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SubjectRe: [patch 2.6.19-rc6] Stop gcc 4.1.0 optimizing wait_hpet_tick away
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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?

--
Nicholas Miell <nmiell@comcast.net>

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