Re: gcc 4.5.1 / as 2.20.51.0.11 miscompiling drivers/char/i8k.c?

[Jeff Law]

On 11/07/10 15:41, Andreas Schwab wrote:
> Andi Kleen<andi@xxxxxxxxxxxxxx>  writes:
>
> > Jim<jim876@xxxxxxxxx>  writes:
> >
> > > After upgrading my Dell laptop, both OS+kernel the i8k interface was giving
> > > nonsensical output. As it turned out it's not the kernel but compiler
> > > upgrade which broke this.
> > >
> > > Guys at Archlinux have found the underlying cause (but don't seem to have
> > > submitted a patch yet):
> > >    https://bbs.archlinux.org/viewtopic.php?pid=780692#p780692
> > > gcc seems to optimize the assembly statements away.
> > >
> > > And indeed, applying this patch makes the i8k interface work again,
> > > i.e. replacing the asm(..) construct by  asm volatile(..)
> > The compiler really should not optimize the asm away, because
> > it has both input and output arguments which are later used.
> > "asm volatile" normally just means "don't move significantly"
> The asm fails to mention that it modifies *regs.
But there's a memory clobber, that should be sufficient to indicate 
*regs is modified.

jeff

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/