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+<!-- Copyright (C) 2003 Red Hat, Inc. -->
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+<HTML
+><HEAD
+><TITLE
+>Editing the Sources</TITLE
+><meta name="MSSmartTagsPreventParsing" content="TRUE">
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+HREF="ecos-user-guide.html"><LINK
+REL="UP"
+TITLE="Manual Configuration"
+HREF="manual-configuration.html"><LINK
+REL="PREVIOUS"
+TITLE="Editing an eCos Savefile"
+HREF="editing-an-ecos-savefile.html"><LINK
+REL="NEXT"
+TITLE="Modifying the Memory Layout"
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+><TH
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+>eCos User Guide</TH
+></TR
+><TR
+><TD
+WIDTH="10%"
+ALIGN="left"
+VALIGN="bottom"
+><A
+HREF="editing-an-ecos-savefile.html"
+ACCESSKEY="P"
+>Prev</A
+></TD
+><TD
+WIDTH="80%"
+ALIGN="center"
+VALIGN="bottom"
+>Chapter 28. Manual Configuration</TD
+><TD
+WIDTH="10%"
+ALIGN="right"
+VALIGN="bottom"
+><A
+HREF="modifying-the-memory-layout.html"
+ACCESSKEY="N"
+>Next</A
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+ALIGN="LEFT"
+WIDTH="100%"></DIV
+><DIV
+CLASS="SECT1"
+><H1
+CLASS="SECT1"
+><A
+NAME="EDITING-THE-SOURCES">Editing the Sources</H1
+><P
+>For many users, controlling the packages and
+ manipulating the available configuration options will be
+ sufficient to create an embedded operating system that meets
+ the application's requirements. However, since <SPAN
+CLASS="PRODUCTNAME"
+>eCos</SPAN
+> is
+ shipped entirely in source form, it is possible to go
+ further when necessary: you can edit the <SPAN
+CLASS="PRODUCTNAME"
+>eCos</SPAN
+> sources themselves. This requires some
+ understanding of the way the <SPAN
+CLASS="PRODUCTNAME"
+>eCos</SPAN
+> build system works.
+ </P
+><P
+>The most obvious place to edit the source code is directly
+in the component repository. For example, you could
+edit the file <TT
+CLASS="FILENAME"
+>kernel/<TT
+CLASS="REPLACEABLE"
+><I
+><version></I
+></TT
+>/src/sync/mutex.cxx</TT
+>
+to change the way kernel mutexes work, or possibly just to add some
+extra diagnostics or assertions. Once the file has been edited,
+it is possible to invoke <B
+CLASS="COMMAND"
+>make</B
+> at
+the top level of the build tree and the target library will be rebuilt
+as required. A small optimization is possible: the build tree is
+largely a mirror of the component repository, so it too will contain
+a subdirectory <TT
+CLASS="FILENAME"
+>kernel/<TT
+CLASS="REPLACEABLE"
+><I
+><version></I
+></TT
+></TT
+>;
+if make is invoked in this directory
+then it will only check for changes to the kernel sources, which
+is a bit more efficient than checking for changes throughout the component
+repository. </P
+><P
+>Editing a file in the component repository is fine if this
+tree is used for only one <SPAN
+CLASS="PRODUCTNAME"
+>eCos</SPAN
+> configuration. If the repository
+is used for several different configurations, however, and especially
+if it is shared by multiple users, then making what may be experimental
+changes to the master sources would be a bad idea. The build system provides
+an alternative. It is possible to make a copy of the file in the
+build tree, in other words copy <TT
+CLASS="FILENAME"
+>mutex.cxx</TT
+> from
+the <TT
+CLASS="FILENAME"
+>kernel/<TT
+CLASS="REPLACEABLE"
+><I
+><version></I
+></TT
+>/src/sync</TT
+> directory
+in the component repository to <TT
+CLASS="FILENAME"
+>kernel/<TT
+CLASS="REPLACEABLE"
+><I
+><version></I
+></TT
+>/src/sync</TT
+> in
+the build tree, and edit the file in the build tree. When <B
+CLASS="COMMAND"
+>make</B
+> is
+invoked it will pick up local copies of any of the sources in preference
+to the master versions in the component repository. Once you have
+finished modifying the <SPAN
+CLASS="PRODUCTNAME"
+>eCos</SPAN
+> sources you can install the final version
+back in the component repository. If the changes were temporary
+in nature and only served to aid the debugging process, then you
+can discard the modified version of the sources. </P
+><P
+>The situation is slightly more complicated for the header
+files that a package may export, such as the C library’s <TT
+CLASS="FILENAME"
+>stdio.h</TT
+> header
+file, which can be found in the directory <TT
+CLASS="FILENAME"
+>language/c/libc/<TT
+CLASS="REPLACEABLE"
+><I
+><version></I
+></TT
+>/include</TT
+>.
+If such a header file is changed, either directly in the component
+repository or after copying it to the build tree, then <B
+CLASS="COMMAND"
+>make</B
+> must
+be invoked at the top level of the build tree. In cases like this
+it is not safe to rebuild just the C library because other packages
+may depend on the contents of <TT
+CLASS="FILENAME"
+>stdio.h</TT
+>. </P
+></DIV
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+SUMMARY="Footer navigation table"
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+WIDTH="33%"
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+HREF="editing-an-ecos-savefile.html"
+ACCESSKEY="P"
+>Prev</A
+></TD
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+WIDTH="34%"
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+>Next</A
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+><TR
+><TD
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+>Editing an <SPAN
+CLASS="PRODUCTNAME"
+>eCos</SPAN
+> Savefile</TD
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