powerpc, hw_breakpoint: Discard extraneous interrupt due to accesses outside symbol length
Many a times, the requested breakpoint length can be less than the
fixed breakpoint length i.e. 8 bytes supported by PowerPC 64-bit
server (Book III S) processors. This could lead to extraneous
interrupts resulting in false breakpoint notifications. This
detects and discards such interrupts for non-ptrace requests.
We don't change ptrace behaviour to avoid breaking compatability.
[Suggestion from Paul Mackerras <paulus@samba.org> to add a new flag in
'struct arch_hw_breakpoint' to identify extraneous interrupts]
Signed-off-by: K.Prasad <prasad@linux.vnet.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>
diff --git a/arch/powerpc/include/asm/hw_breakpoint.h b/arch/powerpc/include/asm/hw_breakpoint.h
index 6576bad..ea87f8a 100644
--- a/arch/powerpc/include/asm/hw_breakpoint.h
+++ b/arch/powerpc/include/asm/hw_breakpoint.h
@@ -27,6 +27,7 @@
#ifdef CONFIG_HAVE_HW_BREAKPOINT
struct arch_hw_breakpoint {
+ bool extraneous_interrupt;
u8 len; /* length of the target data symbol */
int type;
unsigned long address;
diff --git a/arch/powerpc/kernel/hw_breakpoint.c b/arch/powerpc/kernel/hw_breakpoint.c
index 7bd01a5..ed39805 100644
--- a/arch/powerpc/kernel/hw_breakpoint.c
+++ b/arch/powerpc/kernel/hw_breakpoint.c
@@ -204,6 +204,7 @@
int stepped = 1;
struct arch_hw_breakpoint *info;
unsigned int instr;
+ unsigned long dar = regs->dar;
/* Disable breakpoints during exception handling */
set_dabr(0);
@@ -234,6 +235,22 @@
goto out;
}
+ /*
+ * Verify if dar lies within the address range occupied by the symbol
+ * being watched to filter extraneous exceptions.
+ */
+ if (!((bp->attr.bp_addr <= dar) &&
+ (dar <= (bp->attr.bp_addr + bp->attr.bp_len)))) {
+ /*
+ * This exception is triggered not because of a memory access
+ * on the monitored variable but in the double-word address
+ * range in which it is contained. We will consume this
+ * exception, considering it as 'noise'.
+ */
+ info->extraneous_interrupt = true;
+ } else
+ info->extraneous_interrupt = false;
+
/* Do not emulate user-space instructions, instead single-step them */
if (user_mode(regs)) {
bp->ctx->task->thread.last_hit_ubp = bp;
@@ -261,7 +278,8 @@
* As a policy, the callback is invoked in a 'trigger-after-execute'
* fashion
*/
- perf_bp_event(bp, regs);
+ if (!info->extraneous_interrupt)
+ perf_bp_event(bp, regs);
set_dabr(info->address | info->type | DABR_TRANSLATION);
out:
@@ -292,7 +310,8 @@
* We shall invoke the user-defined callback function in the single
* stepping handler to confirm to 'trigger-after-execute' semantics
*/
- perf_bp_event(bp, regs);
+ if (!bp_info->extraneous_interrupt)
+ perf_bp_event(bp, regs);
/*
* Do not disable MSR_SE if the process was already in