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111
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1 /* mmap.c -- Memory allocation with mmap.
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2 Copyright (C) 2012-2017 Free Software Foundation, Inc.
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3 Written by Ian Lance Taylor, Google.
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4
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5 Redistribution and use in source and binary forms, with or without
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6 modification, are permitted provided that the following conditions are
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7 met:
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8
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9 (1) Redistributions of source code must retain the above copyright
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10 notice, this list of conditions and the following disclaimer.
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11
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12 (2) Redistributions in binary form must reproduce the above copyright
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13 notice, this list of conditions and the following disclaimer in
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14 the documentation and/or other materials provided with the
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15 distribution.
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16
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17 (3) The name of the author may not be used to
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18 endorse or promote products derived from this software without
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19 specific prior written permission.
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20
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21 THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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22 IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
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23 WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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24 DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT,
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25 INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
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26 (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
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27 SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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28 HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
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29 STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
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30 IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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31 POSSIBILITY OF SUCH DAMAGE. */
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32
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33 #include "config.h"
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34
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35 #include <errno.h>
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36 #include <string.h>
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37 #include <stdlib.h>
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38 #include <unistd.h>
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39 #include <sys/types.h>
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40 #include <sys/mman.h>
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41
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42 #include "backtrace.h"
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43 #include "internal.h"
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44
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45 /* Memory allocation on systems that provide anonymous mmap. This
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46 permits the backtrace functions to be invoked from a signal
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47 handler, assuming that mmap is async-signal safe. */
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48
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49 #ifndef MAP_ANONYMOUS
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50 #define MAP_ANONYMOUS MAP_ANON
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51 #endif
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52
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53 #ifndef MAP_FAILED
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54 #define MAP_FAILED ((void *)-1)
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55 #endif
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56
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57 /* A list of free memory blocks. */
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58
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59 struct backtrace_freelist_struct
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60 {
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61 /* Next on list. */
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62 struct backtrace_freelist_struct *next;
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63 /* Size of this block, including this structure. */
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64 size_t size;
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65 };
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66
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67 /* Free memory allocated by backtrace_alloc. */
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68
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69 static void
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70 backtrace_free_locked (struct backtrace_state *state, void *addr, size_t size)
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71 {
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72 /* Just leak small blocks. We don't have to be perfect. */
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73 if (size >= sizeof (struct backtrace_freelist_struct))
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74 {
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75 struct backtrace_freelist_struct *p;
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76
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77 p = (struct backtrace_freelist_struct *) addr;
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78 p->next = state->freelist;
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79 p->size = size;
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80 state->freelist = p;
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81 }
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82 }
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83
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84 /* Allocate memory like malloc. If ERROR_CALLBACK is NULL, don't
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85 report an error. */
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86
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87 void *
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88 backtrace_alloc (struct backtrace_state *state,
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89 size_t size, backtrace_error_callback error_callback,
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90 void *data)
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91 {
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92 void *ret;
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93 int locked;
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94 struct backtrace_freelist_struct **pp;
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95 size_t pagesize;
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96 size_t asksize;
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97 void *page;
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98
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99 ret = NULL;
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100
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101 /* If we can acquire the lock, then see if there is space on the
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102 free list. If we can't acquire the lock, drop straight into
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103 using mmap. __sync_lock_test_and_set returns the old state of
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104 the lock, so we have acquired it if it returns 0. */
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105
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106 if (!state->threaded)
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107 locked = 1;
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108 else
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109 locked = __sync_lock_test_and_set (&state->lock_alloc, 1) == 0;
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110
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111 if (locked)
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112 {
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113 for (pp = &state->freelist; *pp != NULL; pp = &(*pp)->next)
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114 {
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115 if ((*pp)->size >= size)
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116 {
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117 struct backtrace_freelist_struct *p;
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118
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119 p = *pp;
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120 *pp = p->next;
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121
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122 /* Round for alignment; we assume that no type we care about
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123 is more than 8 bytes. */
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124 size = (size + 7) & ~ (size_t) 7;
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125 if (size < p->size)
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126 backtrace_free_locked (state, (char *) p + size,
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127 p->size - size);
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128
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129 ret = (void *) p;
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130
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131 break;
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132 }
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133 }
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134
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135 if (state->threaded)
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136 __sync_lock_release (&state->lock_alloc);
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137 }
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138
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139 if (ret == NULL)
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140 {
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141 /* Allocate a new page. */
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142
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143 pagesize = getpagesize ();
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144 asksize = (size + pagesize - 1) & ~ (pagesize - 1);
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145 page = mmap (NULL, asksize, PROT_READ | PROT_WRITE,
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146 MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
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147 if (page == MAP_FAILED)
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148 {
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149 if (error_callback)
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150 error_callback (data, "mmap", errno);
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151 }
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152 else
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153 {
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154 size = (size + 7) & ~ (size_t) 7;
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155 if (size < asksize)
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156 backtrace_free (state, (char *) page + size, asksize - size,
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157 error_callback, data);
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158
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159 ret = page;
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160 }
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161 }
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162
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163 return ret;
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164 }
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165
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166 /* Free memory allocated by backtrace_alloc. */
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167
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168 void
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169 backtrace_free (struct backtrace_state *state, void *addr, size_t size,
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170 backtrace_error_callback error_callback ATTRIBUTE_UNUSED,
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171 void *data ATTRIBUTE_UNUSED)
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172 {
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173 int locked;
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174
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175 /* If we are freeing a large aligned block, just release it back to
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176 the system. This case arises when growing a vector for a large
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177 binary with lots of debug info. Calling munmap here may cause us
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178 to call mmap again if there is also a large shared library; we
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179 just live with that. */
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180 if (size >= 16 * 4096)
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181 {
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182 size_t pagesize;
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183
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184 pagesize = getpagesize ();
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185 if (((uintptr_t) addr & (pagesize - 1)) == 0
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186 && (size & (pagesize - 1)) == 0)
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187 {
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188 /* If munmap fails for some reason, just add the block to
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189 the freelist. */
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190 if (munmap (addr, size) == 0)
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191 return;
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192 }
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193 }
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194
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195 /* If we can acquire the lock, add the new space to the free list.
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196 If we can't acquire the lock, just leak the memory.
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197 __sync_lock_test_and_set returns the old state of the lock, so we
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198 have acquired it if it returns 0. */
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199
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200 if (!state->threaded)
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201 locked = 1;
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202 else
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203 locked = __sync_lock_test_and_set (&state->lock_alloc, 1) == 0;
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204
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205 if (locked)
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206 {
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207 backtrace_free_locked (state, addr, size);
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208
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209 if (state->threaded)
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210 __sync_lock_release (&state->lock_alloc);
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211 }
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212 }
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213
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214 /* Grow VEC by SIZE bytes. */
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215
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216 void *
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217 backtrace_vector_grow (struct backtrace_state *state,size_t size,
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218 backtrace_error_callback error_callback,
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219 void *data, struct backtrace_vector *vec)
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220 {
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221 void *ret;
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222
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223 if (size > vec->alc)
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224 {
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225 size_t pagesize;
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226 size_t alc;
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227 void *base;
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228
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229 pagesize = getpagesize ();
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230 alc = vec->size + size;
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231 if (vec->size == 0)
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232 alc = 16 * size;
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233 else if (alc < pagesize)
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234 {
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235 alc *= 2;
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236 if (alc > pagesize)
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237 alc = pagesize;
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238 }
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239 else
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240 {
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241 alc *= 2;
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242 alc = (alc + pagesize - 1) & ~ (pagesize - 1);
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243 }
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244 base = backtrace_alloc (state, alc, error_callback, data);
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245 if (base == NULL)
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246 return NULL;
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247 if (vec->base != NULL)
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248 {
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249 memcpy (base, vec->base, vec->size);
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250 backtrace_free (state, vec->base, vec->size + vec->alc,
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251 error_callback, data);
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252 }
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253 vec->base = base;
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254 vec->alc = alc - vec->size;
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255 }
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256
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257 ret = (char *) vec->base + vec->size;
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258 vec->size += size;
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259 vec->alc -= size;
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260 return ret;
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261 }
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262
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263 /* Finish the current allocation on VEC. */
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264
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265 void *
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266 backtrace_vector_finish (
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267 struct backtrace_state *state ATTRIBUTE_UNUSED,
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268 struct backtrace_vector *vec,
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269 backtrace_error_callback error_callback ATTRIBUTE_UNUSED,
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270 void *data ATTRIBUTE_UNUSED)
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271 {
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272 void *ret;
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273
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274 ret = vec->base;
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275 vec->base = (char *) vec->base + vec->size;
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276 vec->size = 0;
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277 return ret;
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278 }
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279
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280 /* Release any extra space allocated for VEC. */
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281
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282 int
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283 backtrace_vector_release (struct backtrace_state *state,
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284 struct backtrace_vector *vec,
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285 backtrace_error_callback error_callback,
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286 void *data)
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287 {
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288 size_t size;
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289 size_t alc;
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290 size_t aligned;
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291
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292 /* Make sure that the block that we free is aligned on an 8-byte
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293 boundary. */
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294 size = vec->size;
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295 alc = vec->alc;
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296 aligned = (size + 7) & ~ (size_t) 7;
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297 alc -= aligned - size;
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298
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299 backtrace_free (state, (char *) vec->base + aligned, alc,
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300 error_callback, data);
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301 vec->alc = 0;
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302 return 1;
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303 }
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