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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 >Object Files</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="PREVIOUS"
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13 TITLE="Libraries and LWAR"
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14 HREF="c1006.html"></HEAD
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15 ><BODY
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20 VLINK="#840084"
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21 ALINK="#0000FF"
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22 ><DIV
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25 SUMMARY="Header navigation table"
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29 CELLSPACING="0"
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30 ><TR
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31 ><TH
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32 COLSPAN="3"
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33 ALIGN="center"
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34 >LW Tool Chain</TH
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35 ></TR
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36 ><TR
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37 ><TD
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38 WIDTH="10%"
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39 ALIGN="left"
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40 VALIGN="bottom"
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41 ><A
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42 HREF="c1006.html"
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43 ACCESSKEY="P"
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44 >Prev</A
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45 ></TD
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46 ><TD
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47 WIDTH="80%"
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48 ALIGN="center"
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49 VALIGN="bottom"
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50 ></TD
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51 ><TD
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52 WIDTH="10%"
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53 ALIGN="right"
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54 VALIGN="bottom"
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55 > </TD
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56 ></TR
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57 ></TABLE
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58 ><HR
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59 ALIGN="LEFT"
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60 WIDTH="100%"></DIV
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61 ><DIV
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62 CLASS="CHAPTER"
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63 ><H1
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64 ><A
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65 NAME="OBJCHAP"
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66 ></A
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67 >Chapter 6. Object Files</H1
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68 ><P
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69 >LWTOOLS uses a proprietary object file format. It is proprietary in the sense
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70 that it is specific to LWTOOLS, not that it is a hidden format. It would be
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71 hard to keep it hidden in an open source tool chain anyway. This chapter
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72 documents the object file format.</P
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73 ><P
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74 >An object file consists of a series of sections each of which contains a
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75 list of exported symbols, a list of incomplete references, and a list of
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76 "local" symbols which may be used in calculating incomplete references. Each
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77 section will obviously also contain the object code.</P
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78 ><P
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79 >Exported symbols must be completely resolved to an address within the
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80 section it is exported from. That is, an exported symbol must be a constant
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81 rather than defined in terms of other symbols.</P
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82 ><P
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83 >Each object file starts with a magic number and version number. The magic
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84 number is the string "LWOBJ16" for this 16 bit object file format. The only
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85 defined version number is currently 0. Thus, the first 8 bytes of the object
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86 file are <FONT
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87 COLOR="RED"
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88 >4C574F424A313600</FONT
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89 ></P
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90 ><P
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91 >Each section has the following items in order:</P
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92 ><P
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93 ></P
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94 ><UL
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95 ><LI
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96 ><P
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97 >section name</P
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98 ></LI
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99 ><LI
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100 ><P
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101 >flags</P
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102 ></LI
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103 ><LI
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104 ><P
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105 >list of local symbols (and addresses within the section)</P
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106 ></LI
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107 ><LI
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108 ><P
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109 >list of exported symbols (and addresses within the section)</P
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110 ></LI
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111 ><LI
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112 ><P
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113 >list of incomplete references along with the expressions to calculate them</P
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114 ></LI
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115 ><LI
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116 ><P
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117 >the actual object code (for non-BSS sections)</P
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118 ></LI
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119 ></UL
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120 ><P
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121 >The section starts with the name of the section with a NUL termination
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122 followed by a series of flag bytes terminated by NUL. There are only two
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123 flag bytes defined. A NUL (0) indicates no more flags and a value of 1
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124 indicates the section is a BSS section. For a BSS section, no actual
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125 code is included in the object file.</P
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126 ><P
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127 >Either a NULL section name or end of file indicate the presence of no more
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128 sections.</P
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129 ><P
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130 >Each entry in the exported and local symbols table consists of the symbol
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131 (NUL terminated) followed by two bytes which contain the value in big endian
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132 order. The end of a symbol table is indicated by a NULL symbol name.</P
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133 ><P
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134 >Each entry in the incomplete references table consists of an expression
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135 followed by a 16 bit offset where the reference goes. Expressions are
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136 defined as a series of terms up to an "end of expression" term. Each term
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137 consists of a single byte which identifies the type of term (see below)
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138 followed by any data required by the term. Then end of the list is flagged
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139 by a NULL expression (only an end of expression term).</P
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140 ><DIV
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141 CLASS="TABLE"
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142 ><A
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143 NAME="AEN1093"
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144 ></A
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145 ><P
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146 ><B
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147 >Table 6-1. Object File Term Types</B
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148 ></P
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149 ><TABLE
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150 BORDER="1"
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151 FRAME="border"
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152 CLASS="CALSTABLE"
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153 ><COL><COL><THEAD
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154 ><TR
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155 ><TH
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156 >TERMTYPE</TH
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157 ><TH
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158 >Meaning</TH
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159 ></TR
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160 ></THEAD
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161 ><TBODY
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162 ><TR
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163 ><TD
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164 >00</TD
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165 ><TD
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166 >end of expression</TD
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167 ></TR
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168 ><TR
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169 ><TD
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170 >01</TD
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171 ><TD
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172 >integer (16 bit in big endian order follows)</TD
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173 ></TR
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174 ><TR
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175 ><TD
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176 >02</TD
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177 ><TD
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178 > external symbol reference (NUL terminated symbol name follows)</TD
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179 ></TR
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180 ><TR
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181 ><TD
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182 >03</TD
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183 ><TD
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184 >local symbol reference (NUL terminated symbol name follows)</TD
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185 ></TR
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186 ><TR
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187 ><TD
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188 >04</TD
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189 ><TD
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190 >operator (1 byte operator number)</TD
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191 ></TR
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192 ><TR
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193 ><TD
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194 >05</TD
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195 ><TD
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196 >section base address reference</TD
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197 ></TR
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198 ><TR
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199 ><TD
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200 >FF</TD
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201 ><TD
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202 >This term will set flags for the expression. Each one of these terms will set a single flag. All of them should be specified first in an expression. If they are not, the behaviour is undefined. The byte following is the flag. Flag 01 indicates an 8 bit relocation. Flag 02 indicates a zero-width relocation (see the EXTDEP pseudo op in LWASM).</TD
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203 ></TR
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204 ></TBODY
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205 ></TABLE
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206 ></DIV
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207 ><P
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208 >External references are resolved using other object files while local
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209 references are resolved using the local symbol table(s) from this file. This
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210 allows local symbols that are not exported to have the same names as
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211 exported symbols or external references.</P
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212 ><DIV
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213 CLASS="TABLE"
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214 ><A
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215 NAME="AEN1123"
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216 ></A
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217 ><P
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218 ><B
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219 >Table 6-2. Object File Operator Numbers</B
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220 ></P
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221 ><TABLE
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222 BORDER="1"
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223 FRAME="border"
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224 CLASS="CALSTABLE"
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225 ><COL><COL><THEAD
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226 ><TR
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227 ><TH
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228 >Number</TH
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229 ><TH
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230 >Operator</TH
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231 ></TR
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232 ></THEAD
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233 ><TBODY
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234 ><TR
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235 ><TD
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236 >01</TD
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237 ><TD
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238 >addition (+)</TD
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239 ></TR
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240 ><TR
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241 ><TD
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242 >02</TD
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243 ><TD
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244 >subtraction (-)</TD
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245 ></TR
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246 ><TR
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247 ><TD
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248 >03</TD
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249 ><TD
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250 >multiplication (*)</TD
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251 ></TR
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252 ><TR
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253 ><TD
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254 >04</TD
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255 ><TD
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256 >division (/)</TD
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257 ></TR
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258 ><TR
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259 ><TD
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260 >05</TD
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261 ><TD
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262 >modulus (%)</TD
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263 ></TR
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264 ><TR
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265 ><TD
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266 >06</TD
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267 ><TD
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268 >integer division (\) (same as division)</TD
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269 ></TR
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270 ><TR
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271 ><TD
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272 >07</TD
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273 ><TD
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274 >bitwise and</TD
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275 ></TR
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276 ><TR
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277 ><TD
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278 >08</TD
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279 ><TD
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280 >bitwise or</TD
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281 ></TR
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282 ><TR
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283 ><TD
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284 >09</TD
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285 ><TD
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286 >bitwise xor</TD
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287 ></TR
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288 ><TR
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289 ><TD
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290 >0A</TD
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291 ><TD
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292 >boolean and</TD
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293 ></TR
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294 ><TR
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295 ><TD
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296 >0B</TD
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297 ><TD
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298 >boolean or</TD
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299 ></TR
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300 ><TR
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301 ><TD
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302 >0C</TD
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303 ><TD
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304 >unary negation, 2's complement (-)</TD
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305 ></TR
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306 ><TR
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307 ><TD
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308 >0D</TD
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309 ><TD
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310 >unary 1's complement (^)</TD
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311 ></TR
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312 ></TBODY
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313 ></TABLE
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314 ></DIV
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315 ><P
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316 >An expression is represented in a postfix manner with both operands for
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317 binary operators preceding the operator and the single operand for unary
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318 operators preceding the operator.</P
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319 ></DIV
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320 ><DIV
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321 CLASS="NAVFOOTER"
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334 VALIGN="top"
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337 ACCESSKEY="P"
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338 >Prev</A
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346 ACCESSKEY="H"
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347 >Home</A
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