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| Previous: <a href="Automatic-Overlay-Debugging.html#Automatic-Overlay-Debugging" accesskey="p" rel="prev">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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| <h3 class="section">14.4 Overlay Sample Program</h3> |
| <a name="index-overlay-example-program"></a> |
| |
| <p>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="http://sourceware.org/binutils/docs/ld/Overlay-Description.html#Overlay-Description">Overlay |
| Description</a> in <cite>Using ld: the GNU linker</cite>). 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 <small>GDB</small>’s overlay support. |
| </p> |
| <p>However, the <small>GDB</small> 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>gdb/testsuite/gdb.base</samp>: |
| </p> |
| <dl compact="compact"> |
| <dt><samp>overlays.c</samp></dt> |
| <dd><p>The main program file. |
| </p></dd> |
| <dt><samp>ovlymgr.c</samp></dt> |
| <dd><p>A simple overlay manager, used by <samp>overlays.c</samp>. |
| </p></dd> |
| <dt><samp>foo.c</samp></dt> |
| <dt><samp>bar.c</samp></dt> |
| <dt><samp>baz.c</samp></dt> |
| <dt><samp>grbx.c</samp></dt> |
| <dd><p>Overlay modules, loaded and used by <samp>overlays.c</samp>. |
| </p></dd> |
| <dt><samp>d10v.ld</samp></dt> |
| <dt><samp>m32r.ld</samp></dt> |
| <dd><p>Linker scripts for linking the test program on the <code>d10v-elf</code> |
| and <code>m32r-elf</code> targets. |
| </p></dd> |
| </dl> |
| |
| <p>You can build the test program using the <code>d10v-elf</code> GCC |
| cross-compiler like this: |
| </p> |
| <div class="smallexample"> |
| <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></div> |
| |
| <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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