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