Luke Mewburn wrote:

> > >  > > I noticed that spl*/splx are inlined and re-orderd
> > >  > > with "-O3 -march=pentium", and it produce bad codes as a result.
> > >  > > I actually experienced panics due to this.
> > >  > 
> > >  > I'll commit attached patch some days later if no objection.
> > >  > thanks.
> > > 
> > > Should't we just declare "cpl" as __volatile?
> > 
> > cpl is already volatile, isn't it?
> > am I missing something important?
> 
> (Note: I am not a gcc guru.)
> 
> What if ncpl or ocpl (local variables to the appropriate functions)
> are marked volatile as well, because as far as I can tell, it's the
> reordering of access to those variables which is what's causing the
> problem, not the access to the volatile cpl.

It seems that __asm statements are atomic and gcc won't reschedule
around them.  This seems to work:

static __inline int
splraise(ncpl)
        int ncpl;
{
        int ocpl;

        __asm __volatile("                      \
                        movl %1, %%edx;         \
                        movl %%edx, %0;         \ 
                        orl %2,%%edx;           \
                        movl %%edx, %1" : "=&r" (ocpl), "=m" (cpl) \
                        : "r" (ncpl) : "%edx" );

        return (ocpl);
}

static __inline void
spllower(ncpl)
        int ncpl;
{

        __asm __volatile("movl %1, %0" : "=m" (cpl) : "r" (ncpl));
}

	-- Gregory McGarry <g.mcgarry@ieee.org>