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| <h3 class="section">14.2 Overlay Commands</h3> |
| |
| <p>To use <span class="sc">gdb</span>'s overlay support, each overlay in your program must |
| correspond to a separate section of the executable file. The section's |
| virtual memory address and load memory address must be the overlay's |
| mapped and load addresses. Identifying overlays with sections allows |
| <span class="sc">gdb</span> to determine the appropriate address of a function or |
| variable, depending on whether the overlay is mapped or not. |
| |
| <p><span class="sc">gdb</span>'s overlay commands all start with the word <code>overlay</code>; |
| you can abbreviate this as <code>ov</code> or <code>ovly</code>. The commands are: |
| |
| <dl> |
| <dt><code>overlay off</code><dd><a name="index-overlay-767"></a>Disable <span class="sc">gdb</span>'s overlay support. When overlay support is |
| disabled, <span class="sc">gdb</span> assumes that all functions and variables are |
| always present at their mapped addresses. By default, <span class="sc">gdb</span>'s |
| overlay support is disabled. |
| |
| <br><dt><code>overlay manual</code><dd><a name="index-manual-overlay-debugging-768"></a>Enable <dfn>manual</dfn> overlay debugging. In this mode, <span class="sc">gdb</span> |
| relies on you to tell it which overlays are mapped, and which are not, |
| using the <code>overlay map-overlay</code> and <code>overlay unmap-overlay</code> |
| commands described below. |
| |
| <br><dt><code>overlay map-overlay </code><var>overlay</var><dt><code>overlay map </code><var>overlay</var><dd><a name="index-map-an-overlay-769"></a>Tell <span class="sc">gdb</span> that <var>overlay</var> is now mapped; <var>overlay</var> must |
| be the name of the object file section containing the overlay. When an |
| overlay is mapped, <span class="sc">gdb</span> assumes it can find the overlay's |
| functions and variables at their mapped addresses. <span class="sc">gdb</span> assumes |
| that any other overlays whose mapped ranges overlap that of |
| <var>overlay</var> are now unmapped. |
| |
| <br><dt><code>overlay unmap-overlay </code><var>overlay</var><dt><code>overlay unmap </code><var>overlay</var><dd><a name="index-unmap-an-overlay-770"></a>Tell <span class="sc">gdb</span> that <var>overlay</var> is no longer mapped; <var>overlay</var> |
| must be the name of the object file section containing the overlay. |
| When an overlay is unmapped, <span class="sc">gdb</span> assumes it can find the |
| overlay's functions and variables at their load addresses. |
| |
| <br><dt><code>overlay auto</code><dd>Enable <dfn>automatic</dfn> overlay debugging. In this mode, <span class="sc">gdb</span> |
| consults a data structure the overlay manager maintains in the inferior |
| to see which overlays are mapped. For details, see <a href="Automatic-Overlay-Debugging.html#Automatic-Overlay-Debugging">Automatic Overlay Debugging</a>. |
| |
| <br><dt><code>overlay load-target</code><dt><code>overlay load</code><dd><a name="index-reloading-the-overlay-table-771"></a>Re-read the overlay table from the inferior. Normally, <span class="sc">gdb</span> |
| re-reads the table <span class="sc">gdb</span> automatically each time the inferior |
| stops, so this command should only be necessary if you have changed the |
| overlay mapping yourself using <span class="sc">gdb</span>. This command is only |
| useful when using automatic overlay debugging. |
| |
| <br><dt><code>overlay list-overlays</code><dt><code>overlay list</code><dd><a name="index-listing-mapped-overlays-772"></a>Display a list of the overlays currently mapped, along with their mapped |
| addresses, load addresses, and sizes. |
| |
| </dl> |
| |
| <p>Normally, when <span class="sc">gdb</span> prints a code address, it includes the name |
| of the function the address falls in: |
| |
| <pre class="smallexample"> (gdb) print main |
| $3 = {int ()} 0x11a0 <main> |
| </pre> |
| <p class="noindent">When overlay debugging is enabled, <span class="sc">gdb</span> recognizes code in |
| unmapped overlays, and prints the names of unmapped functions with |
| asterisks around them. For example, if <code>foo</code> is a function in an |
| unmapped overlay, <span class="sc">gdb</span> prints it this way: |
| |
| <pre class="smallexample"> (gdb) overlay list |
| No sections are mapped. |
| (gdb) print foo |
| $5 = {int (int)} 0x100000 <*foo*> |
| </pre> |
| <p class="noindent">When <code>foo</code>'s overlay is mapped, <span class="sc">gdb</span> prints the function's |
| name normally: |
| |
| <pre class="smallexample"> (gdb) overlay list |
| Section .ov.foo.text, loaded at 0x100000 - 0x100034, |
| mapped at 0x1016 - 0x104a |
| (gdb) print foo |
| $6 = {int (int)} 0x1016 <foo> |
| </pre> |
| <p>When overlay debugging is enabled, <span class="sc">gdb</span> can find the correct |
| address for functions and variables in an overlay, whether or not the |
| overlay is mapped. This allows most <span class="sc">gdb</span> commands, like |
| <code>break</code> and <code>disassemble</code>, to work normally, even on unmapped |
| code. However, <span class="sc">gdb</span>'s breakpoint support has some limitations: |
| |
| <ul> |
| <li><a name="index-breakpoints-in-overlays-773"></a><a name="index-overlays_002c-setting-breakpoints-in-774"></a>You can set breakpoints in functions in unmapped overlays, as long as |
| <span class="sc">gdb</span> can write to the overlay at its load address. |
| <li><span class="sc">gdb</span> can not set hardware or simulator-based breakpoints in |
| unmapped overlays. However, if you set a breakpoint at the end of your |
| overlay manager (and tell <span class="sc">gdb</span> which overlays are now mapped, if |
| you are using manual overlay management), <span class="sc">gdb</span> will re-set its |
| breakpoints properly. |
| </ul> |
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