--build and --host

[Steve M. Robbins]

Hello,

In case Henrique's posting wasn't clear, the question is this: is

        ./configure --build=foo ...

different from

        ./configure --build=foo --host=foo ...

or not?  In other words, does configure change its behaviour (e.g. go
into "cross compiling" mode) as soon as --host is specified, even when
the host type is the same as the build type?

There are conflicting pieces of evidence.  The first two suggest
that cross compiling happens only if host != build.  The second
two suggest that things change as soon as you specify --host, no
matter what the value you give it.


1. The autoconf doc (node System Type) says

   If you want to _use_ a cross compiler, that generates code for a
platform different from the build platform, you should specify the host
platform (i.e., that on which the generated programs will eventually be
run) with `--host=TYPE'.  In this case, you should also specify the
build platform with `--build=TYPE', because, in this case, it may not
be possible to guess the build platform (it sometimes involves
compiling and running simple test programs, and this can't be done if
the compiler is a cross compiler).

  [ well, on second reading, I'm not sure what this says about
    host == build ... ]


2. The autoconf doc (node Specifying Names) says

   They all default to the result of running `config.guess', unless you
specify either `--build' or `--host'.  In this case, the default
becomes the system type you specified.  If you specify both, and
they're different, `configure' will enter cross compilation mode, so it
won't run any tests that require execution.


3. Generated configure scripts have this bit

ac_tool_prefix=
test -n "$host_alias" && ac_tool_prefix=$host_alias-


4. Akim posted a note saying

        - passing --host means you cross compile (whatever the relationship
          between host and build)
        [http://sources.redhat.com/ml/autoconf/2002-02/msg00059.html]



So, we really just wanted to know which is the truth?

Thanks,
-Steve


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