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author lost@l-w.ca
date Fri, 29 Oct 2010 19:20:39 -0600
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75 ><A
76 NAME="AEN580"
77 >3.10. 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 >cescapes</DT
151 ><DD
152 ><P
153 >This pragma will cause strings in the FCC, FCS, and FCN pseudo operations to
154 have C-style escape sequences interpreted. The one departure from the official
155 spec is that unrecognized escape sequences will return either the character
156 immediately following the backslash or some undefined value. Do not rely
157 on the behaviour of undefined escape sequences.</P
158 ></DD
159 ><DT
160 >importundefexport</DT
161 ><DD
162 ><P
163 >This pragma is only valid for targets that support external references. When
164 in force, it will cause the EXPORT directive to act as IMPORT if the symbol
165 to be exported is not defined. This is provided for compatibility with the
166 output of gcc6809 and should not be used in hand written code. Because of
167 the confusion this pragma can cause, it is disabled by default.</P
168 ></DD
169 ><DT
170 >undefextern</DT
171 ><DD
172 ><P
173 >This pragma is only valid for targets that support external references. When in
174 force, if the assembler sees an undefined symbol on the second pass, it will
175 automatically define it as an external symbol. This automatic definition will
176 apply for the remainder of the assembly process, even if the pragma is
177 subsequently turned off. Because this behaviour would be potentially surprising,
178 this pragma defaults to off.</P
179 ><P
180 >The primary use for this pragma is for projects that share a large number of
181 symbols between source files. In such cases, it is impractical to enumerate
182 all the external references in every source file. This allows the assembler
183 and linker to do the heavy lifting while not preventing a particular source
184 module from defining a local symbol of the same name as an external symbol
185 if it does not need the external symbol. (This pragma will not cause an
186 automatic external definition if there is already a locally defined symbol.)</P
187 ><P
188 >This pragma will often be specified on the command line for large projects.
189 However, depending on the specific dynamics of the project, it may be sufficient
190 for one or two files to use this pragma internally.</P
191 ></DD
192 ><DT
193 >dollarlocal</DT
194 ><DD
195 ><P
196 >When set, a "$" in a symbol makes it local. When not set, "$" does not
197 cause a symbol to be local. It is set by default except when using the OS9
198 target.</P
199 ></DD
200 ><DT
201 >dollarnotlocal</DT
202 ><DD
203 ><P
204 > This is the same as the "dollarlocal" pragma except its sense is
205 reversed. That is, "dollarlocal" and "nodollarnotlocal" are equivalent and
206 "nodollarlocal" and "dollarnotlocal" are equivalent. </P
207 ></DD
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