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diff --git a/share/doc/gdb/Non_002ddebug-DLL-Symbols.html b/share/doc/gdb/Non_002ddebug-DLL-Symbols.html new file mode 100644 index 0000000..2706d85 --- /dev/null +++ b/share/doc/gdb/Non_002ddebug-DLL-Symbols.html @@ -0,0 +1,195 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> +<html> +<!-- Copyright (C) 1988-2023 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." --> +<!-- Created by GNU Texinfo 5.1, http://www.gnu.org/software/texinfo/ --> +<head> +<title>Debugging with GDB: Non-debug DLL Symbols</title> + +<meta name="description" content="Debugging with GDB: Non-debug DLL Symbols"> +<meta name="keywords" content="Debugging with GDB: Non-debug DLL Symbols"> +<meta name="resource-type" content="document"> +<meta name="distribution" content="global"> +<meta name="Generator" content="makeinfo"> +<meta http-equiv="Content-Type" content="text/html; charset=utf-8"> +<link href="index.html#Top" rel="start" title="Top"> +<link href="Concept-Index.html#Concept-Index" rel="index" title="Concept Index"> +<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents"> +<link href="Cygwin-Native.html#Cygwin-Native" rel="up" title="Cygwin Native"> +<link href="Hurd-Native.html#Hurd-Native" rel="next" title="Hurd Native"> +<link href="Cygwin-Native.html#Cygwin-Native" rel="previous" title="Cygwin Native"> +<style type="text/css"> +<!-- +a.summary-letter {text-decoration: none} +blockquote.smallquotation {font-size: smaller} +div.display {margin-left: 3.2em} +div.example {margin-left: 3.2em} +div.indentedblock {margin-left: 3.2em} +div.lisp {margin-left: 3.2em} +div.smalldisplay {margin-left: 3.2em} +div.smallexample {margin-left: 3.2em} +div.smallindentedblock {margin-left: 3.2em; font-size: smaller} +div.smalllisp {margin-left: 3.2em} +kbd {font-style:oblique} +pre.display {font-family: inherit} +pre.format {font-family: inherit} +pre.menu-comment {font-family: serif} +pre.menu-preformatted {font-family: serif} +pre.smalldisplay {font-family: inherit; font-size: smaller} +pre.smallexample {font-size: smaller} +pre.smallformat {font-family: inherit; font-size: smaller} +pre.smalllisp {font-size: smaller} +span.nocodebreak {white-space:nowrap} +span.nolinebreak {white-space:nowrap} +span.roman {font-family:serif; font-weight:normal} +span.sansserif {font-family:sans-serif; font-weight:normal} +ul.no-bullet {list-style: none} +--> +</style> + + +</head> + +<body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000"> +<a name="Non_002ddebug-DLL-Symbols"></a> +<div class="header"> +<p> +Up: <a href="Cygwin-Native.html#Cygwin-Native" accesskey="u" rel="up">Cygwin Native</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> +</div> +<hr> +<a name="Support-for-DLLs-without-Debugging-Symbols"></a> +<h4 class="subsubsection">21.1.4.1 Support for DLLs without Debugging Symbols</h4> +<a name="index-DLLs-with-no-debugging-symbols"></a> +<a name="index-Minimal-symbols-and-DLLs"></a> + +<p>Very often on windows, some of the DLLs that your program relies on do +not include symbolic debugging information (for example, +<samp>kernel32.dll</samp>). When <small>GDB</small> doesn’t recognize any debugging +symbols in a DLL, it relies on the minimal amount of symbolic +information contained in the DLL’s export table. This section +describes working with such symbols, known internally to <small>GDB</small> as +“minimal symbols”. +</p> +<p>Note that before the debugged program has started execution, no DLLs +will have been loaded. The easiest way around this problem is simply to +start the program — either by setting a breakpoint or letting the +program run once to completion. +</p> +<a name="DLL-Name-Prefixes"></a> +<h4 class="subsubsection">21.1.4.2 DLL Name Prefixes</h4> + +<p>In keeping with the naming conventions used by the Microsoft debugging +tools, DLL export symbols are made available with a prefix based on the +DLL name, for instance <code>KERNEL32!CreateFileA</code>. The plain name is +also entered into the symbol table, so <code>CreateFileA</code> is often +sufficient. In some cases there will be name clashes within a program +(particularly if the executable itself includes full debugging symbols) +necessitating the use of the fully qualified name when referring to the +contents of the DLL. Use single-quotes around the name to avoid the +exclamation mark (“!”) being interpreted as a language operator. +</p> +<p>Note that the internal name of the DLL may be all upper-case, even +though the file name of the DLL is lower-case, or vice-versa. Since +symbols within <small>GDB</small> are <em>case-sensitive</em> this may cause +some confusion. If in doubt, try the <code>info functions</code> and +<code>info variables</code> commands or even <code>maint print msymbols</code> +(see <a href="Symbols.html#Symbols">Symbols</a>). Here’s an example: +</p> +<div class="smallexample"> +<pre class="smallexample">(gdb) info function CreateFileA +All functions matching regular expression "CreateFileA": + +Non-debugging symbols: +0x77e885f4 CreateFileA +0x77e885f4 KERNEL32!CreateFileA +</pre></div> + +<div class="smallexample"> +<pre class="smallexample">(gdb) info function ! +All functions matching regular expression "!": + +Non-debugging symbols: +0x6100114c cygwin1!__assert +0x61004034 cygwin1!_dll_crt0@0 +0x61004240 cygwin1!dll_crt0(per_process *) +[etc...] +</pre></div> + +<a name="Working-with-Minimal-Symbols"></a> +<h4 class="subsubsection">21.1.4.3 Working with Minimal Symbols</h4> + +<p>Symbols extracted from a DLL’s export table do not contain very much +type information. All that <small>GDB</small> can do is guess whether a symbol +refers to a function or variable depending on the linker section that +contains the symbol. Also note that the actual contents of the memory +contained in a DLL are not available unless the program is running. This +means that you cannot examine the contents of a variable or disassemble +a function within a DLL without a running program. +</p> +<p>Variables are generally treated as pointers and dereferenced +automatically. For this reason, it is often necessary to prefix a +variable name with the address-of operator (“&”) and provide explicit +type information in the command. Here’s an example of the type of +problem: +</p> +<div class="smallexample"> +<pre class="smallexample">(gdb) print 'cygwin1!__argv' +'cygwin1!__argv' has unknown type; cast it to its declared type +</pre></div> + +<div class="smallexample"> +<pre class="smallexample">(gdb) x 'cygwin1!__argv' +'cygwin1!__argv' has unknown type; cast it to its declared type +</pre></div> + +<p>And two possible solutions: +</p> +<div class="smallexample"> +<pre class="smallexample">(gdb) print ((char **)'cygwin1!__argv')[0] +$2 = 0x22fd98 "/cygdrive/c/mydirectory/myprogram" +</pre></div> + +<div class="smallexample"> +<pre class="smallexample">(gdb) x/2x &'cygwin1!__argv' +0x610c0aa8 <cygwin1!__argv>: 0x10021608 0x00000000 +(gdb) x/x 0x10021608 +0x10021608: 0x0022fd98 +(gdb) x/s 0x0022fd98 +0x22fd98: "/cygdrive/c/mydirectory/myprogram" +</pre></div> + +<p>Setting a break point within a DLL is possible even before the program +starts execution. However, under these circumstances, <small>GDB</small> can’t +examine the initial instructions of the function in order to skip the +function’s frame set-up code. You can work around this by using “*&” +to set the breakpoint at a raw memory address: +</p> +<div class="smallexample"> +<pre class="smallexample">(gdb) break *&'python22!PyOS_Readline' +Breakpoint 1 at 0x1e04eff0 +</pre></div> + +<p>The author of these extensions is not entirely convinced that setting a +break point within a shared DLL like <samp>kernel32.dll</samp> is completely +safe. +</p> +<hr> +<div class="header"> +<p> +Up: <a href="Cygwin-Native.html#Cygwin-Native" accesskey="u" rel="up">Cygwin Native</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> +</div> + + + +</body> +</html> |