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4924
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1 /* Safe automatic memory allocation. |
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2 Copyright (C) 2003 Free Software Foundation, Inc. |
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3 Written by Bruno Haible <bruno@clisp.org>, 2003. |
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4 |
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5 This program is free software; you can redistribute it and/or modify |
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6 it under the terms of the GNU General Public License as published by |
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7 the Free Software Foundation; either version 2, or (at your option) |
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8 any later version. |
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9 |
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10 This program is distributed in the hope that it will be useful, |
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11 but WITHOUT ANY WARRANTY; without even the implied warranty of |
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12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
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13 GNU General Public License for more details. |
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14 |
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15 You should have received a copy of the GNU General Public License |
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16 along with this program; if not, write to the Free Software Foundation, |
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17 Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. */ |
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18 |
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19 #ifdef HAVE_CONFIG_H |
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20 # include <config.h> |
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21 #endif |
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22 |
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23 /* Specification. */ |
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24 #include "allocsa.h" |
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25 |
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26 /* The speed critical point in this file is freesa() applied to an alloca() |
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27 result: it must be fast, to match the speed of alloca(). The speed of |
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28 mallocsa() and freesa() in the other case are not critical, because they |
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29 are only invoked for big memory sizes. */ |
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30 |
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31 #if HAVE_ALLOCA |
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32 |
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33 /* Store the mallocsa() results in a hash table. This is needed to reliably |
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34 distinguish a mallocsa() result and an alloca() result. |
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35 |
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36 Although it is possible that the same pointer is returned by alloca() and |
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37 by mallocsa() at different times in the same application, it does not lead |
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38 to a bug in freesa(), because: |
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39 - Before a pointer returned by alloca() can point into malloc()ed memory, |
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40 the function must return, and once this has happened the programmer must |
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41 not call freesa() on it anyway. |
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42 - Before a pointer returned by mallocsa() can point into the stack, it |
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43 must be freed. The only function that can free it is freesa(), and |
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44 when freesa() frees it, it also removes it from the hash table. */ |
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45 |
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46 #define MAGIC_NUMBER 0x1415fb4a |
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47 #define MAGIC_SIZE sizeof (int) |
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48 /* This is how the header info would look like without any alignment |
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49 considerations. */ |
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50 struct preliminary_header { void *next; char room[MAGIC_SIZE]; }; |
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51 /* But the header's size must be a multiple of sa_alignment_max. */ |
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52 #define HEADER_SIZE \ |
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53 (((sizeof (struct preliminary_header) + sa_alignment_max - 1) / sa_alignment_max) * sa_alignment_max) |
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54 struct header { void *next; char room[HEADER_SIZE - sizeof (struct preliminary_header) + MAGIC_SIZE]; }; |
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55 /* Verify that HEADER_SIZE == sizeof (struct header). */ |
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56 typedef int verify1[2 * (HEADER_SIZE == sizeof (struct header)) - 1]; |
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57 /* We make the hash table quite big, so that during lookups the probability |
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58 of empty hash buckets is quite high. There is no need to make the hash |
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59 table resizable, because when the hash table gets filled so much that the |
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60 lookup becomes slow, it means that the application has memory leaks. */ |
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61 #define HASH_TABLE_SIZE 257 |
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62 static void * mallocsa_results[HASH_TABLE_SIZE]; |
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63 |
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64 #endif |
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65 |
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66 void * |
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67 mallocsa (size_t n) |
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68 { |
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69 #if HAVE_ALLOCA |
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70 /* Allocate one more word, that serves as an indicator for malloc()ed |
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71 memory, so that freesa() of an alloca() result is fast. */ |
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72 size_t nplus = n + HEADER_SIZE; |
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73 |
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74 if (nplus >= n) |
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75 { |
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76 char *p = (char *) malloc (nplus); |
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77 |
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78 if (p != NULL) |
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79 { |
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80 size_t slot; |
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81 |
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82 p += HEADER_SIZE; |
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83 |
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84 /* Put a magic number into the indicator word. */ |
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85 ((int *) p)[-1] = MAGIC_NUMBER; |
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86 |
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87 /* Enter p into the hash table. */ |
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88 slot = (unsigned long) p % HASH_TABLE_SIZE; |
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89 ((struct header *) (p - HEADER_SIZE))->next = mallocsa_results[slot]; |
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90 mallocsa_results[slot] = p; |
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91 |
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92 return p; |
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93 } |
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94 } |
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95 /* Out of memory. */ |
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96 return NULL; |
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97 #else |
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98 # if !MALLOC_0_IS_NONNULL |
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99 if (n == 0) |
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100 n = 1; |
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101 # endif |
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102 return malloc (n); |
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103 #endif |
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104 } |
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105 |
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106 #if HAVE_ALLOCA |
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107 void |
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108 freesa (void *p) |
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109 { |
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110 /* mallocsa() may have returned NULL. */ |
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111 if (p != NULL) |
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112 { |
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113 /* Attempt to quickly distinguish the mallocsa() result - which has |
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114 a magic indicator word - and the alloca() result - which has an |
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115 uninitialized indicator word. It is for this test that sa_increment |
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116 additional bytes are allocated in the alloca() case. */ |
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117 if (((int *) p)[-1] == MAGIC_NUMBER) |
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118 { |
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119 /* Looks like a mallocsa() result. To see whether it really is one, |
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120 perform a lookup in the hash table. */ |
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121 size_t slot = (unsigned long) p % HASH_TABLE_SIZE; |
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122 void **chain = &mallocsa_results[slot]; |
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123 for (; *chain != NULL;) |
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124 { |
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125 if (*chain == p) |
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126 { |
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127 /* Found it. Remove it from the hash table and free it. */ |
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128 char *p_begin = (char *) p - HEADER_SIZE; |
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129 *chain = ((struct header *) p_begin)->next; |
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130 free (p_begin); |
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131 return; |
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132 } |
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133 chain = &((struct header *) ((char *) *chain - HEADER_SIZE))->next; |
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134 } |
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135 } |
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136 /* At this point, we know it was not a mallocsa() result. */ |
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137 } |
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138 } |
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139 #endif |
