Re: [-mm patch] i386: enable REGPARM by default

[Adrian Bunk <bunk@stusta.de>]

On Sun, May 15, 2005 at 03:00:08PM +0200, Andi Kleen wrote:
> On Sun, May 15, 2005 at 02:37:31PM +0200, Adrian Bunk wrote:
> > On Sun, May 15, 2005 at 02:22:34PM +0200, Andi Kleen wrote:
> > > Adrian Bunk <bunk@stusta.de> writes:
> > > 
> > > > This patch should _not_ go into Linus' tree.
> > > >
> > > > At some time in the future, we want to unconditionally enable REGPARM on 
> > > > i386.
> > > >
> > > > Let's give it a bit broader testing coverage among -mm users.
> > > 
> > > iirc problem is that gcc 2.95 and possibly 3.0.x have some known
> > > miscompilations with regparams. That is why it was only used
> > > with fastcall for a long time. One 3.1.x+ it should be safe.
> > > But you cannot express dependencies on the compiler version
> > > in Kconfig right now.
> > > 
> > > Of course getting rid of gcc 2.95 and 3.0.x support would be a good idea,
> > > that would allow many other nice things.
> > 
> > If you'd read either arch/i386/Makefile or the help text for 
> > CONFIG_REGPARM, you'd have noticed that we do never use regparm with
> > gcc < 3.0 .
> 
> Yes, this means you cannot have binary compatible kernels compiled
> with different compilers. Which might be a bad thing.  For that
> reason alone I would keep the config.

We never guarantee binary compatibility with different compilers.

And gcc 2 <-> gcc 3 is an example where it's easy to see that there's no 
binary compatibility in the kernel.

> -Andi

cu
Adrian

-- 

       "Is there not promise of rain?" Ling Tan asked suddenly out
        of the darkness. There had been need of rain for many days.
       "Only a promise," Lao Er said.
                                       Pearl S. Buck - Dragon Seed