Help building a 32bit GCC that can generate 32/64bit (x86)

[Paul Smith]

On Wed, 2011-04-27 at 10:28 -0700, Ian Lance Taylor wrote:
> Paul Smith <paul@mad-scientist.net> writes:
> 
> >> I think the simplest way to do this would be to configure as usual on a
> >> 64-bit system, and build it using something like
> >>     make BOOT_CFLAGS="-m32 -g -O2"
> >
> > I tried to build on a 64bit system setting CC="gcc -m32" and CXX="g++
> > -m32" when running configure.  But this failed.  I'll look up
> > BOOT_CFLAGS and see what I can find out.
> 
> Setting CC and CXX won't help, because that won't affect the later
> bootstrap stages.  Setting BOOT_CFLAGS should affect the way the later
> bootstrap stages are built, and should cause them to build 32-bit
> binaries.  I haven't actually tried it.

Ah, I see.  So CC/CXX are used to build the stage1 compiler (xgcc) but
not the final compiler... that makes perfect sense now that you mention
it :-).

> > One, build on a 32bit host and use --target=x86_64-pc-linux-gnu (or
> > something) to get a 64bit cross compiler (I assume(?) the resulting
> > compiler will also be able to build 32bit targets).
> 
> That should work.
> 
> > Two, build on a 64bit host and figure out a way to force the resulting
> > compiler to be a 32bit application.  Would the best way of doing that be
> > using configure with CC="gcc -m32"?  Or setting --host=i686-pc-linux-gnu
> > (or similar)?  Or...?
> 
> That should work, but use BOOT_CFLAGS as I suggested.

OK.  I'm going to start with the first (build on a 32bit system with
--target) as it seems the simpler option.

> I'm sorry, you're quite right.  I did not know about that.  You're
> right, using --enable-targets=all when bootstrapping on a 32-bit ought
> to give you a compiler which supports the -m64 option.  What failed when
> you tried that?

Well to be honest I tried so many different things that I've lost track
of what failed when.  Let me start fresh and I'll get back to you with
details if/when I run into things.