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1 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN""http://www.w3.org/TR/html4/loose.dtd">
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2 <HTML
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3 ><HEAD
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4 ><TITLE
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5 >Format Specific Linking Notes</TITLE
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6 ><META
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7 NAME="GENERATOR"
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8 CONTENT="Modular DocBook HTML Stylesheet Version 1.79"><LINK
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9 REL="HOME"
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10 TITLE="LW Tool Chain"
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11 HREF="index.html"><LINK
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12 REL="UP"
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13 TITLE="LWLINK"
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14 HREF="c811.html"><LINK
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15 REL="PREVIOUS"
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16 TITLE="Linking Scripts"
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17 HREF="x925.html"><LINK
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18 REL="NEXT"
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19 TITLE="Libraries and LWAR"
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20 HREF="c1006.html"></HEAD
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21 ><BODY
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22 CLASS="SECTION"
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23 BGCOLOR="#FFFFFF"
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25 LINK="#0000FF"
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26 VLINK="#840084"
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27 ALINK="#0000FF"
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28 ><DIV
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29 CLASS="NAVHEADER"
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30 ><TABLE
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31 SUMMARY="Header navigation table"
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32 WIDTH="100%"
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33 BORDER="0"
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34 CELLPADDING="0"
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35 CELLSPACING="0"
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36 ><TR
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37 ><TH
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38 COLSPAN="3"
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39 ALIGN="center"
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40 >LW Tool Chain</TH
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41 ></TR
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42 ><TR
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43 ><TD
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44 WIDTH="10%"
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45 ALIGN="left"
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46 VALIGN="bottom"
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47 ><A
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48 HREF="x925.html"
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49 ACCESSKEY="P"
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50 >Prev</A
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51 ></TD
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52 ><TD
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53 WIDTH="80%"
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54 ALIGN="center"
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55 VALIGN="bottom"
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56 >Chapter 4. LWLINK</TD
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57 ><TD
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58 WIDTH="10%"
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59 ALIGN="right"
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60 VALIGN="bottom"
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61 ><A
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62 HREF="c1006.html"
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63 ACCESSKEY="N"
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64 >Next</A
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65 ></TD
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66 ></TR
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67 ></TABLE
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68 ><HR
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69 ALIGN="LEFT"
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70 WIDTH="100%"></DIV
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71 ><DIV
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72 CLASS="SECTION"
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73 ><H1
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74 CLASS="SECTION"
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75 ><A
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76 NAME="AEN991"
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77 >4.4. Format Specific Linking Notes</A
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78 ></H1
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79 ><P
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80 >Some formats require special information to be able to generate actual
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81 binaries. If the specific format you are interested in is not listed in
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82 this section, then there is nothing special you need to know about to create
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83 a final binary.</P
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84 ><DIV
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85 CLASS="SECTION"
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86 ><H2
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87 CLASS="SECTION"
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88 ><A
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89 NAME="AEN994"
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90 >4.4.1. OS9 Modules</A
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91 ></H2
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92 ><P
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93 >OS9 modules need to embed several items into the module header. These
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94 items are the type of module, the langauge of the module, the module
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95 attributes, the module revision number, the data size (bss), and the
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96 execution offset. These are all either calculated or default to reasonable
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97 values.</P
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98 ><P
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99 >The data size is calcuated as the sum of all sections named "bss" or
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100 ".bss" in all object files that are linked together.</P
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101 ><P
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102 >The execution offset is calculated from the address of the special
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103 symbol "__start" which must be an exported (external) symbol in one of the
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104 objects to be linked.</P
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105 ><P
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106 >The type defaults to "Prgrm" or "Program module". The language
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107 defaults to "Objct" or "6809 object code". Attributes default to enabling
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108 the re-entrant flag. And finally, the revision defaults to zero.</P
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109 ><P
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110 >The embedded module name is the output filename. If the output
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111 filename includes more than just the filename, this will probably not be
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112 what you want.</P
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113 ><P
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114 >The type, language, attributes, revision, and module name can all be
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115 overridden by providing a special section in exactly one of the object files
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116 to be linked. This section is called "__os9" (note the two underscores).
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117 To override the type, language, attributes, or revision values, define a
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118 non-exported symbol in this section called "type", "lang", "attr", or "rev"
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119 respectively. Any other symbols defined are ignored. To override the
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120 module name, include as the only actual code in the section a NUL terminated
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121 string (the FCN directive is useful for this). If there is no code in the
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122 section or it beings with a NUL, the default name will be used. Any of the
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123 preceeding that are not defined in the special section will retain their
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124 default values.</P
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125 ><P
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126 >The built-in link script for OS9 modules will place the following
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127 sections, in order, in the module: "code", ".text", "data", ".data". It
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128 will merge all sections with the name "bss" or ".bss" into the "data"
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129 section. All other section names are ignored. What this means is that you
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130 must define your data variables in the a section called "bss" or ".bss" even
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131 though you will be refencing them all as offsets from U. This does have the
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132 unpleasant side effect that all BSS references will end up being 16 bit
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133 offsets because the assembler cannot know what the offset will be once the
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134 linker is finished its work. Thus, if the tightest possible code is
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135 required, having LWASM directly output the module is a better choice.</P
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136 ><P
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137 >While the built-in link script is probably sufficient for most
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138 purposes, you can provide your own script. If you provide a custom link
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139 script, you must start your code and data sections at location 000D to
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140 accommodate the module header. Otherwise, you will have an incorrect
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141 location for the execution offset. You must use the ENTRY directive in the
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142 script to define the entry point for the module.</P
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143 ><P
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144 >It should also be obvious from the above that you cannot mix the bss
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145 (rmb) definitions with the module code when linking separately. Those
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146 familiar with typical module creation will probably find this an unpleasant
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147 difference but it is unavoidable.</P
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148 ><P
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149 >It should also be noted that direct page references should also be
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150 avoided because you cannot know ahead of time whether the linker is going to
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151 end up putting a particular variable in the first 256 bytes of the module's
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152 data space. If, however, you know for certain you will have less than 256
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153 bytes of defined data space across all of the object files that will be
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154 linked, you can instead use forced DP addressing for your data addresses
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155 instead of the ,u notation. When linking with 3rd party libraries, this
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156 practice should be avoided. Also, when creating libraries, always use the
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157 offset from U technique.</P
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158 ></DIV
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159 ></DIV
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160 ><DIV
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161 CLASS="NAVFOOTER"
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162 ><HR
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163 ALIGN="LEFT"
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164 WIDTH="100%"><TABLE
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165 SUMMARY="Footer navigation table"
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167 BORDER="0"
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168 CELLPADDING="0"
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169 CELLSPACING="0"
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170 ><TR
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171 ><TD
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172 WIDTH="33%"
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173 ALIGN="left"
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174 VALIGN="top"
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175 ><A
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176 HREF="x925.html"
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177 ACCESSKEY="P"
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178 >Prev</A
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179 ></TD
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180 ><TD
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181 WIDTH="34%"
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182 ALIGN="center"
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183 VALIGN="top"
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184 ><A
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185 HREF="index.html"
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186 ACCESSKEY="H"
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187 >Home</A
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188 ></TD
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189 ><TD
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190 WIDTH="33%"
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191 ALIGN="right"
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192 VALIGN="top"
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193 ><A
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194 HREF="c1006.html"
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195 ACCESSKEY="N"
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196 >Next</A
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197 ></TD
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198 ></TR
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199 ><TR
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200 ><TD
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201 WIDTH="33%"
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202 ALIGN="left"
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203 VALIGN="top"
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204 >Linking Scripts</TD
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205 ><TD
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206 WIDTH="34%"
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207 ALIGN="center"
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208 VALIGN="top"
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209 ><A
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210 HREF="c811.html"
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211 ACCESSKEY="U"
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212 >Up</A
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213 ></TD
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215 WIDTH="33%"
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216 ALIGN="right"
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217 VALIGN="top"
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218 >Libraries and LWAR</TD
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219 ></TR
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220 ></TABLE
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221 ></DIV
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222 ></BODY
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223 ></HTML
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224 > |
