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SubjectRe: [patch 2.6.19-rc6] Stop gcc 4.1.0 optimizing wait_hpet_tick away
On Wed, Nov 29, 2006 at 02:56:20PM +1100, Keith Owens wrote:
> Nicholas Miell (on Tue, 28 Nov 2006 19:08:25 -0800) wrote:
> >On Wed, 2006-11-29 at 13:22 +1100, Keith Owens wrote:
> >> Compiling 2.6.19-rc6 with gcc version 4.1.0 (SUSE Linux),
> >> wait_hpet_tick is optimized away to a never ending loop and the kernel
> >> hangs on boot in timer setup.
> >>
> >> 0000001a <wait_hpet_tick>:
> >> 1a: 55 push %ebp
> >> 1b: 89 e5 mov %esp,%ebp
> >> 1d: eb fe jmp 1d <wait_hpet_tick+0x3>
> >>
> >> This is not a problem with gcc 3.3.5. Adding barrier() calls to
> >> wait_hpet_tick does not help, making the variables volatile does.
> >>
> >> Signed-off-by: Keith Owens <kaos@ocs.com.au>
> >>
> >> ---
> >> arch/i386/kernel/time_hpet.c | 2 +-
> >> 1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> Index: linux-2.6/arch/i386/kernel/time_hpet.c
> >> ===================================================================
> >> --- linux-2.6.orig/arch/i386/kernel/time_hpet.c
> >> +++ linux-2.6/arch/i386/kernel/time_hpet.c
> >> @@ -51,7 +51,7 @@ static void hpet_writel(unsigned long d,
> >> */
> >> static void __devinit wait_hpet_tick(void)
> >> {
> >> - unsigned int start_cmp_val, end_cmp_val;
> >> + unsigned volatile int start_cmp_val, end_cmp_val;
> >>
> >> start_cmp_val = hpet_readl(HPET_T0_CMP);
> >> do {
> >
> >When you examine the inlined functions involved, this looks an awful lot
> >like http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22278
> >
> >Perhaps SUSE should fix their gcc instead of working around compiler
> >problems in the kernel?
>
> Firstly, the fix for 22278 is included in gcc 4.1.0.

This actually sounds more like http://gcc.gnu.org/PR27236
And that one is broken in 4.1.0, fixed in 4.1.1.

Jakub
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