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Commit e3e94084 authored by K.Prasad's avatar K.Prasad Committed by Paul Mackerras
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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: default avatarK.Prasad <prasad@linux.vnet.ibm.com>
Signed-off-by: default avatarPaul Mackerras <paulus@samba.org>
parent 06532a67

arch/powerpc/include/asm/hw_breakpoint.h

+1 −0
Original line number Diff line number Diff line
@@ -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;

arch/powerpc/kernel/hw_breakpoint.c

+21 −2
Original line number Diff line number Diff line
@@ -204,6 +204,7 @@ int __kprobes hw_breakpoint_handler(struct die_args *args) 
	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 @@ int __kprobes hw_breakpoint_handler(struct die_args *args) 
		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;
@@ -261,6 +278,7 @@ int __kprobes hw_breakpoint_handler(struct die_args *args) 
	 * As a policy, the callback is invoked in a 'trigger-after-execute'

	 * fashion

	 */

	if (!info->extraneous_interrupt)

		perf_bp_event(bp, regs);



	set_dabr(info->address | info->type | DABR_TRANSLATION);
@@ -292,6 +310,7 @@ int __kprobes single_step_dabr_instruction(struct die_args *args) 
	 * We shall invoke the user-defined callback function in the single

	 * stepping handler to confirm to 'trigger-after-execute' semantics

	 */

	if (!bp_info->extraneous_interrupt)

		perf_bp_event(bp, regs);



	/*