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111
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1 /* mmap.c -- Memory allocation with mmap.
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145
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2 Copyright (C) 2012-2020 Free Software Foundation, Inc.
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111
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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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131
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72 /* Just leak small blocks. We don't have to be perfect. Don't put
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73 more than 16 entries on the free list, to avoid wasting time
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74 searching when allocating a block. If we have more than 16
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75 entries, leak the smallest entry. */
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76
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111
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77 if (size >= sizeof (struct backtrace_freelist_struct))
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78 {
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131
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79 size_t c;
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80 struct backtrace_freelist_struct **ppsmall;
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81 struct backtrace_freelist_struct **pp;
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82 struct backtrace_freelist_struct *p;
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83
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84 c = 0;
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85 ppsmall = NULL;
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86 for (pp = &state->freelist; *pp != NULL; pp = &(*pp)->next)
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87 {
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88 if (ppsmall == NULL || (*pp)->size < (*ppsmall)->size)
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89 ppsmall = pp;
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90 ++c;
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91 }
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92 if (c >= 16)
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93 {
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94 if (size <= (*ppsmall)->size)
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95 return;
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96 *ppsmall = (*ppsmall)->next;
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97 }
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98
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111
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99 p = (struct backtrace_freelist_struct *) addr;
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100 p->next = state->freelist;
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101 p->size = size;
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102 state->freelist = p;
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103 }
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104 }
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105
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106 /* Allocate memory like malloc. If ERROR_CALLBACK is NULL, don't
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107 report an error. */
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108
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109 void *
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110 backtrace_alloc (struct backtrace_state *state,
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111 size_t size, backtrace_error_callback error_callback,
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112 void *data)
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113 {
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114 void *ret;
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115 int locked;
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116 struct backtrace_freelist_struct **pp;
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117 size_t pagesize;
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118 size_t asksize;
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119 void *page;
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120
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121 ret = NULL;
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122
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123 /* If we can acquire the lock, then see if there is space on the
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124 free list. If we can't acquire the lock, drop straight into
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125 using mmap. __sync_lock_test_and_set returns the old state of
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126 the lock, so we have acquired it if it returns 0. */
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127
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128 if (!state->threaded)
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129 locked = 1;
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130 else
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131 locked = __sync_lock_test_and_set (&state->lock_alloc, 1) == 0;
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132
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133 if (locked)
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134 {
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135 for (pp = &state->freelist; *pp != NULL; pp = &(*pp)->next)
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136 {
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137 if ((*pp)->size >= size)
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138 {
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139 struct backtrace_freelist_struct *p;
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140
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141 p = *pp;
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142 *pp = p->next;
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143
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144 /* Round for alignment; we assume that no type we care about
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145 is more than 8 bytes. */
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146 size = (size + 7) & ~ (size_t) 7;
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147 if (size < p->size)
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148 backtrace_free_locked (state, (char *) p + size,
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149 p->size - size);
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150
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151 ret = (void *) p;
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152
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153 break;
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154 }
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155 }
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156
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157 if (state->threaded)
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158 __sync_lock_release (&state->lock_alloc);
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159 }
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160
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161 if (ret == NULL)
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162 {
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163 /* Allocate a new page. */
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164
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165 pagesize = getpagesize ();
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166 asksize = (size + pagesize - 1) & ~ (pagesize - 1);
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167 page = mmap (NULL, asksize, PROT_READ | PROT_WRITE,
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168 MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
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169 if (page == MAP_FAILED)
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170 {
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171 if (error_callback)
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172 error_callback (data, "mmap", errno);
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173 }
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174 else
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175 {
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176 size = (size + 7) & ~ (size_t) 7;
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177 if (size < asksize)
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178 backtrace_free (state, (char *) page + size, asksize - size,
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179 error_callback, data);
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180
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181 ret = page;
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182 }
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183 }
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184
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185 return ret;
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186 }
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187
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188 /* Free memory allocated by backtrace_alloc. */
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189
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190 void
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191 backtrace_free (struct backtrace_state *state, void *addr, size_t size,
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192 backtrace_error_callback error_callback ATTRIBUTE_UNUSED,
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193 void *data ATTRIBUTE_UNUSED)
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194 {
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195 int locked;
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196
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197 /* If we are freeing a large aligned block, just release it back to
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198 the system. This case arises when growing a vector for a large
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199 binary with lots of debug info. Calling munmap here may cause us
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200 to call mmap again if there is also a large shared library; we
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201 just live with that. */
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202 if (size >= 16 * 4096)
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203 {
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204 size_t pagesize;
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205
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206 pagesize = getpagesize ();
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207 if (((uintptr_t) addr & (pagesize - 1)) == 0
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208 && (size & (pagesize - 1)) == 0)
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209 {
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210 /* If munmap fails for some reason, just add the block to
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211 the freelist. */
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212 if (munmap (addr, size) == 0)
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213 return;
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214 }
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215 }
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216
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217 /* If we can acquire the lock, add the new space to the free list.
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218 If we can't acquire the lock, just leak the memory.
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219 __sync_lock_test_and_set returns the old state of the lock, so we
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220 have acquired it if it returns 0. */
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221
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222 if (!state->threaded)
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223 locked = 1;
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224 else
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225 locked = __sync_lock_test_and_set (&state->lock_alloc, 1) == 0;
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226
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227 if (locked)
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228 {
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229 backtrace_free_locked (state, addr, size);
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230
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231 if (state->threaded)
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232 __sync_lock_release (&state->lock_alloc);
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233 }
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234 }
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235
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236 /* Grow VEC by SIZE bytes. */
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237
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238 void *
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239 backtrace_vector_grow (struct backtrace_state *state,size_t size,
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240 backtrace_error_callback error_callback,
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241 void *data, struct backtrace_vector *vec)
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242 {
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243 void *ret;
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244
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245 if (size > vec->alc)
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246 {
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247 size_t pagesize;
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248 size_t alc;
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249 void *base;
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250
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251 pagesize = getpagesize ();
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252 alc = vec->size + size;
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253 if (vec->size == 0)
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254 alc = 16 * size;
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255 else if (alc < pagesize)
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256 {
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257 alc *= 2;
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258 if (alc > pagesize)
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259 alc = pagesize;
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260 }
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261 else
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262 {
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263 alc *= 2;
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264 alc = (alc + pagesize - 1) & ~ (pagesize - 1);
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265 }
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266 base = backtrace_alloc (state, alc, error_callback, data);
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267 if (base == NULL)
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268 return NULL;
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269 if (vec->base != NULL)
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270 {
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271 memcpy (base, vec->base, vec->size);
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272 backtrace_free (state, vec->base, vec->size + vec->alc,
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273 error_callback, data);
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274 }
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275 vec->base = base;
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276 vec->alc = alc - vec->size;
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277 }
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278
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279 ret = (char *) vec->base + vec->size;
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280 vec->size += size;
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281 vec->alc -= size;
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282 return ret;
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283 }
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284
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285 /* Finish the current allocation on VEC. */
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286
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287 void *
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288 backtrace_vector_finish (
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289 struct backtrace_state *state ATTRIBUTE_UNUSED,
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290 struct backtrace_vector *vec,
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291 backtrace_error_callback error_callback ATTRIBUTE_UNUSED,
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292 void *data ATTRIBUTE_UNUSED)
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293 {
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294 void *ret;
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295
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296 ret = vec->base;
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297 vec->base = (char *) vec->base + vec->size;
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298 vec->size = 0;
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299 return ret;
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300 }
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301
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302 /* Release any extra space allocated for VEC. */
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303
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304 int
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305 backtrace_vector_release (struct backtrace_state *state,
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306 struct backtrace_vector *vec,
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307 backtrace_error_callback error_callback,
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308 void *data)
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309 {
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310 size_t size;
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311 size_t alc;
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312 size_t aligned;
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313
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314 /* Make sure that the block that we free is aligned on an 8-byte
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315 boundary. */
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316 size = vec->size;
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317 alc = vec->alc;
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318 aligned = (size + 7) & ~ (size_t) 7;
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319 alc -= aligned - size;
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320
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321 backtrace_free (state, (char *) vec->base + aligned, alc,
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322 error_callback, data);
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323 vec->alc = 0;
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145
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324 if (vec->size == 0)
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325 vec->base = NULL;
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326 return 1;
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327 }
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