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5 >Assembler Modes and Pragmas</TITLE
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74 CLASS="SECTION"
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75 ><A
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76 NAME="AEN407"
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77 >3.9. Assembler Modes and Pragmas</A
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78 ></H1
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79 ><P
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80 >There are a number of options that affect the way assembly is performed.
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81 Some of these options can only be specified on the command line because
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82 they determine something absolute about the assembly process. These include
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83 such things as the output target. Other things may be switchable during
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84 the assembly process. These are known as pragmas and are, by definition,
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85 not portable between assemblers.</P
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86 ><P
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87 >LWASM supports a number of pragmas that affect code generation or
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88 otherwise affect the behaviour of the assembler. These may be specified by
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89 way of a command line option or by assembler directives. The directives
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90 are as follows.</P
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91 ><P
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92 ></P
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93 ><DIV
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94 CLASS="VARIABLELIST"
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95 ><DL
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96 ><DT
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97 >PRAGMA <CODE
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98 CLASS="PARAMETER"
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99 >pragma[,...]</CODE
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100 ></DT
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101 ><DD
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102 ><P
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103 >Specifies that the assembler should bring into force all <CODE
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104 CLASS="PARAMETER"
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105 >pragma</CODE
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106 >s
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107 specified. Any unrecognized pragma will cause an assembly error. The new
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108 pragmas will take effect immediately. This directive should be used when
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109 the program will assemble incorrectly if the pragma is ignored or not supported.</P
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110 ></DD
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111 ><DT
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112 >*PRAGMA <CODE
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113 CLASS="PARAMETER"
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114 >pragma[,...]</CODE
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115 ></DT
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116 ><DD
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117 ><P
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118 >This is identical to the PRAGMA directive except no error will occur with
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119 unrecognized or unsupported pragmas. This directive, by virtue of starting
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120 with a comment character, will also be ignored by assemblers that do not
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121 support this directive. Use this variation if the pragma is not required
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122 for correct functioning of the code.</P
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123 ></DD
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124 ></DL
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125 ></DIV
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126 ><P
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127 >Each pragma supported has a positive version and a negative version.
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128 The positive version enables the pragma while the negative version disables
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129 it. The negatitve version is simply the positive version with "no" prefixed
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130 to it. For instance, "pragma" vs. "nopragma". Only the positive version is
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131 listed below.</P
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132 ><P
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133 >Pragmas are not case sensitive.</P
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134 ><P
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135 ></P
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136 ><DIV
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137 CLASS="VARIABLELIST"
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138 ><DL
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139 ><DT
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140 >index0tonone</DT
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141 ><DD
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142 ><P
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143 >When in force, this pragma enables an optimization affecting indexed addressing
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144 modes. When the offset expression in an indexed mode evaluates to zero but is
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145 not explicity written as 0, this will replace the operand with the equivalent
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146 no offset mode, thus creating slightly faster code. Because of the advantages
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147 of this optimization, it is enabled by default.</P
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148 ></DD
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149 ><DT
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150 >undefextern</DT
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151 ><DD
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152 ><P
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153 >This pragma is only valid for targets that support external references. When in
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154 force, if the assembler sees an undefined symbol on the second pass, it will
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155 automatically define it as an external symbol. This automatic definition will
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156 apply for the remainder of the assembly process, even if the pragma is
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157 subsequently turned off. Because this behaviour would be potentially surprising,
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158 this pragma defaults to off.</P
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159 ><P
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160 >The primary use for this pragma is for projects that share a large number of
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161 symbols between source files. In such cases, it is impractical to enumerate
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162 all the external references in every source file. This allows the assembler
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163 and linker to do the heavy lifting while not preventing a particular source
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164 module from defining a local symbol of the same name as an external symbol
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165 if it does not need the external symbol. (This pragma will not cause an
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166 automatic external definition if there is already a locally defined symbol.)</P
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167 ><P
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168 >This pragma will often be specified on the command line for large projects.
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169 However, depending on the specific dynamics of the project, it may be sufficient
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170 for one or two files to use this pragma internally.</P
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171 ></DD
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