gcc-4_6_3-mobile/libstdc++-v3/doc/html/manual/debug.html

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   3 <html xmlns="http://www.w3.org/1999/xhtml"><head><title>Debugging Support</title><meta name="generator" content="DocBook XSL-NS Stylesheets V1.76.1"/><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"/><link rel="up" href="using.html" title="Chapter 3. Using"/><link rel="prev" href="using_exceptions.html" title="Exceptions"/><link rel="next" href="bk01pt02.html" title="Part II.  Standard Contents"/></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Debugging Support</th></tr><tr><td align="left"><a accesskey="p" href="using_exceptions.html">Prev</a> </td><th width="60%" align="center">Chapter 3. Using</th><td align="right"> <a accesskey="n" href="bk01pt02.html">Next</a></td></tr></table><hr/></div><div class="section" title="Debugging Support"><div class="titlepage"><div><div><h2 class="title"><a id="manual.intro.using.debug"/>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="section" title="Using g++"><div class="titlepage"><div><div><h3 class="title"><a id="debug.compiler"/>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="link" href="http://gcc.gnu.org/onlinedocs/gcc/Debugging-Options.html#Debugging%20Options">"Options
  32   for Debugging Your Program"</a> in Using the GNU Compiler
  33   Collection (GCC) for a complete list.
  34 </p></div><div class="section" title="Debug Versions of Library Binary Files"><div class="titlepage"><div><div><h3 class="title"><a id="debug.req"/>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 17. Debug Mode">debug mode</a>.</p></div><div class="section" title="Memory Leak Hunting"><div class="titlepage"><div><div><h3 class="title"><a id="debug.memory"/>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="section" title="Data Race Hunting"><div class="titlepage"><div><div><h3 class="title"><a id="debug.races"/>Data Race Hunting</h3></div></div></div><p>
 125   All synchronization primitives used in the library internals need to be
 126   understood by race detectors so that they do not produce false reports.
 127 </p><p>
 128   Two annotation macros are used to explain low-level synchronization
 129   to race detectors:
 130   <code class="code">_GLIBCXX_SYNCHRONIZATION_HAPPENS_BEFORE()</code> and
 131   <code class="code"> _GLIBCXX_SYNCHRONIZATION_HAPPENS_AFTER()</code>.
 132   By default, these macros are defined empty -- anyone who wants
 133   to use a race detector needs to redefine them to call an
 134   appropriate API.
 135   Since these macros are empty by default when the library is built,
 136   redefining them will only affect inline functions and template
 137   instantiations which are compiled in user code. This allows annotation
 138   of templates such as <code class="code">shared_ptr</code>, but not code which is
 139   only instantiated in the library.
 140   In order to annotate <code class="code">basic_string</code> reference counting it
 141   is necessary to disable extern templates (by defining
 142   <code class="code">_GLIBCXX_EXTERN_TEMPLATE=-1</code>) or to rebuild the
 143   <code class="code">.so</code> file.
 144   Annotating the remaining atomic operations (at the time of writing these
 145   are in <code class="code">ios_base::Init::~Init</code>, <code class="code">locale::_Impl</code> and
 146   <code class="code">locale::facet</code>) requires rebuilding the <code class="code">.so</code> file.
 147 </p><p>
 148   The approach described above is known to work with the following race
 149   detection tools:
 150   <a class="link" href="http://valgrind.org/docs/manual/drd-manual.html">
 151   DRD</a>,
 152   <a class="link" href="http://valgrind.org/docs/manual/hg-manual.html">
 153   Helgrind</a>, and
 154   <a class="link" href="http://code.google.com/p/data-race-test">
 155   ThreadSanitizer</a>.
 156 </p><p>
 157   With DRD, Helgrind and ThreadSanitizer you will need to define
 158   the macros like this:
 159 </p><pre class="programlisting">
 160   #define _GLIBCXX_SYNCHRONIZATION_HAPPENS_BEFORE(A) ANNOTATE_HAPPENS_BEFORE(A)
 161   #define _GLIBCXX_SYNCHRONIZATION_HAPPENS_AFTER(A)  ANNOTATE_HAPPENS_AFTER(A)
 162 </pre><p>
 163   Refer to the documentation of each particular tool for details.
 164 </p></div><div class="section" title="Using gdb"><div class="titlepage"><div><div><h3 class="title"><a id="debug.gdb"/>Using <span class="command"><strong>gdb</strong></span></h3></div></div></div><p>
 165   </p><p>
 166   Many options are available for GDB itself: please see <a class="link" href="http://sources.redhat.com/gdb/current/onlinedocs/gdb/">
 167   "GDB features for C++" </a> in the GDB documentation. Also
 168   recommended: the other parts of this manual.
 169 </p><p>
 170   These settings can either be switched on in at the GDB command line,
 171   or put into a .gdbint file to establish default debugging
 172   characteristics, like so:
 173 </p><pre class="programlisting">
 174    set print pretty on
 175    set print object on
 176    set print static-members on
 177    set print vtbl on
 178    set print demangle on
 179    set demangle-style gnu-v3
 180 </pre><p>
 181   Starting with version 7.0, GDB includes support for writing
 182   pretty-printers in Python.  Pretty printers for STL classes are
 183   distributed with GCC from version 4.5.0.  The most recent version of
 184   these printers are always found in libstdc++ svn repository.
 185   To enable these printers, check-out the latest printers to a local
 186   directory:
 187 </p><pre class="programlisting">
 188   svn co svn://gcc.gnu.org/svn/gcc/trunk/libstdc++-v3/python
 189 </pre><p>
 190   Next, add the following section to your ~/.gdbinit  The path must
 191   match the location where the Python module above was checked-out.
 192   So if checked out to: /home/maude/gdb_printers/, the path would be as
 193   written in the example below.
 194 </p><pre class="programlisting">
 195   python
 196   import sys
 197   sys.path.insert(0, '/home/maude/gdb_printers/python')
 198   from libstdcxx.v6.printers import register_libstdcxx_printers
 199   register_libstdcxx_printers (None)
 200   end
 201 </pre><p>
 202   The path should be the only element that needs to be adjusted in the
 203   example.  Once loaded, STL classes that the printers support
 204   should print in a more human-readable format.  To print the classes
 205   in the old style, use the /r (raw) switch in the print command
 206   (i.e., print /r foo).  This will print the classes as if the Python
 207   pretty-printers were not loaded.
 208 </p><p>
 209   For additional information on STL support and GDB please visit:
 210   <a class="link" href="http://sourceware.org/gdb/wiki/STLSupport"> "GDB Support
 211   for STL" </a> in the GDB wiki.  Additionally, in-depth
 212   documentation and discussion of the pretty printing feature can be
 213   found in "Pretty Printing" node in the GDB manual.  You can find
 214   on-line versions of the GDB user manual in GDB's homepage, at
 215   <a class="link" href="http://sourceware.org/gdb/"> "GDB: The GNU Project
 216   Debugger" </a>.
 217 </p></div><div class="section" title="Tracking uncaught exceptions"><div class="titlepage"><div><div><h3 class="title"><a id="debug.exceptions"/>Tracking uncaught exceptions</h3></div></div></div><p>
 218   The <a class="link" href="termination.html#support.termination.verbose" title="Verbose Terminate Handler">verbose
 219   termination handler</a> gives information about uncaught
 220   exceptions which are killing the program.  It is described in the
 221   linked-to page.
 222 </p></div><div class="section" title="Debug Mode"><div class="titlepage"><div><div><h3 class="title"><a id="debug.debug_mode"/>Debug Mode</h3></div></div></div><p> The <a class="link" href="debug_mode.html" title="Chapter 17. Debug Mode">Debug Mode</a>
 223   has compile and run-time checks for many containers.
 224   </p></div><div class="section" title="Compile Time Checking"><div class="titlepage"><div><div><h3 class="title"><a id="debug.compile_time_checks"/>Compile Time Checking</h3></div></div></div><p> The <a class="link" href="ext_compile_checks.html" title="Chapter 16. Compile Time Checks">Compile-Time
 225   Checks</a> Extension has compile-time checks for many algorithms.
 226   </p></div><div class="section" title="Profile-based Performance Analysis"><div class="titlepage"><div><div><h3 class="title"><a id="debug.profile_mode"/>Profile-based Performance Analysis</h3></div></div></div><p> The <a class="link" href="profile_mode.html" title="Chapter 19. Profile Mode">Profile-based
 227   Performance Analysis</a> Extension has performance checks for many
 228   algorithms.
 229   </p></div></div><div class="navfooter"><hr/><table width="100%" summary="Navigation footer"><tr><td align="left"><a accesskey="p" href="using_exceptions.html">Prev</a> </td><td align="center"><a accesskey="u" href="using.html">Up</a></td><td align="right"> <a accesskey="n" href="bk01pt02.html">Next</a></td></tr><tr><td align="left" valign="top">Exceptions </td><td align="center"><a accesskey="h" href="../spine.html">Home</a></td><td align="right" valign="top"> Part II.
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