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Subject[Patch 12/12] Reset bits in dr6 after the corresponding exception is handled
This patch resets the bit in dr6 after the corresponding exception is
handled in code.

Signed-off-by: K.Prasad <prasad@linux.vnet.ibm.com>
---
arch/x86/kernel/hw_breakpoint.c | 13 +++++++++++--
arch/x86/kernel/kgdb.c | 6 ++++++
arch/x86/kernel/kprobes.c | 9 ++++++++-
arch/x86/kernel/traps.c | 4 ++--
arch/x86/mm/kmmio.c | 8 +++++++-
5 files changed, 34 insertions(+), 6 deletions(-)
Index: linux-2.6-tip.hbkpt/arch/x86/kernel/hw_breakpoint.c
===================================================================
--- linux-2.6-tip.hbkpt.orig/arch/x86/kernel/hw_breakpoint.c
+++ linux-2.6-tip.hbkpt/arch/x86/kernel/hw_breakpoint.c
@@ -314,8 +314,12 @@ int __kprobes hw_breakpoint_handler(stru
{
int i, cpu, rc = NOTIFY_STOP;
struct hw_breakpoint *bp;
- /* The DR6 value is stored in args->err */
- unsigned long dr7, dr6 = args->err;
+ unsigned long dr7, dr6;
+ unsigned long *dr6_p;
+
+ /* The DR6 value is pointed by args->err */
+ dr6_p = (unsigned long *)ERR_PTR(args->err);
+ dr6 = *dr6_p;

/* Do an early return if no trap bits are set in DR6 */
if ((dr6 & DR_TRAP_BITS) == 0)
@@ -352,6 +356,11 @@ int __kprobes hw_breakpoint_handler(stru
rc = NOTIFY_DONE;
}
/*
+ * Reset the 'i'th TRAP bit in dr6 to denote completion of
+ * exception handling
+ */
+ (*dr6_p) &= ~(DR_TRAP0 << i);
+ /*
* bp can be NULL due to lazy debug register switching
* or due to the delay between updates of hbp_kernel_pos
* and this_hbp_kernel.
Index: linux-2.6-tip.hbkpt/arch/x86/kernel/kgdb.c
===================================================================
--- linux-2.6-tip.hbkpt.orig/arch/x86/kernel/kgdb.c
+++ linux-2.6-tip.hbkpt/arch/x86/kernel/kgdb.c
@@ -43,6 +43,7 @@
#include <linux/smp.h>
#include <linux/nmi.h>

+#include <asm/debugreg.h>
#include <asm/apicdef.h>
#include <asm/system.h>

@@ -434,6 +435,11 @@ single_step_cont(struct pt_regs *regs, s
"resuming...\n");
kgdb_arch_handle_exception(args->trapnr, args->signr,
args->err, "c", "", regs);
+ /*
+ * Reset the BS bit in dr6 (pointed by args->err) to
+ * denote completion of processing
+ */
+ (*(unsigned long *)ERR_PTR(args->err)) &= ~DR_STEP;

return NOTIFY_STOP;
}
Index: linux-2.6-tip.hbkpt/arch/x86/kernel/kprobes.c
===================================================================
--- linux-2.6-tip.hbkpt.orig/arch/x86/kernel/kprobes.c
+++ linux-2.6-tip.hbkpt/arch/x86/kernel/kprobes.c
@@ -54,6 +54,7 @@
#include <asm/pgtable.h>
#include <asm/uaccess.h>
#include <asm/alternative.h>
+#include <asm/debugreg.h>

void jprobe_return_end(void);

@@ -967,8 +968,14 @@ int __kprobes kprobe_exceptions_notify(s
ret = NOTIFY_STOP;
break;
case DIE_DEBUG:
- if (post_kprobe_handler(args->regs))
+ if (post_kprobe_handler(args->regs)) {
+ /*
+ * Reset the BS bit in dr6 (pointed by args->err) to
+ * denote completion of processing
+ */
+ (*(unsigned long *)ERR_PTR(args->err)) &= ~DR_STEP;
ret = NOTIFY_STOP;
+ }
break;
case DIE_GPF:
/*
Index: linux-2.6-tip.hbkpt/arch/x86/kernel/traps.c
===================================================================
--- linux-2.6-tip.hbkpt.orig/arch/x86/kernel/traps.c
+++ linux-2.6-tip.hbkpt/arch/x86/kernel/traps.c
@@ -550,8 +550,8 @@ dotraplinkage void __kprobes do_debug(st
/* Store the virtualized DR6 value */
tsk->thread.debugreg6 = dr6;

- if (notify_die(DIE_DEBUG, "debug", regs, dr6, error_code,
- SIGTRAP) == NOTIFY_STOP)
+ if (notify_die(DIE_DEBUG, "debug", regs, PTR_ERR(&dr6), error_code,
+ SIGTRAP) == NOTIFY_STOP)
return;

/* It's safe to allow irq's after DR6 has been saved */
Index: linux-2.6-tip.hbkpt/arch/x86/mm/kmmio.c
===================================================================
--- linux-2.6-tip.hbkpt.orig/arch/x86/mm/kmmio.c
+++ linux-2.6-tip.hbkpt/arch/x86/mm/kmmio.c
@@ -540,8 +540,14 @@ kmmio_die_notifier(struct notifier_block
struct die_args *arg = args;

if (val == DIE_DEBUG && (arg->err & DR_STEP))
- if (post_kmmio_handler(arg->err, arg->regs) == 1)
+ if (post_kmmio_handler(arg->err, arg->regs) == 1) {
+ /*
+ * Reset the BS bit in dr6 (pointed by args->err) to
+ * denote completion of processing
+ */
+ (*(unsigned long *)ERR_PTR(arg->err)) &= ~DR_STEP;
return NOTIFY_STOP;
+ }

return NOTIFY_DONE;
}


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