| <html lang="en"> |
| <head> |
| <title>Automatic Overlay Debugging - Debugging with GDB</title> |
| <meta http-equiv="Content-Type" content="text/html"> |
| <meta name="description" content="Debugging with GDB"> |
| <meta name="generator" content="makeinfo 4.13"> |
| <link title="Top" rel="start" href="index.html#Top"> |
| <link rel="up" href="Overlays.html#Overlays" title="Overlays"> |
| <link rel="prev" href="Overlay-Commands.html#Overlay-Commands" title="Overlay Commands"> |
| <link rel="next" href="Overlay-Sample-Program.html#Overlay-Sample-Program" title="Overlay Sample Program"> |
| <link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage"> |
| <!-- |
| Copyright (C) 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, |
| 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010 |
| Free Software Foundation, Inc. |
| |
| Permission is granted to copy, distribute and/or modify this document |
| under the terms of the GNU Free Documentation License, Version 1.3 or |
| any later version published by the Free Software Foundation; with the |
| Invariant Sections being ``Free Software'' and ``Free Software Needs |
| Free Documentation'', with the Front-Cover Texts being ``A GNU Manual,'' |
| and with the Back-Cover Texts as in (a) below. |
| |
| (a) The FSF's Back-Cover Text is: ``You are free to copy and modify |
| this GNU Manual. Buying copies from GNU Press supports the FSF in |
| developing GNU and promoting software freedom.''--> |
| <meta http-equiv="Content-Style-Type" content="text/css"> |
| <style type="text/css"><!-- |
| pre.display { font-family:inherit } |
| pre.format { font-family:inherit } |
| pre.smalldisplay { font-family:inherit; font-size:smaller } |
| pre.smallformat { font-family:inherit; font-size:smaller } |
| pre.smallexample { font-size:smaller } |
| pre.smalllisp { font-size:smaller } |
| span.sc { font-variant:small-caps } |
| span.roman { font-family:serif; font-weight:normal; } |
| span.sansserif { font-family:sans-serif; font-weight:normal; } |
| --></style> |
| <link rel="stylesheet" type="text/css" href="../cs.css"> |
| </head> |
| <body> |
| <div class="node"> |
| <a name="Automatic-Overlay-Debugging"></a> |
| <p> |
| Next: <a rel="next" accesskey="n" href="Overlay-Sample-Program.html#Overlay-Sample-Program">Overlay Sample Program</a>, |
| Previous: <a rel="previous" accesskey="p" href="Overlay-Commands.html#Overlay-Commands">Overlay Commands</a>, |
| Up: <a rel="up" accesskey="u" href="Overlays.html#Overlays">Overlays</a> |
| <hr> |
| </div> |
| |
| <h3 class="section">14.3 Automatic Overlay Debugging</h3> |
| |
| <p><a name="index-automatic-overlay-debugging-775"></a> |
| <span class="sc">gdb</span> can automatically track which overlays are mapped and which |
| are not, given some simple co-operation from the overlay manager in the |
| inferior. If you enable automatic overlay debugging with the |
| <code>overlay auto</code> command (see <a href="Overlay-Commands.html#Overlay-Commands">Overlay Commands</a>), <span class="sc">gdb</span> |
| looks in the inferior's memory for certain variables describing the |
| current state of the overlays. |
| |
| <p>Here are the variables your overlay manager must define to support |
| <span class="sc">gdb</span>'s automatic overlay debugging: |
| |
| <dl> |
| <dt><code>_ovly_table</code>:<dd>This variable must be an array of the following structures: |
| |
| <pre class="smallexample"> struct |
| { |
| /* The overlay's mapped address. */ |
| unsigned long vma; |
| |
| /* The size of the overlay, in bytes. */ |
| unsigned long size; |
| |
| /* The overlay's load address. */ |
| unsigned long lma; |
| |
| /* Non-zero if the overlay is currently mapped; |
| zero otherwise. */ |
| unsigned long mapped; |
| } |
| </pre> |
| <br><dt><code>_novlys</code>:<dd>This variable must be a four-byte signed integer, holding the total |
| number of elements in <code>_ovly_table</code>. |
| |
| </dl> |
| |
| <p>To decide whether a particular overlay is mapped or not, <span class="sc">gdb</span> |
| looks for an entry in <code>_ovly_table</code><!-- /@w --> whose <code>vma</code> and |
| <code>lma</code> members equal the VMA and LMA of the overlay's section in the |
| executable file. When <span class="sc">gdb</span> finds a matching entry, it consults |
| the entry's <code>mapped</code> member to determine whether the overlay is |
| currently mapped. |
| |
| <p>In addition, your overlay manager may define a function called |
| <code>_ovly_debug_event</code>. If this function is defined, <span class="sc">gdb</span> |
| will silently set a breakpoint there. If the overlay manager then |
| calls this function whenever it has changed the overlay table, this |
| will enable <span class="sc">gdb</span> to accurately keep track of which overlays |
| are in program memory, and update any breakpoints that may be set |
| in overlays. This will allow breakpoints to work even if the |
| overlays are kept in ROM or other non-writable memory while they |
| are not being executed. |
| |
| </body></html> |
| |
