linux-kernel - [patch 2.6.19-rc6] Stop gcc 4.1.0 optimizing wait_hpet

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Date:	Wed, 29 Nov 2006 13:22:03 +1100
From:	Keith Owens <kaos@....com.au>
To:	linux-kernel@...r.kernel.org
Subject: [patch 2.6.19-rc6] Stop gcc 4.1.0 optimizing wait_hpet_tick away

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@....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 {

-
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