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| -<html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>Design</title><meta name="generator" content="DocBook XSL Stylesheets V1.74.0" /><meta name="keywords" content=" C++ , library , debug " /><meta name="keywords" content=" ISO C++ , library " /><link rel="home" href="../spine.html" title="The GNU C++ Library Documentation" /><link rel="up" href="debug_mode.html" title="Chapter 30. Debug Mode" /><link rel="prev" href="bk01pt12ch30s03.html" title="Using" /><link rel="next" href="parallel_mode.html" title="Chapter 31. Parallel Mode" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Design</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="bk01pt12ch30s03.html">Prev</a> </td><th width="60%" align="center">Chapter 30. Debug Mode</th><td width="20%" align="right"> <a accesskey="n" href="parallel_mode.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.ext.debug_mode.design"></a>Design</h2></div></div></div><p>
|
| - </p><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="manual.ext.debug_mode.design.goals"></a>Goals</h3></div></div></div><p>
|
| - </p><p> 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:</p><div class="itemizedlist"><ul type="disc"><li><p><span class="emphasis"><em>Correctness</em></span>: 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.</p></li><li><p><span class="emphasis"><em>Performance</em></span>: 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).</p></li><li><p><span class="emphasis"><em>Usability</em></span>: 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.</p></li><li><p><span class="emphasis"><em>Minimize recompilation</em></span>: 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.
|
| - </p><div class="orderedlist"><ol type="1"><li><p><span class="emphasis"><em>Full recompilation</em></span>: 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.</p></li><li><p><span class="emphasis"><em>Full user recompilation</em></span>: 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.</p></li><li><p><span class="emphasis"><em>Partial recompilation</em></span>: 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.</p></li><li><p><span class="emphasis"><em>Per-use recompilation</em></span>: 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 <span class="emphasis"><em>A</em></span> that contains a
|
| - particular instantiation
|
| - (say, <code class="code">std::vector<int></code>) compiled in release
|
| - mode can be linked against a translation unit <span class="emphasis"><em>B</em></span> 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. </p></li><li><p><span class="emphasis"><em>Per-unit recompilation</em></span>: 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 class="code">-g</code> mode",
|
| - because the <code class="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 class="code">new</code> (changes the program
|
| - semantics).</p></li></ol></div><p>
|
| - </p></li></ul></div></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="manual.ext.debug_mode.design.methods"></a>Methods</h3></div></div></div><p>
|
| - </p><p>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.</p><div class="sect3" lang="en" xml:lang="en"><div class="titlepage"><div><div><h4 class="title"><a id="debug_mode.design.methods.wrappers"></a>The Wrapper Model</h4></div></div></div><p>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 <a class="ulink" href="#mixing" target="_top">mixing debug and release code</a> at link time,
|
| - although that will not be discussed at this time.</p><p>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.</p><div class="sect4" lang="en" xml:lang="en"><div class="titlepage"><div><div><h5 class="title"><a id="debug_mode.design.methods.safe_iter"></a>Safe Iterators</h5></div></div></div><p>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 class="code">__gnu_debug::_Safe_iterator</code>,
|
| - which takes two template parameters:</p><div class="itemizedlist"><ul type="disc"><li><p><code class="code">Iterator</code>: The underlying iterator type, which must
|
| - be either the <code class="code">iterator</code> or <code class="code">const_iterator</code>
|
| - typedef from the sequence type this iterator can reference.</p></li><li><p><code class="code">Sequence</code>: The type of sequence that this iterator
|
| - references. This sequence must be a safe sequence (discussed below)
|
| - whose <code class="code">iterator</code> or <code class="code">const_iterator</code> typedef
|
| - is the type of the safe iterator.</p></li></ul></div></div><div class="sect4" lang="en" xml:lang="en"><div class="titlepage"><div><div><h5 class="title"><a id="debug_mode.design.methods.safe_seq"></a>Safe Sequences (Containers)</h5></div></div></div><p>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 class="code">std::list</code> duplicates the entire
|
| - interface of <code class="code">std::list</code>, adding additional semantic
|
| - checks and then forwarding operations to the
|
| - real <code class="code">std::list</code> (a public base class of the debugging
|
| - version) as appropriate. However, all safe containers inherit from
|
| - the class template <code class="code">__gnu_debug::_Safe_sequence</code>,
|
| - instantiated with the type of the safe container itself (an instance
|
| - of the curiously recurring template pattern).</p><p>The iterators of a container wrapper will be
|
| - <a class="ulink" href="#safe_iterator" target="_top">safe iterators</a> 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.</p><p> The debugging version of <code class="code">std::list</code> will have the
|
| - following basic structure:</p><pre class="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
|
| - };
|
| -</pre></div></div><div class="sect3" lang="en" xml:lang="en"><div class="titlepage"><div><div><h4 class="title"><a id="debug_mode.design.methods.precond"></a>Precondition Checking</h4></div></div></div><p>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 class="code">__check_xxx</code> macros defined
|
| - and documented in the source
|
| - file <code class="code">include/debug/debug.h</code>. Preconditions that may or
|
| - may not be checked, depending on the debug-mode
|
| - macro <code class="code">_GLIBCXX_DEBUG</code>, are checked via
|
| - the <code class="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.</p><p>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 class="code">_GLIBCXX_DEBUG_ASSERT</code> , its pedantic
|
| - cousin <code class="code">_GLIBCXX_DEBUG_PEDASSERT</code>, or the assertion
|
| - check macro that supports more advance formulation of error
|
| - messages, <code class="code">_GLIBCXX_DEBUG_VERIFY</code>. These macros are
|
| - documented more thoroughly in the debug mode source code.</p></div><div class="sect3" lang="en" xml:lang="en"><div class="titlepage"><div><div><h4 class="title"><a id="debug_mode.design.methods.coexistence"></a>Release- and debug-mode coexistence</h4></div></div></div><p>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.</p><p>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 <a class="ulink" href="http://gcc.gnu.org/onlinedocs/gcc/Strong-Using.html" target="_top">strong
|
| - using</a>), 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 class="code">std::basic_string</code> class template (namely, safe
|
| - iterators).
|
| -</p><div class="sect4" lang="en" xml:lang="en"><div class="titlepage"><div><div><h5 class="title"><a id="methods.coexistence.compile"></a>Compile-time coexistence of release- and debug-mode components</h5></div></div></div><p>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 class="code">std::list</code>. </p><p>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 class="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++.</p><pre class="programlisting">
|
| -namespace std
|
| -{
|
| - template<typename _Tp, typename _Alloc = allocator<_Tp> >
|
| - class list
|
| - {
|
| - // ...
|
| - };
|
| -} // namespace std
|
| -</pre><p>In debug mode we include the release-mode container (which is now
|
| -defined in in the namespace <code class="code">__norm</code>) and also the
|
| -debug-mode container. The debug-mode container is defined within the
|
| -namespace <code class="code">__debug</code>, which is associated with namespace
|
| -<code class="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:</p><pre class="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));
|
| -}
|
| -</pre></div><div class="sect4" lang="en" xml:lang="en"><div class="titlepage"><div><div><h5 class="title"><a id="methods.coexistence.link"></a>Link- and run-time coexistence of release- and
|
| - debug-mode components</h5></div></div></div><p>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.</p><p>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 class="code"> std::moneypunct</code> return
|
| -<code class="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 class="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.
|
| -</p><p> Take this translation unit, compiled in debug-mode: </p><pre class="programlisting">
|
| -// -D_GLIBCXX_DEBUG
|
| -#include <string>
|
| -
|
| -std::string test02();
|
| -
|
| -std::string test01()
|
| -{
|
| - return test02();
|
| -}
|
| -
|
| -int main()
|
| -{
|
| - test01();
|
| - return 0;
|
| -}
|
| -</pre><p> ... and linked to this translation unit, compiled in release mode:</p><pre class="programlisting">
|
| -#include <string>
|
| -
|
| -std::string
|
| -test02()
|
| -{
|
| - return std::string("toast");
|
| -}
|
| -</pre><p> For this reason we cannot easily provide safe iterators for
|
| - the <code class="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 class="code">basic_string</code>: in a mixed
|
| - debug/release program, should that typedef be based on the
|
| - debug-mode <code class="code">basic_string</code> or the
|
| - release-mode <code class="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:</p><div class="orderedlist"><ol type="1"><li><p>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.</p></li><li><p>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.</p></li></ol></div><p>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 class="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 class="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.</p></div><div class="sect4" lang="en" xml:lang="en"><div class="titlepage"><div><div><h5 class="title"><a id="methods.coexistence.alt"></a>Alternatives for Coexistence</h5></div></div></div><p>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.</p><div class="itemizedlist"><ul type="disc"><li><p><span class="emphasis"><em>Completely separate debug/release libraries</em></span>: 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 <span class="emphasis"><em>usability</em></span> or <span class="emphasis"><em>minimize recompilation</em></span> criteria
|
| - well.</p></li><li><p><span class="emphasis"><em>Add a <code class="code">Debug</code> boolean template parameter</em></span>:
|
| - Partial specialization could be used to select the debug
|
| - implementation when <code class="code">Debug == true</code>, and the state
|
| - of <code class="code">_GLIBCXX_DEBUG</code> could decide whether the
|
| - default <code class="code">Debug</code> argument is <code class="code">true</code>
|
| - or <code class="code">false</code>. This option would break conformance with the
|
| - C++ standard in both debug <span class="emphasis"><em>and</em></span> release modes. This would
|
| - not meet our <span class="emphasis"><em>correctness</em></span> criteria. </p></li><li><p><span class="emphasis"><em>Packaging a debug flag in the allocators</em></span>: We could
|
| - reuse the <code class="code">Allocator</code> template parameter of containers
|
| - by adding a sentinel wrapper <code class="code">debug<></code> that
|
| - signals the user's intention to use debugging, and pick up
|
| - the <code class="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 class="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 <span class="emphasis"><em>correctness</em></span>
|
| - criteria.</p></li><li><p><span class="emphasis"><em>Define debug containers in another namespace, and employ
|
| - a <code class="code">using</code> declaration (or directive)</em></span>: This is an
|
| - enticing option, because it would eliminate the need for
|
| - the <code class="code">link_name</code> extension by aliasing the
|
| - templates. However, there is no true template aliasing mechanism
|
| - is C++, because both <code class="code">using</code> directives and using
|
| - declarations disallow specialization. This method fails
|
| - the <span class="emphasis"><em>correctness</em></span> criteria.</p></li><li><p><span class="emphasis"><em> Use implementation-specific properties of anonymous
|
| - namespaces. </em></span>
|
| - See <a class="ulink" href="http://gcc.gnu.org/ml/libstdc++/2003-08/msg00004.html" target="_top"> this post
|
| - </a>
|
| - This method fails the <span class="emphasis"><em>correctness</em></span> criteria.</p></li><li><p><span class="emphasis"><em>Extension: allow reopening on namespaces</em></span>: This would
|
| - allow the debug mode to effectively alias the
|
| - namespace <code class="code">std</code> to an internal namespace, such
|
| - as <code class="code">__gnu_std_debug</code>, so that it is completely
|
| - separate from the release-mode <code class="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 class="code">std::cout</code>
|
| - objects! This solution would fails the <span class="emphasis"><em>minimize
|
| - recompilation</em></span> requirement, because we would only be able to
|
| - support option (1) or (2).</p></li><li><p><span class="emphasis"><em>Extension: use link name</em></span>: This option involves
|
| - complicated re-naming between debug-mode and release-mode
|
| - components at compile time, and then a g++ extension called <span class="emphasis"><em>
|
| - link name </em></span> 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 class="code"> vector::push_back() </code> being
|
| - one example.
|
| - See <a class="ulink" href="http://gcc.gnu.org/ml/libstdc++/2003-08/msg00177.html" target="_top">link
|
| - name</a> </p></li></ul></div><p>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 class="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.</p></div></div></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="manual.ext.debug_mode.design.other"></a>Other Implementations</h3></div></div></div><p>
|
| - </p><p> 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:</p><div class="itemizedlist"><ul type="disc"><li><p><a class="ulink" href="http://www.mathcs.sjsu.edu/faculty/horstman/safestl.html" target="_top">SafeSTL</a>:
|
| - 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.</p></li><li><p><a class="ulink" href="http://www.stlport.org/" target="_top">STLport</a>: STLport is a free
|
| - implementation of the C++ standard library derived from the <a class="ulink" href="http://www.sgi.com/tech/stl/" target="_top">SGI implementation</a>, 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.</p></li><li><p><a class="ulink" href="http://www.metrowerks.com/mw/default.htm" target="_top">Metrowerks
|
| - CodeWarrior</a>: 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.</p></li></ul></div></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="bk01pt12ch30s03.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="debug_mode.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="parallel_mode.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Using </td><td width="20%" align="center"><a accesskey="h" href="../spine.html">Home</a></td><td width="40%" align="right" valign="top"> Chapter 31. Parallel Mode</td></tr></table></div></body></html>
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Issue 3050029:
[gcc] GCC 4.5.0=>4.5.1 (Closed)
Base URL: ssh://git@gitrw.chromium.org:9222/nacl-toolchain.git