[RFC Patch 1/2][Bugfix][x86][hw-breakpoint] Clear reserved bits ofDR6 in do_debug()

From: K.Prasad
Date: Sat Dec 26 2009 - 13:27:41 EST


Clear the reserved bits from the stored copy of debug status register (DR6).
This will help easy bitwise operations.

Signed-off-by: K.Prasad <prasad@xxxxxxxxxxxxxxxxxx>
---
arch/x86/include/asm/debugreg.h | 3 +++
arch/x86/kernel/traps.c | 3 +++
2 files changed, 6 insertions(+)

Index: linux-2.6-tip/arch/x86/include/asm/debugreg.h
===================================================================
--- linux-2.6-tip.orig/arch/x86/include/asm/debugreg.h
+++ linux-2.6-tip/arch/x86/include/asm/debugreg.h
@@ -14,6 +14,9 @@
which debugging register was responsible for the trap. The other bits
are either reserved or not of interest to us. */

+/* Define reserved bits in DR6 which are always set to 1 */
+#define DR6_RESERVED (0xFFFF0FF0)
+
#define DR_TRAP0 (0x1) /* db0 */
#define DR_TRAP1 (0x2) /* db1 */
#define DR_TRAP2 (0x4) /* db2 */
Index: linux-2.6-tip/arch/x86/kernel/traps.c
===================================================================
--- linux-2.6-tip.orig/arch/x86/kernel/traps.c
+++ linux-2.6-tip/arch/x86/kernel/traps.c
@@ -534,6 +534,9 @@ dotraplinkage void __kprobes do_debug(st

get_debugreg(dr6, 6);

+ /* Filter out all the reserved bits which are preset to 1 */
+ dr6 &= ~DR6_RESERVED;
+
/* Catch kmemcheck conditions first of all! */
if ((dr6 & DR_STEP) && kmemcheck_trap(regs))
return;

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