Re: GLIBC wont compile for MPC860

[Michael Meissner <meissner@cygnus.com>]

On Fri, Sep 03, 1999 at 12:15:34PM +1000, Graham Stoney wrote:
> 
> Hi Marcus,
> 
> Thanks for your great tips on building glibc for the '860. It would be great if
> we could get some mods into the next glibc release so that it would configure
> out-of-the-box without patching...
> 
> Marcus Sundberg writes:
> > Configuring gcc with --with-cpu=860 and --nfp will make the
> > _compiler_ default to -msoft-float. It will however _not_ make the 
> > pre-processor define -D_SOFT_FLOAT by default, which will cause
> > all variable arguments functions taking floating point arguments
> > (like the *print[fs] family) to be mis-compiled.
> > 
> > The fix is to add this code to your gcc's 'specs' file under the
> > section '*cpp_sysv':
> > %{!mhard-float: -D_SOFT_FLOAT}
> 
> Is this a general fix though; won't it cause _SOFT_FLOAT to be defined by
> default for all other cpu types as well?
> 
> The specs file from gcc 2.95.1 includes '%{mcpu=403: -D_SOFT_FLOAT}' in the
> cpp_sysv rule, and adding '%{mcpu=860: -D_SOFT_FLOAT}' has the advantage of not
> affecting other cpu types. Problem is, it only kicks in when I pass -mcpu=860
> explicitly, even though I configured gcc --with-cpu=860. I'm confused...

Because I forgot about --with-cpu=xxx.  Sigh.  I'll try to get to it tomorrorow
in the egcs tree.

> > First you must remove the assumption that cachelines are 32 bytes:
> > Apply this diff, and simply move sysdeps/powerpc/memset.S out of the
> > way for now:
> 
> Perhaps the gcc specs file could have a #define for the cache line size, so
> this is also automatically set via the -mcpu option. Alternatively, a #define
> giving the -mcpu= value would allow the code to work this out, kind of like the
> __i386, __i486, __i586 family for x86 architectures. There doesn't seem to be
> an equivalent for PowerPC's at present.

I would prefer not to define the cache size.

> > My vote is to have a special sysctl entry for the cacheline size,
> > for fast and easy access (one syscall compared to the open()/read()/close()
> > triplet for normal /proc entries, and you also don't have to have the
> > /proc fs mounted), and then cache the result in a static variable.)
> 
> I'd be happy with a compile-time option, but I don't mind either way.
> 
> > Secondly you will want to remove the floating point assembler.
> 
> Cool! It would be nice to get the fpu code re-arranged in the official glibc
> too...
> 
> Thanks!
> Graham
> 

-- 
Michael Meissner, Cygnus Solutions
PMB 198, 174 Littleton Road #3, Westford, Massachusetts 01886
email: meissner@cygnus.com	phone: 978-486-9304	fax: 978-692-4482

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