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1 Copyright (c) 1992,1993,1995,1996, Jens-Uwe Mager, Helios Software GmbH |
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2 Not derived from licensed software. |
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3 |
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4 Permission is granted to freely use, copy, modify, and redistribute |
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5 this software, provided that the author is not construed to be liable |
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6 for any results of using the software, alterations are clearly marked |
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7 as such, and this notice is not modified. |
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8 |
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9 libdl.a |
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10 ------- |
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11 |
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12 This is an emulation library to emulate the SunOS/System V.4 functions |
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13 to access the runtime linker. The functions are emulated by using the |
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14 AIX load() function and by reading the .loader section of the loaded |
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15 module to find the exports. The to be loaded module should be linked as |
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16 follows (if using AIX 3): |
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17 |
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18 cc -o module.so -bM:SRE -bE:module.exp -e _nostart $(OBJS) |
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19 |
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20 For AIX 4: |
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21 |
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22 cc -o module.so -bM:SRE -bE:module.exp -bnoentry $(OBJS) |
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23 |
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24 The module export file contains the symbols to be exported. Because |
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25 this library uses the loader section, the final module.so file can be |
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26 stripped. C++ users should build their shared objects using the script |
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27 makeC++SharedLib (part of the IBM C++ compiler), this will make sure |
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28 that constructors and destructors for static and global objects will be |
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29 called upon loading and unloading the module. |
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30 |
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31 Usage |
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32 ----- |
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33 |
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34 void *dlopen(const char *path, int mode); |
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35 |
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36 This routine loads the module pointed to by path and reads its export |
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37 table. If the path does not contain a '/' character, dlopen will search |
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38 for the module using the LIBPATH environment variable. It returns an |
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39 opaque handle to the module or NULL on error. The mode parameter can be |
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40 either RTLD_LAZY (for lazy function binding) or RTLD_NOW for immediate |
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41 function binding. The AIX implementation currently does treat RTLD_NOW |
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42 the same as RTLD_LAZY. The flag RTLD_GLOBAL might be or'ed into the |
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43 mode parameter to allow loaded modules to bind to global variables or |
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44 functions in other loaded modules loaded by dlopen(). If RTLD_GLOBAL is |
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45 not specified, only globals from the main part of the executable or |
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46 shared libraries are used to look for undefined symbols in loaded |
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47 modules. |
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48 |
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49 |
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50 void *dlsym(void *handle, const char *symbol); |
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51 |
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52 This routine searches for the symbol in the module referred to by |
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53 handle and returns its address. If the symbol could not be found, the |
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54 function returns NULL. The return value must be casted to a proper |
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55 function pointer before it can be used. SunOS/System V.4 allows handle |
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56 to be a NULL pointer to refer to the module the call is made from, this |
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57 is not implemented. |
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58 |
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59 int dlclose(void *handle); |
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60 |
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61 This routine unloads the module referred to by the handle and disposes |
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62 of any local storage. this function returns -1 on failure. |
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63 |
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64 char *dlerror(void); |
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65 |
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66 This routine can be used to retrieve a text message describing the most |
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67 recent error that occured on on of the above routines. This function |
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68 returns NULL if there is no error information. |
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69 |
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70 Initialization and termination handlers |
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71 --------------------------------------- |
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72 |
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73 The emulation provides for an initialization and a termination |
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74 handler. The dlfcn.h file contains a structure declaration named |
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75 dl_info with following members: |
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76 |
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77 void (*init)(void); |
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78 void (*fini)(void); |
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79 |
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80 The init function is called upon first referencing the library. The |
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81 fini function is called at dlclose() time or when the process exits. |
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82 The module should declare a variable named dl_info that contains this |
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83 structure which must be exported. These functions correspond to the |
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84 documented _init() and _fini() functions of SunOS 4.x, but these are |
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85 appearently not implemented in SunOS. When using SunOS 5.0, these |
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86 correspond to #pragma init and #pragma fini respectively. At the same |
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87 time any static or global C++ object's constructors or destructors will |
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88 be called. |
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89 |
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90 BUGS |
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91 ---- |
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92 |
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93 Please note that there is currently a problem with implicitely loaded |
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94 shared C++ libaries: if you refer to a shared C++ library from a loaded |
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95 module that is not yet used by the main program, the dlopen() emulator |
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96 does not notice this and does not call the static constructors for the |
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97 implicitely loaded library. This can be easily demonstrated by |
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98 referencing the C++ standard streams from a loaded module if the main |
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99 program is a plain C program. |
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100 |
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101 Jens-Uwe Mager |
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102 |
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103 HELIOS Software GmbH |
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104 Lavesstr. 80 |
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105 30159 Hannover |
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106 Germany |
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107 |
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108 Phone: +49 511 36482-0 |
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109 FAX: +49 511 36482-69 |
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110 AppleLink: helios.de/jum |
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111 Internet: jum@helios.de |
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112 |
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113 Revison History |
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114 --------------- |
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115 |
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116 SCCS/s.dlfcn.h: |
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117 |
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118 D 1.4 95/04/25 09:36:52 jum 4 3 00018/00004/00028 |
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119 MRs: |
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120 COMMENTS: |
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121 added RTLD_GLOBAL, include and C++ guards |
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122 |
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123 D 1.3 92/12/27 20:58:32 jum 3 2 00001/00001/00031 |
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124 MRs: |
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125 COMMENTS: |
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126 we always have prototypes on RS/6000 |
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127 |
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128 D 1.2 92/08/16 17:45:11 jum 2 1 00009/00000/00023 |
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129 MRs: |
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130 COMMENTS: |
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131 added dl_info structure to implement initialize and terminate functions |
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132 |
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133 D 1.1 92/08/02 18:08:45 jum 1 0 00023/00000/00000 |
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134 MRs: |
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135 COMMENTS: |
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136 Erstellungsdatum und -uhrzeit 92/08/02 18:08:45 von jum |
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137 |
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138 SCCS/s.dlfcn.c: |
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139 |
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140 D 1.10 96/02/15 17:42:44 jum 12 10 00012/00007/00521 |
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141 MRs: |
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142 COMMENTS: |
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143 the C++ constructor and destructor chains are now called properly for either |
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144 xlC 2 or xlC 3 (CSet++). |
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145 |
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146 D 1.9 95/09/22 11:09:38 markus 10 9 00001/00008/00527 |
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147 MRs: |
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148 COMMENTS: |
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149 Fix version number |
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150 |
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151 D 1.8 95/09/22 10:14:34 markus 9 8 00008/00001/00527 |
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152 MRs: |
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153 COMMENTS: |
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154 Added version number for dl lib |
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155 |
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156 D 1.7 95/08/14 19:08:38 jum 8 6 00026/00004/00502 |
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157 MRs: |
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158 COMMENTS: |
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159 Integrated the fixes from Kirk Benell (kirk@rsinc.com) to allow loading of |
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160 shared objects generated under AIX 4. Fixed bug that symbols with exactly |
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161 8 characters would use garbage characters from the following symbol value. |
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162 |
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163 D 1.6 95/04/25 09:38:03 jum 6 5 00046/00006/00460 |
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164 MRs: |
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165 COMMENTS: |
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166 added handling of C++ static constructors and destructors, added RTLD_GLOBAL to bind against other loaded modules |
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167 |
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168 D 1.5 93/02/14 20:14:17 jum 5 4 00002/00000/00464 |
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169 MRs: |
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170 COMMENTS: |
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171 added path to dlopen error message to make clear where there error occured. |
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172 |
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173 D 1.4 93/01/03 19:13:56 jum 4 3 00061/00005/00403 |
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174 MRs: |
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175 COMMENTS: |
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176 to allow calling symbols in the main module call load with L_NOAUTODEFER and |
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177 do a loadbind later with the main module. |
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178 |
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179 D 1.3 92/12/27 20:59:55 jum 3 2 00066/00008/00342 |
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180 MRs: |
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181 COMMENTS: |
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182 added search by L_GETINFO if module got loaded by LIBPATH |
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183 |
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184 D 1.2 92/08/16 17:45:43 jum 2 1 00074/00006/00276 |
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185 MRs: |
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186 COMMENTS: |
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187 implemented initialize and terminate functions, added reference counting to avoid multiple loads of the same library |
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188 |
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189 D 1.1 92/08/02 18:08:45 jum 1 0 00282/00000/00000 |
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190 MRs: |
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191 COMMENTS: |
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192 Erstellungsdatum und -uhrzeit 92/08/02 18:08:45 von jum |
