Re: Moving along Pure64

[Greg Johnson <gjohnson@lanl.gov>]

On Thu, Apr 01, 2004 at 02:13:37PM -0600, John Goerzen wrote:
> On Thu, Apr 01, 2004 at 01:09:08PM -0700, Greg Johnson wrote:
> > On Thu, Apr 01, 2004 at 10:38:21AM -0600, John Goerzen wrote:
> > > Hi,
> > > 
> > > We need a few things to happen to get pure64 going better.
> > > 
> > > At the top of the list is a gcc that can build 32- and 64-bit binaries
> > > but defaults to 64-bit mode.  This is more difficult than it may appear
> > > at first.
> > 
> > I was able to build a working cross compiler for building 32bit binaries
> > on x64-64.  The existing binutils are already biarch.  Unfortunately,
> > the harddrive my cross compiler was on failed.  If anybody's interested,
> > I might be able to recreate it. 
> 
> That would be excellent.

Ok, I'll give it a shot.  As I remember, I needed some 32bit libraries
to build the cross compiler which I copied from my chroot.  

> > With the cross compiler, I could build a 64 bit kernel with 32 bit support.
> > The kernel (2.6.x) actually only has one C file that needs to be
> > compiled in 32bit mode.  That file is arch/x86_64/boot/compressed/misc.c
> 
> Does that hold if one wants to run 32-bit binaries also?

Yes.  Actually, the support for running 32-bit binaries depends only on
a 32-bit arch/x86_64/ia32/vsyscall.o which can be generated from
arch/x86_64/ia32/vsyscall.S with our as.  

It is actually possible to build a complete kernel capable of running 32-bit
binaries with our current tools.  The problem is that there are also
some 32-bit components needed to boot the kernel.  The misc.c file I
mentioned contains some gzip decompression stuff needed for booting
bzImages. 

I think that with a little work, the dependance on a 32-bit gcc could be
removed from the kernel.  I had patches to eliminate it for everything
but misc.c, which I unfortunately lost.  Shouldn't be too hard to
recreate, though.  Maybe misc.c counld be shipped as an assembly file.  


> 
> > All the other 32bit objects are generated from assembly files which our
> > as can already handle.  The kernel makefiles have to be fixed, though to
> > call as rather than gcc for the .S files.
> 
> Ah, that could be an issue to.
> 
> > BTW, is the biarch gcc necessary for anything other than the kernel?
> 
> No, unless it requires a 32-bit libc.

Not unless what requires a 32-bit libc?

Greg