configure.build_arch

[Jack Howarth]

On Tue, Sep 15, 2009 at 02:43:29PM -0700, Toby Peterson wrote:
> On Tue, Sep 15, 2009 at 14:23, Jack Howarth <howarth at bromo.med.uc.edu> wrote:
> >   Reading through the commits on the configure.build_arch feature
> > in port, I am rather surprised that invoking that doesn't also
> > set the triplets for configure as well as passing the -m32 or
> > -m64 compiler flags.
> 
> It does pass -m32/-m64 if the configure.compiler setting refers to a
> compiler that doesn't support -arch flags.
> 
> > Wouldn't you at least want to set
> > --target= to the appropriate value so that configure understood
> > what architecture it was going to build for?
> 
> Passing --target doesn't make any sense, as we are not cross-compiling.
> 
> - Toby

The last statement would be true if the current config.guess weren't
reporting the wrong architecture on EMT64-capable processors on 10.6.
I assume invoking...

configure.build_arch x86_64

sets the CFLAGS to -m64, right. So here we have the same issue all over
again. The configure execution reports back i386-apple-darwin10 (even
though the compiler is now generating code with -m64). Configure makes
decisions based on its understanding that the target architecture is
actually 32-bit while the compiler actually is generating 64-bit code behind
its back. This isn't rocket science. You can't go around changing the
code generation behind configure's back like this. Consider the text
at...

http://www.gnu.org/prep/standards/html_node/Configuration.html

which states...

The target type normally defaults to the host type. Programs for which cross-operation is not meaningful need not accept the ‘--target’ option, because configuring an entire operating system for cross-operation is not a meaningful operation.

Now what you say would normally be true but as 10.6 is a hybrid OS so
the first clause is NOT true. The target type for -m64 code (x86_64-apple-darwin10)
is not the same as the *reported* host type (i386-apple-darwin10). You
have to consider that configure is free to make decisions about setting up the 
Makefiles based on its understanding (without additional options like
--target=) that the host type (i386-apple-darwin10) is the operative
target (which it isn't when the compiler is generating x86_64 code).
  I guess I can go upstream and try to find one of the maintainers of autoconf 
to provide an authorative clarification from upstream for the group here.
        Jack