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+<p><hr>
+Node:<a name="Top">Top</a>,
+Next:<a rel=next href="#Operating%20system">Operating system</a>
+<br>
+
+<h1>Porting libstdc++-v3</h1>
+
+<p>This document explains how to port libstdc++-v3 (the GNU C++ library) to
+a new target.
+
+<p>In order to make the GNU C++ library (libstdc++-v3) work with a new
+target, you must edit some configuration files and provide some new
+header files.
+
+<p>Before you get started, make sure that you have a working C library on
+your target. The C library need not precisely comply with any
+particular standard, but should generally conform to the requirements
+imposed by the ANSI/ISO standard.
+
+<p>In addition, you should try to verify that the C++ compiler generally
+works. It is difficult to test the C++ compiler without a working
+library, but you should at least try some minimal test cases.
+
+<p>Here are the primary steps required to port the library:
+
+<ul>
+<li><a href="#Operating%20system">Operating system</a>: Configuring for your operating system.
+<li><a href="#Character%20types">Character types</a>: Implementing character classification.
+<li><a href="#Thread%20safety">Thread safety</a>: Implementing atomic operations.
+<li><a href="#Numeric%20limits">Numeric limits</a>: Implementing numeric limits.
+<li><a href="#Libtool">Libtool</a>: Using libtool.
+<li><a href="#GNU%20Free%20Documentation%20License">GNU Free Documentation License</a>: How you can copy and share this manual.
+</ul>
+
+<p><hr>
+Node:<a name="Operating%20system">Operating system</a>,
+Next:<a rel=next href="#Character%20types">Character types</a>,
+Previous:<a rel=previous href="#Top">Top</a>,
+Up:<a rel=up href="#Top">Top</a>
+<br>
+
+<h1>Operating system</h1>
+
+<p>If you are porting to a new operating-system (as opposed to a new chip
+using an existing operating system), you will need to create a new
+directory in the <code>config/os</code> hierarchy. For example, the IRIX
+configuration files are all in <code>config/os/irix</code>. There is no set
+way to organize the OS configuration directory. For example,
+<code>config/os/solaris/solaris-2.6</code> and
+<code>config/os/solaris/solaris-2.7</code> are used as configuration
+directories for these two versions of Solaris. On the other hand, both
+Solaris 2.7 and Solaris 2.8 use the <code>config/os/solaris/solaris-2.7</code>
+directory. The important information is that there needs to be a
+directory under <code>config/os</code> to store the files for your operating
+system.
+
+<p>You'll have to change the <code>configure.target</code> file to ensure that
+your new directory is activated. Look for the switch statement that
+sets <code>os_include_dir</code>, and add a pattern to handle your operating
+system. The switch statement switches on only the OS portion of the
+standard target triplet; e.g., the <code>solaris2.8</code> in
+<code>sparc-sun-solaris2.8</code>.
+
+<p>The first file to create in this directory, should be called
+<code>bits/os_defines.h</code>. This file contains basic macro definitions
+that are required to allow the C++ library to work with your C library.
+This file should provide macro definitions for <code>__off_t</code>,
+<code>__off64_t</code>, and <code>__ssize_t</code>. Typically, this just looks
+like:
+
+<pre>#define __off_t off_t
+#define __off64_t off64_t
+#define __ssize_t ssize_t
+</pre>
+
+<p>You don't have to provide these definitions if your system library
+already defines these types - but the only library known to provide
+these types is the GNU C Library, so you will almost certainly have to
+provide these macros. Note that this file does not have to include a
+header file that defines <code>off_t</code>, or the other types; you simply
+have to provide the macros.
+
+<p>In addition, several libstdc++-v3 source files unconditionally define
+the macro <code>_POSIX_SOURCE</code>. On many systems, defining this macro
+causes large portions of the C library header files to be eliminated
+at preprocessing time. Therefore, you may have to <code>#undef</code> this
+macro, or define other macros (like <code>_LARGEFILE_SOURCE</code> or
+<code>__EXTENSIONS__</code>). You won't know what macros to define or
+undefine at this point; you'll have to try compiling the library and
+seeing what goes wrong. If you see errors about calling functions
+that have not been declared, look in your C library headers to see if
+the functions are declared there, and then figure out what macros you
+need to define. You will need to add them to the
+<code>CPLUSPLUS_CPP_SPEC</code> macro in the GCC configuration file for your
+target. It will not work to simply define these macros in
+<code>os_defines.h</code>.
+
+<p>At this time, there are two libstdc++-v3-specific macros which may be
+defined. <code>_G_USING_THUNKS</code> may be defined to 0 to express that the
+port doesn't use thunks (although it is unclear that this is still
+useful since libio support isn't currently working and the g++ v3 ABI
+invalidates the assumption that some ports don't use thunks).
+<code>_GLIBCPP_AVOID_FSEEK</code> may be defined if seeking on an interactive
+stream (or one hooked to a pipe) is not allowed by the OS. In this
+case, getc()/ungetc() will be used at some key locations in the library
+implementation instead of fseek(). Currently, the code path to avoid
+fseek() is only enabled when the seek size is 1 character away from the
+current stream position. This is known to improve *-unknown-freebsd*
+and sparc-sun-solaris2.*.
+
+<p>Finally, you should bracket the entire file in an include-guard, like
+this:
+
+<pre>#ifndef _GLIBCPP_OS_DEFINES
+#define _GLIBCPP_OS_DEFINES
+...
+#endif
+</pre>
+
+<p>We recommend copying an existing <code>bits/os_defines.h</code> to use as a
+starting point.
+
+<p><hr>
+Node:<a name="Character%20types">Character types</a>,
+Next:<a rel=next href="#Thread%20safety">Thread safety</a>,
+Previous:<a rel=previous href="#Operating%20system">Operating system</a>,
+Up:<a rel=up href="#Top">Top</a>
+<br>
+
+<h1>Character types</h1>
+
+<p>The library requires that you provide three header files to implement
+character classification, analagous to that provided by the C libraries
+<code><ctype.h></code> header. You can model these on the files provided in
+<code>config/os/generic/bits</code>. However, these files will almost
+certainly need some modification.
+
+<p>The first file to write is <code>bits/ctype_base.h</code>. This file provides
+some very basic information about character classification. The libstdc++-v3
+library assumes that your C library implements <code><ctype.h></code> by using
+a table (indexed by character code) containing integers, where each of
+these integers is a bit-mask indicating whether the charcter is
+upper-case, lower-case, alphabetic, etc. The <code>bits/ctype_base.h</code>
+file gives the type of the integer, and the values of the various bit
+masks. You will have to peer at your own <code><ctype.h></code> to figure out
+how to define the values required by this file.
+
+<p>The <code>bits/ctype_base.h</code> header file does not need include guards.
+It should contain a single <code>struct</code> definition called
+<code>ctype_base</code>. This <code>struct</code> should contain two type
+declarations, and one enumeration declaration, like this example, taken
+from the IRIX configuration:
+
+<pre>struct ctype_base
+{
+ typedef unsigned int mask;
+ typedef int* __to_type;
+
+ enum
+ {
+ space = _ISspace,
+ print = _ISprint,
+ cntrl = _IScntrl,
+ upper = _ISupper,
+ lower = _ISlower,
+ alpha = _ISalpha,
+ digit = _ISdigit,
+ punct = _ISpunct,
+ xdigit = _ISxdigit,
+ alnum = _ISalnum,
+ graph = _ISgraph
+ };
+};
+</pre>
+
+<p>The <code>mask</code> type is the type of the elements in the table. If your
+C library uses a table to map lower-case numbers to upper-case numbers,
+and vice versa, you should define <code>__to_type</code> to be the type of the
+elements in that table. If you don't mind taking a minor performance
+penalty, or if your library doesn't implement <code>toupper</code> and
+<code>tolower</code> in this way, you can pick any pointer-to-integer type,
+but you must still define the type.
+
+<p>The enumeration should give definitions for all the values in the above
+example, using the values from your native <code><ctype.h></code>. They can
+be given symbolically (as above), or numerically, if you prefer. You do
+not have to include <code><ctype.h></code> in this header; it will always be
+included before <code>bits/ctype_base.h</code> is included.
+
+<p>The next file to write is <code>bits/ctype_noninline.h</code>, which also does
+not require include guards. This file defines a few member functions
+that will be included in <code>include/bits/locale_facets.h</code>. The first
+function that must be written is the <code>ctype<char>::ctype</code>
+constructor. Here is the IRIX example:
+
+<pre>ctype<char>::ctype(const mask* __table = 0, bool __del = false,
+ size_t __refs = 0)
+ : _Ctype_nois<char>(__refs), _M_del(__table != 0 && __del),
+ _M_toupper(NULL),
+ _M_tolower(NULL),
+ _M_ctable(NULL),
+ _M_table(!__table
+ ? (const mask*) (__libc_attr._ctype_tbl->_class + 1)
+ : __table)
+ { }
+</pre>
+
+<p>There are two parts of this that you might choose to alter. The first,
+and most important, is the line involving <code>__libc_attr</code>. That is
+IRIX system-dependent code that gets the base of the table mapping
+character codes to attributes. You need to substitute code that obtains
+the address of this table on your system. If you want to use your
+operating system's tables to map upper-case letters to lower-case, and
+vice versa, you should initialize <code>_M_toupper</code> and
+<code>_M_tolower</code> with those tables, in similar fashion.
+
+<p>Now, you have to write two functions to convert from upper-case to
+lower-case, and vice versa. Here are the IRIX versions:
+
+<pre>char
+ctype<char>::do_toupper(char __c) const
+{ return _toupper(__c); }
+
+char
+ctype<char>::do_tolower(char __c) const
+{ return _tolower(__c); }
+</pre>
+
+<p>Your C library provides equivalents to IRIX's <code>_toupper</code> and
+<code>_tolower</code>. If you initialized <code>_M_toupper</code> and
+<code>_M_tolower</code> above, then you could use those tables instead.
+
+<p>Finally, you have to provide two utility functions that convert strings
+of characters. The versions provided here will always work - but you
+could use specialized routines for greater performance if you have
+machinery to do that on your system:
+
+<pre>const char*
+ctype<char>::do_toupper(char* __low, const char* __high) const
+{
+ while (__low < __high)
+ {
+ *__low = do_toupper(*__low);
+ ++__low;
+ }
+ return __high;
+}
+
+const char*
+ctype<char>::do_tolower(char* __low, const char* __high) const
+{
+ while (__low < __high)
+ {
+ *__low = do_tolower(*__low);
+ ++__low;
+ }
+ return __high;
+}
+</pre>
+
+<p>You must also provide the <code>bits/ctype_inline.h</code> file, which
+contains a few more functions. On most systems, you can just copy
+<code>config/os/generic/ctype_inline.h</code> and use it on your system.
+
+<p>In detail, the functions provided test characters for particular
+properties; they are analagous to the functions like <code>isalpha</code> and
+<code>islower</code> provided by the C library.
+
+<p>The first function is implemented like this on IRIX:
+
+<pre>bool
+ctype<char>::
+is(mask __m, char __c) const throw()
+{ return (_M_table)[(unsigned char)(__c)] & __m; }
+</pre>
+
+<p>The <code>_M_table</code> is the table passed in above, in the constructor.
+This is the table that contains the bitmasks for each character. The
+implementation here should work on all systems.
+
+<p>The next function is:
+
+<pre>const char*
+ctype<char>::
+is(const char* __low, const char* __high, mask* __vec) const throw()
+{
+ while (__low < __high)
+ *__vec++ = (_M_table)[(unsigned char)(*__low++)];
+ return __high;
+}
+</pre>
+
+<p>This function is similar; it copies the masks for all the characters
+from <code>__low</code> up until <code>__high</code> into the vector given by
+<code>__vec</code>.
+
+<p>The last two functions again are entirely generic:
+
+<pre>const char*
+ctype<char>::
+scan_is(mask __m, const char* __low, const char* __high) const throw()
+{
+ while (__low < __high && !this->is(__m, *__low))
+ ++__low;
+ return __low;
+}
+
+const char*
+ctype<char>::
+scan_not(mask __m, const char* __low, const char* __high) const throw()
+{
+ while (__low < __high && this->is(__m, *__low))
+ ++__low;
+ return __low;
+}
+</pre>
+
+<p><hr>
+Node:<a name="Thread%20safety">Thread safety</a>,
+Next:<a rel=next href="#Numeric%20limits">Numeric limits</a>,
+Previous:<a rel=previous href="#Character%20types">Character types</a>,
+Up:<a rel=up href="#Top">Top</a>
+<br>
+
+<h1>Thread safety</h1>
+
+<p>The C++ library string functionality requires a couple of atomic
+operations to provide thread-safety. If you don't take any special
+action, the library will use stub versions of these functions that are
+not thread-safe. They will work fine, unless your applications are
+multi-threaded.
+
+<p>If you want to provide custom, safe, versions of these functions, there
+are two distinct approaches. One is to provide a version for your CPU,
+using assembly language constructs. The other is to use the
+thread-safety primitives in your operating system. In either case, you
+make a file called <code>bits/atomicity.h</code>.
+
+<p>If you are using the assembly-language approach, put this code in
+<code>config/cpu/<chip>/bits/atomicity.h</code>, where chip is the name of
+your processor. In that case, edit the switch statement in
+<code>configure.target</code> to set the <code>cpu_include_dir</code>. In either
+case, set the switch statement that sets <code>ATOMICITYH</code> to be the
+directory containing <code>bits/atomicity.h</code>.
+
+<p>With those bits out of the way, you have to actually write
+<code>bits/atomicity.h</code> itself. This file should be wrapped in an
+include guard named <code>_BITS_ATOMICITY_H</code>. It should define one
+type, and two functions.
+
+<p>The type is <code>_Atomic_word</code>. Here is the version used on IRIX:
+
+<pre>typedef long _Atomic_word;
+</pre>
+
+<p>This type must be a signed integral type supporting atomic operations.
+If you're using the OS approach, use the same type used by your system's
+primitives. Otherwise, use the type for which your CPU provides atomic
+primitives.
+
+<p>Then, you must provide two functions. The bodies of these functions
+must be equivalent to those provided here, but using atomic operations:
+
+<pre>static inline _Atomic_word
+__attribute__ ((__unused__))
+__exchange_and_add (_Atomic_word* __mem, int __val)
+{
+ _Atomic_word __result = *__mem;
+ *__mem += __val;
+ return __result;
+}
+
+static inline void
+__attribute__ ((__unused__))
+__atomic_add (_Atomic_word* __mem, int __val)
+{
+ *__mem += __val;
+}
+</pre>
+
+<p><hr>
+Node:<a name="Numeric%20limits">Numeric limits</a>,
+Next:<a rel=next href="#Libtool">Libtool</a>,
+Previous:<a rel=previous href="#Thread%20safety">Thread safety</a>,
+Up:<a rel=up href="#Top">Top</a>
+<br>
+
+<h1>Numeric limits</h1>
+
+<p>The C++ library requires information about the fundamental data types,
+such as the minimum and maximum representable values of each type.
+You can define each of these values individually, but it is usually
+easiest just to indicate how many bits are used in each of the data
+types and let the library do the rest. For information about the
+macros to define, see the top of <code>include/bits/std_limits.h</code>.
+
+<p>If you need to define any macros, you can do so in
+<code>os_defines.h</code>. However, if all operating systems for your CPU
+are likely to use the same values, you can provide a CPU-specific file
+instead so that you do not have to provide the same definitions for
+each operating system. To take that approach, create a new file
+called <code>limits.h</code> in your CPU configuration directory (e.g.,
+<code>config/cpu/i386/bits</code>) and then modify <code>configure.target</code>
+so that <code>LIMITSH</code> is set to the CPU directory (e.g.,
+<code>config/cpu/i386</code>). Note that <code>LIMITSH</code> should not include
+the <code>bits</code> part of the directory name.
+
+<p><hr>
+Node:<a name="Libtool">Libtool</a>,
+Next:<a rel=next href="#GNU%20Free%20Documentation%20License">GNU Free Documentation License</a>,
+Previous:<a rel=previous href="#Numeric%20limits">Numeric limits</a>,
+Up:<a rel=up href="#Top">Top</a>
+<br>
+
+<h1>Libtool</h1>
+
+<p>The C++ library is compiled, archived and linked with libtool.
+Explaining the full workings of libtool is beyond the scope of this
+document, but there are a few, particular bits that are necessary for
+porting.
+
+<p>Some parts of the libstdc++-v3 library are compiled with the libtool
+<code>--tags CXX</code> option (the C++ definitions for libtool). Therefore,
+<code>ltcf-cxx.sh</code> in the top-level directory needs to have the correct
+logic to compile and archive objects equivalent to the C version of libtool,
+<code>ltcf-c.sh</code>. Some libtool targets have definitions for C but not
+for C++, or C++ definitions which have not been kept up to date.
+
+<p>The C++ run-time library contains initialization code that needs to be
+run as the library is loaded. Often, that requires linking in special
+object files when the C++ library is built as a shared library, or
+taking other system-specific actions.
+
+<p>The libstdc++-v3 library is linked with the C version of libtool, even though it
+is a C++ library. Therefore, the C version of libtool needs to ensure
+that the run-time library initializers are run. The usual way to do
+this is to build the library using <code>gcc -shared</code>.
+
+<p>If you need to change how the library is linked, look at
+<code>ltcf-c.sh</code> in the top-level directory. Find the switch statement
+that sets <code>archive_cmds</code>. Here, adjust the setting for your
+operating system.
+
+<p><hr>
+Node:<a name="GNU%20Free%20Documentation%20License">GNU Free Documentation License</a>,
+Previous:<a rel=previous href="#Libtool">Libtool</a>,
+Up:<a rel=up href="#Top">Top</a>
+<br>
+
+<h1>GNU Free Documentation License</h1>
+
+<div align="center">Version 1.1, March 2000</div>
+<pre>Copyright © 2000 Free Software Foundation, Inc.
+59 Temple Place, Suite 330, Boston, MA 02111-1307, USA
+
+Everyone is permitted to copy and distribute verbatim copies
+of this license document, but changing it is not allowed.
+</pre>
+
+<ol type=1 start=0>
+</p><li>PREAMBLE
+
+<p>The purpose of this License is to make a manual, textbook, or other
+written document <dfn>free</dfn> in the sense of freedom: to assure everyone
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+
+<p>This License is a kind of "copyleft", which means that derivative
+works of the document must themselves be free in the same sense. It
+complements the GNU General Public License, which is a copyleft
+license designed for free software.
+
+<p>We have designed this License in order to use it for manuals for free
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+
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+
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+
+</p><li>FUTURE REVISIONS OF THIS LICENSE
+
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+</ol>
+
+<h2>ADDENDUM: How to use this License for your documents</h2>
+
+<p>To use this License in a document you have written, include a copy of
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+license notices just after the title page:
+
+<pre> Copyright (C) <var>year</var> <var>your name</var>.
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+ under the terms of the GNU Free Documentation License, Version 1.1
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+ A copy of the license is included in the section entitled ``GNU
+ Free Documentation License''.
+</pre>
+
+<p>If you have no Invariant Sections, write "with no Invariant Sections"
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+
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+to permit their use in free software.
+
+
+<h1>Table of Contents</h1>
+<ul>
+<li><a href="#Top">Porting libstdc++-v3</a>
+<li><a href="#Operating%20system">Operating system</a>
+<li><a href="#Character%20types">Character types</a>
+<li><a href="#Thread%20safety">Thread safety</a>
+<li><a href="#Numeric%20limits">Numeric limits</a>
+<li><a href="#Libtool">Libtool</a>
+<li><a href="#GNU%20Free%20Documentation%20License">GNU Free Documentation License</a>
+<ul>
+<li><a href="#GNU%20Free%20Documentation%20License">ADDENDUM: How to use this License for your documents</a>
+</ul>
+</ul>
+
+</body></html>
+
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