| Index: gcc/libstdc++-v3/doc/xml/manual/debug_mode.xml
|
| diff --git a/gcc/libstdc++-v3/doc/xml/manual/debug_mode.xml b/gcc/libstdc++-v3/doc/xml/manual/debug_mode.xml
|
| deleted file mode 100644
|
| index 223abcf9ae81ad48bfe23b59a13380d2b81017cc..0000000000000000000000000000000000000000
|
| --- a/gcc/libstdc++-v3/doc/xml/manual/debug_mode.xml
|
| +++ /dev/null
|
| @@ -1,888 +0,0 @@
|
| -<?xml version='1.0'?>
|
| -<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
|
| - "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd"
|
| -[ ]>
|
| -
|
| -<chapter id="manual.ext.debug_mode" xreflabel="Debug Mode">
|
| -<?dbhtml filename="debug_mode.html"?>
|
| -
|
| -<chapterinfo>
|
| - <keywordset>
|
| - <keyword>
|
| - C++
|
| - </keyword>
|
| - <keyword>
|
| - library
|
| - </keyword>
|
| - <keyword>
|
| - debug
|
| - </keyword>
|
| - </keywordset>
|
| -</chapterinfo>
|
| -
|
| -<title>Debug Mode</title>
|
| -
|
| -<sect1 id="manual.ext.debug_mode.intro" xreflabel="Intro">
|
| - <title>Intro</title>
|
| - <para>
|
| - By default, libstdc++ is built with efficiency in mind, and
|
| - therefore performs little or no error checking that is not
|
| - required by the C++ standard. This means that programs that
|
| - incorrectly use the C++ standard library will exhibit behavior
|
| - that is not portable and may not even be predictable, because they
|
| - tread into implementation-specific or undefined behavior. To
|
| - detect some of these errors before they can become problematic,
|
| - libstdc++ offers a debug mode that provides additional checking of
|
| - library facilities, and will report errors in the use of libstdc++
|
| - as soon as they can be detected by emitting a description of the
|
| - problem to standard error and aborting the program. This debug
|
| - mode is available with GCC 3.4.0 and later versions.
|
| - </para>
|
| -
|
| - <para>
|
| - The libstdc++ debug mode performs checking for many areas of the
|
| - C++ standard, but the focus is on checking interactions among
|
| - standard iterators, containers, and algorithms, including:
|
| - </para>
|
| -
|
| - <itemizedlist>
|
| - <listitem><para><emphasis>Safe iterators</emphasis>: Iterators keep track of the
|
| - container whose elements they reference, so errors such as
|
| - incrementing a past-the-end iterator or dereferencing an iterator
|
| - that points to a container that has been destructed are diagnosed
|
| - immediately.</para></listitem>
|
| -
|
| - <listitem><para><emphasis>Algorithm preconditions</emphasis>: Algorithms attempt to
|
| - validate their input parameters to detect errors as early as
|
| - possible. For instance, the <code>set_intersection</code>
|
| - algorithm requires that its iterator
|
| - parameters <code>first1</code> and <code>last1</code> form a valid
|
| - iterator range, and that the sequence
|
| - [<code>first1</code>, <code>last1</code>) is sorted according to
|
| - the same predicate that was passed
|
| - to <code>set_intersection</code>; the libstdc++ debug mode will
|
| - detect an error if the sequence is not sorted or was sorted by a
|
| - different predicate.</para></listitem>
|
| - </itemizedlist>
|
| -
|
| -</sect1>
|
| -
|
| -<sect1 id="manual.ext.debug_mode.semantics" xreflabel="Semantics">
|
| - <title>Semantics</title>
|
| - <para>
|
| - </para>
|
| -
|
| -<para>A program that uses the C++ standard library correctly
|
| - will maintain the same semantics under debug mode as it had with
|
| - the normal (release) library. All functional and exception-handling
|
| - guarantees made by the normal library also hold for the debug mode
|
| - library, with one exception: performance guarantees made by the
|
| - normal library may not hold in the debug mode library. For
|
| - instance, erasing an element in a <code>std::list</code> is a
|
| - constant-time operation in normal library, but in debug mode it is
|
| - linear in the number of iterators that reference that particular
|
| - list. So while your (correct) program won't change its results, it
|
| - is likely to execute more slowly.</para>
|
| -
|
| -<para>libstdc++ includes many extensions to the C++ standard library. In
|
| - some cases the extensions are obvious, such as the hashed
|
| - associative containers, whereas other extensions give predictable
|
| - results to behavior that would otherwise be undefined, such as
|
| - throwing an exception when a <code>std::basic_string</code> is
|
| - constructed from a NULL character pointer. This latter category also
|
| - includes implementation-defined and unspecified semantics, such as
|
| - the growth rate of a vector. Use of these extensions is not
|
| - considered incorrect, so code that relies on them will not be
|
| - rejected by debug mode. However, use of these extensions may affect
|
| - the portability of code to other implementations of the C++ standard
|
| - library, and is therefore somewhat hazardous. For this reason, the
|
| - libstdc++ debug mode offers a "pedantic" mode (similar to
|
| - GCC's <code>-pedantic</code> compiler flag) that attempts to emulate
|
| - the semantics guaranteed by the C++ standard. For
|
| - instance, constructing a <code>std::basic_string</code> with a NULL
|
| - character pointer would result in an exception under normal mode or
|
| - non-pedantic debug mode (this is a libstdc++ extension), whereas
|
| - under pedantic debug mode libstdc++ would signal an error. To enable
|
| - the pedantic debug mode, compile your program with
|
| - both <code>-D_GLIBCXX_DEBUG</code>
|
| - and <code>-D_GLIBCXX_DEBUG_PEDANTIC</code> .
|
| - (N.B. In GCC 3.4.x and 4.0.0, due to a bug,
|
| - <code>-D_GLIBXX_DEBUG_PEDANTIC</code> was also needed. The problem has
|
| - been fixed in GCC 4.0.1 and later versions.) </para>
|
| -
|
| -<para>The following library components provide extra debugging
|
| - capabilities in debug mode:</para>
|
| -<itemizedlist>
|
| - <listitem><para><code>std::basic_string</code> (no safe iterators and see note below)</para></listitem>
|
| - <listitem><para><code>std::bitset</code></para></listitem>
|
| - <listitem><para><code>std::deque</code></para></listitem>
|
| - <listitem><para><code>std::list</code></para></listitem>
|
| - <listitem><para><code>std::map</code></para></listitem>
|
| - <listitem><para><code>std::multimap</code></para></listitem>
|
| - <listitem><para><code>std::multiset</code></para></listitem>
|
| - <listitem><para><code>std::set</code></para></listitem>
|
| - <listitem><para><code>std::vector</code></para></listitem>
|
| - <listitem><para><code>std::unordered_map</code></para></listitem>
|
| - <listitem><para><code>std::unordered_multimap</code></para></listitem>
|
| - <listitem><para><code>std::unordered_set</code></para></listitem>
|
| - <listitem><para><code>std::unordered_multiset</code></para></listitem>
|
| -</itemizedlist>
|
| -
|
| -<para>N.B. although there are precondition checks for some string operations,
|
| -e.g. <code>operator[]</code>,
|
| -they will not always be run when using the <code>char</code> and
|
| -<code>wchar_t</code> specialisations (<code>std::string</code> and
|
| -<code>std::wstring</code>). This is because libstdc++ uses GCC's
|
| -<code>extern template</code> extension to provide explicit instantiations
|
| -of <code>std::string</code> and <code>std::wstring</code>, and those
|
| -explicit instantiations don't include the debug-mode checks. If the
|
| -containing functions are inlined then the checks will run, so compiling
|
| -with <code>-O1</code> might be enough to enable them. Alternatively
|
| -<code>-D_GLIBCXX_EXTERN_TEMPLATE=0</code> will suppress the declarations
|
| -of the explicit instantiations and cause the functions to be instantiated
|
| -with the debug-mode checks included, but this is unsupported and not
|
| -guaranteed to work. For full debug-mode support you can use the
|
| -<code>__gnu_debug::basic_string</code> debugging container directly,
|
| -which always works correctly.
|
| -</para>
|
| -
|
| -</sect1>
|
| -
|
| -<sect1 id="manual.ext.debug_mode.using" xreflabel="Using">
|
| - <title>Using</title>
|
| - <para>
|
| - </para>
|
| -<sect2 id="debug_mode.using.mode" xreflabel="Using Mode">
|
| - <title>Using the Debug Mode</title>
|
| -
|
| -<para>To use the libstdc++ debug mode, compile your application with the
|
| - compiler flag <code>-D_GLIBCXX_DEBUG</code>. Note that this flag
|
| - changes the sizes and behavior of standard class templates such
|
| - as <code>std::vector</code>, and therefore you can only link code
|
| - compiled with debug mode and code compiled without debug mode if no
|
| - instantiation of a container is passed between the two translation
|
| - units.</para>
|
| -
|
| -<para>By default, error messages are formatted to fit on lines of about
|
| - 78 characters. The environment variable
|
| - <code>GLIBCXX_DEBUG_MESSAGE_LENGTH</code> can be used to request a
|
| - different length.</para>
|
| -
|
| -</sect2>
|
| -
|
| -<sect2 id="debug_mode.using.specific" xreflabel="Using Specific">
|
| - <title>Using a Specific Debug Container</title>
|
| -<para>When it is not feasible to recompile your entire application, or
|
| - only specific containers need checking, debugging containers are
|
| - available as GNU extensions. These debugging containers are
|
| - functionally equivalent to the standard drop-in containers used in
|
| - debug mode, but they are available in a separate namespace as GNU
|
| - extensions and may be used in programs compiled with either release
|
| - mode or with debug mode. The
|
| - following table provides the names and headers of the debugging
|
| - containers:
|
| -</para>
|
| -
|
| -<table frame='all'>
|
| -<title>Debugging Containers</title>
|
| -<tgroup cols='6' align='left' colsep='1' rowsep='1'>
|
| -<colspec colname='c1'></colspec>
|
| -<colspec colname='c2'></colspec>
|
| -<colspec colname='c3'></colspec>
|
| -<colspec colname='c4'></colspec>
|
| -
|
| -<thead>
|
| - <row>
|
| - <entry>Container</entry>
|
| - <entry>Header</entry>
|
| - <entry>Debug container</entry>
|
| - <entry>Debug header</entry>
|
| - </row>
|
| -</thead>
|
| -<tbody>
|
| - <row>
|
| - <entry><classname>std::bitset</classname></entry>
|
| - <entry><filename class="headerfile">bitset</filename></entry>
|
| - <entry><classname>__gnu_debug::bitset</classname></entry>
|
| - <entry><filename class="headerfile">bitset</filename></entry>
|
| - </row>
|
| - <row>
|
| - <entry><classname>std::deque</classname></entry>
|
| - <entry><filename class="headerfile">deque</filename></entry>
|
| - <entry><classname>__gnu_debug::deque</classname></entry>
|
| - <entry><filename class="headerfile">deque</filename></entry>
|
| - </row>
|
| - <row>
|
| - <entry><classname>std::list</classname></entry>
|
| - <entry><filename class="headerfile">list</filename></entry>
|
| - <entry><classname>__gnu_debug::list</classname></entry>
|
| - <entry><filename class="headerfile">list</filename></entry>
|
| - </row>
|
| - <row>
|
| - <entry><classname>std::map</classname></entry>
|
| - <entry><filename class="headerfile">map</filename></entry>
|
| - <entry><classname>__gnu_debug::map</classname></entry>
|
| - <entry><filename class="headerfile">map</filename></entry>
|
| - </row>
|
| - <row>
|
| - <entry><classname>std::multimap</classname></entry>
|
| - <entry><filename class="headerfile">map</filename></entry>
|
| - <entry><classname>__gnu_debug::multimap</classname></entry>
|
| - <entry><filename class="headerfile">map</filename></entry>
|
| - </row>
|
| - <row>
|
| - <entry><classname>std::multiset</classname></entry>
|
| - <entry><filename class="headerfile">set</filename></entry>
|
| - <entry><classname>__gnu_debug::multiset</classname></entry>
|
| - <entry><filename class="headerfile">set</filename></entry>
|
| - </row>
|
| - <row>
|
| - <entry><classname>std::set</classname></entry>
|
| - <entry><filename class="headerfile">set</filename></entry>
|
| - <entry><classname>__gnu_debug::set</classname></entry>
|
| - <entry><filename class="headerfile">set</filename></entry>
|
| - </row>
|
| - <row>
|
| - <entry><classname>std::string</classname></entry>
|
| - <entry><filename class="headerfile">string</filename></entry>
|
| - <entry><classname>__gnu_debug::string</classname></entry>
|
| - <entry><filename class="headerfile">string</filename></entry>
|
| - </row>
|
| - <row>
|
| - <entry><classname>std::wstring</classname></entry>
|
| - <entry><filename class="headerfile">string</filename></entry>
|
| - <entry><classname>__gnu_debug::wstring</classname></entry>
|
| - <entry><filename class="headerfile">string</filename></entry>
|
| - </row>
|
| - <row>
|
| - <entry><classname>std::basic_string</classname></entry>
|
| - <entry><filename class="headerfile">string</filename></entry>
|
| - <entry><classname>__gnu_debug::basic_string</classname></entry>
|
| - <entry><filename class="headerfile">string</filename></entry>
|
| - </row>
|
| - <row>
|
| - <entry><classname>std::vector</classname></entry>
|
| - <entry><filename class="headerfile">vector</filename></entry>
|
| - <entry><classname>__gnu_debug::vector</classname></entry>
|
| - <entry><filename class="headerfile">vector</filename></entry>
|
| - </row>
|
| -</tbody>
|
| -</tgroup>
|
| -</table>
|
| -
|
| -<para>In addition, when compiling in C++0x mode, these additional
|
| -containers have additional debug capability.
|
| -</para>
|
| -
|
| -<table frame='all'>
|
| -<title>Debugging Containers C++0x</title>
|
| -<tgroup cols='6' align='left' colsep='1' rowsep='1'>
|
| -<colspec colname='c1'></colspec>
|
| -<colspec colname='c2'></colspec>
|
| -<colspec colname='c3'></colspec>
|
| -<colspec colname='c4'></colspec>
|
| -
|
| -<thead>
|
| - <row>
|
| - <entry>Container</entry>
|
| - <entry>Header</entry>
|
| - <entry>Debug container</entry>
|
| - <entry>Debug header</entry>
|
| - </row>
|
| -</thead>
|
| -<tbody>
|
| - <row>
|
| - <entry><classname>std::unordered_map</classname></entry>
|
| - <entry><filename class="headerfile">unordered_map</filename></entry>
|
| - <entry><classname>__gnu_debug::unordered_map</classname></entry>
|
| - <entry><filename class="headerfile">unordered_map</filename></entry>
|
| - </row>
|
| - <row>
|
| - <entry><classname>std::unordered_multimap</classname></entry>
|
| - <entry><filename class="headerfile">unordered_map</filename></entry>
|
| - <entry><classname>__gnu_debug::unordered_multimap</classname></entry>
|
| - <entry><filename class="headerfile">unordered_map</filename></entry>
|
| - </row>
|
| - <row>
|
| - <entry><classname>std::unordered_set</classname></entry>
|
| - <entry><filename class="headerfile">unordered_set</filename></entry>
|
| - <entry><classname>__gnu_debug::unordered_set</classname></entry>
|
| - <entry><filename class="headerfile">unordered_set</filename></entry>
|
| - </row>
|
| - <row>
|
| - <entry><classname>std::unordered_multiset</classname></entry>
|
| - <entry><filename class="headerfile">unordered_set</filename></entry>
|
| - <entry><classname>__gnu_debug::unordered_multiset</classname></entry>
|
| - <entry><filename class="headerfile">unordered_set</filename></entry>
|
| - </row>
|
| -</tbody>
|
| -</tgroup>
|
| -</table>
|
| -</sect2>
|
| -</sect1>
|
| -
|
| -<sect1 id="manual.ext.debug_mode.design" xreflabel="Design">
|
| - <title>Design</title>
|
| - <para>
|
| - </para>
|
| - <sect2 id="manual.ext.debug_mode.design.goals" xreflabel="Goals">
|
| - <title>Goals</title>
|
| - <para>
|
| - </para>
|
| -<para> The libstdc++ debug mode replaces unsafe (but efficient) standard
|
| - containers and iterators with semantically equivalent safe standard
|
| - containers and iterators to aid in debugging user programs. The
|
| - following goals directed the design of the libstdc++ debug mode:</para>
|
| -
|
| - <itemizedlist>
|
| -
|
| - <listitem><para><emphasis>Correctness</emphasis>: the libstdc++ debug mode must not change
|
| - the semantics of the standard library for all cases specified in
|
| - the ANSI/ISO C++ standard. The essence of this constraint is that
|
| - any valid C++ program should behave in the same manner regardless
|
| - of whether it is compiled with debug mode or release mode. In
|
| - particular, entities that are defined in namespace std in release
|
| - mode should remain defined in namespace std in debug mode, so that
|
| - legal specializations of namespace std entities will remain
|
| - valid. A program that is not valid C++ (e.g., invokes undefined
|
| - behavior) is not required to behave similarly, although the debug
|
| - mode will abort with a diagnostic when it detects undefined
|
| - behavior.</para></listitem>
|
| -
|
| - <listitem><para><emphasis>Performance</emphasis>: the additional of the libstdc++ debug mode
|
| - must not affect the performance of the library when it is compiled
|
| - in release mode. Performance of the libstdc++ debug mode is
|
| - secondary (and, in fact, will be worse than the release
|
| - mode).</para></listitem>
|
| -
|
| - <listitem><para><emphasis>Usability</emphasis>: the libstdc++ debug mode should be easy to
|
| - use. It should be easily incorporated into the user's development
|
| - environment (e.g., by requiring only a single new compiler switch)
|
| - and should produce reasonable diagnostics when it detects a
|
| - problem with the user program. Usability also involves detection
|
| - of errors when using the debug mode incorrectly, e.g., by linking
|
| - a release-compiled object against a debug-compiled object if in
|
| - fact the resulting program will not run correctly.</para></listitem>
|
| -
|
| - <listitem><para><emphasis>Minimize recompilation</emphasis>: While it is expected that
|
| - users recompile at least part of their program to use debug
|
| - mode, the amount of recompilation affects the
|
| - detect-compile-debug turnaround time. This indirectly affects the
|
| - usefulness of the debug mode, because debugging some applications
|
| - may require rebuilding a large amount of code, which may not be
|
| - feasible when the suspect code may be very localized. There are
|
| - several levels of conformance to this requirement, each with its
|
| - own usability and implementation characteristics. In general, the
|
| - higher-numbered conformance levels are more usable (i.e., require
|
| - less recompilation) but are more complicated to implement than
|
| - the lower-numbered conformance levels.
|
| - <orderedlist>
|
| - <listitem><para><emphasis>Full recompilation</emphasis>: The user must recompile his or
|
| - her entire application and all C++ libraries it depends on,
|
| - including the C++ standard library that ships with the
|
| - compiler. This must be done even if only a small part of the
|
| - program can use debugging features.</para></listitem>
|
| -
|
| - <listitem><para><emphasis>Full user recompilation</emphasis>: The user must recompile
|
| - his or her entire application and all C++ libraries it depends
|
| - on, but not the C++ standard library itself. This must be done
|
| - even if only a small part of the program can use debugging
|
| - features. This can be achieved given a full recompilation
|
| - system by compiling two versions of the standard library when
|
| - the compiler is installed and linking against the appropriate
|
| - one, e.g., a multilibs approach.</para></listitem>
|
| -
|
| - <listitem><para><emphasis>Partial recompilation</emphasis>: The user must recompile the
|
| - parts of his or her application and the C++ libraries it
|
| - depends on that will use the debugging facilities
|
| - directly. This means that any code that uses the debuggable
|
| - standard containers would need to be recompiled, but code
|
| - that does not use them (but may, for instance, use IOStreams)
|
| - would not have to be recompiled.</para></listitem>
|
| -
|
| - <listitem><para><emphasis>Per-use recompilation</emphasis>: The user must recompile the
|
| - parts of his or her application and the C++ libraries it
|
| - depends on where debugging should occur, and any other code
|
| - that interacts with those containers. This means that a set of
|
| - translation units that accesses a particular standard
|
| - container instance may either be compiled in release mode (no
|
| - checking) or debug mode (full checking), but must all be
|
| - compiled in the same way; a translation unit that does not see
|
| - that standard container instance need not be recompiled. This
|
| - also means that a translation unit <emphasis>A</emphasis> that contains a
|
| - particular instantiation
|
| - (say, <code>std::vector<int></code>) compiled in release
|
| - mode can be linked against a translation unit <emphasis>B</emphasis> that
|
| - contains the same instantiation compiled in debug mode (a
|
| - feature not present with partial recompilation). While this
|
| - behavior is technically a violation of the One Definition
|
| - Rule, this ability tends to be very important in
|
| - practice. The libstdc++ debug mode supports this level of
|
| - recompilation. </para></listitem>
|
| -
|
| - <listitem><para><emphasis>Per-unit recompilation</emphasis>: The user must only
|
| - recompile the translation units where checking should occur,
|
| - regardless of where debuggable standard containers are
|
| - used. This has also been dubbed "<code>-g</code> mode",
|
| - because the <code>-g</code> compiler switch works in this way,
|
| - emitting debugging information at a per--translation-unit
|
| - granularity. We believe that this level of recompilation is in
|
| - fact not possible if we intend to supply safe iterators, leave
|
| - the program semantics unchanged, and not regress in
|
| - performance under release mode because we cannot associate
|
| - extra information with an iterator (to form a safe iterator)
|
| - without either reserving that space in release mode
|
| - (performance regression) or allocating extra memory associated
|
| - with each iterator with <code>new</code> (changes the program
|
| - semantics).</para></listitem>
|
| - </orderedlist>
|
| - </para></listitem>
|
| - </itemizedlist>
|
| - </sect2>
|
| -
|
| - <sect2 id="manual.ext.debug_mode.design.methods" xreflabel="Methods">
|
| - <title>Methods</title>
|
| - <para>
|
| - </para>
|
| -<para>This section provides an overall view of the design of the
|
| - libstdc++ debug mode and details the relationship between design
|
| - decisions and the stated design goals.</para>
|
| -
|
| - <sect3 id="debug_mode.design.methods.wrappers" xreflabel="Method Wrapper">
|
| - <title>The Wrapper Model</title>
|
| -<para>The libstdc++ debug mode uses a wrapper model where the debugging
|
| - versions of library components (e.g., iterators and containers) form
|
| - a layer on top of the release versions of the library
|
| - components. The debugging components first verify that the operation
|
| - is correct (aborting with a diagnostic if an error is found) and
|
| - will then forward to the underlying release-mode container that will
|
| - perform the actual work. This design decision ensures that we cannot
|
| - regress release-mode performance (because the release-mode
|
| - containers are left untouched) and partially enables <ulink url="#mixing">mixing debug and release code</ulink> at link time,
|
| - although that will not be discussed at this time.</para>
|
| -
|
| -<para>Two types of wrappers are used in the implementation of the debug
|
| - mode: container wrappers and iterator wrappers. The two types of
|
| - wrappers interact to maintain relationships between iterators and
|
| - their associated containers, which are necessary to detect certain
|
| - types of standard library usage errors such as dereferencing
|
| - past-the-end iterators or inserting into a container using an
|
| - iterator from a different container.</para>
|
| -
|
| - <sect4 id="debug_mode.design.methods.safe_iter" xreflabel="Method Safe Iter">
|
| - <title>Safe Iterators</title>
|
| -<para>Iterator wrappers provide a debugging layer over any iterator that
|
| - is attached to a particular container, and will manage the
|
| - information detailing the iterator's state (singular,
|
| - dereferenceable, etc.) and tracking the container to which the
|
| - iterator is attached. Because iterators have a well-defined, common
|
| - interface the iterator wrapper is implemented with the iterator
|
| - adaptor class template <code>__gnu_debug::_Safe_iterator</code>,
|
| - which takes two template parameters:</para>
|
| -
|
| -<itemizedlist>
|
| - <listitem><para><code>Iterator</code>: The underlying iterator type, which must
|
| - be either the <code>iterator</code> or <code>const_iterator</code>
|
| - typedef from the sequence type this iterator can reference.</para></listitem>
|
| -
|
| - <listitem><para><code>Sequence</code>: The type of sequence that this iterator
|
| - references. This sequence must be a safe sequence (discussed below)
|
| - whose <code>iterator</code> or <code>const_iterator</code> typedef
|
| - is the type of the safe iterator.</para></listitem>
|
| -</itemizedlist>
|
| - </sect4>
|
| -
|
| - <sect4 id="debug_mode.design.methods.safe_seq" xreflabel="Method Safe Seq">
|
| - <title>Safe Sequences (Containers)</title>
|
| -
|
| -<para>Container wrappers provide a debugging layer over a particular
|
| - container type. Because containers vary greatly in the member
|
| - functions they support and the semantics of those member functions
|
| - (especially in the area of iterator invalidation), container
|
| - wrappers are tailored to the container they reference, e.g., the
|
| - debugging version of <code>std::list</code> duplicates the entire
|
| - interface of <code>std::list</code>, adding additional semantic
|
| - checks and then forwarding operations to the
|
| - real <code>std::list</code> (a public base class of the debugging
|
| - version) as appropriate. However, all safe containers inherit from
|
| - the class template <code>__gnu_debug::_Safe_sequence</code>,
|
| - instantiated with the type of the safe container itself (an instance
|
| - of the curiously recurring template pattern).</para>
|
| -
|
| -<para>The iterators of a container wrapper will be
|
| - <ulink url="#safe_iterator">safe iterators</ulink> that reference sequences
|
| - of this type and wrap the iterators provided by the release-mode
|
| - base class. The debugging container will use only the safe
|
| - iterators within its own interface (therefore requiring the user to
|
| - use safe iterators, although this does not change correct user
|
| - code) and will communicate with the release-mode base class with
|
| - only the underlying, unsafe, release-mode iterators that the base
|
| - class exports.</para>
|
| -
|
| -<para> The debugging version of <code>std::list</code> will have the
|
| - following basic structure:</para>
|
| -
|
| -<programlisting>
|
| -template<typename _Tp, typename _Allocator = allocator<_Tp>
|
| - class debug-list :
|
| - public release-list<_Tp, _Allocator>,
|
| - public __gnu_debug::_Safe_sequence<debug-list<_Tp, _Allocator> >
|
| - {
|
| - typedef release-list<_Tp, _Allocator> _Base;
|
| - typedef debug-list<_Tp, _Allocator> _Self;
|
| -
|
| - public:
|
| - typedef __gnu_debug::_Safe_iterator<typename _Base::iterator, _Self> iterator;
|
| - typedef __gnu_debug::_Safe_iterator<typename _Base::const_iterator, _Self> const_iterator;
|
| -
|
| - // duplicate std::list interface with debugging semantics
|
| - };
|
| -</programlisting>
|
| - </sect4>
|
| - </sect3>
|
| -
|
| - <sect3 id="debug_mode.design.methods.precond" xreflabel="Precondition check">
|
| - <title>Precondition Checking</title>
|
| -<para>The debug mode operates primarily by checking the preconditions of
|
| - all standard library operations that it supports. Preconditions that
|
| - are always checked (regardless of whether or not we are in debug
|
| - mode) are checked via the <code>__check_xxx</code> macros defined
|
| - and documented in the source
|
| - file <code>include/debug/debug.h</code>. Preconditions that may or
|
| - may not be checked, depending on the debug-mode
|
| - macro <code>_GLIBCXX_DEBUG</code>, are checked via
|
| - the <code>__requires_xxx</code> macros defined and documented in the
|
| - same source file. Preconditions are validated using any additional
|
| - information available at run-time, e.g., the containers that are
|
| - associated with a particular iterator, the position of the iterator
|
| - within those containers, the distance between two iterators that may
|
| - form a valid range, etc. In the absence of suitable information,
|
| - e.g., an input iterator that is not a safe iterator, these
|
| - precondition checks will silently succeed.</para>
|
| -
|
| -<para>The majority of precondition checks use the aforementioned macros,
|
| - which have the secondary benefit of having prewritten debug
|
| - messages that use information about the current status of the
|
| - objects involved (e.g., whether an iterator is singular or what
|
| - sequence it is attached to) along with some static information
|
| - (e.g., the names of the function parameters corresponding to the
|
| - objects involved). When not using these macros, the debug mode uses
|
| - either the debug-mode assertion
|
| - macro <code>_GLIBCXX_DEBUG_ASSERT</code> , its pedantic
|
| - cousin <code>_GLIBCXX_DEBUG_PEDASSERT</code>, or the assertion
|
| - check macro that supports more advance formulation of error
|
| - messages, <code>_GLIBCXX_DEBUG_VERIFY</code>. These macros are
|
| - documented more thoroughly in the debug mode source code.</para>
|
| - </sect3>
|
| -
|
| - <sect3 id="debug_mode.design.methods.coexistence" xreflabel="Coexistence">
|
| - <title>Release- and debug-mode coexistence</title>
|
| -<para>The libstdc++ debug mode is the first debug mode we know of that
|
| - is able to provide the "Per-use recompilation" (4) guarantee, that
|
| - allows release-compiled and debug-compiled code to be linked and
|
| - executed together without causing unpredictable behavior. This
|
| - guarantee minimizes the recompilation that users are required to
|
| - perform, shortening the detect-compile-debug bug hunting cycle
|
| - and making the debug mode easier to incorporate into development
|
| - environments by minimizing dependencies.</para>
|
| -
|
| -<para>Achieving link- and run-time coexistence is not a trivial
|
| - implementation task. To achieve this goal we required a small
|
| - extension to the GNU C++ compiler (described in the GCC Manual for
|
| - C++ Extensions, see <ulink url="http://gcc.gnu.org/onlinedocs/gcc/Strong-Using.html">strong
|
| - using</ulink>), and a complex organization of debug- and
|
| - release-modes. The end result is that we have achieved per-use
|
| - recompilation but have had to give up some checking of the
|
| - <code>std::basic_string</code> class template (namely, safe
|
| - iterators).
|
| -</para>
|
| -
|
| - <sect4 id="methods.coexistence.compile" xreflabel="Compile">
|
| - <title>Compile-time coexistence of release- and debug-mode components</title>
|
| -
|
| -<para>Both the release-mode components and the debug-mode
|
| - components need to exist within a single translation unit so that
|
| - the debug versions can wrap the release versions. However, only one
|
| - of these components should be user-visible at any particular
|
| - time with the standard name, e.g., <code>std::list</code>. </para>
|
| -
|
| -<para>In release mode, we define only the release-mode version of the
|
| - component with its standard name and do not include the debugging
|
| - component at all. The release mode version is defined within the
|
| - namespace <code>std</code>. Minus the namespace associations, this
|
| - method leaves the behavior of release mode completely unchanged from
|
| - its behavior prior to the introduction of the libstdc++ debug
|
| - mode. Here's an example of what this ends up looking like, in
|
| - C++.</para>
|
| -
|
| -<programlisting>
|
| -namespace std
|
| -{
|
| - template<typename _Tp, typename _Alloc = allocator<_Tp> >
|
| - class list
|
| - {
|
| - // ...
|
| - };
|
| -} // namespace std
|
| -</programlisting>
|
| -
|
| -<para>In debug mode we include the release-mode container (which is now
|
| -defined in in the namespace <code>__norm</code>) and also the
|
| -debug-mode container. The debug-mode container is defined within the
|
| -namespace <code>__debug</code>, which is associated with namespace
|
| -<code>std</code> via the GNU namespace association extension. This
|
| -method allows the debug and release versions of the same component to
|
| -coexist at compile-time and link-time without causing an unreasonable
|
| -maintenance burden, while minimizing confusion. Again, this boils down
|
| -to C++ code as follows:</para>
|
| -
|
| -<programlisting>
|
| -namespace std
|
| -{
|
| - namespace __norm
|
| - {
|
| - template<typename _Tp, typename _Alloc = allocator<_Tp> >
|
| - class list
|
| - {
|
| - // ...
|
| - };
|
| - } // namespace __gnu_norm
|
| -
|
| - namespace __debug
|
| - {
|
| - template<typename _Tp, typename _Alloc = allocator<_Tp> >
|
| - class list
|
| - : public __norm::list<_Tp, _Alloc>,
|
| - public __gnu_debug::_Safe_sequence<list<_Tp, _Alloc> >
|
| - {
|
| - // ...
|
| - };
|
| - } // namespace __norm
|
| -
|
| - using namespace __debug __attribute__ ((strong));
|
| -}
|
| -</programlisting>
|
| - </sect4>
|
| -
|
| - <sect4 id="methods.coexistence.link" xreflabel="Link">
|
| - <title>Link- and run-time coexistence of release- and
|
| - debug-mode components</title>
|
| -
|
| -<para>Because each component has a distinct and separate release and
|
| -debug implementation, there are are no issues with link-time
|
| -coexistence: the separate namespaces result in different mangled
|
| -names, and thus unique linkage.</para>
|
| -
|
| -<para>However, components that are defined and used within the C++
|
| -standard library itself face additional constraints. For instance,
|
| -some of the member functions of <code> std::moneypunct</code> return
|
| -<code>std::basic_string</code>. Normally, this is not a problem, but
|
| -with a mixed mode standard library that could be using either
|
| -debug-mode or release-mode <code> basic_string</code> objects, things
|
| -get more complicated. As the return value of a function is not
|
| -encoded into the mangled name, there is no way to specify a
|
| -release-mode or a debug-mode string. In practice, this results in
|
| -runtime errors. A simplified example of this problem is as follows.
|
| -</para>
|
| -
|
| -<para> Take this translation unit, compiled in debug-mode: </para>
|
| -<programlisting>
|
| -// -D_GLIBCXX_DEBUG
|
| -#include <string>
|
| -
|
| -std::string test02();
|
| -
|
| -std::string test01()
|
| -{
|
| - return test02();
|
| -}
|
| -
|
| -int main()
|
| -{
|
| - test01();
|
| - return 0;
|
| -}
|
| -</programlisting>
|
| -
|
| -<para> ... and linked to this translation unit, compiled in release mode:</para>
|
| -
|
| -<programlisting>
|
| -#include <string>
|
| -
|
| -std::string
|
| -test02()
|
| -{
|
| - return std::string("toast");
|
| -}
|
| -</programlisting>
|
| -
|
| -<para> For this reason we cannot easily provide safe iterators for
|
| - the <code>std::basic_string</code> class template, as it is present
|
| - throughout the C++ standard library. For instance, locale facets
|
| - define typedefs that include <code>basic_string</code>: in a mixed
|
| - debug/release program, should that typedef be based on the
|
| - debug-mode <code>basic_string</code> or the
|
| - release-mode <code>basic_string</code>? While the answer could be
|
| - "both", and the difference hidden via renaming a la the
|
| - debug/release containers, we must note two things about locale
|
| - facets:</para>
|
| -
|
| -<orderedlist>
|
| - <listitem><para>They exist as shared state: one can create a facet in one
|
| - translation unit and access the facet via the same type name in a
|
| - different translation unit. This means that we cannot have two
|
| - different versions of locale facets, because the types would not be
|
| - the same across debug/release-mode translation unit barriers.</para></listitem>
|
| -
|
| - <listitem><para>They have virtual functions returning strings: these functions
|
| - mangle in the same way regardless of the mangling of their return
|
| - types (see above), and their precise signatures can be relied upon
|
| - by users because they may be overridden in derived classes.</para></listitem>
|
| -</orderedlist>
|
| -
|
| -<para>With the design of libstdc++ debug mode, we cannot effectively hide
|
| - the differences between debug and release-mode strings from the
|
| - user. Failure to hide the differences may result in unpredictable
|
| - behavior, and for this reason we have opted to only
|
| - perform <code>basic_string</code> changes that do not require ABI
|
| - changes. The effect on users is expected to be minimal, as there are
|
| - simple alternatives (e.g., <code>__gnu_debug::basic_string</code>),
|
| - and the usability benefit we gain from the ability to mix debug- and
|
| - release-compiled translation units is enormous.</para>
|
| - </sect4>
|
| -
|
| - <sect4 id="methods.coexistence.alt" xreflabel="Alternatives">
|
| -<title>Alternatives for Coexistence</title>
|
| -
|
| -<para>The coexistence scheme above was chosen over many alternatives,
|
| - including language-only solutions and solutions that also required
|
| - extensions to the C++ front end. The following is a partial list of
|
| - solutions, with justifications for our rejection of each.</para>
|
| -
|
| -<itemizedlist>
|
| - <listitem><para><emphasis>Completely separate debug/release libraries</emphasis>: This is by
|
| - far the simplest implementation option, where we do not allow any
|
| - coexistence of debug- and release-compiled translation units in a
|
| - program. This solution has an extreme negative affect on usability,
|
| - because it is quite likely that some libraries an application
|
| - depends on cannot be recompiled easily. This would not meet
|
| - our <emphasis>usability</emphasis> or <emphasis>minimize recompilation</emphasis> criteria
|
| - well.</para></listitem>
|
| -
|
| - <listitem><para><emphasis>Add a <code>Debug</code> boolean template parameter</emphasis>:
|
| - Partial specialization could be used to select the debug
|
| - implementation when <code>Debug == true</code>, and the state
|
| - of <code>_GLIBCXX_DEBUG</code> could decide whether the
|
| - default <code>Debug</code> argument is <code>true</code>
|
| - or <code>false</code>. This option would break conformance with the
|
| - C++ standard in both debug <emphasis>and</emphasis> release modes. This would
|
| - not meet our <emphasis>correctness</emphasis> criteria. </para></listitem>
|
| -
|
| - <listitem><para><emphasis>Packaging a debug flag in the allocators</emphasis>: We could
|
| - reuse the <code>Allocator</code> template parameter of containers
|
| - by adding a sentinel wrapper <code>debug<></code> that
|
| - signals the user's intention to use debugging, and pick up
|
| - the <code>debug<></code> allocator wrapper in a partial
|
| - specialization. However, this has two drawbacks: first, there is a
|
| - conformance issue because the default allocator would not be the
|
| - standard-specified <code>std::allocator<T></code>. Secondly
|
| - (and more importantly), users that specify allocators instead of
|
| - implicitly using the default allocator would not get debugging
|
| - containers. Thus this solution fails the <emphasis>correctness</emphasis>
|
| - criteria.</para></listitem>
|
| -
|
| - <listitem><para><emphasis>Define debug containers in another namespace, and employ
|
| - a <code>using</code> declaration (or directive)</emphasis>: This is an
|
| - enticing option, because it would eliminate the need for
|
| - the <code>link_name</code> extension by aliasing the
|
| - templates. However, there is no true template aliasing mechanism
|
| - is C++, because both <code>using</code> directives and using
|
| - declarations disallow specialization. This method fails
|
| - the <emphasis>correctness</emphasis> criteria.</para></listitem>
|
| -
|
| - <listitem><para><emphasis> Use implementation-specific properties of anonymous
|
| - namespaces. </emphasis>
|
| - See <ulink url="http://gcc.gnu.org/ml/libstdc++/2003-08/msg00004.html"> this post
|
| - </ulink>
|
| - This method fails the <emphasis>correctness</emphasis> criteria.</para></listitem>
|
| -
|
| - <listitem><para><emphasis>Extension: allow reopening on namespaces</emphasis>: This would
|
| - allow the debug mode to effectively alias the
|
| - namespace <code>std</code> to an internal namespace, such
|
| - as <code>__gnu_std_debug</code>, so that it is completely
|
| - separate from the release-mode <code>std</code> namespace. While
|
| - this will solve some renaming problems and ensure that
|
| - debug- and release-compiled code cannot be mixed unsafely, it ensures that
|
| - debug- and release-compiled code cannot be mixed at all. For
|
| - instance, the program would have two <code>std::cout</code>
|
| - objects! This solution would fails the <emphasis>minimize
|
| - recompilation</emphasis> requirement, because we would only be able to
|
| - support option (1) or (2).</para></listitem>
|
| -
|
| - <listitem><para><emphasis>Extension: use link name</emphasis>: This option involves
|
| - complicated re-naming between debug-mode and release-mode
|
| - components at compile time, and then a g++ extension called <emphasis>
|
| - link name </emphasis> to recover the original names at link time. There
|
| - are two drawbacks to this approach. One, it's very verbose,
|
| - relying on macro renaming at compile time and several levels of
|
| - include ordering. Two, ODR issues remained with container member
|
| - functions taking no arguments in mixed-mode settings resulting in
|
| - equivalent link names, <code> vector::push_back() </code> being
|
| - one example.
|
| - See <ulink url="http://gcc.gnu.org/ml/libstdc++/2003-08/msg00177.html">link
|
| - name</ulink> </para></listitem>
|
| -</itemizedlist>
|
| -
|
| -<para>Other options may exist for implementing the debug mode, many of
|
| - which have probably been considered and others that may still be
|
| - lurking. This list may be expanded over time to include other
|
| - options that we could have implemented, but in all cases the full
|
| - ramifications of the approach (as measured against the design goals
|
| - for a libstdc++ debug mode) should be considered first. The DejaGNU
|
| - testsuite includes some testcases that check for known problems with
|
| - some solutions (e.g., the <code>using</code> declaration solution
|
| - that breaks user specialization), and additional testcases will be
|
| - added as we are able to identify other typical problem cases. These
|
| - test cases will serve as a benchmark by which we can compare debug
|
| - mode implementations.</para>
|
| - </sect4>
|
| - </sect3>
|
| - </sect2>
|
| -
|
| - <sect2 id="manual.ext.debug_mode.design.other" xreflabel="Other">
|
| - <title>Other Implementations</title>
|
| - <para>
|
| - </para>
|
| -<para> There are several existing implementations of debug modes for C++
|
| - standard library implementations, although none of them directly
|
| - supports debugging for programs using libstdc++. The existing
|
| - implementations include:</para>
|
| -<itemizedlist>
|
| - <listitem><para><ulink url="http://www.mathcs.sjsu.edu/faculty/horstman/safestl.html">SafeSTL</ulink>:
|
| - SafeSTL was the original debugging version of the Standard Template
|
| - Library (STL), implemented by Cay S. Horstmann on top of the
|
| - Hewlett-Packard STL. Though it inspired much work in this area, it
|
| - has not been kept up-to-date for use with modern compilers or C++
|
| - standard library implementations.</para></listitem>
|
| -
|
| - <listitem><para><ulink url="http://www.stlport.org/">STLport</ulink>: STLport is a free
|
| - implementation of the C++ standard library derived from the <ulink url="http://www.sgi.com/tech/stl/">SGI implementation</ulink>, and
|
| - ported to many other platforms. It includes a debug mode that uses a
|
| - wrapper model (that in some way inspired the libstdc++ debug mode
|
| - design), although at the time of this writing the debug mode is
|
| - somewhat incomplete and meets only the "Full user recompilation" (2)
|
| - recompilation guarantee by requiring the user to link against a
|
| - different library in debug mode vs. release mode.</para></listitem>
|
| -
|
| - <listitem><para><ulink url="http://www.metrowerks.com/mw/default.htm">Metrowerks
|
| - CodeWarrior</ulink>: The C++ standard library that ships with Metrowerks
|
| - CodeWarrior includes a debug mode. It is a full debug-mode
|
| - implementation (including debugging for CodeWarrior extensions) and
|
| - is easy to use, although it meets only the "Full recompilation" (1)
|
| - recompilation guarantee.</para></listitem>
|
| -</itemizedlist>
|
| -
|
| - </sect2>
|
| -</sect1>
|
| -
|
| -</chapter>
|
|
|
Chromium Code Reviews
Issue 3050029:
[gcc] GCC 4.5.0=>4.5.1 (Closed)
Base URL: ssh://git@gitrw.chromium.org:9222/nacl-toolchain.git