1 | /* alloca.c -- allocate automatically reclaimed memory |
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2 | (Mostly) portable public-domain implementation -- D A Gwyn |
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3 | |
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4 | This implementation of the PWB library alloca function, |
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5 | which is used to allocate space off the run-time stack so |
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6 | that it is automatically reclaimed upon procedure exit, |
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7 | was inspired by discussions with J. Q. Johnson of Cornell. |
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8 | J.Otto Tennant <jot@cray.com> contributed the Cray support. |
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9 | |
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10 | There are some preprocessor constants that can |
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11 | be defined when compiling for your specific system, for |
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12 | improved efficiency; however, the defaults should be okay. |
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13 | |
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14 | The general concept of this implementation is to keep |
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15 | track of all alloca-allocated blocks, and reclaim any |
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16 | that are found to be deeper in the stack than the current |
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17 | invocation. This heuristic does not reclaim storage as |
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18 | soon as it becomes invalid, but it will do so eventually. |
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19 | |
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20 | As a special case, alloca(0) reclaims storage without |
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21 | allocating any. It is a good idea to use alloca(0) in |
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22 | your main control loop, etc. to force garbage collection. */ |
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23 | |
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24 | #ifdef HAVE_CONFIG_H |
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25 | #include <config.h> |
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26 | #endif |
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27 | |
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28 | #ifdef emacs |
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29 | #include "blockinput.h" |
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30 | #endif |
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31 | |
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32 | /* If compiling with GCC 2, this file's not needed. */ |
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33 | #if !defined (__GNUC__) || __GNUC__ < 2 |
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34 | |
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35 | /* If someone has defined alloca as a macro, |
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36 | there must be some other way alloca is supposed to work. */ |
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37 | #ifndef alloca |
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38 | |
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39 | #ifdef emacs |
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40 | #ifdef static |
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41 | /* actually, only want this if static is defined as "" |
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42 | -- this is for usg, in which emacs must undefine static |
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43 | in order to make unexec workable |
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44 | */ |
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45 | #ifndef STACK_DIRECTION |
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46 | you |
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47 | lose |
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48 | -- must know STACK_DIRECTION at compile-time |
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49 | #endif /* STACK_DIRECTION undefined */ |
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50 | #endif /* static */ |
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51 | #endif /* emacs */ |
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52 | |
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53 | /* If your stack is a linked list of frames, you have to |
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54 | provide an "address metric" ADDRESS_FUNCTION macro. */ |
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55 | |
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56 | #if defined (CRAY) && defined (CRAY_STACKSEG_END) |
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57 | long i00afunc (); |
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58 | #define ADDRESS_FUNCTION(arg) (char *) i00afunc (&(arg)) |
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59 | #else |
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60 | #define ADDRESS_FUNCTION(arg) &(arg) |
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61 | #endif |
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62 | |
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63 | #if __STDC__ |
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64 | typedef void *pointer; |
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65 | #else |
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66 | typedef char *pointer; |
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67 | #endif |
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68 | |
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69 | #define NULL 0 |
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70 | |
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71 | /* Different portions of Emacs need to call different versions of |
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72 | malloc. The Emacs executable needs alloca to call xmalloc, because |
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73 | ordinary malloc isn't protected from input signals. On the other |
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74 | hand, the utilities in lib-src need alloca to call malloc; some of |
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75 | them are very simple, and don't have an xmalloc routine. |
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76 | |
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77 | Non-Emacs programs expect this to call use xmalloc. |
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78 | |
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79 | Callers below should use malloc. */ |
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80 | |
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81 | #ifndef emacs |
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82 | #define malloc xmalloc |
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83 | #endif |
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84 | extern pointer malloc (); |
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85 | |
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86 | /* Define STACK_DIRECTION if you know the direction of stack |
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87 | growth for your system; otherwise it will be automatically |
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88 | deduced at run-time. |
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89 | |
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90 | STACK_DIRECTION > 0 => grows toward higher addresses |
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91 | STACK_DIRECTION < 0 => grows toward lower addresses |
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92 | STACK_DIRECTION = 0 => direction of growth unknown */ |
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93 | |
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94 | #ifndef STACK_DIRECTION |
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95 | #define STACK_DIRECTION 0 /* Direction unknown. */ |
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96 | #endif |
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97 | |
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98 | #if STACK_DIRECTION != 0 |
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99 | |
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100 | #define STACK_DIR STACK_DIRECTION /* Known at compile-time. */ |
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101 | |
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102 | #else /* STACK_DIRECTION == 0; need run-time code. */ |
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103 | |
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104 | static int stack_dir; /* 1 or -1 once known. */ |
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105 | #define STACK_DIR stack_dir |
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106 | |
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107 | static void |
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108 | find_stack_direction () |
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109 | { |
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110 | static char *addr = NULL; /* Address of first `dummy', once known. */ |
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111 | auto char dummy; /* To get stack address. */ |
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112 | |
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113 | if (addr == NULL) |
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114 | { /* Initial entry. */ |
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115 | addr = ADDRESS_FUNCTION (dummy); |
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116 | |
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117 | find_stack_direction (); /* Recurse once. */ |
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118 | } |
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119 | else |
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120 | { |
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121 | /* Second entry. */ |
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122 | if (ADDRESS_FUNCTION (dummy) > addr) |
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123 | stack_dir = 1; /* Stack grew upward. */ |
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124 | else |
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125 | stack_dir = -1; /* Stack grew downward. */ |
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126 | } |
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127 | } |
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128 | |
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129 | #endif /* STACK_DIRECTION == 0 */ |
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130 | |
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131 | /* An "alloca header" is used to: |
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132 | (a) chain together all alloca'ed blocks; |
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133 | (b) keep track of stack depth. |
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134 | |
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135 | It is very important that sizeof(header) agree with malloc |
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136 | alignment chunk size. The following default should work okay. */ |
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137 | |
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138 | #ifndef ALIGN_SIZE |
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139 | #define ALIGN_SIZE sizeof(double) |
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140 | #endif |
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141 | |
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142 | typedef union hdr |
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143 | { |
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144 | char align[ALIGN_SIZE]; /* To force sizeof(header). */ |
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145 | struct |
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146 | { |
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147 | union hdr *next; /* For chaining headers. */ |
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148 | char *deep; /* For stack depth measure. */ |
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149 | } h; |
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150 | } header; |
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151 | |
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152 | static header *last_alloca_header = NULL; /* -> last alloca header. */ |
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153 | |
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154 | /* Return a pointer to at least SIZE bytes of storage, |
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155 | which will be automatically reclaimed upon exit from |
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156 | the procedure that called alloca. Originally, this space |
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157 | was supposed to be taken from the current stack frame of the |
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158 | caller, but that method cannot be made to work for some |
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159 | implementations of C, for example under Gould's UTX/32. */ |
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160 | |
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161 | pointer |
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162 | alloca (size) |
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163 | unsigned size; |
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164 | { |
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165 | auto char probe; /* Probes stack depth: */ |
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166 | register char *depth = ADDRESS_FUNCTION (probe); |
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167 | |
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168 | #if STACK_DIRECTION == 0 |
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169 | if (STACK_DIR == 0) /* Unknown growth direction. */ |
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170 | find_stack_direction (); |
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171 | #endif |
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172 | |
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173 | /* Reclaim garbage, defined as all alloca'd storage that |
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174 | was allocated from deeper in the stack than currently. */ |
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175 | |
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176 | { |
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177 | register header *hp; /* Traverses linked list. */ |
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178 | |
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179 | #ifdef emacs |
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180 | BLOCK_INPUT; |
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181 | #endif |
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182 | |
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183 | for (hp = last_alloca_header; hp != NULL;) |
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184 | if ((STACK_DIR > 0 && hp->h.deep > depth) |
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185 | || (STACK_DIR < 0 && hp->h.deep < depth)) |
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186 | { |
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187 | register header *np = hp->h.next; |
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188 | |
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189 | free ((pointer) hp); /* Collect garbage. */ |
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190 | |
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191 | hp = np; /* -> next header. */ |
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192 | } |
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193 | else |
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194 | break; /* Rest are not deeper. */ |
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195 | |
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196 | last_alloca_header = hp; /* -> last valid storage. */ |
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197 | |
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198 | #ifdef emacs |
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199 | UNBLOCK_INPUT; |
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200 | #endif |
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201 | } |
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202 | |
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203 | if (size == 0) |
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204 | return NULL; /* No allocation required. */ |
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205 | |
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206 | /* Allocate combined header + user data storage. */ |
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207 | |
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208 | { |
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209 | register pointer new = malloc (sizeof (header) + size); |
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210 | /* Address of header. */ |
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211 | |
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212 | ((header *) new)->h.next = last_alloca_header; |
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213 | ((header *) new)->h.deep = depth; |
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214 | |
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215 | last_alloca_header = (header *) new; |
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216 | |
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217 | /* User storage begins just after header. */ |
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218 | |
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219 | return (pointer) ((char *) new + sizeof (header)); |
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220 | } |
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221 | } |
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222 | |
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223 | #if defined (CRAY) && defined (CRAY_STACKSEG_END) |
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224 | |
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225 | #ifdef DEBUG_I00AFUNC |
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226 | #include <stdio.h> |
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227 | #endif |
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228 | |
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229 | #ifndef CRAY_STACK |
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230 | #define CRAY_STACK |
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231 | #ifndef CRAY2 |
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232 | /* Stack structures for CRAY-1, CRAY X-MP, and CRAY Y-MP */ |
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233 | struct stack_control_header |
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234 | { |
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235 | long shgrow:32; /* Number of times stack has grown. */ |
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236 | long shaseg:32; /* Size of increments to stack. */ |
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237 | long shhwm:32; /* High water mark of stack. */ |
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238 | long shsize:32; /* Current size of stack (all segments). */ |
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239 | }; |
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240 | |
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241 | /* The stack segment linkage control information occurs at |
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242 | the high-address end of a stack segment. (The stack |
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243 | grows from low addresses to high addresses.) The initial |
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244 | part of the stack segment linkage control information is |
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245 | 0200 (octal) words. This provides for register storage |
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246 | for the routine which overflows the stack. */ |
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247 | |
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248 | struct stack_segment_linkage |
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249 | { |
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250 | long ss[0200]; /* 0200 overflow words. */ |
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251 | long sssize:32; /* Number of words in this segment. */ |
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252 | long ssbase:32; /* Offset to stack base. */ |
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253 | long:32; |
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254 | long sspseg:32; /* Offset to linkage control of previous |
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255 | segment of stack. */ |
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256 | long:32; |
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257 | long sstcpt:32; /* Pointer to task common address block. */ |
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258 | long sscsnm; /* Private control structure number for |
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259 | microtasking. */ |
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260 | long ssusr1; /* Reserved for user. */ |
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261 | long ssusr2; /* Reserved for user. */ |
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262 | long sstpid; /* Process ID for pid based multi-tasking. */ |
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263 | long ssgvup; /* Pointer to multitasking thread giveup. */ |
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264 | long sscray[7]; /* Reserved for Cray Research. */ |
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265 | long ssa0; |
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266 | long ssa1; |
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267 | long ssa2; |
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268 | long ssa3; |
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269 | long ssa4; |
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270 | long ssa5; |
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271 | long ssa6; |
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272 | long ssa7; |
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273 | long sss0; |
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274 | long sss1; |
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275 | long sss2; |
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276 | long sss3; |
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277 | long sss4; |
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278 | long sss5; |
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279 | long sss6; |
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280 | long sss7; |
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281 | }; |
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282 | |
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283 | #else /* CRAY2 */ |
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284 | /* The following structure defines the vector of words |
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285 | returned by the STKSTAT library routine. */ |
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286 | struct stk_stat |
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287 | { |
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288 | long now; /* Current total stack size. */ |
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289 | long maxc; /* Amount of contiguous space which would |
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290 | be required to satisfy the maximum |
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291 | stack demand to date. */ |
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292 | long high_water; /* Stack high-water mark. */ |
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293 | long overflows; /* Number of stack overflow ($STKOFEN) calls. */ |
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294 | long hits; /* Number of internal buffer hits. */ |
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295 | long extends; /* Number of block extensions. */ |
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296 | long stko_mallocs; /* Block allocations by $STKOFEN. */ |
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297 | long underflows; /* Number of stack underflow calls ($STKRETN). */ |
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298 | long stko_free; /* Number of deallocations by $STKRETN. */ |
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299 | long stkm_free; /* Number of deallocations by $STKMRET. */ |
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300 | long segments; /* Current number of stack segments. */ |
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301 | long maxs; /* Maximum number of stack segments so far. */ |
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302 | long pad_size; /* Stack pad size. */ |
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303 | long current_address; /* Current stack segment address. */ |
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304 | long current_size; /* Current stack segment size. This |
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305 | number is actually corrupted by STKSTAT to |
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306 | include the fifteen word trailer area. */ |
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307 | long initial_address; /* Address of initial segment. */ |
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308 | long initial_size; /* Size of initial segment. */ |
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309 | }; |
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310 | |
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311 | /* The following structure describes the data structure which trails |
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312 | any stack segment. I think that the description in 'asdef' is |
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313 | out of date. I only describe the parts that I am sure about. */ |
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314 | |
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315 | struct stk_trailer |
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316 | { |
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317 | long this_address; /* Address of this block. */ |
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318 | long this_size; /* Size of this block (does not include |
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319 | this trailer). */ |
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320 | long unknown2; |
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321 | long unknown3; |
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322 | long link; /* Address of trailer block of previous |
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323 | segment. */ |
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324 | long unknown5; |
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325 | long unknown6; |
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326 | long unknown7; |
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327 | long unknown8; |
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328 | long unknown9; |
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329 | long unknown10; |
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330 | long unknown11; |
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331 | long unknown12; |
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332 | long unknown13; |
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333 | long unknown14; |
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334 | }; |
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335 | |
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336 | #endif /* CRAY2 */ |
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337 | #endif /* not CRAY_STACK */ |
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338 | |
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339 | #ifdef CRAY2 |
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340 | /* Determine a "stack measure" for an arbitrary ADDRESS. |
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341 | I doubt that "lint" will like this much. */ |
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342 | |
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343 | static long |
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344 | i00afunc (long *address) |
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345 | { |
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346 | struct stk_stat status; |
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347 | struct stk_trailer *trailer; |
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348 | long *block, size; |
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349 | long result = 0; |
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350 | |
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351 | /* We want to iterate through all of the segments. The first |
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352 | step is to get the stack status structure. We could do this |
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353 | more quickly and more directly, perhaps, by referencing the |
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354 | $LM00 common block, but I know that this works. */ |
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355 | |
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356 | STKSTAT (&status); |
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357 | |
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358 | /* Set up the iteration. */ |
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359 | |
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360 | trailer = (struct stk_trailer *) (status.current_address |
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361 | + status.current_size |
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362 | - 15); |
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363 | |
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364 | /* There must be at least one stack segment. Therefore it is |
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365 | a fatal error if "trailer" is null. */ |
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366 | |
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367 | if (trailer == 0) |
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368 | abort (); |
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369 | |
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370 | /* Discard segments that do not contain our argument address. */ |
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371 | |
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372 | while (trailer != 0) |
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373 | { |
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374 | block = (long *) trailer->this_address; |
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375 | size = trailer->this_size; |
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376 | if (block == 0 || size == 0) |
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377 | abort (); |
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378 | trailer = (struct stk_trailer *) trailer->link; |
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379 | if ((block <= address) && (address < (block + size))) |
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380 | break; |
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381 | } |
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382 | |
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383 | /* Set the result to the offset in this segment and add the sizes |
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384 | of all predecessor segments. */ |
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385 | |
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386 | result = address - block; |
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387 | |
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388 | if (trailer == 0) |
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389 | { |
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390 | return result; |
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391 | } |
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392 | |
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393 | do |
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394 | { |
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395 | if (trailer->this_size <= 0) |
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396 | abort (); |
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397 | result += trailer->this_size; |
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398 | trailer = (struct stk_trailer *) trailer->link; |
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399 | } |
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400 | while (trailer != 0); |
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401 | |
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402 | /* We are done. Note that if you present a bogus address (one |
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403 | not in any segment), you will get a different number back, formed |
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404 | from subtracting the address of the first block. This is probably |
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405 | not what you want. */ |
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406 | |
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407 | return (result); |
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408 | } |
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409 | |
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410 | #else /* not CRAY2 */ |
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411 | /* Stack address function for a CRAY-1, CRAY X-MP, or CRAY Y-MP. |
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412 | Determine the number of the cell within the stack, |
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413 | given the address of the cell. The purpose of this |
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414 | routine is to linearize, in some sense, stack addresses |
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415 | for alloca. */ |
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416 | |
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417 | static long |
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418 | i00afunc (long address) |
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419 | { |
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420 | long stkl = 0; |
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421 | |
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422 | long size, pseg, this_segment, stack; |
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423 | long result = 0; |
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424 | |
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425 | struct stack_segment_linkage *ssptr; |
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426 | |
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427 | /* Register B67 contains the address of the end of the |
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428 | current stack segment. If you (as a subprogram) store |
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429 | your registers on the stack and find that you are past |
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430 | the contents of B67, you have overflowed the segment. |
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431 | |
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432 | B67 also points to the stack segment linkage control |
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433 | area, which is what we are really interested in. */ |
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434 | |
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435 | stkl = CRAY_STACKSEG_END (); |
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436 | ssptr = (struct stack_segment_linkage *) stkl; |
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437 | |
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438 | /* If one subtracts 'size' from the end of the segment, |
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439 | one has the address of the first word of the segment. |
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440 | |
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441 | If this is not the first segment, 'pseg' will be |
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442 | nonzero. */ |
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443 | |
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444 | pseg = ssptr->sspseg; |
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445 | size = ssptr->sssize; |
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446 | |
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447 | this_segment = stkl - size; |
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448 | |
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449 | /* It is possible that calling this routine itself caused |
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450 | a stack overflow. Discard stack segments which do not |
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451 | contain the target address. */ |
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452 | |
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453 | while (!(this_segment <= address && address <= stkl)) |
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454 | { |
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455 | #ifdef DEBUG_I00AFUNC |
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456 | fprintf (stderr, "%011o %011o %011o\n", this_segment, address, stkl); |
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457 | #endif |
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458 | if (pseg == 0) |
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459 | break; |
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460 | stkl = stkl - pseg; |
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461 | ssptr = (struct stack_segment_linkage *) stkl; |
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462 | size = ssptr->sssize; |
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463 | pseg = ssptr->sspseg; |
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464 | this_segment = stkl - size; |
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465 | } |
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466 | |
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467 | result = address - this_segment; |
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468 | |
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469 | /* If you subtract pseg from the current end of the stack, |
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470 | you get the address of the previous stack segment's end. |
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471 | This seems a little convoluted to me, but I'll bet you save |
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472 | a cycle somewhere. */ |
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473 | |
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474 | while (pseg != 0) |
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475 | { |
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476 | #ifdef DEBUG_I00AFUNC |
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477 | fprintf (stderr, "%011o %011o\n", pseg, size); |
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478 | #endif |
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479 | stkl = stkl - pseg; |
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480 | ssptr = (struct stack_segment_linkage *) stkl; |
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481 | size = ssptr->sssize; |
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482 | pseg = ssptr->sspseg; |
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483 | result += size; |
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484 | } |
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485 | return (result); |
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486 | } |
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487 | |
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488 | #endif /* not CRAY2 */ |
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489 | #endif /* CRAY */ |
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490 | |
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491 | #endif /* no alloca */ |
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492 | #endif /* not GCC version 2 */ |
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