autoconf and cross-compiling?

autoconf and cross-compiling?

[Dan Kegel]

I'm trying to document the right way to cross-compile
applications which use autoconf/automake.  configure
has a --target flag, but I can't see how to get it to do anything
useful.

The goat book has what looks like a helpful section
  http://sources.redhat.com/autobook/autobook/autobook_261.html#SEC261
which talks about the macros AC_CANONICAL_SYSTEM and AC_ARG_PROGRAM,
but it turns out this only affects tool names *when installing*.
It's useful when *building* cross compilers, not when using them.

My best guess at the moment is:
  Before running 'configure', set the environment variables
  CC, CXX, RANLIB, and AR to point to the cross-development
  tools you want to use, *and* tell configure the target name,
  e.g.
    CC=powerpc-linux-gcc CXX=powerpc-linux-g++ RANLIB=powerpc-linux-ranlib AR=powerpc-linux-ar ./configure --target=powerpc-linux

Is this right?

If so, this is suprisingly clumsy.  I would expect configure to let you set
both the target name and the tool names in one fell swoop, e.g.
    ./configure --with-target=powerpc-linux
but since few people do cross-development, maybe this hasn't been made easy.

- Dan

(originally posted to gnu.gcc.help, but no response there)

** Sent via the linuxppc-embedded mail list. See http://lists.linuxppc.org/

Re: autoconf and cross-compiling?

[Dan Kegel]

Someone wrote:
> This helps in some situations, but does  only  part  of  the  job  in
> others.  In general, autoconf/automake based stuff will fail to build
> more or less completely when it comes to situations where it tries to
> get information of the (supposed target) system by trying to run some
> test programs.
>
> Either it uses the cross compiler to build the test programs - the it
> dies because these programs cannot be run on the host system;  or  it
> uses  the native compiler and it dies later (sometimes REALLY late on
> the target) because it gathers information from the build host  which
> does  not apply on the target (simple case: getting information about
> endianess when building on a x86 host for a PPC target).
> ...
> There was another posting about this issue by Magnus Damm, see
> http://lists.linuxppc.org/linuxppc-embedded/200109/msg00355.html

Thanks for the link!

I believe there's a fix for the endian problem; see
http://www.gnu.org/software/ac-archive/Cross_Compilation/ac_c_bigendian_cross.html

A similar approch should work for sizeof, shouldn't it?

Don't know about the other ones, like fork etc. :-(

- Dan

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