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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 /* Synched up with: FSF 19.30. */
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25
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26 /* Authorsip:
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27
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28 FSF: A long time ago.
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29 Very few changes for XEmacs.
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30 */
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31
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32 #ifdef HAVE_CONFIG_H
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33 #include <config.h>
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34 #endif
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35
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36 /* XEmacs: If compiling with GCC 2, this file is theoretically not needed.
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37 However, alloca() is broken under GCC 2 on many machines: you
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38 cannot put a call to alloca() as part of an argument to a function.
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39 */
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40 /* If someone has defined alloca as a macro,
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41 there must be some other way alloca is supposed to work. */
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42 /* XEmacs sometimes uses the C alloca even when a builtin alloca is available,
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43 because it's safer. */
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44 #if defined (EMACS_WANTS_C_ALLOCA) || (!defined (alloca) && (!defined (__GNUC__) || __GNUC__ < 2))
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45
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46 #ifdef emacs
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47 #ifdef static
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48 /* actually, only want this if static is defined as ""
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49 -- this is for usg, in which emacs must undefine static
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50 in order to make unexec workable
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51 */
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52 #ifndef STACK_DIRECTION
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53 you
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54 lose
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55 -- must know STACK_DIRECTION at compile-time
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56 #endif /* STACK_DIRECTION undefined */
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57 #endif /* static */
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58 #endif /* emacs */
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59
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60 /* If your stack is a linked list of frames, you have to
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61 provide an "address metric" ADDRESS_FUNCTION macro. */
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62
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63 #if defined (CRAY) && defined (CRAY_STACKSEG_END)
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64 long i00afunc ();
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65 #define ADDRESS_FUNCTION(arg) (char *) i00afunc (&(arg))
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66 #else
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67 #define ADDRESS_FUNCTION(arg) &(arg)
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68 #endif
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69
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70 #ifdef __STDC__ /* XEmacs change */
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71 typedef void *pointer;
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72 #else
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73 typedef char *pointer;
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74 #endif
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75
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76 /* XEmacs: With ERROR_CHECK_MALLOC defined, there is no xfree -- it's
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77 a macro that does some stuff to try and trap invalid frees,
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78 and then calls xfree_1 to actually do the work. */
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79
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80 #ifdef emacs
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81 # ifdef ERROR_CHECK_MALLOC
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82 void xfree_1 (pointer);
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83 # define xfree xfree_1
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84 # else
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85 void xfree (pointer);
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86 # endif
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87 #endif
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88
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89 #define NULL 0
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90
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91 /* Different portions of Emacs need to call different versions of
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92 malloc. The Emacs executable needs alloca to call xmalloc, because
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93 ordinary malloc isn't protected from input signals. On the other
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94 hand, the utilities in lib-src need alloca to call malloc; some of
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95 them are very simple, and don't have an xmalloc routine.
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96
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97 Non-Emacs programs expect this to call use xmalloc.
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98
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99 Callers below should use malloc. */
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100
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101 #ifndef emacs
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102 #define malloc xmalloc
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103 #endif
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104 extern pointer malloc ();
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105
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106 /* Define STACK_DIRECTION if you know the direction of stack
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107 growth for your system; otherwise it will be automatically
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108 deduced at run-time.
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109
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110 STACK_DIRECTION > 0 => grows toward higher addresses
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111 STACK_DIRECTION < 0 => grows toward lower addresses
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112 STACK_DIRECTION = 0 => direction of growth unknown */
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113
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114 #ifndef STACK_DIRECTION
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115 #define STACK_DIRECTION 0 /* Direction unknown. */
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116 #endif
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117
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118 #if STACK_DIRECTION != 0
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119
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120 #define STACK_DIR STACK_DIRECTION /* Known at compile-time. */
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121
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122 #else /* STACK_DIRECTION == 0; need run-time code. */
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123
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124 static int stack_dir; /* 1 or -1 once known. */
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125 #define STACK_DIR stack_dir
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126
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127 static void
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128 find_stack_direction ()
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129 {
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130 static char *addr = NULL; /* Address of first `dummy', once known. */
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131 auto char dummy; /* To get stack address. */
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132
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133 if (addr == NULL)
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134 { /* Initial entry. */
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135 addr = ADDRESS_FUNCTION (dummy);
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136
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137 find_stack_direction (); /* Recurse once. */
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138 }
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139 else
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140 {
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141 /* Second entry. */
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142 if (ADDRESS_FUNCTION (dummy) > addr)
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143 stack_dir = 1; /* Stack grew upward. */
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144 else
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145 stack_dir = -1; /* Stack grew downward. */
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146 }
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147 }
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148
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149 #endif /* STACK_DIRECTION == 0 */
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150
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151 /* An "alloca header" is used to:
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152 (a) chain together all alloca'ed blocks;
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153 (b) keep track of stack depth.
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154
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155 It is very important that sizeof(header) agree with malloc
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156 alignment chunk size. The following default should work okay. */
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157
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158 #ifndef ALIGN_SIZE
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159 #define ALIGN_SIZE sizeof(double)
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160 #endif
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161
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162 typedef union hdr
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163 {
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164 char align[ALIGN_SIZE]; /* To force sizeof(header). */
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165 struct
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166 {
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167 union hdr *next; /* For chaining headers. */
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168 char *deep; /* For stack depth measure. */
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169 } h;
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170 } header;
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171
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172 static header *last_alloca_header = NULL; /* -> last alloca header. */
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173
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174 /* Return a pointer to at least SIZE bytes of storage,
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175 which will be automatically reclaimed upon exit from
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176 the procedure that called alloca. Originally, this space
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177 was supposed to be taken from the current stack frame of the
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178 caller, but that method cannot be made to work for some
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179 implementations of C, for example under Gould's UTX/32. */
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180
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181 pointer
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182 #ifdef EMACS_WANTS_C_ALLOCA
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183 c_alloca (size)
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184 #else
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185 alloca (size)
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186 #endif
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187 unsigned size;
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188 {
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189 auto char probe; /* Probes stack depth: */
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190 register char *depth = ADDRESS_FUNCTION (probe);
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191
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192 #if STACK_DIRECTION == 0
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193 if (STACK_DIR == 0) /* Unknown growth direction. */
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194 find_stack_direction ();
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195 #endif
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196
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197 /* Reclaim garbage, defined as all alloca'd storage that
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198 was allocated from deeper in the stack than currently. */
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199
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200 {
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201 register header *hp; /* Traverses linked list. */
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202
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203 for (hp = last_alloca_header; hp != NULL;)
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204 if ((STACK_DIR > 0 && hp->h.deep > depth)
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205 || (STACK_DIR < 0 && hp->h.deep < depth))
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206 {
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207 register header *np = hp->h.next;
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208
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209 free ((pointer) hp); /* Collect garbage. */
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210
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211 hp = np; /* -> next header. */
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212 }
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213 else
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214 break; /* Rest are not deeper. */
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215
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216 last_alloca_header = hp; /* -> last valid storage. */
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217 }
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218
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219 if (size == 0)
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220 return NULL; /* No allocation required. */
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221
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222 /* Allocate combined header + user data storage. */
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223
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224 {
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225 register pointer new = malloc (sizeof (header) + size);
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226 /* Address of header. */
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227
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228 ((header *) new)->h.next = last_alloca_header;
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229 ((header *) new)->h.deep = depth;
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230
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231 last_alloca_header = (header *) new;
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232
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233 /* User storage begins just after header. */
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234
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235 return (pointer) ((char *) new + sizeof (header));
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236 }
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237 }
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238
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239 #if defined (CRAY) && defined (CRAY_STACKSEG_END)
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240
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241 #ifdef DEBUG_I00AFUNC
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242 #include <stdio.h>
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243 #endif
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244
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245 #ifndef CRAY_STACK
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246 #define CRAY_STACK
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247 #ifndef CRAY2
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248 /* Stack structures for CRAY-1, CRAY X-MP, and CRAY Y-MP */
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249 struct stack_control_header
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250 {
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251 long shgrow:32; /* Number of times stack has grown. */
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252 long shaseg:32; /* Size of increments to stack. */
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253 long shhwm:32; /* High water mark of stack. */
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254 long shsize:32; /* Current size of stack (all segments). */
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255 };
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256
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257 /* The stack segment linkage control information occurs at
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258 the high-address end of a stack segment. (The stack
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259 grows from low addresses to high addresses.) The initial
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260 part of the stack segment linkage control information is
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261 0200 (octal) words. This provides for register storage
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262 for the routine which overflows the stack. */
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263
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264 struct stack_segment_linkage
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265 {
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266 long ss[0200]; /* 0200 overflow words. */
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267 long sssize:32; /* Number of words in this segment. */
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268 long ssbase:32; /* Offset to stack base. */
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269 long:32;
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270 long sspseg:32; /* Offset to linkage control of previous
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271 segment of stack. */
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272 long:32;
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273 long sstcpt:32; /* Pointer to task common address block. */
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274 long sscsnm; /* Private control structure number for
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275 microtasking. */
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276 long ssusr1; /* Reserved for user. */
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277 long ssusr2; /* Reserved for user. */
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278 long sstpid; /* Process ID for pid based multi-tasking. */
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279 long ssgvup; /* Pointer to multitasking thread giveup. */
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280 long sscray[7]; /* Reserved for Cray Research. */
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281 long ssa0;
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282 long ssa1;
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283 long ssa2;
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284 long ssa3;
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285 long ssa4;
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286 long ssa5;
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287 long ssa6;
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288 long ssa7;
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289 long sss0;
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290 long sss1;
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291 long sss2;
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292 long sss3;
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293 long sss4;
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294 long sss5;
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295 long sss6;
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296 long sss7;
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297 };
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298
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299 #else /* CRAY2 */
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300 /* The following structure defines the vector of words
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301 returned by the STKSTAT library routine. */
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302 struct stk_stat
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303 {
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304 long now; /* Current total stack size. */
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305 long maxc; /* Amount of contiguous space which would
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306 be required to satisfy the maximum
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307 stack demand to date. */
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308 long high_water; /* Stack high-water mark. */
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309 long overflows; /* Number of stack overflow ($STKOFEN) calls. */
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310 long hits; /* Number of internal buffer hits. */
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311 long extends; /* Number of block extensions. */
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312 long stko_mallocs; /* Block allocations by $STKOFEN. */
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313 long underflows; /* Number of stack underflow calls ($STKRETN). */
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314 long stko_free; /* Number of deallocations by $STKRETN. */
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315 long stkm_free; /* Number of deallocations by $STKMRET. */
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316 long segments; /* Current number of stack segments. */
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317 long maxs; /* Maximum number of stack segments so far. */
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318 long pad_size; /* Stack pad size. */
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319 long current_address; /* Current stack segment address. */
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320 long current_size; /* Current stack segment size. This
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321 number is actually corrupted by STKSTAT to
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322 include the fifteen word trailer area. */
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323 long initial_address; /* Address of initial segment. */
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324 long initial_size; /* Size of initial segment. */
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325 };
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326
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327 /* The following structure describes the data structure which trails
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328 any stack segment. I think that the description in 'asdef' is
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329 out of date. I only describe the parts that I am sure about. */
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330
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331 struct stk_trailer
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332 {
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333 long this_address; /* Address of this block. */
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334 long this_size; /* Size of this block (does not include
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335 this trailer). */
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336 long unknown2;
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337 long unknown3;
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338 long link; /* Address of trailer block of previous
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339 segment. */
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340 long unknown5;
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341 long unknown6;
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342 long unknown7;
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343 long unknown8;
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344 long unknown9;
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345 long unknown10;
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346 long unknown11;
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347 long unknown12;
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348 long unknown13;
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349 long unknown14;
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350 };
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351
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352 #endif /* CRAY2 */
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353 #endif /* not CRAY_STACK */
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354
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355 #ifdef CRAY2
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356 /* Determine a "stack measure" for an arbitrary ADDRESS.
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357 I doubt that "lint" will like this much. */
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358
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359 static long
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360 i00afunc (long *address)
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361 {
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362 struct stk_stat status;
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363 struct stk_trailer *trailer;
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364 long *block, size;
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365 long result = 0;
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366
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367 /* We want to iterate through all of the segments. The first
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368 step is to get the stack status structure. We could do this
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369 more quickly and more directly, perhaps, by referencing the
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370 $LM00 common block, but I know that this works. */
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371
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372 STKSTAT (&status);
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373
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374 /* Set up the iteration. */
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375
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376 trailer = (struct stk_trailer *) (status.current_address
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377 + status.current_size
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378 - 15);
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379
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380 /* There must be at least one stack segment. Therefore it is
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381 a fatal error if "trailer" is null. */
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382
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383 if (trailer == 0)
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384 abort ();
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385
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386 /* Discard segments that do not contain our argument address. */
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387
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388 while (trailer != 0)
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389 {
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390 block = (long *) trailer->this_address;
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391 size = trailer->this_size;
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392 if (block == 0 || size == 0)
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393 abort ();
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394 trailer = (struct stk_trailer *) trailer->link;
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395 if ((block <= address) && (address < (block + size)))
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396 break;
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397 }
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398
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399 /* Set the result to the offset in this segment and add the sizes
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400 of all predecessor segments. */
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401
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402 result = address - block;
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403
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404 if (trailer == 0)
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405 {
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406 return result;
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407 }
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408
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409 do
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410 {
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411 if (trailer->this_size <= 0)
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412 abort ();
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413 result += trailer->this_size;
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414 trailer = (struct stk_trailer *) trailer->link;
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415 }
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416 while (trailer != 0);
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417
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418 /* We are done. Note that if you present a bogus address (one
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419 not in any segment), you will get a different number back, formed
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420 from subtracting the address of the first block. This is probably
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421 not what you want. */
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422
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423 return (result);
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424 }
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425
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426 #else /* not CRAY2 */
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427 /* Stack address function for a CRAY-1, CRAY X-MP, or CRAY Y-MP.
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428 Determine the number of the cell within the stack,
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429 given the address of the cell. The purpose of this
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430 routine is to linearize, in some sense, stack addresses
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431 for alloca. */
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432
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433 static long
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434 i00afunc (long address)
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435 {
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436 long stkl = 0;
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437
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438 long size, pseg, this_segment, stack;
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439 long result = 0;
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440
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441 struct stack_segment_linkage *ssptr;
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442
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443 /* Register B67 contains the address of the end of the
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444 current stack segment. If you (as a subprogram) store
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445 your registers on the stack and find that you are past
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446 the contents of B67, you have overflowed the segment.
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447
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448 B67 also points to the stack segment linkage control
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449 area, which is what we are really interested in. */
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450
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451 stkl = CRAY_STACKSEG_END ();
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452 ssptr = (struct stack_segment_linkage *) stkl;
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453
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454 /* If one subtracts 'size' from the end of the segment,
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455 one has the address of the first word of the segment.
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456
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457 If this is not the first segment, 'pseg' will be
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458 nonzero. */
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459
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460 pseg = ssptr->sspseg;
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461 size = ssptr->sssize;
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462
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463 this_segment = stkl - size;
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464
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465 /* It is possible that calling this routine itself caused
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466 a stack overflow. Discard stack segments which do not
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467 contain the target address. */
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468
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469 while (!(this_segment <= address && address <= stkl))
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470 {
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471 #ifdef DEBUG_I00AFUNC
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472 fprintf (stderr, "%011o %011o %011o\n", this_segment, address, stkl);
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473 #endif
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474 if (pseg == 0)
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475 break;
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476 stkl = stkl - pseg;
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477 ssptr = (struct stack_segment_linkage *) stkl;
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478 size = ssptr->sssize;
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479 pseg = ssptr->sspseg;
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480 this_segment = stkl - size;
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481 }
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482
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483 result = address - this_segment;
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484
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485 /* If you subtract pseg from the current end of the stack,
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486 you get the address of the previous stack segment's end.
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487 This seems a little convoluted to me, but I'll bet you save
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488 a cycle somewhere. */
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489
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490 while (pseg != 0)
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491 {
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492 #ifdef DEBUG_I00AFUNC
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493 fprintf (stderr, "%011o %011o\n", pseg, size);
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494 #endif
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495 stkl = stkl - pseg;
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496 ssptr = (struct stack_segment_linkage *) stkl;
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497 size = ssptr->sssize;
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498 pseg = ssptr->sspseg;
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499 result += size;
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500 }
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501 return (result);
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502 }
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503
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504 #endif /* not CRAY2 */
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505 #endif /* CRAY */
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506
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507 #endif /* complicated expression at top of file */
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