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140 lines
6.2 KiB
HTML
140 lines
6.2 KiB
HTML
4 years ago
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html>
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<!-- Copyright (C) 1988-2019 Free Software Foundation, Inc.
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3 or
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any later version published by the Free Software Foundation; with the
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Invariant Sections being "Free Software" and "Free Software Needs
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Free Documentation", with the Front-Cover Texts being "A GNU Manual,"
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and with the Back-Cover Texts as in (a) below.
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(a) The FSF's Back-Cover Text is: "You are free to copy and modify
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this GNU Manual. Buying copies from GNU Press supports the FSF in
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developing GNU and promoting software freedom." -->
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<!-- Created by GNU Texinfo 6.4, http://www.gnu.org/software/texinfo/ -->
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<head>
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<title>Automatic Overlay Debugging (Debugging with GDB)</title>
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<meta name="description" content="Automatic Overlay Debugging (Debugging with GDB)">
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<meta name="keywords" content="Automatic Overlay Debugging (Debugging with GDB)">
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<meta name="resource-type" content="document">
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<meta name="distribution" content="global">
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<meta name="Generator" content="makeinfo">
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<link href="index.html#Top" rel="start" title="Top">
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<link href="Concept-Index.html#Concept-Index" rel="index" title="Concept Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="Overlays.html#Overlays" rel="up" title="Overlays">
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<link href="Overlay-Sample-Program.html#Overlay-Sample-Program" rel="next" title="Overlay Sample Program">
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<link href="Overlay-Commands.html#Overlay-Commands" rel="prev" title="Overlay Commands">
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<style type="text/css">
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a.summary-letter {text-decoration: none}
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div.example {margin-left: 3.2em}
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kbd {font-style: oblique}
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pre.smalllisp {font-size: smaller}
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span.nolinebreak {white-space: nowrap}
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ul.no-bullet {list-style: none}
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-->
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</style>
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</head>
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<body lang="en">
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<a name="Automatic-Overlay-Debugging"></a>
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<div class="header">
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<p>
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Next: <a href="Overlay-Sample-Program.html#Overlay-Sample-Program" accesskey="n" rel="next">Overlay Sample Program</a>, Previous: <a href="Overlay-Commands.html#Overlay-Commands" accesskey="p" rel="prev">Overlay Commands</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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</div>
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<hr>
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<a name="Automatic-Overlay-Debugging-1"></a>
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<h3 class="section">14.3 Automatic Overlay Debugging</h3>
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<a name="index-automatic-overlay-debugging"></a>
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<p><small>GDB</small> can automatically track which overlays are mapped and which
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are not, given some simple co-operation from the overlay manager in the
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inferior. If you enable automatic overlay debugging with the
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<code>overlay auto</code> command (see <a href="Overlay-Commands.html#Overlay-Commands">Overlay Commands</a>), <small>GDB</small>
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looks in the inferior’s memory for certain variables describing the
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current state of the overlays.
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</p>
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<p>Here are the variables your overlay manager must define to support
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<small>GDB</small>’s automatic overlay debugging:
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</p>
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<dl compact="compact">
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<dt><code>_ovly_table</code>:</dt>
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<dd><p>This variable must be an array of the following structures:
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</p>
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<div class="smallexample">
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<pre class="smallexample">struct
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{
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/* The overlay's mapped address. */
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unsigned long vma;
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/* The size of the overlay, in bytes. */
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unsigned long size;
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/* The overlay's load address. */
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unsigned long lma;
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/* Non-zero if the overlay is currently mapped;
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zero otherwise. */
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unsigned long mapped;
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}
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</pre></div>
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</dd>
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<dt><code>_novlys</code>:</dt>
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<dd><p>This variable must be a four-byte signed integer, holding the total
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number of elements in <code>_ovly_table</code>.
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</p>
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</dd>
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</dl>
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<p>To decide whether a particular overlay is mapped or not, <small>GDB</small>
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looks for an entry in <code><span class="nolinebreak">_ovly_table</span></code><!-- /@w --> whose <code>vma</code> and
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<code>lma</code> members equal the VMA and LMA of the overlay’s section in the
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executable file. When <small>GDB</small> finds a matching entry, it consults
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the entry’s <code>mapped</code> member to determine whether the overlay is
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currently mapped.
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</p>
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<p>In addition, your overlay manager may define a function called
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<code>_ovly_debug_event</code>. If this function is defined, <small>GDB</small>
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will silently set a breakpoint there. If the overlay manager then
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calls this function whenever it has changed the overlay table, this
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will enable <small>GDB</small> to accurately keep track of which overlays
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are in program memory, and update any breakpoints that may be set
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in overlays. This will allow breakpoints to work even if the
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overlays are kept in ROM or other non-writable memory while they
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are not being executed.
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</p>
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<hr>
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<div class="header">
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<p>
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Next: <a href="Overlay-Sample-Program.html#Overlay-Sample-Program" accesskey="n" rel="next">Overlay Sample Program</a>, Previous: <a href="Overlay-Commands.html#Overlay-Commands" accesskey="p" rel="prev">Overlay Commands</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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</div>
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</body>
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</html>
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