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* 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