[PATCH 0/4] ARM64: More flexible HW watchpoint

[PATCH 0/4] ARM64: More flexible HW watchpoint

[Pratyush Anand]

Currently, we do not support all the byte select option provided by ARM64
specs for a HW watchpoint.

This patch set will help user to instrument a watchpoint with all possible
byte select options.

Pratyush Anand (4):
  hw_breakpoint: Allow watchpoint of length 3,5,6 and 7
  arm64: Allow hw watchpoint at varied offset from base address
  arm64: Allow hw watchpoint of length 3,5,6 and 7
  selftests: arm64: add test for unaligned watchpoint address handling

 arch/arm64/include/asm/hw_breakpoint.h             |   6 +-
 arch/arm64/kernel/hw_breakpoint.c                  |  79 ++++++--
 arch/arm64/kernel/ptrace.c                         |   5 +-
 include/uapi/linux/hw_breakpoint.h                 |   4 +
 tools/include/uapi/linux/hw_breakpoint.h           |   4 +
 tools/testing/selftests/breakpoints/Makefile       |   5 +-
 .../selftests/breakpoints/breakpoint_test_arm64.c  | 223 +++++++++++++++++++++
 7 files changed, 300 insertions(+), 26 deletions(-)
 create mode 100644 tools/testing/selftests/breakpoints/breakpoint_test_arm64.c

-- 
2.7.4

[PATCH 1/4] hw_breakpoint: Allow watchpoint of length 3,5,6 and 7

[Pratyush Anand]

We only support breakpoint/watchpoint of length 1, 2, 4 and 8. If we can
support other length as well, then user may watch more data with less
number of watchpoints (provided hardware supports it). For example: if we
have to watch only 4th, 5th and 6th byte from a 64 bit aligned address, we
will have to use two slots to implement it currently. One slot will watch a
half word at offset 4 and other a byte at offset 6. If we can have a
watchpoint of length 3 then we can watch it with single slot as well.

ARM64 hardware does support such functionality, therefore adding these new
definitions in generic layer.

Signed-off-by: Pratyush Anand <panand@redhat.com>
---
 include/uapi/linux/hw_breakpoint.h       | 4 ++++
 tools/include/uapi/linux/hw_breakpoint.h | 4 ++++
 2 files changed, 8 insertions(+)

diff --git a/include/uapi/linux/hw_breakpoint.h b/include/uapi/linux/hw_breakpoint.h
index b04000a2296a..2b65efd19a46 100644
--- a/include/uapi/linux/hw_breakpoint.h
+++ b/include/uapi/linux/hw_breakpoint.h
@@ -4,7 +4,11 @@
 enum {
 	HW_BREAKPOINT_LEN_1 = 1,
 	HW_BREAKPOINT_LEN_2 = 2,
+	HW_BREAKPOINT_LEN_3 = 3,
 	HW_BREAKPOINT_LEN_4 = 4,
+	HW_BREAKPOINT_LEN_5 = 5,
+	HW_BREAKPOINT_LEN_6 = 6,
+	HW_BREAKPOINT_LEN_7 = 7,
 	HW_BREAKPOINT_LEN_8 = 8,
 };
 
diff --git a/tools/include/uapi/linux/hw_breakpoint.h b/tools/include/uapi/linux/hw_breakpoint.h
index b04000a2296a..2b65efd19a46 100644
--- a/tools/include/uapi/linux/hw_breakpoint.h
+++ b/tools/include/uapi/linux/hw_breakpoint.h
@@ -4,7 +4,11 @@
 enum {
 	HW_BREAKPOINT_LEN_1 = 1,
 	HW_BREAKPOINT_LEN_2 = 2,
+	HW_BREAKPOINT_LEN_3 = 3,
 	HW_BREAKPOINT_LEN_4 = 4,
+	HW_BREAKPOINT_LEN_5 = 5,
+	HW_BREAKPOINT_LEN_6 = 6,
+	HW_BREAKPOINT_LEN_7 = 7,
 	HW_BREAKPOINT_LEN_8 = 8,
 };
 
-- 
2.7.4

[PATCH 2/4] arm64: Allow hw watchpoint at varied offset from base address

[Pratyush Anand]

ARM64 hardware supports watchpoint at any double word aligned address.
However, it can select any consecutive bytes from offset 0 to 7 from that
base address. For example, if base address is programmed as 0x420030 and
byte select is 0x1C, then access of 0x420032,0x420033 and 0x420034 will
generate a watchpoint exception.

Currently, we do not have such modularity. We can only program byte,
halfword, word and double word access exception from any base address.

This patch adds support to overcome above limitations.

Signed-off-by: Pratyush Anand <panand@redhat.com>
---
 arch/arm64/include/asm/hw_breakpoint.h |  2 +-
 arch/arm64/kernel/hw_breakpoint.c      | 43 +++++++++++++++++-----------------
 arch/arm64/kernel/ptrace.c             |  5 ++--
 3 files changed, 25 insertions(+), 25 deletions(-)

diff --git a/arch/arm64/include/asm/hw_breakpoint.h b/arch/arm64/include/asm/hw_breakpoint.h
index 115ea2a64520..4f4e58bee9bc 100644
--- a/arch/arm64/include/asm/hw_breakpoint.h
+++ b/arch/arm64/include/asm/hw_breakpoint.h
@@ -118,7 +118,7 @@ struct perf_event;
 struct pmu;
 
 extern int arch_bp_generic_fields(struct arch_hw_breakpoint_ctrl ctrl,
-				  int *gen_len, int *gen_type);
+				  int *gen_len, int *gen_type, int *offset);
 extern int arch_check_bp_in_kernelspace(struct perf_event *bp);
 extern int arch_validate_hwbkpt_settings(struct perf_event *bp);
 extern int hw_breakpoint_exceptions_notify(struct notifier_block *unused,
diff --git a/arch/arm64/kernel/hw_breakpoint.c b/arch/arm64/kernel/hw_breakpoint.c
index 26a6bf77d272..c888c23149ad 100644
--- a/arch/arm64/kernel/hw_breakpoint.c
+++ b/arch/arm64/kernel/hw_breakpoint.c
@@ -349,7 +349,7 @@ int arch_check_bp_in_kernelspace(struct perf_event *bp)
  * to generic breakpoint descriptions.
  */
 int arch_bp_generic_fields(struct arch_hw_breakpoint_ctrl ctrl,
-			   int *gen_len, int *gen_type)
+			   int *gen_len, int *gen_type, int *offset)
 {
 	/* Type */
 	switch (ctrl.type) {
@@ -369,8 +369,10 @@ int arch_bp_generic_fields(struct arch_hw_breakpoint_ctrl ctrl,
 		return -EINVAL;
 	}
 
+	*offset = ffs(ctrl.len) - 1;
+
 	/* Len */
-	switch (ctrl.len) {
+	switch (ctrl.len >> *offset) {
 	case ARM_BREAKPOINT_LEN_1:
 		*gen_len = HW_BREAKPOINT_LEN_1;
 		break;
@@ -517,18 +519,17 @@ int arch_validate_hwbkpt_settings(struct perf_event *bp)
 		default:
 			return -EINVAL;
 		}
-
-		info->address &= ~alignment_mask;
-		info->ctrl.len <<= offset;
 	} else {
 		if (info->ctrl.type == ARM_BREAKPOINT_EXECUTE)
 			alignment_mask = 0x3;
 		else
 			alignment_mask = 0x7;
-		if (info->address & alignment_mask)
-			return -EINVAL;
+		offset = info->address & alignment_mask;
 	}
 
+	info->address &= ~alignment_mask;
+	info->ctrl.len <<= offset;
+
 	/*
 	 * Disallow per-task kernel breakpoints since these would
 	 * complicate the stepping code.
@@ -671,6 +672,7 @@ static int watchpoint_handler(unsigned long addr, unsigned int esr,
 	struct debug_info *debug_info;
 	struct arch_hw_breakpoint *info;
 	struct arch_hw_breakpoint_ctrl ctrl;
+	u32 lens, lene;
 
 	slots = this_cpu_ptr(wp_on_reg);
 	debug_info = &current->thread.debug;
@@ -684,25 +686,22 @@ static int watchpoint_handler(unsigned long addr, unsigned int esr,
 			goto unlock;
 
 		info = counter_arch_bp(wp);
-		/* AArch32 watchpoints are either 4 or 8 bytes aligned. */
-		if (is_compat_task()) {
-			if (info->ctrl.len == ARM_BREAKPOINT_LEN_8)
-				alignment_mask = 0x7;
-			else
-				alignment_mask = 0x3;
-		} else {
-			alignment_mask = 0x7;
-		}
 
-		/* Check if the watchpoint value matches. */
+		/* Check if the watchpoint value and byte select match. */
 		val = read_wb_reg(AARCH64_DBG_REG_WVR, i);
-		if (val != (addr & ~alignment_mask))
-			goto unlock;
-
-		/* Possible match, check the byte address select to confirm. */
 		ctrl_reg = read_wb_reg(AARCH64_DBG_REG_WCR, i);
 		decode_ctrl_reg(ctrl_reg, &ctrl);
-		if (!((1 << (addr & alignment_mask)) & ctrl.len))
+		lens = ffs(ctrl.len) - 1;
+		lene = fls(ctrl.len) - 1;
+		/*
+		 * Ideally, a read/write type information such as
+		 * byte/hw/word/dw would have provided a good check. But
+		 * I do not see such possibility. So, considering that max
+		 * rd/wr size as 8, i.e. this watchpoint interrupt would
+		 * have generated because any of the address from `addr` to
+		 * `addr + 7` would have been accessed.
+		 */
+		if (addr + 7 < val + lens || addr > val + lene)
 			goto unlock;
 
 		/*
diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
index e0c81da60f76..0eb366a94382 100644
--- a/arch/arm64/kernel/ptrace.c
+++ b/arch/arm64/kernel/ptrace.c
@@ -327,13 +327,13 @@ static int ptrace_hbp_fill_attr_ctrl(unsigned int note_type,
 				     struct arch_hw_breakpoint_ctrl ctrl,
 				     struct perf_event_attr *attr)
 {
-	int err, len, type, disabled = !ctrl.enabled;
+	int err, len, type, offset, disabled = !ctrl.enabled;
 
 	attr->disabled = disabled;
 	if (disabled)
 		return 0;
 
-	err = arch_bp_generic_fields(ctrl, &len, &type);
+	err = arch_bp_generic_fields(ctrl, &len, &type, &offset);
 	if (err)
 		return err;
 
@@ -352,6 +352,7 @@ static int ptrace_hbp_fill_attr_ctrl(unsigned int note_type,
 
 	attr->bp_len	= len;
 	attr->bp_type	= type;
+	attr->bp_addr	+= offset;
 
 	return 0;
 }
-- 
2.7.4

[PATCH 3/4] arm64: Allow hw watchpoint of length 3,5,6 and 7

[Pratyush Anand]

Since, arm64 can support all offset within a double word limit. Therefore,
now support other lengths within that range as well.

Signed-off-by: Pratyush Anand <panand@redhat.com>
---
 arch/arm64/include/asm/hw_breakpoint.h |  4 ++++
 arch/arm64/kernel/hw_breakpoint.c      | 36 ++++++++++++++++++++++++++++++++++
 2 files changed, 40 insertions(+)

diff --git a/arch/arm64/include/asm/hw_breakpoint.h b/arch/arm64/include/asm/hw_breakpoint.h
index 4f4e58bee9bc..7a18c8520588 100644
--- a/arch/arm64/include/asm/hw_breakpoint.h
+++ b/arch/arm64/include/asm/hw_breakpoint.h
@@ -76,7 +76,11 @@ static inline void decode_ctrl_reg(u32 reg,
 /* Lengths */
 #define ARM_BREAKPOINT_LEN_1	0x1
 #define ARM_BREAKPOINT_LEN_2	0x3
+#define ARM_BREAKPOINT_LEN_3	0x7
 #define ARM_BREAKPOINT_LEN_4	0xf
+#define ARM_BREAKPOINT_LEN_5	0x1f
+#define ARM_BREAKPOINT_LEN_6	0x3f
+#define ARM_BREAKPOINT_LEN_7	0x7f
 #define ARM_BREAKPOINT_LEN_8	0xff
 
 /* Kernel stepping */
diff --git a/arch/arm64/kernel/hw_breakpoint.c b/arch/arm64/kernel/hw_breakpoint.c
index c888c23149ad..7ff2c3cfeb46 100644
--- a/arch/arm64/kernel/hw_breakpoint.c
+++ b/arch/arm64/kernel/hw_breakpoint.c
@@ -317,9 +317,21 @@ static int get_hbp_len(u8 hbp_len)
 	case ARM_BREAKPOINT_LEN_2:
 		len_in_bytes = 2;
 		break;
+	case ARM_BREAKPOINT_LEN_3:
+		len_in_bytes = 3;
+		break;
 	case ARM_BREAKPOINT_LEN_4:
 		len_in_bytes = 4;
 		break;
+	case ARM_BREAKPOINT_LEN_5:
+		len_in_bytes = 5;
+		break;
+	case ARM_BREAKPOINT_LEN_6:
+		len_in_bytes = 6;
+		break;
+	case ARM_BREAKPOINT_LEN_7:
+		len_in_bytes = 7;
+		break;
 	case ARM_BREAKPOINT_LEN_8:
 		len_in_bytes = 8;
 		break;
@@ -379,9 +391,21 @@ int arch_bp_generic_fields(struct arch_hw_breakpoint_ctrl ctrl,
 	case ARM_BREAKPOINT_LEN_2:
 		*gen_len = HW_BREAKPOINT_LEN_2;
 		break;
+	case ARM_BREAKPOINT_LEN_3:
+		*gen_len = HW_BREAKPOINT_LEN_3;
+		break;
 	case ARM_BREAKPOINT_LEN_4:
 		*gen_len = HW_BREAKPOINT_LEN_4;
 		break;
+	case ARM_BREAKPOINT_LEN_5:
+		*gen_len = HW_BREAKPOINT_LEN_5;
+		break;
+	case ARM_BREAKPOINT_LEN_6:
+		*gen_len = HW_BREAKPOINT_LEN_6;
+		break;
+	case ARM_BREAKPOINT_LEN_7:
+		*gen_len = HW_BREAKPOINT_LEN_7;
+		break;
 	case ARM_BREAKPOINT_LEN_8:
 		*gen_len = HW_BREAKPOINT_LEN_8;
 		break;
@@ -425,9 +449,21 @@ static int arch_build_bp_info(struct perf_event *bp)
 	case HW_BREAKPOINT_LEN_2:
 		info->ctrl.len = ARM_BREAKPOINT_LEN_2;
 		break;
+	case HW_BREAKPOINT_LEN_3:
+		info->ctrl.len = ARM_BREAKPOINT_LEN_3;
+		break;
 	case HW_BREAKPOINT_LEN_4:
 		info->ctrl.len = ARM_BREAKPOINT_LEN_4;
 		break;
+	case HW_BREAKPOINT_LEN_5:
+		info->ctrl.len = ARM_BREAKPOINT_LEN_5;
+		break;
+	case HW_BREAKPOINT_LEN_6:
+		info->ctrl.len = ARM_BREAKPOINT_LEN_6;
+		break;
+	case HW_BREAKPOINT_LEN_7:
+		info->ctrl.len = ARM_BREAKPOINT_LEN_7;
+		break;
 	case HW_BREAKPOINT_LEN_8:
 		info->ctrl.len = ARM_BREAKPOINT_LEN_8;
 		break;
-- 
2.7.4

[PATCH 3/4] arm64: Allow hw watchpoint of length 3,5,6 and 7

[Yao Qi]

On Wed, Oct 12, 2016 at 6:58 AM, Pratyush Anand <panand@redhat.com> wrote:
> Since, arm64 can support all offset within a double word limit. Therefore,
> now support other lengths within that range as well.

How does ptracer (like GDB) detect kernel has already supported all byte
address select values?  I suppose ptrace(NT_ARM_HW_WATCH, ) with
len is 3 or 5 fail on current kernel but is of success after your patches
applied.

GDB is aware of the byte address select limitation in kernel, so it always
sets 1,2,4,8 in len in ctrl.  GDB needs to know whether the limitation is still
there or not.

-- 
Yao (??)

[PATCH 3/4] arm64: Allow hw watchpoint of length 3,5,6 and 7

[Pratyush Anand]

On Wednesday 12 October 2016 04:46 PM, Yao Qi wrote:
> On Wed, Oct 12, 2016 at 6:58 AM, Pratyush Anand <panand@redhat.com> wrote:
>> Since, arm64 can support all offset within a double word limit. Therefore,
>> now support other lengths within that range as well.
>
> How does ptracer (like GDB) detect kernel has already supported all byte
> address select values?  I suppose ptrace(NT_ARM_HW_WATCH, ) with
> len is 3 or 5 fail on current kernel but is of success after your patches
> applied.
>

Thanks for testing these patches.

I do not know if we can know that other than the failure of 
ptrace(PTRACE_SETREGSET, .., NT_ARM_HW_WATCH, ..). I do not see any such 
option in `man ptrace`.


> GDB is aware of the byte address select limitation in kernel, so it always
> sets 1,2,4,8 in len in ctrl.  GDB needs to know whether the limitation is still
> there or not.
>

Not sure if other than "kernel version" anything will help here.

~Pratyush

[PATCH 3/4] arm64: Allow hw watchpoint of length 3,5,6 and 7

[Pavel Labath]

On 13 October 2016 at 11:22, Pratyush Anand <panand@redhat.com> wrote:
>
>
> On Wednesday 12 October 2016 04:46 PM, Yao Qi wrote:
>>
>> On Wed, Oct 12, 2016 at 6:58 AM, Pratyush Anand <panand@redhat.com> wrote:
>>>
>>> Since, arm64 can support all offset within a double word limit.
>>> Therefore,
>>> now support other lengths within that range as well.
>>
>>
>> How does ptracer (like GDB) detect kernel has already supported all byte
>> address select values?  I suppose ptrace(NT_ARM_HW_WATCH, ) with
>> len is 3 or 5 fail on current kernel but is of success after your patches
>> applied.
>>
>
> Thanks for testing these patches.
>
> I do not know if we can know that other than the failure of
> ptrace(PTRACE_SETREGSET, .., NT_ARM_HW_WATCH, ..). I do not see any such
> option in `man ptrace`.
That's how I intend to implement support for this in LLDB.
if (setExactWatchpoint())
  return true; // watchpoint set, new kernel
if (setApproxWatchpoint())
  return true; // watchpoint set, old kernel
return false; // watchpoints not working

seems straight-forward enough to me.

[PATCH 4/4] selftests: arm64: add test for unaligned watchpoint address handling

[Pratyush Anand]

ARM64 hardware expects 64bit aligned address for watchpoint invocation.
However, it provides byte selection method to select any number of
consecutive byte set within the range of 1-8.

This patch adds support to test all such byte selection option for
different memory write sizes.

Signed-off-by: Pratyush Anand <panand@redhat.com>
---
 tools/testing/selftests/breakpoints/Makefile       |   5 +-
 .../selftests/breakpoints/breakpoint_test_arm64.c  | 223 +++++++++++++++++++++
 2 files changed, 227 insertions(+), 1 deletion(-)
 create mode 100644 tools/testing/selftests/breakpoints/breakpoint_test_arm64.c

diff --git a/tools/testing/selftests/breakpoints/Makefile b/tools/testing/selftests/breakpoints/Makefile
index 74e533fd4bc5..61b79e8df1f4 100644
--- a/tools/testing/selftests/breakpoints/Makefile
+++ b/tools/testing/selftests/breakpoints/Makefile
@@ -5,6 +5,9 @@ ARCH ?= $(shell echo $(uname_M) | sed -e s/i.86/x86/ -e s/x86_64/x86/)
 ifeq ($(ARCH),x86)
 TEST_PROGS := breakpoint_test
 endif
+ifeq ($(ARCH),aarch64)
+TEST_PROGS := breakpoint_test_arm64
+endif
 
 TEST_PROGS += step_after_suspend_test
 
@@ -13,4 +16,4 @@ all: $(TEST_PROGS)
 include ../lib.mk
 
 clean:
-	rm -fr breakpoint_test step_after_suspend_test
+	rm -fr breakpoint_test breakpoint_test_arm64 step_after_suspend_test
diff --git a/tools/testing/selftests/breakpoints/breakpoint_test_arm64.c b/tools/testing/selftests/breakpoints/breakpoint_test_arm64.c
new file mode 100644
index 000000000000..f56331831182
--- /dev/null
+++ b/tools/testing/selftests/breakpoints/breakpoint_test_arm64.c
@@ -0,0 +1,223 @@
+/*
+ * Copyright (C) 2016 Google, Inc.
+ *
+ * This software is licensed under the terms of the GNU General Public
+ * License version 2, as published by the Free Software Foundation, and
+ * may be copied, distributed, and modified under those terms.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * Original Code by Pavel Labath <test.tberghammer@gmail.com>
+ *
+ * Code modified by Pratyush Anand <panand@redhat.com>
+ * for testing different byte select for each access size.
+ *
+ */
+
+#define _GNU_SOURCE
+
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <sys/ptrace.h>
+#include <sys/param.h>
+#include <sys/uio.h>
+#include <stdint.h>
+#include <stdbool.h>
+#include <stddef.h>
+#include <string.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <elf.h>
+#include <errno.h>
+#include <signal.h>
+
+#include "../kselftest.h"
+
+static volatile uint8_t var[96] __attribute__((__aligned__(32)));
+
+static void child(int size, int wr)
+{
+	volatile uint8_t *addr = &var[32 + wr];
+
+	if (ptrace(PTRACE_TRACEME, 0, NULL, NULL) != 0) {
+		perror("ptrace(PTRACE_TRACEME) failed");
+		_exit(1);
+	}
+
+	if (raise(SIGSTOP) != 0) {
+		perror("raise(SIGSTOP) failed");
+		_exit(1);
+	}
+
+	if ((uintptr_t) addr % size) {
+		perror("Wrong address write for the given size\n");
+		_exit(1);
+	}
+	switch (size) {
+	case 1:
+		*addr = 47;
+		break;
+	case 2:
+		*(uint16_t *)addr = 47;
+		break;
+	case 4:
+		*(uint32_t *)addr = 47;
+		break;
+	case 8:
+		*(uint64_t *)addr = 47;
+		break;
+	case 16:
+		__asm__ volatile ("stp x29, x30, %0" : "=m" (addr[0]));
+		break;
+	case 32:
+		__asm__ volatile ("stp q29, q30, %0" : "=m" (addr[0]));
+		break;
+	}
+
+	_exit(0);
+}
+
+static bool set_watchpoint(pid_t pid, int size, int wp)
+{
+	const volatile uint8_t *addr = &var[32 + wp];
+	const int offset = (uintptr_t)addr % 8;
+	const unsigned int byte_mask = ((1 << size) - 1) << offset;
+	const unsigned int type = 2; /* Write */
+	const unsigned int enable = 1;
+	const unsigned int control = byte_mask << 5 | type << 3 | enable;
+	struct user_hwdebug_state dreg_state;
+	struct iovec iov;
+
+	memset(&dreg_state, 0, sizeof(dreg_state));
+	dreg_state.dbg_regs[0].addr = (uintptr_t)(addr - offset);
+	dreg_state.dbg_regs[0].ctrl = control;
+	iov.iov_base = &dreg_state;
+	iov.iov_len = offsetof(struct user_hwdebug_state, dbg_regs) +
+				sizeof(dreg_state.dbg_regs[0]);
+	if (ptrace(PTRACE_SETREGSET, pid, NT_ARM_HW_WATCH, &iov) == 0)
+		return true;
+
+	if (errno == EIO) {
+		printf("ptrace(PTRACE_SETREGSET, NT_ARM_HW_WATCH) "
+			"not supported on this hardware\n");
+		ksft_exit_skip();
+	}
+	perror("ptrace(PTRACE_SETREGSET, NT_ARM_HW_WATCH) failed");
+	return false;
+}
+
+static bool run_test(int size, int wr, int wp)
+{
+	int status;
+	siginfo_t siginfo;
+	pid_t pid = fork();
+	pid_t wpid;
+
+	if (pid < 0) {
+		perror("fork() failed");
+		return false;
+	}
+	if (pid == 0)
+		child(size, wr);
+
+	wpid = waitpid(pid, &status, __WALL);
+	if (wpid != pid) {
+		perror("waitpid() failed");
+		return false;
+	}
+	if (!WIFSTOPPED(status)) {
+		printf("child did not stop\n");
+		return false;
+	}
+	if (WSTOPSIG(status) != SIGSTOP) {
+		printf("child did not stop with SIGSTOP\n");
+		return false;
+	}
+
+	if (!set_watchpoint(pid, MIN(size, 8), wp))
+		return false;
+
+	if (ptrace(PTRACE_CONT, pid, NULL, NULL) < 0) {
+		perror("ptrace(PTRACE_SINGLESTEP) failed");
+		return false;
+	}
+
+	alarm(3);
+	wpid = waitpid(pid, &status, __WALL);
+	if (wpid != pid) {
+		perror("waitpid() failed");
+		return false;
+	}
+	alarm(0);
+	if (WIFEXITED(status)) {
+		printf("child did not single-step\t");
+		return false;
+	}
+	if (!WIFSTOPPED(status)) {
+		printf("child did not stop\n");
+		return false;
+	}
+	if (WSTOPSIG(status) != SIGTRAP) {
+		printf("child did not stop with SIGTRAP\n");
+		return false;
+	}
+	if (ptrace(PTRACE_GETSIGINFO, pid, NULL, &siginfo) != 0) {
+		perror("ptrace(PTRACE_GETSIGINFO)");
+		return false;
+	}
+	if (siginfo.si_code != TRAP_HWBKPT) {
+		printf("Unexpected si_code %d\n", siginfo.si_code);
+		return false;
+	}
+
+	kill(pid, SIGKILL);
+	wpid = waitpid(pid, &status, 0);
+	if (wpid != pid) {
+		perror("waitpid() failed");
+		return false;
+	}
+	return true;
+}
+
+static void sigalrm(int sig)
+{
+}
+
+int main(int argc, char **argv)
+{
+	int opt;
+	bool succeeded = true;
+	struct sigaction act;
+	int wr, wp, size;
+	bool result;
+
+	act.sa_handler = sigalrm;
+	sigemptyset(&act.sa_mask);
+	act.sa_flags = 0;
+	sigaction(SIGALRM, &act, NULL);
+	for (size = 1; size <= 32; size = size*2) {
+		for (wr = 0; wr <= 32; wr = wr + size) {
+			for (wp = wr - size; wp <= wr + size; wp = wp + size) {
+				printf("Test size = %d write offset = %d watchpoint offset = %d\t", size, wr, wp);
+				result = run_test(size, wr, wp);
+				if ((result && wr == wp) || (!result && wr != wp)) {
+					printf("[OK]\n");
+					ksft_inc_pass_cnt();
+				} else {
+					printf("[FAILED]\n");
+					ksft_inc_fail_cnt();
+					succeeded = false;
+				}
+			}
+		}
+	}
+
+	ksft_print_cnts();
+	if (succeeded)
+		ksft_exit_pass();
+	else
+		ksft_exit_fail();
+}
-- 
2.7.4