etc/configure.info-2

This is configure.info, produced by makeinfo version 4.0 from
./configure.texi.

INFO-DIR-SECTION GNU admin
START-INFO-DIR-ENTRY
* configure: (configure).	The GNU configure and build system
END-INFO-DIR-ENTRY

   This file documents the GNU configure and build system.

   Copyright (C) 1998 Cygnus Solutions.

   Permission is granted to make and distribute verbatim copies of this
manual provided the copyright notice and this permission notice are
preserved on all copies.

   Permission is granted to copy and distribute modified versions of
this manual under the conditions for verbatim copying, provided that
the entire resulting derived work is distributed under the terms of a
permission notice identical to this one.

   Permission is granted to copy and distribute translations of this
manual into another language, under the above conditions for modified
versions, except that this permission notice may be stated in a
translation approved by the Foundation.


File: configure.info,  Node: Configuration Name Definition,  Next: Using Configuration Names,  Up: Configuration Names

Configuration Name Definition
=============================

   This is a string of the form CPU-MANUFACTURER-OPERATING_SYSTEM.  In
some cases, this is extended to a four part form:
CPU-MANUFACTURER-KERNEL-OPERATING_SYSTEM.

   When using a configuration name in a configure option, it is normally
not necessary to specify an entire name.  In particular, the
MANUFACTURER field is often omitted, leading to strings such as
`i386-linux' or `sparc-sunos'.  The shell script `config.sub' will
translate these shortened strings into the canonical form.  autoconf
will arrange for `config.sub' to be run automatically when it is needed.

   The fields of a configuration name are as follows:

CPU
     The type of processor.  This is typically something like `i386' or
     `sparc'.  More specific variants are used as well, such as
     `mipsel' to indicate a little endian MIPS processor.

MANUFACTURER
     A somewhat freeform field which indicates the manufacturer of the
     system.  This is often simply `unknown'.  Other common strings are
     `pc' for an IBM PC compatible system, or the name of a workstation
     vendor, such as `sun'.

OPERATING_SYSTEM
     The name of the operating system which is run on the system.  This
     will be something like `solaris2.5' or `irix6.3'.  There is no
     particular restriction on the version number, and strings like
     `aix4.1.4.0' are seen.  For an embedded system, which has no
     operating system, this field normally indicates the type of object
     file format, such as `elf' or `coff'.

KERNEL
     This is used mainly for GNU/Linux.  A typical GNU/Linux
     configuration name is `i586-pc-linux-gnulibc1'.  In this case the
     kernel, `linux', is separated from the operating system,
     `gnulibc1'.

   The shell script `config.guess' will normally print the correct
configuration name for the system on which it is run.  It does by
running `uname' and by examining other characteristics of the system.

   Because `config.guess' can normally determine the configuration name
for a machine, it is normally only necessary to specify a configuration
name when building a cross-compiler or when building using a
cross-compiler.


File: configure.info,  Node: Using Configuration Names,  Prev: Configuration Name Definition,  Up: Configuration Names

Using Configuration Names
=========================

   A configure script will sometimes have to make a decision based on a
configuration name.  You will need to do this if you have to compile
code differently based on something which can not be tested using a
standard autoconf feature test.

   It is normally better to test for particular features, rather than to
test for a particular system.  This is because as Unix evolves,
different systems copy features from one another.  Even if you need to
determine whether the feature is supported based on a configuration
name, you should define a macro which describes the feature, rather than
defining a macro which describes the particular system you are on.

   Testing for a particular system is normally done using a case
statement in `configure.in'.  The case statement might look something
like the following, assuming that `host' is a shell variable holding a
canonical configuration name (which will be the case if `configure.in'
uses the `AC_CANONICAL_HOST' or `AC_CANONICAL_SYSTEM' macro).

     case "${host}" in
     i[3456]86-*-linux-gnu*) do something ;;
     sparc*-sun-solaris2.[56789]*) do something ;;
     sparc*-sun-solaris*) do something ;;
     mips*-*-elf*) do something ;;
     esac

   It is particularly important to use `*' after the operating system
field, in order to match the version number which will be generated by
`config.guess'.

   In most cases you must be careful to match a range of processor
types.  For most processor families, a trailing `*' suffices, as in
`mips*' above.  For the i386 family, something along the lines of
`i[3456]86' suffices at present.  For the m68k family, you will need
something like `m68*'.  Of course, if you do not need to match on the
processor, it is simpler to just replace the entire field by a `*', as
in `*-*-irix*'.


File: configure.info,  Node: Cross Compilation Tools,  Next: Canadian Cross,  Prev: Configuration Names,  Up: Top

Cross Compilation Tools
***********************

   The GNU configure and build system can be used to build "cross
compilation" tools.  A cross compilation tool is a tool which runs on
one system and produces code which runs on another system.

* Menu:

* Cross Compilation Concepts::		Cross Compilation Concepts.
* Host and Target::			Host and Target.
* Using the Host Type::			Using the Host Type.
* Specifying the Target::       	Specifying the Target.
* Using the Target Type::		Using the Target Type.
* Cross Tools in the Cygnus Tree::	Cross Tools in the Cygnus Tree


File: configure.info,  Node: Cross Compilation Concepts,  Next: Host and Target,  Up: Cross Compilation Tools

Cross Compilation Concepts
==========================

   A compiler which produces programs which run on a different system
is a cross compilation compiler, or simply a "cross compiler".
Similarly, we speak of cross assemblers, cross linkers, etc.

   In the normal case, a compiler produces code which runs on the same
system as the one on which the compiler runs.  When it is necessary to
distinguish this case from the cross compilation case, such a compiler
is called a "native compiler".  Similarly, we speak of native
assemblers, etc.

   Although the debugger is not strictly speaking a compilation tool,
it is nevertheless meaningful to speak of a cross debugger: a debugger
which is used to debug code which runs on another system.  Everything
that is said below about configuring cross compilation tools applies to
the debugger as well.


File: configure.info,  Node: Host and Target,  Next: Using the Host Type,  Prev: Cross Compilation Concepts,  Up: Cross Compilation Tools

Host and Target
===============

   When building cross compilation tools, there are two different
systems involved: the system on which the tools will run, and the
system for which the tools generate code.

   The system on which the tools will run is called the "host" system.

   The system for which the tools generate code is called the "target"
system.

   For example, suppose you have a compiler which runs on a GNU/Linux
system and generates ELF programs for a MIPS embedded system.  In this
case the GNU/Linux system is the host, and the MIPS ELF system is the
target.  Such a compiler could be called a GNU/Linux cross MIPS ELF
compiler, or, equivalently, a `i386-linux-gnu' cross `mips-elf'
compiler.

   Naturally, most programs are not cross compilation tools.  For those
programs, it does not make sense to speak of a target.  It only makes
sense to speak of a target for tools like `gcc' or the `binutils' which
actually produce running code.  For example, it does not make sense to
speak of the target of a tool like `bison' or `make'.

   Most cross compilation tools can also serve as native tools.  For a
native compilation tool, it is still meaningful to speak of a target.
For a native tool, the target is the same as the host.  For example, for
a GNU/Linux native compiler, the host is GNU/Linux, and the target is
also GNU/Linux.


File: configure.info,  Node: Using the Host Type,  Next: Specifying the Target,  Prev: Host and Target,  Up: Cross Compilation Tools

Using the Host Type
===================

   In almost all cases the host system is the system on which you run
the `configure' script, and on which you build the tools (for the case
when they differ, *note Canadian Cross::).

   If your configure script needs to know the configuration name of the
host system, and the package is not a cross compilation tool and
therefore does not have a target, put `AC_CANONICAL_HOST' in
`configure.in'.  This macro will arrange to define a few shell
variables when the `configure' script is run.

`host'
     The canonical configuration name of the host.  This will normally
     be determined by running the `config.guess' shell script, although
     the user is permitted to override this by using an explicit
     `--host' option.

`host_alias'
     In the unusual case that the user used an explicit `--host' option,
     this will be the argument to `--host'.  In the normal case, this
     will be the same as the `host' variable.

`host_cpu'
`host_vendor'
`host_os'
     The first three parts of the canonical configuration name.

   The shell variables may be used by putting shell code in
`configure.in'.  For an example, see *Note Using Configuration Names::.


File: configure.info,  Node: Specifying the Target,  Next: Using the Target Type,  Prev: Using the Host Type,  Up: Cross Compilation Tools

Specifying the Target
=====================

   By default, the `configure' script will assume that the target is
the same as the host.  This is the more common case; for example, it
leads to a native compiler rather than a cross compiler.

   If you want to build a cross compilation tool, you must specify the
target explicitly by using the `--target' option when you run
`configure'.  The argument to `--target' is the configuration name of
the system for which you wish to generate code.  *Note Configuration
Names::.

   For example, to build tools which generate code for a MIPS ELF
embedded system, you would use `--target mips-elf'.


File: configure.info,  Node: Using the Target Type,  Next: Cross Tools in the Cygnus Tree,  Prev: Specifying the Target,  Up: Cross Compilation Tools

Using the Target Type
=====================

   When writing `configure.in' for a cross compilation tool, you will
need to use information about the target.  To do this, put
`AC_CANONICAL_SYSTEM' in `configure.in'.

   `AC_CANONICAL_SYSTEM' will look for a `--target' option and
canonicalize it using the `config.sub' shell script.  It will also run
`AC_CANONICAL_HOST' (*note Using the Host Type::).

   The target type will be recorded in the following shell variables.
Note that the host versions of these variables will also be defined by
`AC_CANONICAL_HOST'.

`target'
     The canonical configuration name of the target.

`target_alias'
     The argument to the `--target' option.  If the user did not specify
     a `--target' option, this will be the same as `host_alias'.

`target_cpu'
`target_vendor'
`target_os'
     The first three parts of the canonical target configuration name.

   Note that if `host' and `target' are the same string, you can assume
a native configuration.  If they are different, you can assume a cross
configuration.

   It is arguably possible for `host' and `target' to represent the
same system, but for the strings to not be identical.  For example, if
`config.guess' returns `sparc-sun-sunos4.1.4', and somebody configures
with `--target sparc-sun-sunos4.1', then the slight differences between
the two versions of SunOS may be unimportant for your tool.  However,
in the general case it can be quite difficult to determine whether the
differences between two configuration names are significant or not.
Therefore, by convention, if the user specifies a `--target' option
without specifying a `--host' option, it is assumed that the user wants
to configure a cross compilation tool.

   The variables `target' and `target_alias' should be handled
differently.

   In general, whenever the user may actually see a string,
`target_alias' should be used.  This includes anything which may appear
in the file system, such as a directory name or part of a tool name.
It also includes any tool output, unless it is clearly labelled as the
canonical target configuration name.  This permits the user to use the
`--target' option to specify how the tool will appear to the outside
world.

   On the other hand, when checking for characteristics of the target
system, `target' should be used.  This is because a wide variety of
`--target' options may map into the same canonical configuration name.
You should not attempt to duplicate the canonicalization done by
`config.sub' in your own code.

   By convention, cross tools are installed with a prefix of the
argument used with the `--target' option, also known as `target_alias'
(*note Using the Target Type::).  If the user does not use the
`--target' option, and thus is building a native tool, no prefix is
used.

   For example, if gcc is configured with `--target mips-elf', then the
installed binary will be named `mips-elf-gcc'.  If gcc is configured
without a `--target' option, then the installed binary will be named
`gcc'.

   The autoconf macro `AC_ARG_PROGRAM' will handle this for you.  If
you are using automake, no more need be done; the programs will
automatically be installed with the correct prefixes.  Otherwise, see
the autoconf documentation for `AC_ARG_PROGRAM'.


File: configure.info,  Node: Cross Tools in the Cygnus Tree,  Prev: Using the Target Type,  Up: Cross Compilation Tools

Cross Tools in the Cygnus Tree
==============================

   The Cygnus tree is used for various packages including gdb, the GNU
binutils, and egcs.  It is also, of course, used for Cygnus releases.

   In the Cygnus tree, the top level `configure' script uses the old
Cygnus configure system, not autoconf.  The top level `Makefile.in' is
written to build packages based on what is in the source tree, and
supports building a large number of tools in a single
`configure'/`make' step.

   The Cygnus tree may be configured with a `--target' option.  The
`--target' option applies recursively to every subdirectory, and
permits building an entire set of cross tools at once.

* Menu:

* Host and Target Libraries::		Host and Target Libraries.
* Target Library Configure Scripts::	Target Library Configure Scripts.
* Make Targets in Cygnus Tree::         Make Targets in Cygnus Tree.
* Target libiberty::			Target libiberty


File: configure.info,  Node: Host and Target Libraries,  Next: Target Library Configure Scripts,  Up: Cross Tools in the Cygnus Tree

Host and Target Libraries
-------------------------

   The Cygnus tree distinguishes host libraries from target libraries.

   Host libraries are built with the compiler used to build the programs
which run on the host, which is called the host compiler.  This includes
libraries such as `bfd' and `tcl'.  These libraries are built with the
host compiler, and are linked into programs like the binutils or gcc
which run on the host.

   Target libraries are built with the target compiler.  If gcc is
present in the source tree, then the target compiler is the gcc that is
built using the host compiler.  Target libraries are libraries such as
`newlib' and `libstdc++'.  These libraries are not linked into the host
programs, but are instead made available for use with programs built
with the target compiler.

   For the rest of this section, assume that gcc is present in the
source tree, so that it will be used to build the target libraries.

   There is a complication here.  The configure process needs to know
which compiler you are going to use to build a tool; otherwise, the
feature tests will not work correctly.  The Cygnus tree handles this by
not configuring the target libraries until the target compiler is
built.  In order to permit everything to build using a single
`configure'/`make', the configuration of the target libraries is
actually triggered during the make step.

   When the target libraries are configured, the `--target' option is
not used.  Instead, the `--host' option is used with the argument of
the `--target' option for the overall configuration.  If no `--target'
option was used for the overall configuration, the `--host' option will
be passed with the output of the `config.guess' shell script.  Any
`--build' option is passed down unchanged.

   This translation of configuration options is done because since the
target libraries are compiled with the target compiler, they are being
built in order to run on the target of the overall configuration.  By
the definition of host, this means that their host system is the same as
the target system of the overall configuration.

   The same process is used for both a native configuration and a cross
configuration.  Even when using a native configuration, the target
libraries will be configured and built using the newly built compiler.
This is particularly important for the C++ libraries, since there is no
reason to assume that the C++ compiler used to build the host tools (if
there even is one) uses the same ABI as the g++ compiler which will be
used to build the target libraries.

   There is one difference between a native configuration and a cross
configuration.  In a native configuration, the target libraries are
normally configured and built as siblings of the host tools.  In a cross
configuration, the target libraries are normally built in a subdirectory
whose name is the argument to `--target'.  This is mainly for
historical reasons.

   To summarize, running `configure' in the Cygnus tree configures all
the host libraries and tools, but does not configure any of the target
libraries.  Running `make' then does the following steps:

   * Build the host libraries.

   * Build the host programs, including gcc.  Note that we call gcc
     both a host program (since it runs on the host) and a target
     compiler (since it generates code for the target).

   * Using the newly built target compiler, configure the target
     libraries.

   * Build the target libraries.

   The steps need not be done in precisely this order, since they are
actually controlled by `Makefile' targets.


File: configure.info,  Node: Target Library Configure Scripts,  Next: Make Targets in Cygnus Tree,  Prev: Host and Target Libraries,  Up: Cross Tools in the Cygnus Tree

Target Library Configure Scripts
--------------------------------

   There are a few things you must know in order to write a configure
script for a target library.  This is just a quick sketch, and beginners
shouldn't worry if they don't follow everything here.

   The target libraries are configured and built using a newly built
target compiler.  There may not be any startup files or libraries for
this target compiler.  In fact, those files will probably be built as
part of some target library, which naturally means that they will not
exist when your target library is configured.

   This means that the configure script for a target library may not use
any test which requires doing a link.  This unfortunately includes many
useful autoconf macros, such as `AC_CHECK_FUNCS'.  autoconf macros
which do a compile but not a link, such as `AC_CHECK_HEADERS', may be
used.

   This is a severe restriction, but normally not a fatal one, as target
libraries can often assume the presence of other target libraries, and
thus know which functions will be available.

   As of this writing, the autoconf macro `AC_PROG_CC' does a link to
make sure that the compiler works.  This may fail in a target library,
so target libraries must use a different set of macros to locate the
compiler.  See the `configure.in' file in a directory like `libiberty'
or `libgloss' for an example.

   As noted in the previous section, target libraries are sometimes
built in directories which are siblings to the host tools, and are
sometimes built in a subdirectory.  The `--with-target-subdir' configure
option will be passed when the library is configured.  Its value will be
an empty string if the target library is a sibling.  Its value will be
the name of the subdirectory if the target library is in a subdirectory.

   If the overall build is not a native build (i.e., the overall
configure used the `--target' option), then the library will be
configured with the `--with-cross-host' option.  The value of this
option will be the host system of the overall build.  Recall that the
host system of the library will be the target of the overall build.  If
the overall build is a native build, the `--with-cross-host' option
will not be used.

   A library which can be built both standalone and as a target library
may want to install itself into different directories depending upon the
case.  When built standalone, or when built native, the library should
be installed in `$(libdir)'.  When built as a target library which is
not native, the library should be installed in `$(tooldir)/lib'.  The
`--with-cross-host' option may be used to distinguish these cases.

   This same test of `--with-cross-host' may be used to see whether it
is OK to use link tests in the configure script.  If the
`--with-cross-host' option is not used, then the library is being built
either standalone or native, and a link should work.


File: configure.info,  Node: Make Targets in Cygnus Tree,  Next: Target libiberty,  Prev: Target Library Configure Scripts,  Up: Cross Tools in the Cygnus Tree

Make Targets in Cygnus Tree
---------------------------

   The top level `Makefile' in the Cygnus tree defines targets for
every known subdirectory.

   For every subdirectory DIR which holds a host library or program,
the `Makefile' target `all-DIR' will build that library or program.

   There are dependencies among host tools.  For example, building gcc
requires first building gas, because the gcc build process invokes the
target assembler.  These dependencies are reflected in the top level
`Makefile'.

   For every subdirectory DIR which holds a target library, the
`Makefile' target `configure-target-DIR' will configure that library.
The `Makefile' target `all-target-DIR' will build that library.

   Every `configure-target-DIR' target depends upon `all-gcc', since
gcc, the target compiler, is required to configure the tool.  Every
`all-target-DIR' target depends upon the corresponding
`configure-target-DIR' target.

   There are several other targets which may be of interest for each
directory: `install-DIR', `clean-DIR', and `check-DIR'.  There are also
corresponding `target' versions of these for the target libraries ,
such as `install-target-DIR'.


File: configure.info,  Node: Target libiberty,  Prev: Make Targets in Cygnus Tree,  Up: Cross Tools in the Cygnus Tree

Target libiberty
----------------

   The `libiberty' subdirectory is currently a special case, in that it
is the only directory which is built both using the host compiler and
using the target compiler.

   This is because the files in `libiberty' are used when building the
host tools, and they are also incorporated into the `libstdc++' target
library as support code.

   This duality does not pose any particular difficulties.  It means
that there are targets for both `all-libiberty' and
`all-target-libiberty'.

   In a native configuration, when target libraries are not built in a
subdirectory, the same objects are normally used as both the host build
and the target build.  This is normally OK, since libiberty contains
only C code, and in a native configuration the results of the host
compiler and the target compiler are normally interoperable.

   Irix 6 is again an exception here, since the SGI native compiler
defaults to using the `O32' ABI, and gcc defaults to using the `N32'
ABI.  On Irix 6, the target libraries are built in a subdirectory even
for a native configuration, avoiding this problem.

   There are currently no other libraries built for both the host and
the target, but there is no conceptual problem with adding more.


File: configure.info,  Node: Canadian Cross,  Next: Cygnus Configure,  Prev: Cross Compilation Tools,  Up: Top

Canadian Cross
**************

   It is possible to use the GNU configure and build system to build a
program which will run on a system which is different from the system on
which the tools are built.  In other words, it is possible to build
programs using a cross compiler.

   This is referred to as a "Canadian Cross".

* Menu:

* Canadian Cross Example::		Canadian Cross Example.
* Canadian Cross Concepts::		Canadian Cross Concepts.
* Build Cross Host Tools::		Build Cross Host Tools.
* Build and Host Options::		Build and Host Options.
* CCross not in Cygnus Tree::		Canadian Cross not in Cygnus Tree.
* CCross in Cygnus Tree::		Canadian Cross in Cygnus Tree.
* Supporting Canadian Cross::		Supporting Canadian Cross.


File: configure.info,  Node: Canadian Cross Example,  Next: Canadian Cross Concepts,  Up: Canadian Cross

Canadian Cross Example
======================

   Here is an example of a Canadian Cross.

   While running on a GNU/Linux, you can build a program which will run
on a Solaris system.  You would use a GNU/Linux cross Solaris compiler
to build the program.

   Of course, you could not run the resulting program on your GNU/Linux
system.  You would have to copy it over to a Solaris system before you
would run it.

   Of course, you could also simply build the programs on the Solaris
system in the first place.  However, perhaps the Solaris system is not
available for some reason; perhaps you actually don't have one, but you
want to build the tools for somebody else to use.  Or perhaps your
GNU/Linux system is much faster than your Solaris system.

   A Canadian Cross build is most frequently used when building
programs to run on a non-Unix system, such as DOS or Windows.  It may
be simpler to configure and build on a Unix system than to support the
configuration machinery on a non-Unix system.


File: configure.info,  Node: Canadian Cross Concepts,  Next: Build Cross Host Tools,  Prev: Canadian Cross Example,  Up: Canadian Cross

Canadian Cross Concepts
=======================

   When building a Canadian Cross, there are at least two different
systems involved: the system on which the tools are being built, and
the system on which the tools will run.

   The system on which the tools are being built is called the "build"
system.

   The system on which the tools will run is called the host system.

   For example, if you are building a Solaris program on a GNU/Linux
system, as in the previous section, the build system would be GNU/Linux,
and the host system would be Solaris.

   It is, of course, possible to build a cross compiler using a Canadian
Cross (i.e., build a cross compiler using a cross compiler).  In this
case, the system for which the resulting cross compiler generates code
is called the target system.  (For a more complete discussion of host
and target systems, *note Host and Target::).

   An example of building a cross compiler using a Canadian Cross would
be building a Windows cross MIPS ELF compiler on a GNU/Linux system.  In
this case the build system would be GNU/Linux, the host system would be
Windows, and the target system would be MIPS ELF.

   The name Canadian Cross comes from the case when the build, host, and
target systems are all different.  At the time that these issues were
all being hashed out, Canada had three national political parties.


File: configure.info,  Node: Build Cross Host Tools,  Next: Build and Host Options,  Prev: Canadian Cross Concepts,  Up: Canadian Cross

Build Cross Host Tools
======================

   In order to configure a program for a Canadian Cross build, you must
first build and install the set of cross tools you will use to build the
program.

   These tools will be build cross host tools.  That is, they will run
on the build system, and will produce code that runs on the host system.

   It is easy to confuse the meaning of build and host here.  Always
remember that the build system is where you are doing the build, and the
host system is where the resulting program will run.  Therefore, you
need a build cross host compiler.

   In general, you must have a complete cross environment in order to do
the build.  This normally means a cross compiler, cross assembler, and
so forth, as well as libraries and include files for the host system.


File: configure.info,  Node: Build and Host Options,  Next: CCross not in Cygnus Tree,  Prev: Build Cross Host Tools,  Up: Canadian Cross

Build and Host Options
======================

   When you run `configure', you must use both the `--build' and
`--host' options.

   The `--build' option is used to specify the configuration name of
the build system.  This can normally be the result of running the
`config.guess' shell script, and it is reasonable to use
`--build=`config.guess`'.

   The `--host' option is used to specify the configuration name of the
host system.

   As we explained earlier, `config.guess' is used to set the default
value for the `--host' option (*note Using the Host Type::).  We can
now see that since `config.guess' returns the type of system on which
it is run, it really identifies the build system.  Since the host
system is normally the same as the build system (i.e., people do not
normally build using a cross compiler), it is reasonable to use the
result of `config.guess' as the default for the host system when the
`--host' option is not used.

   It might seem that if the `--host' option were used without the
`--build' option that the configure script could run `config.guess' to
determine the build system, and presume a Canadian Cross if the result
of `config.guess' differed from the `--host' option.  However, for
historical reasons, some configure scripts are routinely run using an
explicit `--host' option, rather than using the default from
`config.guess'.  As noted earlier, it is difficult or impossible to
reliably compare configuration names (*note Using the Target Type::).
Therefore, by convention, if the `--host' option is used, but the
`--build' option is not used, then the build system defaults to the
host system.


File: configure.info,  Node: CCross not in Cygnus Tree,  Next: CCross in Cygnus Tree,  Prev: Build and Host Options,  Up: Canadian Cross

Canadian Cross not in Cygnus Tree.
==================================

   If you are not using the Cygnus tree, you must explicitly specify the
cross tools which you want to use to build the program.  This is done by
setting environment variables before running the `configure' script.

   You must normally set at least the environment variables `CC', `AR',
and `RANLIB' to the cross tools which you want to use to build.

   For some programs, you must set additional cross tools as well, such
as `AS', `LD', or `NM'.

   You would set these environment variables to the build cross tools
which you are going to use.

   For example, if you are building a Solaris program on a GNU/Linux
system, and your GNU/Linux cross Solaris compiler were named
`solaris-gcc', then you would set the environment variable `CC' to
`solaris-gcc'.


File: configure.info,  Node: CCross in Cygnus Tree,  Next: Supporting Canadian Cross,  Prev: CCross not in Cygnus Tree,  Up: Canadian Cross

Canadian Cross in Cygnus Tree
=============================

   This section describes configuring and building a Canadian Cross when
using the Cygnus tree.

* Menu:

* Standard Cygnus CCross::	Building a Normal Program.
* Cross Cygnus CCross::		Building a Cross Program.


File: configure.info,  Node: Standard Cygnus CCross,  Next: Cross Cygnus CCross,  Up: CCross in Cygnus Tree

Building a Normal Program
-------------------------

   When configuring a Canadian Cross in the Cygnus tree, all the
appropriate environment variables are automatically set to `HOST-TOOL',
where HOST is the value used for the `--host' option, and TOOL is the
name of the tool (e.g., `gcc', `as', etc.).  These tools must be on
your `PATH'.

   Adding a prefix of HOST will give the usual name for the build cross
host tools.  To see this, consider that when these cross tools were
built, they were configured to run on the build system and to produce
code for the host system.  That is, they were configured with a
`--target' option that is the same as the system which we are now
calling the host.  Recall that the default name for installed cross
tools uses the target system as a prefix (*note Using the Target
Type::).  Since that is the system which we are now calling the host,
HOST is the right prefix to use.

   For example, if you configure with `--build=i386-linux-gnu' and
`--host=solaris', then the Cygnus tree will automatically default to
using the compiler `solaris-gcc'.  You must have previously built and
installed this compiler, probably by doing a build with no `--host'
option and with a `--target' option of `solaris'.


File: configure.info,  Node: Cross Cygnus CCross,  Prev: Standard Cygnus CCross,  Up: CCross in Cygnus Tree

Building a Cross Program
------------------------

   There are additional considerations if you want to build a cross
compiler, rather than a native compiler, in the Cygnus tree using a
Canadian Cross.

   When you build a cross compiler using the Cygnus tree, then the
target libraries will normally be built with the newly built target
compiler (*note Host and Target Libraries::).  However, this will not
work when building with a Canadian Cross.  This is because the newly
built target compiler will be a program which runs on the host system,
and therefore will not be able to run on the build system.

   Therefore, when building a cross compiler with the Cygnus tree, you
must first install a set of build cross target tools.  These tools will
be used when building the target libraries.

   Note that this is not a requirement of a Canadian Cross in general.
For example, it would be possible to build just the host cross target
tools on the build system, to copy the tools to the host system, and to
build the target libraries on the host system.  The requirement for
build cross target tools is imposed by the Cygnus tree, which expects
to be able to build both host programs and target libraries in a single
`configure'/`make' step.  Because it builds these in a single step, it
expects to be able to build the target libraries on the build system,
which means that it must use a build cross target toolchain.

   For example, suppose you want to build a Windows cross MIPS ELF
compiler on a GNU/Linux system.  You must have previously installed
both a GNU/Linux cross Windows compiler and a GNU/Linux cross MIPS ELF
compiler.

   In order to build the Windows (configuration name `i386-cygwin32')
cross MIPS ELF (configure name `mips-elf') compiler, you might execute
the following commands (long command lines are broken across lines with
a trailing backslash as a continuation character).

     mkdir linux-x-cygwin32
     cd linux-x-cygwin32
     SRCDIR/configure --target i386-cygwin32 --prefix=INSTALLDIR \
       --exec-prefix=INSTALLDIR/H-i386-linux
     make
     make install
     cd ..
     mkdir linux-x-mips-elf
     cd linux-x-mips-elf
     SRCDIR/configure --target mips-elf --prefix=INSTALLDIR \
       --exec-prefix=INSTALLDIR/H-i386-linux
     make
     make install
     cd ..
     mkdir cygwin32-x-mips-elf
     cd cygwin32-x-mips-elf
     SRCDIR/configure --build=i386-linux-gnu --host=i386-cygwin32 \
       --target=mips-elf --prefix=WININSTALLDIR \
       --exec-prefix=WININSTALLDIR/H-i386-cygwin32
     make
     make install

   You would then copy the contents of WININSTALLDIR over to the
Windows machine, and run the resulting programs.


File: configure.info,  Node: Supporting Canadian Cross,  Prev: CCross in Cygnus Tree,  Up: Canadian Cross

Supporting Canadian Cross
=========================

   If you want to make it possible to build a program you are developing
using a Canadian Cross, you must take some care when writing your
configure and make rules.  Simple cases will normally work correctly.
However, it is not hard to write configure and make tests which will
fail in a Canadian Cross.

* Menu:

* CCross in Configure::		Supporting Canadian Cross in Configure Scripts.
* CCross in Make::		Supporting Canadian Cross in Makefiles.


File: configure.info,  Node: CCross in Configure,  Next: CCross in Make,  Up: Supporting Canadian Cross

Supporting Canadian Cross in Configure Scripts
----------------------------------------------

   In a `configure.in' file, after calling `AC_PROG_CC', you can find
out whether this is a Canadian Cross configure by examining the shell
variable `cross_compiling'.  In a Canadian Cross, which means that the
compiler is a cross compiler, `cross_compiling' will be `yes'.  In a
normal configuration, `cross_compiling' will be `no'.

   You ordinarily do not need to know the type of the build system in a
configure script.  However, if you do need that information, you can get
it by using the macro `AC_CANONICAL_SYSTEM', the same macro that is
used to determine the target system.  This macro will set the variables
`build', `build_alias', `build_cpu', `build_vendor', and `build_os',
which correspond to the similar `target' and `host' variables, except
that they describe the build system.

   When writing tests in `configure.in', you must remember that you
want to test the host environment, not the build environment.

   Macros like `AC_CHECK_FUNCS' which use the compiler will test the
host environment.  That is because the tests will be done by running the
compiler, which is actually a build cross host compiler.  If the
compiler can find the function, that means that the function is present
in the host environment.

   Tests like `test -f /dev/ptyp0', on the other hand, will test the
build environment.  Remember that the configure script is running on the
build system, not the host system.  If your configure scripts examines
files, those files will be on the build system.  Whatever you determine
based on those files may or may not be the case on the host system.

   Most autoconf macros will work correctly for a Canadian Cross.  The
main exception is `AC_TRY_RUN'.  This macro tries to compile and run a
test program.  This will fail in a Canadian Cross, because the program
will be compiled for the host system, which means that it will not run
on the build system.

   The `AC_TRY_RUN' macro provides an optional argument to tell the
configure script what to do in a Canadian Cross.  If that argument is
not present, you will get a warning when you run `autoconf':
     warning: AC_TRY_RUN called without default to allow cross compiling

This tells you that the resulting `configure' script will not work with
a Canadian Cross.

   In some cases while it may better to perform a test at configure
time, it is also possible to perform the test at run time.  In such a
case you can use the cross compiling argument to `AC_TRY_RUN' to tell
your program that the test could not be performed at configure time.

   There are a few other autoconf macros which will not work correctly
with a Canadian Cross: a partial list is `AC_FUNC_GETPGRP',
`AC_FUNC_SETPGRP', `AC_FUNC_SETVBUF_REVERSED', and
`AC_SYS_RESTARTABLE_SYSCALLS'.  The `AC_CHECK_SIZEOF' macro is
generally not very useful with a Canadian Cross; it permits an optional
argument indicating the default size, but there is no way to know what
the correct default should be.


File: configure.info,  Node: CCross in Make,  Prev: CCross in Configure,  Up: Supporting Canadian Cross

Supporting Canadian Cross in Makefiles.
---------------------------------------

   The main Canadian Cross issue in a `Makefile' arises when you want
to use a subsidiary program to generate code or data which you will then
include in your real program.

   If you compile this subsidiary program using `$(CC)' in the usual
way, you will not be able to run it.  This is because `$(CC)' will
build a program for the host system, but the program is being built on
the build system.

   You must instead use a compiler for the build system, rather than the
host system.  In the Cygnus tree, this make variable `$(CC_FOR_BUILD)'
will hold a compiler for the build system.

   Note that you should not include `config.h' in a file you are
compiling with `$(CC_FOR_BUILD)'.  The `configure' script will build
`config.h' with information for the host system.  However, you are
compiling the file using a compiler for the build system (a native
compiler).  Subsidiary programs are normally simple filters which do no
user interaction, and it is normally possible to write them in a highly
portable fashion so that the absence of `config.h' is not crucial.

   The gcc `Makefile.in' shows a complex situation in which certain
files, such as `rtl.c', must be compiled into both subsidiary programs
run on the build system and into the final program.  This approach may
be of interest for advanced build system hackers.  Note that the build
system compiler is rather confusingly called `HOST_CC'.


File: configure.info,  Node: Cygnus Configure,  Next: Multilibs,  Prev: Canadian Cross,  Up: Top

Cygnus Configure
****************

   The Cygnus configure script predates autoconf.  All of its
interesting features have been incorporated into autoconf.  No new
programs should be written to use the Cygnus configure script.

   However, the Cygnus configure script is still used in a few places:
at the top of the Cygnus tree and in a few target libraries in the
Cygnus tree.  Until those uses have been replaced with autoconf, some
brief notes are appropriate here.  This is not complete documentation,
but it should be possible to use this as a guide while examining the
scripts themselves.

* Menu:

* Cygnus Configure Basics::		Cygnus Configure Basics.
* Cygnus Configure in C++ Libraries::	Cygnus Configure in C++ Libraries.


File: configure.info,  Node: Cygnus Configure Basics,  Next: Cygnus Configure in C++ Libraries,  Up: Cygnus Configure

Cygnus Configure Basics
=======================

   Cygnus configure does not use any generated files; there is no
program corresponding to `autoconf'.  Instead, there is a single shell
script named `configure' which may be found at the top of the Cygnus
tree.  This shell script was written by hand; it was not generated by
autoconf, and it is incorrect, and indeed harmful, to run `autoconf' in
the top level of a Cygnus tree.

   Cygnus configure works in a particular directory by examining the
file `configure.in' in that directory.  That file is broken into four
separate shell scripts.

   The first is the contents of `configure.in' up to a line that starts
with `# per-host:'.  This is the common part.

   The second is the rest of `configure.in' up to a line that starts
with `# per-target:'.  This is the per host part.

   The third is the rest of `configure.in' up to a line that starts
with `# post-target:'.  This is the per target part.

   The fourth is the remainder of `configure.in'.  This is the post
target part.

   If any of these comment lines are missing, the corresponding shell
script is empty.

   Cygnus configure will first execute the common part.  This must set
the shell variable `srctrigger' to the name of a source file, to
confirm that Cygnus configure is looking at the right directory.  This
may set the shell variables `package_makefile_frag' and
`package_makefile_rules_frag'.

   Cygnus configure will next set the `build' and `host' shell
variables, and execute the per host part.  This may set the shell
variable `host_makefile_frag'.

   Cygnus configure will next set the `target' variable, and execute
the per target part.  This may set the shell variable
`target_makefile_frag'.

   Any of these scripts may set the `subdirs' shell variable.  This
variable is a list of subdirectories where a `Makefile.in' file may be
found.  Cygnus configure will automatically look for a `Makefile.in'
file in the current directory.  The `subdirs' shell variable is not
normally used, and I believe that the only directory which uses it at
present is `newlib'.

   For each `Makefile.in', Cygnus configure will automatically create a
`Makefile' by adding definitions for `make' variables such as `host'
and `target', and automatically editing the values of `make' variables
such as `prefix' if they are present.

   Also, if any of the `makefile_frag' shell variables are set, Cygnus
configure will interpret them as file names relative to either the
working directory or the source directory, and will read the contents of
the file into the generated `Makefile'.  The file contents will be read
in after the first line in `Makefile.in' which starts with `####'.

   These `Makefile' fragments are used to customize behaviour for a
particular host or target.  They serve to select particular files to
compile, and to define particular preprocessor macros by providing
values for `make' variables which are then used during compilation.
Cygnus configure, unlike autoconf, normally does not do feature tests,
and normally requires support to be added manually for each new host.

   The `Makefile' fragment support is similar to the autoconf
`AC_SUBST_FILE' macro.

   After creating each `Makefile', the post target script will be run
(i.e., it may be run several times).  This script may further customize
the `Makefile'.  When it is run, the shell variable `Makefile' will
hold the name of the `Makefile', including the appropriate directory
component.

   Like an autoconf generated `configure' script, Cygnus configure will
create a file named `config.status' which, when run, will automatically
recreate the configuration.  The `config.status' file will simply
execute the Cygnus configure script again with the appropriate
arguments.

   Any of the parts of `configure.in' may set the shell variables
`files' and `links'.  Cygnus configure will set up symlinks from the
names in `links' to the files named in `files'.  This is similar to the
autoconf `AC_LINK_FILES' macro.

   Finally, any of the parts of `configure.in' may set the shell
variable `configdirs' to a set of subdirectories.  If it is set, Cygnus
configure will recursively run the configure process in each
subdirectory.  If the subdirectory uses Cygnus configure, it will
contain a `configure.in' file but no `configure' file, in which case
Cygnus configure will invoke itself recursively.  If the subdirectory
has a `configure' file, Cygnus configure assumes that it is an autoconf
generated `configure' script, and simply invokes it directly.


File: configure.info,  Node: Cygnus Configure in C++ Libraries,  Prev: Cygnus Configure Basics,  Up: Cygnus Configure

Cygnus Configure in C++ Libraries
=================================

   The C++ library configure system, written by Per Bothner, deserves
special mention.  It uses Cygnus configure, but it does feature testing
like that done by autoconf generated `configure' scripts.  This
approach is used in the libraries `libio', `libstdc++', and `libg++'.

   Most of the `Makefile' information is written out by the shell
script `libio/config.shared'.  Each `configure.in' file sets certain
shell variables, and then invokes `config.shared' to create two package
`Makefile' fragments.  These fragments are then incorporated into the
resulting `Makefile' by the Cygnus configure script.

   The file `_G_config.h' is created in the `libio' object directory by
running the shell script `libio/gen-params'.  This shell script uses
feature tests to define macros and typedefs in `_G_config.h'.


File: configure.info,  Node: Multilibs,  Next: FAQ,  Prev: Cygnus Configure,  Up: Top

Multilibs
*********

   For some targets gcc may have different processor requirements
depending upon command line options.  An obvious example is the
`-msoft-float' option supported on several processors.  This option
means that the floating point registers are not available, which means
that floating point operations must be done by calling an emulation
subroutine rather than by using machine instructions.

   For such options, gcc is often configured to compile target libraries
twice: once with `-msoft-float' and once without.  When gcc compiles
target libraries more than once, the resulting libraries are called
"multilibs".

   Multilibs are not really part of the GNU configure and build system,
but we discuss them here since they require support in the `configure'
scripts and `Makefile's used for target libraries.

* Menu:

* Multilibs in gcc::		        Multilibs in gcc.
* Multilibs in Target Libraries::	Multilibs in Target Libraries.


File: configure.info,  Node: Multilibs in gcc,  Next: Multilibs in Target Libraries,  Up: Multilibs

Multilibs in gcc
================

   In gcc, multilibs are defined by setting the variable
`MULTILIB_OPTIONS' in the target `Makefile' fragment.  Several other
`MULTILIB' variables may also be defined there.  *Note The Target
Makefile Fragment: (gcc)Target Fragment.

   If you have built gcc, you can see what multilibs it uses by running
it with the `-print-multi-lib' option.  The output `.;' means that no
multilibs are used.  In general, the output is a sequence of lines, one
per multilib.  The first part of each line, up to the `;', is the name
of the multilib directory.  The second part is a list of compiler
options separated by `@' characters.

   Multilibs are built in a tree of directories.  The top of the tree,
represented by `.' in the list of multilib directories, is the default
library to use when no special compiler options are used.  The
subdirectories of the tree hold versions of the library to use when
particular compiler options are used.