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@c Copyright (C) 2001, 2002, 2004, 2008 Free Software Foundation, Inc.

@c This is part of the GCC manual.

@c For copying conditions, see the file gcc.texi.

@node Configure Terms

@section Configure Terms and History

@cindex configure terms

@cindex canadian

The configure and build process has a long and colorful history, and can

be confusing to anyone who doesn't know why things are the way they are.

While there are other documents which describe the configuration process

in detail, here are a few things that everyone working on GCC should

know.

There are three system names that the build knows about: the machine you

are building on (@dfn{build}), the machine that you are building for

(@dfn{host}), and the machine that GCC will produce code for

(@dfn{target}).  When you configure GCC, you specify these with

@option{--build=}, @option{--host=}, and @option{--target=}.

Specifying the host without specifying the build should be avoided, as

@command{configure} may (and once did) assume that the host you specify

is also the build, which may not be true.

If build, host, and target are all the same, this is called a

@dfn{native}.  If build and host are the same but target is different,

this is called a @dfn{cross}.  If build, host, and target are all

different this is called a @dfn{canadian} (for obscure reasons dealing

with Canada's political party and the background of the person working

on the build at that time).  If host and target are the same, but build

is different, you are using a cross-compiler to build a native for a

different system.  Some people call this a @dfn{host-x-host},

@dfn{crossed native}, or @dfn{cross-built native}.  If build and target

are the same, but host is different, you are using a cross compiler to

build a cross compiler that produces code for the machine you're

building on.  This is rare, so there is no common way of describing it.

There is a proposal to call this a @dfn{crossback}.

If build and host are the same, the GCC you are building will also be

used to build the target libraries (like @code{libstdc++}).  If build and host

are different, you must have already built and installed a cross

compiler that will be used to build the target libraries (if you

configured with @option{--target=foo-bar}, this compiler will be called

@command{foo-bar-gcc}).

In the case of target libraries, the machine you're building for is the

machine you specified with @option{--target}.  So, build is the machine

you're building on (no change there), host is the machine you're

building for (the target libraries are built for the target, so host is

the target you specified), and target doesn't apply (because you're not

building a compiler, you're building libraries).  The configure/make

process will adjust these variables as needed.  It also sets

@code{$with_cross_host} to the original @option{--host} value in case you

need it.

The @code{libiberty} support library is built up to three times: once

for the host, once for the target (even if they are the same), and once

for the build if build and host are different.  This allows it to be

used by all programs which are generated in the course of the build

process.