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