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<title>Debugging with GDB: Overlay Sample Program</title>
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<a name="Overlay-Sample-Program"></a>
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Previous: <a href="Automatic-Overlay-Debugging.html#Automatic-Overlay-Debugging" accesskey="p" rel="previous">Automatic Overlay Debugging</a>, Up: <a href="Overlays.html#Overlays" accesskey="u" rel="up">Overlays</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
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<a name="Overlay-Sample-Program-1"></a>
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<h3 class="section">14.4 Overlay Sample Program</h3>
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<a name="index-overlay-example-program"></a>
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<p>When linking a program which uses overlays, you must place the overlays
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at their load addresses, while relocating them to run at their mapped
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addresses. To do this, you must write a linker script (see <a href="http://sourceware.org/binutils/docs/ld/Overlay-Description.html#Overlay-Description">Overlay
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Description</a> in <cite>Using ld: the GNU linker</cite>). Unfortunately,
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since linker scripts are specific to a particular host system, target
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architecture, and target memory layout, this manual cannot provide
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portable sample code demonstrating <small>GDB</small>’s overlay support.
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</p>
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<p>However, the <small>GDB</small> source distribution does contain an overlaid
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program, with linker scripts for a few systems, as part of its test
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suite. The program consists of the following files from
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<samp>gdb/testsuite/gdb.base</samp>:
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</p>
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<dl compact="compact">
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<dt><samp>overlays.c</samp></dt>
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<dd><p>The main program file.
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</p></dd>
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<dt><samp>ovlymgr.c</samp></dt>
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<dd><p>A simple overlay manager, used by <samp>overlays.c</samp>.
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</p></dd>
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<dt><samp>foo.c</samp></dt>
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<dt><samp>bar.c</samp></dt>
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<dt><samp>baz.c</samp></dt>
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<dt><samp>grbx.c</samp></dt>
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<dd><p>Overlay modules, loaded and used by <samp>overlays.c</samp>.
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</p></dd>
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<dt><samp>d10v.ld</samp></dt>
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<dt><samp>m32r.ld</samp></dt>
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<dd><p>Linker scripts for linking the test program on the <code>d10v-elf</code>
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and <code>m32r-elf</code> targets.
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</p></dd>
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</dl>
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<p>You can build the test program using the <code>d10v-elf</code> GCC
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cross-compiler like this:
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</p>
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<div class="smallexample">
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<pre class="smallexample">$ d10v-elf-gcc -g -c overlays.c
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$ d10v-elf-gcc -g -c ovlymgr.c
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$ d10v-elf-gcc -g -c foo.c
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$ d10v-elf-gcc -g -c bar.c
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$ d10v-elf-gcc -g -c baz.c
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$ d10v-elf-gcc -g -c grbx.c
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$ d10v-elf-gcc -g overlays.o ovlymgr.o foo.o bar.o \
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baz.o grbx.o -Wl,-Td10v.ld -o overlays
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</pre></div>
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<p>The build process is identical for any other architecture, except that
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you must substitute the appropriate compiler and linker script for the
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target system for <code>d10v-elf-gcc</code> and <code>d10v.ld</code>.
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