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diff docs/manual/x864.html @ 254:155799f6cfa5
Add documentation for the FILL pseudo operation
| author | William Astle <lost@l-w.ca> |
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| date | Wed, 30 Jan 2013 21:32:14 -0700 |
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--- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/docs/manual/x864.html Wed Jan 30 21:32:14 2013 -0700 @@ -0,0 +1,224 @@ +<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN""http://www.w3.org/TR/html4/loose.dtd"> +<HTML +><HEAD +><TITLE +>Format Specific Linking Notes</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="LWLINK" +HREF="c693.html"><LINK +REL="PREVIOUS" +TITLE="Linking Scripts" +HREF="x807.html"><LINK +REL="NEXT" +TITLE="Libraries and LWAR" +HREF="c879.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="x807.html" +ACCESSKEY="P" +>Prev</A +></TD +><TD +WIDTH="80%" +ALIGN="center" +VALIGN="bottom" +>Chapter 4. LWLINK</TD +><TD +WIDTH="10%" +ALIGN="right" +VALIGN="bottom" +><A +HREF="c879.html" +ACCESSKEY="N" +>Next</A +></TD +></TR +></TABLE +><HR +ALIGN="LEFT" +WIDTH="100%"></DIV +><DIV +CLASS="SECTION" +><H1 +CLASS="SECTION" +><A +NAME="AEN864" +>4.4. Format Specific Linking Notes</A +></H1 +><P +>Some formats require special information to be able to generate actual +binaries. If the specific format you are interested in is not listed in +this section, then there is nothing special you need to know about to create +a final binary.</P +><DIV +CLASS="SECTION" +><H2 +CLASS="SECTION" +><A +NAME="AEN867" +>4.4.1. OS9 Modules</A +></H2 +><P +>OS9 modules need to embed several items into the module header. These +items are the type of module, the langauge of the module, the module +attributes, the module revision number, the data size (bss), and the +execution offset. These are all either calculated or default to reasonable +values.</P +><P +>The data size is calcuated as the sum of all sections named "bss" or +".bss" in all object files that are linked together.</P +><P +>The execution offset is calculated from the address of the special +symbol "__start" which must be an exported (external) symbol in one of the +objects to be linked.</P +><P +>The type defaults to "Prgrm" or "Program module". The language +defaults to "Objct" or "6809 object code". Attributes default to enabling +the re-entrant flag. And finally, the revision defaults to zero.</P +><P +>The embedded module name is the output filename. If the output +filename includes more than just the filename, this will probably not be +what you want.</P +><P +>The type, language, attributes, revision, and module name can all be +overridden by providing a special section in exactly one of the object files +to be linked. This section is called "__os9" (note the two underscores). +To override the type, language, attributes, or revision values, define a +non-exported symbol in this section called "type", "lang", "attr", or "rev" +respectively. Any other symbols defined are ignored. To override the +module name, include as the only actual code in the section a NUL terminated +string (the FCN directive is useful for this). If there is no code in the +section or it beings with a NUL, the default name will be used. Any of the +preceeding that are not defined in the special section will retain their +default values.</P +><P +>The built-in link script for OS9 modules will place the following +sections, in order, in the module: "code", ".text", "data", ".data". It +will merge all sections with the name "bss" or ".bss" into the "data" +section. All other section names are ignored. What this means is that you +must define your data variables in the a section called "bss" or ".bss" even +though you will be refencing them all as offsets from U. This does have the +unpleasant side effect that all BSS references will end up being 16 bit +offsets because the assembler cannot know what the offset will be once the +linker is finished its work. Thus, if the tightest possible code is +required, having LWASM directly output the module is a better choice.</P +><P +>While the built-in link script is probably sufficient for most +purposes, you can provide your own script. If you provide a custom link +script, you must start your code and data sections at location 000D to +accommodate the module header. Otherwise, you will have an incorrect +location for the execution offset. You must use the ENTRY directive in the +script to define the entry point for the module.</P +><P +>It should also be obvious from the above that you cannot mix the bss +(rmb) definitions with the module code when linking separately. Those +familiar with typical module creation will probably find this an unpleasant +difference but it is unavoidable.</P +><P +>It should also be noted that direct page references should also be +avoided because you cannot know ahead of time whether the linker is going to +end up putting a particular variable in the first 256 bytes of the module's +data space. If, however, you know for certain you will have less than 256 +bytes of defined data space across all of the object files that will be +linked, you can instead use forced DP addressing for your data addresses +instead of the ,u notation. When linking with 3rd party libraries, this +practice should be avoided. Also, when creating libraries, always use the +offset from U technique.</P +></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="x807.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="c879.html" +ACCESSKEY="N" +>Next</A +></TD +></TR +><TR +><TD +WIDTH="33%" +ALIGN="left" +VALIGN="top" +>Linking Scripts</TD +><TD +WIDTH="34%" +ALIGN="center" +VALIGN="top" +><A +HREF="c693.html" +ACCESSKEY="U" +>Up</A +></TD +><TD +WIDTH="33%" +ALIGN="right" +VALIGN="top" +>Libraries and LWAR</TD +></TR +></TABLE +></DIV +></BODY +></HTML +> \ No newline at end of file