1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
|
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>Debugging Support</title><meta name="generator" content="DocBook XSL Stylesheets V1.74.0" /><meta name="keywords" content=" C++ , debug " /><meta name="keywords" content=" ISO C++ , library " /><link rel="home" href="../spine.html" title="The GNU C++ Library Documentation" /><link rel="up" href="using.html" title="Chapter 3. Using" /><link rel="prev" href="using_exceptions.html" title="Exceptions" /><link rel="next" href="support.html" title="Part II. Support" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Debugging Support</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="using_exceptions.html">Prev</a> </td><th width="60%" align="center">Chapter 3. Using</th><td width="20%" align="right"> <a accesskey="n" href="support.html">Next</a></td></tr></table><hr /></div><div class="sect1" lang="en" xml:lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="manual.intro.using.debug"></a>Debugging Support</h2></div></div></div><p>
There are numerous things that can be done to improve the ease with
which C++ binaries are debugged when using the GNU tool chain. Here
are some of them.
</p><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="debug.compiler"></a>Using <span class="command"><strong>g++</strong></span></h3></div></div></div><p>
Compiler flags determine how debug information is transmitted
between compilation and debug or analysis tools.
</p><p>
The default optimizations and debug flags for a libstdc++ build
are <code class="code">-g -O2</code>. However, both debug and optimization
flags can be varied to change debugging characteristics. For
instance, turning off all optimization via the <code class="code">-g -O0
-fno-inline</code> flags will disable inlining and optimizations,
and add debugging information, so that stepping through all functions,
(including inlined constructors and destructors) is possible. In
addition, <code class="code">-fno-eliminate-unused-debug-types</code> can be
used when additional debug information, such as nested class info,
is desired.
</p><p>
Or, the debug format that the compiler and debugger use to
communicate information about source constructs can be changed via
<code class="code">-gdwarf-2</code> or <code class="code">-gstabs</code> flags: some debugging
formats permit more expressive type and scope information to be
shown in gdb. Expressiveness can be enhanced by flags like
<code class="code">-g3</code>. The default debug information for a particular
platform can be identified via the value set by the
PREFERRED_DEBUGGING_TYPE macro in the gcc sources.
</p><p>
Many other options are available: please see <a class="ulink" href="http://gcc.gnu.org/onlinedocs/gcc/Debugging-Options.html#Debugging%20Options" target="_top">"Options
for Debugging Your Program"</a> in Using the GNU Compiler
Collection (GCC) for a complete list.
</p></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="debug.req"></a>Debug Versions of Library Binary Files</h3></div></div></div><p>
If you would like debug symbols in libstdc++, there are two ways to
build libstdc++ with debug flags. The first is to run make from the
toplevel in a freshly-configured tree with
</p><pre class="programlisting">
--enable-libstdcxx-debug
</pre><p>and perhaps</p><pre class="programlisting">
--enable-libstdcxx-debug-flags='...'
</pre><p>
to create a separate debug build. Both the normal build and the
debug build will persist, without having to specify
<code class="code">CXXFLAGS</code>, and the debug library will be installed in a
separate directory tree, in <code class="code">(prefix)/lib/debug</code>. For
more information, look at the <a class="link" href="configure.html" title="Configure">configuration</a> section.
</p><p>
A second approach is to use the configuration flags
</p><pre class="programlisting">
make CXXFLAGS='-g3 -fno-inline -O0' all
</pre><p>
This quick and dirty approach is often sufficient for quick
debugging tasks, when you cannot or don't want to recompile your
application to use the <a class="link" href="debug_mode.html" title="Chapter 30. Debug Mode">debug mode</a>.</p></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="debug.memory"></a>Memory Leak Hunting</h3></div></div></div><p>
There are various third party memory tracing and debug utilities
that can be used to provide detailed memory allocation information
about C++ code. An exhaustive list of tools is not going to be
attempted, but includes <code class="code">mtrace</code>, <code class="code">valgrind</code>,
<code class="code">mudflap</code>, and the non-free commercial product
<code class="code">purify</code>. In addition, <code class="code">libcwd</code> has a
replacement for the global new and delete operators that can track
memory allocation and deallocation and provide useful memory
statistics.
</p><p>
Regardless of the memory debugging tool being used, there is one
thing of great importance to keep in mind when debugging C++ code
that uses <code class="code">new</code> and <code class="code">delete</code>: there are
different kinds of allocation schemes that can be used by <code class="code">
std::allocator </code>. For implementation details, see the <a class="link" href="ext_allocators.html#manual.ext.allocator.mt" title="mt_allocator">mt allocator</a> documentation and
look specifically for <code class="code">GLIBCXX_FORCE_NEW</code>.
</p><p>
In a nutshell, the default allocator used by <code class="code">
std::allocator</code> is a high-performance pool allocator, and can
give the mistaken impression that in a suspect executable, memory is
being leaked, when in reality the memory "leak" is a pool being used
by the library's allocator and is reclaimed after program
termination.
</p><p>
For valgrind, there are some specific items to keep in mind. First
of all, use a version of valgrind that will work with current GNU
C++ tools: the first that can do this is valgrind 1.0.4, but later
versions should work at least as well. Second of all, use a
completely unoptimized build to avoid confusing valgrind. Third, use
GLIBCXX_FORCE_NEW to keep extraneous pool allocation noise from
cluttering debug information.
</p><p>
Fourth, it may be necessary to force deallocation in other libraries
as well, namely the "C" library. On linux, this can be accomplished
with the appropriate use of the <code class="code">__cxa_atexit</code> or
<code class="code">atexit</code> functions.
</p><pre class="programlisting">
#include <cstdlib>
extern "C" void __libc_freeres(void);
void do_something() { }
int main()
{
atexit(__libc_freeres);
do_something();
return 0;
}
</pre><p>or, using <code class="code">__cxa_atexit</code>:</p><pre class="programlisting">
extern "C" void __libc_freeres(void);
extern "C" int __cxa_atexit(void (*func) (void *), void *arg, void *d);
void do_something() { }
int main()
{
extern void* __dso_handle __attribute__ ((__weak__));
__cxa_atexit((void (*) (void *)) __libc_freeres, NULL,
&__dso_handle ? __dso_handle : NULL);
do_test();
return 0;
}
</pre><p>
Suggested valgrind flags, given the suggestions above about setting
up the runtime environment, library, and test file, might be:
</p><pre class="programlisting">
valgrind -v --num-callers=20 --leak-check=yes --leak-resolution=high --show-reachable=yes a.out
</pre></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="debug.gdb"></a>Using <span class="command"><strong>gdb</strong></span></h3></div></div></div><p>
</p><p>
Many options are available for gdb itself: please see <a class="ulink" href="http://sources.redhat.com/gdb/current/onlinedocs/gdb_13.html#SEC125" target="_top">
"GDB features for C++" </a> in the gdb documentation. Also
recommended: the other parts of this manual.
</p><p>
These settings can either be switched on in at the gdb command line,
or put into a .gdbint file to establish default debugging
characteristics, like so:
</p><pre class="programlisting">
set print pretty on
set print object on
set print static-members on
set print vtbl on
set print demangle on
set demangle-style gnu-v3
</pre></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="debug.exceptions"></a>Tracking uncaught exceptions</h3></div></div></div><p>
The <a class="link" href="verbose_termination.html" title="Verbose Terminate Handler">verbose
termination handler</a> gives information about uncaught
exceptions which are killing the program. It is described in the
linked-to page.
</p></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="debug.debug_mode"></a>Debug Mode</h3></div></div></div><p> The <a class="link" href="debug_mode.html" title="Chapter 30. Debug Mode">Debug Mode</a>
has compile and run-time checks for many containers.
</p></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="debug.compile_time_checks"></a>Compile Time Checking</h3></div></div></div><p> The <a class="link" href="ext_compile_checks.html" title="Chapter 29. Compile Time Checks">Compile-Time
Checks</a> Extension has compile-time checks for many algorithms.
</p></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="using_exceptions.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="using.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="support.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Exceptions </td><td width="20%" align="center"><a accesskey="h" href="../spine.html">Home</a></td><td width="40%" align="right" valign="top"> Part II.
Support
</td></tr></table></div></body></html>
|
