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<!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="x173.html"><LINK REL="NEXT" TITLE="Object Files and Sections" HREF="x467.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="x173.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="x467.html" ACCESSKEY="N" >Next</A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><DIV CLASS="SECTION" ><H1 CLASS="SECTION" ><A NAME="AEN445" >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 my 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="x173.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="x467.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" >Object Files and Sections</TD ></TR ></TABLE ></DIV ></BODY ></HTML >