Re: 64-bit configure hell

[Daniel Jacobowitz <drow at false dot org>]

On Wed, Nov 24, 2004 at 03:08:55PM -0800, Stan Shebs wrote:
> I have a messy configure problem with 64-bit Darwin, and would
> like to get some ideas about how to solve. The situation is that
> Darwin 8.x aka Tiger is capable of running 64-bit-address-space
> programs on G5s, and to support that in GCC I've set up a multilib
> for the -m64 option that enables it. This all works on G5 Tiger
> now, at least on prime-number days of the month when the moon is
> full :-) , and I hope to check in the last bits soon.
> 
> The problem is that Tiger also runs on G4s, which are not capable
> of running 64-bit programs - all the machinery is there to build
> complete and correct binaries, the kernel just refuses to execute
> them. This causes problems for some configure scripts, in particular
> those in libstdc++ and libobjc, which want to be able to run
> executables. It's not entirely clear to me why that's important,
> since the libraries already build and run perfectly fine for
> cross-compilers.
> 
> Although it would be good for sales to require that people
> building GCC on Darwin upgrade to G5s :-) that's kind of
> unfriendly, while producing different results from configure
> and make depending on one's CPU is also just asking for
> trouble. What other options do I have?

Whatever we do to solve this problem, let's try to make it general -
there are lots of affected systems.  I've seen listed so far:

  32-bit AIX
  s390-ibm-linux-gnu
  sparc-sun-solaris2.7

I also know of:
  i386-pc-solaris2.10

And I'd like to be able to enable a 64-bit multilib for:
  i386-pc-linux-gnu

For the last one, Debian hacks it using a change to config-ml.in; we
tell the other library builds that they are cross compiling if a
trivial 64-bit program can't be run.  It works for libstdc++.  It
doesn't work for libjava due to some bug I never tracked down, and it
doesn't work for libgcc (which doesn't have the execute tests problem,
but does have the problem Ulrich mentioned of not building if 64-bit
libraries are not installed).

I think moving libgcc to the top level, followed by cleaning up the
tests in config-ml.in, should be enough.  Maybe any multilib that can't
be linked should be automatically disabled, too?

-- 
Daniel Jacobowitz