* porting.texi: New file.

From-SVN: r37630

libstdc++-v3/ChangeLog

+2000-11-21  Mark Mitchell  <mark@codesourcery.com>
+
+	* porting.texi: New file.
+
 2000-11-21  Branko Cibej  <brankoe@xbc.nu>
 
         * config/os/solaris/solaris2.6/bits/os_defines.h: Define

libstdc++-v3/porting.texi

+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%
+% File:   porting.texi
+% Author: Mark Mitchell
+% Date:   11/21/2000
+%
+% Contents:
+%
+% Copyright (c) 2000 by CodeSourcery, LLC.  All rights reserved. 
+%
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+
+\input texinfo
+
+@c ---------------------------------------------------------------------
+@c Prologue
+@c ---------------------------------------------------------------------
+
+@setfilename porting.info
+@settitle Porting libstdc++-v3
+@setchapternewpage odd
+
+@ifinfo
+This file explains how to port libstdc++-v3 (the GNU C++ library) to 
+a new target.
+
+Copyright (c) 2000 Free Software Foundation, Inc.
+@end ifinfo
+
+@c ---------------------------------------------------------------------
+@c Titlepage
+@c ---------------------------------------------------------------------
+
+@titlepage
+@title Porting libstdc++-v3
+@author Mark Mitchell
+@page
+@vskip 0pt plus 1filll
+Copyright @copyright{} 2000 Free Software Foundation, Inc.
+@end titlepage
+
+@c ---------------------------------------------------------------------
+@c Top
+@c ---------------------------------------------------------------------
+
+@node Top
+@top Porting libstdc++-v3
+
+This document explains how to port libstdc++-v3 (the GNU C++ library) to 
+a new target.
+
+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.  
+
+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.
+
+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.
+
+Here are the primary steps required to port the library:
+
+@menu
+* Operating system::    Configuring for your operating system.
+* Character types::     Implementing character classification.
+* Thread safety::       Implementing atomic operations.
+* Libtool::             Using libtool.
+@end menu
+
+@c ---------------------------------------------------------------------
+@c Operating system
+@c ---------------------------------------------------------------------
+
+@node Operating system
+@chapter Operating system
+
+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 @file{config/os} hierarchy.  For example, the IRIX
+configuration files are all in @file{config/os/irix}.  There is no set
+way to organize the OS configuration directory.  For example,
+@file{config/os/solaris/solaris-2.6} and
+@file{config/os/solaris/solaris-2.7} 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 @file{config/os/solaris/solaris-2.7}
+directory.  The important information is that there needs to be a
+directory under @file{config/os} to store the files for your operating
+system.
+
+You'll have to change the @file{configure.target} file to ensure that
+your new directory is activated.  Look for the switch statement that
+sets @code{os_include_dir}, 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} in
+@code{sparc-sun-solaris2.8}.
+
+The first file to create in this directory, should be called
+@file{bits/os_defines.h}.  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{__off64_t}, and @code{__ssize_t}.  Typically, this just looks
+like:
+
+@example
+#define __off_t off_t
+#define __off64_t off64_t
+#define __ssize_t ssize_t
+@end example
+
+@noindent
+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}, or the other types; you simply
+have to provide the macros.
+
+In addition, several V3 source files unconditionally define the macro
+@code{_POSIX_SOURCE}.  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} this macro, or define
+other macros (like @code{_LARGEFILE_SOURCE} or @code{__EXTENSIONS__}).
+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 should but in @file{bits/os_defines.h}
+to make these declarations available.
+
+Finally, you should bracket the entire file in an include-guard, like
+this:
+
+@example
+#ifndef _GLIBCPP_OS_DEFINES
+#define _GLIBCPP_OS_DEFINES
+...
+#endif
+@end example
+
+@c ---------------------------------------------------------------------
+@c Character types
+@c ---------------------------------------------------------------------
+
+@node Character types
+@chapter Character types
+
+The library requires that you provide three header files to implement
+character classification, analagous to that provided by the C libraries
+@file{<ctype.h>} header.  You can model these on the files provided in
+@file{config/os/generic/bits}.  However, these files will almost
+certainly need some modification.
+
+The first file to write is @file{bits/ctype_base.h}.  This file provides
+some very basic information about character classification.  The V3
+library assumes that your C library implements @file{<ctype.h>} 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 @file{bits/ctype_base.h}
+file gives the type of the integer, and the values of the various bit
+masks.  You will have to peer at your own @file{<ctype.h>} to figure out
+how to define the values required by this file.
+
+The @file{bits/ctype_base.h} header file does not need include guards.
+It should contain a single @code{struct} definition called
+@code{ctype_base}.  This @code{struct} should contain two type
+declarations, and one enumeration declaration, like this example, taken
+from the IRIX configuration:
+
+@example
+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
+  @};
+@};
+@end example
+
+@noindent
+The @code{mask} 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} 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} and
+@code{tolower} in this way, you can pick any pointer-to-integer type,
+but you must still define the type.
+
+The enumeration should give definitions for all the values in the above
+example, using the values from your native @file{<ctype.h>}.  They can
+be given symbolically (as above), or numerically, if you prefer.  You do
+not have to include @file{<ctype.h>} in this header; it will always be
+included before @file{bits/ctype_base.h} is included.
+
+The next file to write is @file{bits/ctype_noninline.h}, which also does
+not require include guards.  This file defines a few member functions
+that will be included in @file{include/bits/locale_facets.h}.  The first
+function that must be written is the @code{ctype<char>::ctype}
+constructor.  Here is the IRIX example:
+
+@example
+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) 
+  @{ @}
+@end example
+
+@noindent
+There are two parts of this that you might choose to alter. The first,
+and most important, is the line involving @code{__libc_attr}.  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} and
+@code{_M_tolower} with those tables, in similar fashion.
+
+Now, you have to write two functions to convert from upper-case to
+lower-case, and vice versa.  Here are the IRIX versions:
+
+@example
+char
+ctype<char>::do_toupper(char __c) const
+@{ return _toupper(__c); @}
+
+char
+ctype<char>::do_tolower(char __c) const
+@{ return _tolower(__c); @}
+@end example
+
+@noindent
+Your C library provides equivalents to IRIX's @code{_toupper} and
+@code{_tolower}.  If you initialized @code{_M_toupper} and
+@code{_M_tolower} above, then you could use those tables instead.
+
+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:
+
+@example
+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;
+@}
+@end example
+
+You must also provide the @file{bits/ctype_inline.h} file, which
+contains a few more functions.  On most systems, you can just copy
+@file{config/os/generic/ctype_inline.h} and use it on your system.
+
+In detail, the functions provided test characters for particular
+properties; they are analagous to the functions like @code{isalpha} and
+@code{islower} provided by the C library.
+
+The first function is implemented like this on IRIX:
+
+@example
+bool
+ctype<char>::
+is(mask __m, char __c) const throw()
+@{ return (_M_table)[(unsigned char)(__c)] & __m; @}
+@end example
+
+@noindent
+The @code{_M_table} 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.
+
+The next function is:
+
+@example
+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;
+@}
+@end example
+
+@noindent
+This function is similar; it copies the masks for all the characters
+from @code{__low} up until @code{__high} into the vector given by
+@code{__vec}.
+
+The last two functions again are entirely generic:
+
+@example
+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;
+@}
+@end example
+
+@c ---------------------------------------------------------------------
+@c Thread safety
+@c ---------------------------------------------------------------------
+
+@node Thread safety
+@chapter Thread safety
+
+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.
+
+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 @file{bits/atomicity.h}.  
+
+If you are using the assembly-language approach, put this code in
+@file{config/cpu/<chip>/bits/atomicity.h}, where chip is the name of
+your chip.  In that case, edit the switch statement in
+@file{configure.target} to set the @code{cpu_include_dir}.  In either
+case, set the switch statement that sets @code{ATOMICITYH} to be the
+directory containing @file{bits/atomicity.h}.
+
+With those bits out of the way, you have to actually write
+@file{bits/atomicity.h} itself.  This file should be wrapped in an
+include guard named @code{_BITS_ATOMICITY_H}.  It should define one
+type, and two functions.  
+
+The type is @code{_Atomic_word}.  Here is the version used on IRIX:
+
+@example
+typedef long _Atomic_word;
+@end example
+
+@noindent
+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.
+
+Then, you must provide two functions.  The bodies of these functions
+must be equivalent to those provided here, but using atomic operations:
+
+@example
+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;
+@}
+@end example
+
+@c ---------------------------------------------------------------------
+@c Libtool
+@c ---------------------------------------------------------------------
+
+@node Libtool
+@chapter Libtool
+
+The C++ library is linked with libtool.  Explaining the full workings of
+libtool is beyond the scope of this document, but there is one
+particular bit that should be explained here.  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.
+
+The 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}.
+
+If you need to change how the library is linked, look at
+@file{ltcf-c.sh} in the top-level directory.  Find the switch statement
+that sets @code{archive_cmds}.  Here, adjust the setting for your
+operating system.
+
+@c ---------------------------------------------------------------------
+@c Epilogue
+@c ---------------------------------------------------------------------
+
+@contents
+@bye