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| author | lost@l-w.ca |
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| date | Sun, 19 Sep 2010 01:33:24 -0600 |
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--- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/doc/manual/x473.html Sun Sep 19 01:33:24 2010 -0600 @@ -0,0 +1,223 @@ +<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN""http://www.w3.org/TR/html4/loose.dtd"> +<HTML +><HEAD +><TITLE +>Macros</TITLE +><META +NAME="GENERATOR" +CONTENT="Modular DocBook HTML Stylesheet Version 1.79"><LINK +REL="HOME" +TITLE="LW Tool Chain" +HREF="index.html"><LINK +REL="UP" +TITLE="LWASM" +HREF="c43.html"><LINK +REL="PREVIOUS" +TITLE="Assembler Directives" +HREF="x190.html"><LINK +REL="NEXT" +TITLE="Structures" +HREF="x495.html"></HEAD +><BODY +CLASS="SECTION" +BGCOLOR="#FFFFFF" +TEXT="#000000" +LINK="#0000FF" +VLINK="#840084" +ALINK="#0000FF" +><DIV +CLASS="NAVHEADER" +><TABLE +SUMMARY="Header navigation table" +WIDTH="100%" +BORDER="0" +CELLPADDING="0" +CELLSPACING="0" +><TR +><TH +COLSPAN="3" +ALIGN="center" +>LW Tool Chain</TH +></TR +><TR +><TD +WIDTH="10%" +ALIGN="left" +VALIGN="bottom" +><A +HREF="x190.html" +ACCESSKEY="P" +>Prev</A +></TD +><TD +WIDTH="80%" +ALIGN="center" +VALIGN="bottom" +>Chapter 3. LWASM</TD +><TD +WIDTH="10%" +ALIGN="right" +VALIGN="bottom" +><A +HREF="x495.html" +ACCESSKEY="N" +>Next</A +></TD +></TR +></TABLE +><HR +ALIGN="LEFT" +WIDTH="100%"></DIV +><DIV +CLASS="SECTION" +><H1 +CLASS="SECTION" +><A +NAME="AEN473" +>3.7. Macros</A +></H1 +><P +>LWASM is a macro assembler. A macro is simply a name that stands in for a +series of instructions. Once a macro is defined, it is used like any other +assembler directive. Defining a macro can be considered equivalent to adding +additional assembler directives.</P +><P +>Macros may accept parameters. These parameters are referenced within +a macro by the a backslash ("\") followed by a digit 1 through 9 for the first +through ninth parameters. They may also be referenced by enclosing the +decimal parameter number in braces ("{num}"). These parameter references +are replaced with the verbatim text of the parameter passed to the macro. A +reference to a non-existent parameter will be replaced by an empty string. +Macro parameters are expanded everywhere on each source line. That means +the parameter to a macro could be used as a symbol or it could even appear +in a comment or could cause an entire source line to be commented out +when the macro is expanded.</P +><P +>Parameters passed to a macro are separated by commas and the parameter list +is terminated by any whitespace. This means that neither a comma nor whitespace +may be included in a macro parameter.</P +><P +>Macro expansion is done recursively. That is, within a macro, macros are +expanded. This can lead to infinite loops in macro expansion. If the assembler +hangs for a long time while assembling a file that uses macros, this may be +the reason.</P +><P +>Each macro expansion receives its own local symbol context which is not +inherited by any macros called by it nor is it inherited from the context +the macro was instantiated in. That means it is possible to use local symbols +within macros without having them collide with symbols in other macros or +outside the macro itself. However, this also means that using a local symbol +as a parameter to a macro, while legal, will not do what it would seem to do +as it will result in looking up the local symbol in the macro's symbol context +rather than the enclosing context where it came from, likely yielding either +an undefined symbol error or bizarre assembly results.</P +><P +>Note that there is no way to define a macro as local to a symbol context. All +macros are part of the global macro namespace. However, macros have a separate +namespace from symbols so it is possible to have a symbol with the same name +as a macro.</P +><P +>Macros are defined only during the first pass. Macro expansion also +only occurs during the first pass. On the second pass, the macro +definition is simply ignored. Macros must be defined before they are used.</P +><P +>The following directives are used when defining macros.</P +><P +></P +><DIV +CLASS="VARIABLELIST" +><DL +><DT +><CODE +CLASS="PARAMETER" +>macroname</CODE +> MACRO</DT +><DD +><P +>This directive is used to being the definition of a macro called +<CODE +CLASS="PARAMETER" +>macroname</CODE +>. If <CODE +CLASS="PARAMETER" +>macroname</CODE +> already +exists, it is considered an error. Attempting to define a macro within a +macro is undefined. It may work and it may not so the behaviour should not +be relied upon.</P +></DD +><DT +>ENDM</DT +><DD +><P +>This directive indicates the end of the macro currently being defined. It +causes the assembler to resume interpreting source lines as normal.</P +></DD +></DL +></DIV +></DIV +><DIV +CLASS="NAVFOOTER" +><HR +ALIGN="LEFT" +WIDTH="100%"><TABLE +SUMMARY="Footer navigation table" +WIDTH="100%" +BORDER="0" +CELLPADDING="0" +CELLSPACING="0" +><TR +><TD +WIDTH="33%" +ALIGN="left" +VALIGN="top" +><A +HREF="x190.html" +ACCESSKEY="P" +>Prev</A +></TD +><TD +WIDTH="34%" +ALIGN="center" +VALIGN="top" +><A +HREF="index.html" +ACCESSKEY="H" +>Home</A +></TD +><TD +WIDTH="33%" +ALIGN="right" +VALIGN="top" +><A +HREF="x495.html" +ACCESSKEY="N" +>Next</A +></TD +></TR +><TR +><TD +WIDTH="33%" +ALIGN="left" +VALIGN="top" +>Assembler Directives</TD +><TD +WIDTH="34%" +ALIGN="center" +VALIGN="top" +><A +HREF="c43.html" +ACCESSKEY="U" +>Up</A +></TD +><TD +WIDTH="33%" +ALIGN="right" +VALIGN="top" +>Structures</TD +></TR +></TABLE +></DIV +></BODY +></HTML +> \ No newline at end of file