alc = (alc + pagesize - 1) & ~ (pagesize - 1);
243 }
244 base = backtrace_alloc (state, alc, error_callback, data);
245 if (base == NULL)
246 return NULL;
247 if (vec->base != NULL)
248 {
249 memcpy (base, vec->base, vec->size);
250 backtrace_free (state, vec->base, vec->size + vec->alc,
251 error_callback, data);
252 }
253 vec->base = base;
254 vec->alc = alc - vec->size;
255 }
256
257 ret = (char *) vec->base + vec->size;
258 vec->size += size;
259 vec->alc -= size;
260 return ret;
261}
262
263/* Finish the current allocation on VEC. */
264
265void *
266backtrace_vector_finish (
267 struct backtrace_state *state ATTRIBUTE_UNUSED,
268 struct backtrace_vector *vec,
269 backtrace_error_callback error_callback ATTRIBUTE_UNUSED,
270 void *data ATTRIBUTE_UNUSED)
271{
272 void *ret;
273
274 ret = vec->base;
275 vec->base = (char *) vec->base + vec->size;
276 vec->size = 0;
277 return ret;
278}
279
280/* Release any extra space allocated for VEC. */
281
282int
283backtrace_vector_release (struct backtrace_state *state,
284 struct backtrace_vector *vec,
285 backtrace_error_callback error_callback,
286 void *data)
287{
288 size_t size;
289 size_t alc;
290 size_t aligned;
291
292 /* Make sure that the block that we free is aligned on an 8-byte
293 boundary. */
294 size = vec->size;
295 alc = vec->alc;
296 aligned = (size + 7) & ~ (size_t) 7;
297 alc -= aligned - size;
298
299 backtrace_free (state, (char *) vec->base + aligned, alc,
300 error_callback, data);
301 vec->alc = 0;
302 return 1;
303}
304