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<h3 class="section">14.4 Overlay Sample Program</h3>

<p><a name="index-overlay-example-program-776"></a>
When linking a program which uses overlays, you must place the overlays
at their load addresses, while relocating them to run at their mapped
addresses.  To do this, you must write a linker script (see <a href="../ld/Overlay-Description.html#Overlay-Description">Overlay Description</a>).  Unfortunately,
since linker scripts are specific to a particular host system, target
architecture, and target memory layout, this manual cannot provide
portable sample code demonstrating <span class="sc">gdb</span>'s overlay support.

   <p>However, the <span class="sc">gdb</span> source distribution does contain an overlaid
program, with linker scripts for a few systems, as part of its test
suite.  The program consists of the following files from
<samp><span class="file">gdb/testsuite/gdb.base</span></samp>:

     <dl>
<dt><samp><span class="file">overlays.c</span></samp><dd>The main program file. 
<br><dt><samp><span class="file">ovlymgr.c</span></samp><dd>A simple overlay manager, used by <samp><span class="file">overlays.c</span></samp>. 
<br><dt><samp><span class="file">foo.c</span></samp><dt><samp><span class="file">bar.c</span></samp><dt><samp><span class="file">baz.c</span></samp><dt><samp><span class="file">grbx.c</span></samp><dd>Overlay modules, loaded and used by <samp><span class="file">overlays.c</span></samp>. 
<br><dt><samp><span class="file">d10v.ld</span></samp><dt><samp><span class="file">m32r.ld</span></samp><dd>Linker scripts for linking the test program on the <code>d10v-elf</code>
and <code>m32r-elf</code> targets. 
</dl>

   <p>You can build the test program using the <code>d10v-elf</code> GCC
cross-compiler like this:

<pre class="smallexample">     $ d10v-elf-gcc -g -c overlays.c
     $ d10v-elf-gcc -g -c ovlymgr.c
     $ d10v-elf-gcc -g -c foo.c
     $ d10v-elf-gcc -g -c bar.c
     $ d10v-elf-gcc -g -c baz.c
     $ d10v-elf-gcc -g -c grbx.c
     $ d10v-elf-gcc -g overlays.o ovlymgr.o foo.o bar.o \
                       baz.o grbx.o -Wl,-Td10v.ld -o overlays
</pre>
   <p>The build process is identical for any other architecture, except that
you must substitute the appropriate compiler and linker script for the
target system for <code>d10v-elf-gcc</code> and <code>d10v.ld</code>.

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