libstdc++-v3/doc/html/manual/debug.html

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   3 <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 V1.75.2" /><meta name="keywords" content="&#10;      C++&#10;    , &#10;      debug&#10;    " /><meta name="keywords" content="&#10;      ISO C++&#10;    , &#10;      library&#10;    " /><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" title="Debugging Support"><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>
   4   There are numerous things that can be done to improve the ease with
   5   which C++ binaries are debugged when using the GNU tool chain. Here
   6   are some of them.
   7 </p><div class="sect2" title="Using g++"><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>
   8     Compiler flags determine how debug information is transmitted
   9     between compilation and debug or analysis tools.
  10   </p><p>
  11     The default optimizations and debug flags for a libstdc++ build
  12     are <code class="code">-g -O2</code>. However, both debug and optimization
  13     flags can be varied to change debugging characteristics. For
  14     instance, turning off all optimization via the <code class="code">-g -O0
  15     -fno-inline</code> flags will disable inlining and optimizations,
  16     and add debugging information, so that stepping through all functions,
  17     (including inlined constructors and destructors) is possible. In
  18     addition, <code class="code">-fno-eliminate-unused-debug-types</code> can be
  19     used when additional debug information, such as nested class info,
  20     is desired.
  21 </p><p>
  22   Or, the debug format that the compiler and debugger use to
  23   communicate information about source constructs can be changed via
  24   <code class="code">-gdwarf-2</code> or <code class="code">-gstabs</code> flags: some debugging
  25   formats permit more expressive type and scope information to be
  26   shown in gdb. Expressiveness can be enhanced by flags like
  27   <code class="code">-g3</code>. The default debug information for a particular
  28   platform can be identified via the value set by the
  29   PREFERRED_DEBUGGING_TYPE macro in the gcc sources.
  30 </p><p>
  31   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
  32   for Debugging Your Program"</a> in Using the GNU Compiler
  33   Collection (GCC) for a complete list.
  34 </p></div><div class="sect2" title="Debug Versions of Library Binary Files"><div class="titlepage"><div><div><h3 class="title"><a id="debug.req"></a>Debug Versions of Library Binary Files</h3></div></div></div><p>
  35   If you would like debug symbols in libstdc++, there are two ways to
  36   build libstdc++ with debug flags. The first is to run make from the
  37   toplevel in a freshly-configured tree with
  38 </p><pre class="programlisting">
  39      --enable-libstdcxx-debug
  40 </pre><p>and perhaps</p><pre class="programlisting">
  41      --enable-libstdcxx-debug-flags='...'
  42 </pre><p>
  43   to create a separate debug build. Both the normal build and the
  44   debug build will persist, without having to specify
  45   <code class="code">CXXFLAGS</code>, and the debug library will be installed in a
  46   separate directory tree, in <code class="code">(prefix)/lib/debug</code>. For
  47   more information, look at the <a class="link" href="configure.html" title="Configure">configuration</a> section.
  48 </p><p>
  49   A second approach is to use the configuration flags
  50 </p><pre class="programlisting">
  51      make CXXFLAGS='-g3 -fno-inline -O0' all
  52 </pre><p>
  53   This quick and dirty approach is often sufficient for quick
  54   debugging tasks, when you cannot or don't want to recompile your
  55   application to use the <a class="link" href="debug_mode.html" title="Chapter 30. Debug Mode">debug mode</a>.</p></div><div class="sect2" title="Memory Leak Hunting"><div class="titlepage"><div><div><h3 class="title"><a id="debug.memory"></a>Memory Leak Hunting</h3></div></div></div><p>
  56   There are various third party memory tracing and debug utilities
  57   that can be used to provide detailed memory allocation information
  58   about C++ code. An exhaustive list of tools is not going to be
  59   attempted, but includes <code class="code">mtrace</code>, <code class="code">valgrind</code>,
  60   <code class="code">mudflap</code>, and the non-free commercial product
  61   <code class="code">purify</code>. In addition, <code class="code">libcwd</code> has a
  62   replacement for the global new and delete operators that can track
  63   memory allocation and deallocation and provide useful memory
  64   statistics.
  65 </p><p>
  66   Regardless of the memory debugging tool being used, there is one
  67   thing of great importance to keep in mind when debugging C++ code
  68   that uses <code class="code">new</code> and <code class="code">delete</code>: there are
  69   different kinds of allocation schemes that can be used by <code class="code">
  70   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
  71   look specifically for <code class="code">GLIBCXX_FORCE_NEW</code>.
  72 </p><p>
  73   In a nutshell, the default allocator used by <code class="code">
  74   std::allocator</code> is a high-performance pool allocator, and can
  75   give the mistaken impression that in a suspect executable, memory is
  76   being leaked, when in reality the memory "leak" is a pool being used
  77   by the library's allocator and is reclaimed after program
  78   termination.
  79 </p><p>
  80   For valgrind, there are some specific items to keep in mind. First
  81   of all, use a version of valgrind that will work with current GNU
  82   C++ tools: the first that can do this is valgrind 1.0.4, but later
  83   versions should work at least as well. Second of all, use a
  84   completely unoptimized build to avoid confusing valgrind. Third, use
  85   GLIBCXX_FORCE_NEW to keep extraneous pool allocation noise from
  86   cluttering debug information.
  87 </p><p>
  88   Fourth, it may be necessary to force deallocation in other libraries
  89   as well, namely the "C" library. On linux, this can be accomplished
  90   with the appropriate use of the <code class="code">__cxa_atexit</code> or
  91   <code class="code">atexit</code> functions.
  92 </p><pre class="programlisting">
  93    #include &lt;cstdlib&gt;
  94
  95    extern "C" void __libc_freeres(void);
  96
  97    void do_something() { }
  98
  99    int main()
 100    {
 101      atexit(__libc_freeres);
 102      do_something();
 103      return 0;
 104    }
 105 </pre><p>or, using <code class="code">__cxa_atexit</code>:</p><pre class="programlisting">
 106    extern "C" void __libc_freeres(void);
 107    extern "C" int __cxa_atexit(void (*func) (void *), void *arg, void *d);
 108
 109    void do_something() { }
 110
 111    int main()
 112    {
 113       extern void* __dso_handle __attribute__ ((__weak__));
 114       __cxa_atexit((void (*) (void *)) __libc_freeres, NULL,
 115                    &amp;__dso_handle ? __dso_handle : NULL);
 116       do_test();
 117       return 0;
 118    }
 119 </pre><p>
 120   Suggested valgrind flags, given the suggestions above about setting
 121   up the runtime environment, library, and test file, might be:
 122 </p><pre class="programlisting">
 123    valgrind -v --num-callers=20 --leak-check=yes --leak-resolution=high --show-reachable=yes a.out
 124 </pre></div><div class="sect2" title="Using gdb"><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>
 125   </p><p>
 126   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">
 127   "GDB features for C++" </a> in the gdb documentation. Also
 128   recommended: the other parts of this manual.
 129 </p><p>
 130   These settings can either be switched on in at the gdb command line,
 131   or put into a .gdbint file to establish default debugging
 132   characteristics, like so:
 133 </p><pre class="programlisting">
 134    set print pretty on
 135    set print object on
 136    set print static-members on
 137    set print vtbl on
 138    set print demangle on
 139    set demangle-style gnu-v3
 140 </pre><p>
 141   Starting with version 7.0, GDB includes support for writing
 142   pretty-printers in Python.  Pretty printers for STL classes are
 143   distributed with GCC from version 4.5.0.  The most recent version of
 144   these printers are always found in libstdc++ svn repository.
 145   To enable these printers, check-out the latest printers to a local
 146   directory:
 147 </p><pre class="programlisting">
 148   svn co svn://gcc.gnu.org/svn/gcc/trunk/libstdc++-v3/python
 149 </pre><p>
 150   Next, add the following section to your ~/.gdbinit  The path must
 151   match the location where the Python module above was checked-out.
 152   So if checked out to: /home/maude/gdb_printers/, the path would be as
 153   written in the example below.
 154 </p><pre class="programlisting">
 155   python
 156   import sys
 157   sys.path.insert(0, '/home/maude/gdb_printers/python')
 158   from libstdcxx.v6.printers import register_libstdcxx_printers
 159   register_libstdcxx_printers (None)
 160   end
 161 </pre><p>
 162   The path should be the only element that needs to be adjusted in the
 163   example.  Once loaded, STL classes that the printers support
 164   should print in a more human-readable format.  To print the classes
 165   in the old style, use the /r (raw) switch in the print command
 166   (i.e., print /r foo).  This will print the classes as if the Python
 167   pretty-printers were not loaded.
 168 </p><p>
 169   For additional information on STL support and GDB please visit:
 170   <a class="ulink" href="http://sourceware.org/gdb/wiki/STLSupport" target="_top"> "GDB Support
 171   for STL" </a> in the GDB wiki.  Additionally, in-depth
 172   documentation and discussion of the pretty printing feature can be
 173   found in "Pretty Printing" node in the GDB manual.  You can find
 174   on-line versions of the GDB user manual in GDB's homepage, at
 175   <a class="ulink" href="http://sourceware.org/gdb/" target="_top"> "GDB: The GNU Project
 176   Debugger" </a>.
 177 </p></div><div class="sect2" title="Tracking uncaught exceptions"><div class="titlepage"><div><div><h3 class="title"><a id="debug.exceptions"></a>Tracking uncaught exceptions</h3></div></div></div><p>
 178   The <a class="link" href="verbose_termination.html" title="Verbose Terminate Handler">verbose
 179   termination handler</a> gives information about uncaught
 180   exceptions which are killing the program.  It is described in the
 181   linked-to page.
 182 </p></div><div class="sect2" title="Debug Mode"><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>
 183   has compile and run-time checks for many containers.
 184   </p></div><div class="sect2" title="Compile Time Checking"><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
 185   Checks</a> Extension has compile-time checks for many algorithms.
 186   </p></div><div class="sect2" title="Profile-based Performance Analysis"><div class="titlepage"><div><div><h3 class="title"><a id="debug.profile_mode"></a>Profile-based Performance Analysis</h3></div></div></div><p> The <a class="link" href="profile_mode.html" title="Chapter 32. Profile Mode">Profile-based
 187   Performance Analysis</a> Extension has performance checks for many
 188   algorithms.
 189   </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.
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