[RFC PATCH 0/4] ARM: add support for hw-breakpoints [v3]

[RFC PATCH 0/4] ARM: add support for hw-breakpoints [v3]

[Will Deacon]

This is version 3 of the RFC patches originally posted at:

v1.) http://lists.infradead.org/pipermail/linux-arm-kernel/2010-February/009084.html
v2.) http://lists.infradead.org/pipermail/linux-arm-kernel/2010-March/011170.html

Changes from v2 include:
	- Based on 2.6.35-rc2
	- Updated to use new hw-breakpoint API features
	- Addressed some comments from Frederic on LKML
	- Complete redesign of the ptrace interface so that it
	  follows the ARM ARM (v7) register structure more closely.

Unfortunately, I've only managed to compile-test this and check that the
resulting image boots. The main reasons for posting are (a) to support
current GDB development and (b) to attract comments on the code.

All comments welcome.

Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: S. Karthikeyan <informkarthik@gmail.com>

Will Deacon (4):
  ARM: hw-breakpoint: add mechanism for hooking into prefetch aborts
  ARM: hw-breakpoint: add ARM backend for the hw-breakpoint framework
  ARM: hw-breakpoint: add new ptrace requests for hw-breakpoint
    interaction
  ARM: hw-breakpoint: add HAVE_HW_BREAKPOINT to Kconfig

 arch/arm/Kconfig                     |    1 +
 arch/arm/include/asm/hw_breakpoint.h |  117 ++++++
 arch/arm/include/asm/processor.h     |    4 +
 arch/arm/include/asm/ptrace.h        |    2 +
 arch/arm/include/asm/system.h        |    3 +
 arch/arm/kernel/Makefile             |    1 +
 arch/arm/kernel/hw_breakpoint.c      |  734 ++++++++++++++++++++++++++++++++++
 arch/arm/kernel/ptrace.c             |  196 +++++++++
 arch/arm/mm/fault.c                  |   11 +
 9 files changed, 1069 insertions(+), 0 deletions(-)
 create mode 100644 arch/arm/include/asm/hw_breakpoint.h
 create mode 100644 arch/arm/kernel/hw_breakpoint.c

[PATCH 1/4] ARM: hw-breakpoint: add mechanism for hooking into prefetch aborts

[Will Deacon]

On ARM processors with hardware breakpoint and watchpoint support,
triggering these events results in a debug exception. These manifest
as prefetch and data aborts respectively.

arch/arm/mm/fault.c already provides hook_fault_code for hooking
into data aborts dependent on the DFSR. This patch adds a new function,
hook_ifault_code for hooking into prefetch aborts in the same manner.

Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: S. Karthikeyan <informkarthik@gmail.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
---
 arch/arm/include/asm/system.h |    3 +++
 arch/arm/mm/fault.c           |   11 +++++++++++
 2 files changed, 14 insertions(+), 0 deletions(-)

diff --git a/arch/arm/include/asm/system.h b/arch/arm/include/asm/system.h
index 5f4f480..42da2f8 100644
--- a/arch/arm/include/asm/system.h
+++ b/arch/arm/include/asm/system.h
@@ -84,6 +84,9 @@ void arm_notify_die(const char *str, struct pt_regs *regs, struct siginfo *info,
 void hook_fault_code(int nr, int (*fn)(unsigned long, unsigned int,
 				       struct pt_regs *),
 		     int sig, const char *name);
+void hook_ifault_code(int nr, int (*fn)(unsigned long, unsigned int,
+				       struct pt_regs *),
+		     int sig, const char *name);
 
 #define xchg(ptr,x) \
 	((__typeof__(*(ptr)))__xchg((unsigned long)(x),(ptr),sizeof(*(ptr))))
diff --git a/arch/arm/mm/fault.c b/arch/arm/mm/fault.c
index 92f5801..a71b410 100644
--- a/arch/arm/mm/fault.c
+++ b/arch/arm/mm/fault.c
@@ -572,6 +572,17 @@ static struct fsr_info ifsr_info[] = {
 	{ do_bad,		SIGBUS,  0,		"unknown 31"			   },
 };
 
+void __init
+hook_ifault_code(int nr, int (*fn)(unsigned long, unsigned int, struct pt_regs *),
+			int sig, const char *name)
+{
+	if (nr >= 0 && nr < ARRAY_SIZE(ifsr_info)) {
+		ifsr_info[nr].fn   = fn;
+		ifsr_info[nr].sig  = sig;
+		ifsr_info[nr].name = name;
+	}
+}
+
 asmlinkage void __exception
 do_PrefetchAbort(unsigned long addr, unsigned int ifsr, struct pt_regs *regs)
 {
-- 
1.6.3.3

[PATCH 2/4] ARM: hw-breakpoint: add ARM backend for the hw-breakpoint framework

[Will Deacon]

The hw-breakpoint framework in the kernel requires architecture-specific
support in order to install, remove, validate and manage hardware
breakpoints.

This patch adds preliminary support for this framework to the ARM
architecture, but restricts the number of watchpoints to a single resource
to get around the fact that the Data Fault Address Register is unpredictable
when a watchpoint debug exception is taken.

Currently, clients must handle synchronous breakpoint exceptions.
This requires the ability to single-step over the causative instruction to
avoid getting stuck in an infinite loop.

The memory-mapped extended debug interface is unsupported due to its
unreliability in real implementations.

Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: S. Karthikeyan <informkarthik@gmail.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
---
 arch/arm/include/asm/hw_breakpoint.h |  117 ++++++
 arch/arm/kernel/hw_breakpoint.c      |  721 ++++++++++++++++++++++++++++++++++
 2 files changed, 838 insertions(+), 0 deletions(-)
 create mode 100644 arch/arm/include/asm/hw_breakpoint.h
 create mode 100644 arch/arm/kernel/hw_breakpoint.c

diff --git a/arch/arm/include/asm/hw_breakpoint.h b/arch/arm/include/asm/hw_breakpoint.h
new file mode 100644
index 0000000..c995219
--- /dev/null
+++ b/arch/arm/include/asm/hw_breakpoint.h
@@ -0,0 +1,117 @@
+#ifndef _ARM_HW_BREAKPOINT_H
+#define _ARM_HW_BREAKPOINT_H
+
+#ifdef __KERNEL__
+struct arch_hw_breakpoint_ctrl {
+		u32 __reserved	: 19,
+		len		: 8,
+		type		: 2,
+		privilege	: 2,
+		enabled		: 1;
+};
+
+struct arch_hw_breakpoint {
+	u32	address;
+	u32	trigger;
+	struct arch_hw_breakpoint_ctrl ctrl;
+};
+
+static inline u32 encode_ctrl_reg(struct arch_hw_breakpoint_ctrl ctrl)
+{
+	return (ctrl.len << 5) | (ctrl.type << 3) |
+		(ctrl.privilege << 1) | ctrl.enabled;
+}
+
+static inline void decode_ctrl_reg(u32 reg,
+				   struct arch_hw_breakpoint_ctrl *ctrl)
+{
+	ctrl->enabled	= reg & 0x1;
+	reg >>= 1;
+	ctrl->privilege	= reg & 0x3;
+	reg >>= 2;
+	ctrl->type	= reg & 0x3;
+	reg >>= 2;
+	ctrl->len	= reg & 0xff;
+}
+
+/* Debug architecture numbers. */
+#define ARM_DEBUG_ARCH_V6	1
+#define ARM_DEBUG_ARCH_V6_1	2
+#define ARM_DEBUG_ARCH_V7_ECP14	3
+#define ARM_DEBUG_ARCH_V7_MM	4
+
+/* Breakpoint */
+#define ARM_BREAKPOINT_EXECUTE	0
+
+/* Watchpoints */
+#define ARM_BREAKPOINT_LOAD	1
+#define ARM_BREAKPOINT_STORE	2
+
+/* Privilege Levels */
+#define ARM_BREAKPOINT_PRIV	1
+#define ARM_BREAKPOINT_USER	2
+
+/* Lengths */
+#define ARM_BREAKPOINT_LEN_1	0x1
+#define ARM_BREAKPOINT_LEN_2	0x3
+#define ARM_BREAKPOINT_LEN_4	0xf
+#define ARM_BREAKPOINT_LEN_8	0xff
+
+/* Limits */
+#define ARM_MAX_BRP		16
+#define ARM_MAX_WRP		16
+#define ARM_MAX_HBP_SLOTS	(ARM_MAX_BRP + ARM_MAX_WRP)
+
+/* DSCR method of entry bits. */
+#define ARM_DSCR_MOE(x)			((x >> 2) & 0xf)
+#define ARM_ENTRY_BREAKPOINT		0x1
+#define ARM_ENTRY_ASYNC_WATCHPOINT	0x2
+#define ARM_ENTRY_SYNC_WATCHPOINT	0xa
+
+/* DSCR monitor/halting bits. */
+#define ARM_DSCR_HDBGEN		(1 << 14)
+#define ARM_DSCR_MDBGEN		(1 << 15)
+
+/* opcode2 numbers for the co-processor instructions. */
+#define ARM_OP2_BVR		4
+#define ARM_OP2_BCR		5
+#define ARM_OP2_WVR		6
+#define ARM_OP2_WCR		7
+
+/* Base register numbers for the debug registers. */
+#define ARM_BASE_BVR		64
+#define ARM_BASE_BCR		80
+#define ARM_BASE_WVR		96
+#define ARM_BASE_WCR		112
+
+/* Accessor macros for the debug registers. */
+#define ARM_DBG_READ(M, OP2, VAL) do {\
+	asm volatile("mrc p14, 0, %0, c0," #M ", " #OP2 : "=r" (VAL));\
+} while (0)
+
+#define ARM_DBG_WRITE(M, OP2, VAL) do {\
+	asm volatile("mcr p14, 0, %0, c0," #M ", " #OP2 : : "r" (VAL));\
+} while (0)
+
+struct notifier_block;
+struct perf_event;
+struct pmu;
+struct task_struct;
+
+extern struct pmu perf_ops_bp;
+extern int arch_bp_generic_fields(struct arch_hw_breakpoint_ctrl ctrl,
+				  int *gen_len, int *gen_type);
+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,
+					   unsigned long val, void *data);
+extern u8 arch_get_debug_arch(void);
+extern u8 arch_get_max_wp_len(void);
+
+int arch_install_hw_breakpoint(struct perf_event *bp);
+void arch_uninstall_hw_breakpoint(struct perf_event *bp);
+void hw_breakpoint_pmu_read(struct perf_event *bp);
+int hw_breakpoint_slots(int type);
+
+#endif	/* __KERNEL__ */
+#endif	/* _ARM_HW_BREAKPOINT_H */
diff --git a/arch/arm/kernel/hw_breakpoint.c b/arch/arm/kernel/hw_breakpoint.c
new file mode 100644
index 0000000..b249cd7
--- /dev/null
+++ b/arch/arm/kernel/hw_breakpoint.c
@@ -0,0 +1,721 @@
+/*
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * 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.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ *
+ * Copyright (C) 2009, 2010 ARM Limited
+ *
+ * Author: Will Deacon <will.deacon@arm.com>
+ */
+
+/*
+ * HW_breakpoint: a unified kernel/user-space hardware breakpoint facility,
+ * using the CPU's debug registers.
+ */
+
+#define pr_fmt(fmt) "hw-breakpoint: " fmt
+
+#include <linux/errno.h>
+#include <linux/perf_event.h>
+#include <linux/hw_breakpoint.h>
+#include <linux/smp.h>
+
+#include <asm/cacheflush.h>
+#include <asm/cputype.h>
+#include <asm/current.h>
+#include <asm/hw_breakpoint.h>
+#include <asm/kdebug.h>
+#include <asm/system.h>
+#include <asm/thread_notify.h>
+#include <asm/traps.h>
+
+/* Breakpoint currently in use for each BRP. */
+static DEFINE_PER_CPU(struct perf_event *, bp_on_reg[ARM_MAX_BRP]);
+
+/* Watchpoint currently in use for each WRP. */
+static DEFINE_PER_CPU(struct perf_event *, wp_on_reg[ARM_MAX_WRP]);
+
+/* Number of BRP/WRP registers on this CPU. */
+static int core_num_brps;
+static int core_num_wrps;
+
+/* Debug architecture version. */
+static u8 debug_arch;
+
+/* Maximum supported watchpoint length. */
+static u8 max_watchpoint_len;
+
+/* Determine number of BRP registers available. */
+static int get_num_brps(void)
+{
+	u32 didr;
+	ARM_DBG_READ(c0, 0, didr);
+	return ((didr >> 24) & 0xf) + 1;
+}
+
+/* Determine number of WRP registers available. */
+static int get_num_wrps(void)
+{
+	/*
+	 * FIXME: When a watchpoint fires, the only way to work out which
+	 * watchpoint it was is by disassembling the faulting instruction
+	 * and working out the address of the memory access.
+	 *
+	 * Furthermore, we can only do this if the watchpoint was precise
+	 * since imprecise watchpoints prevent us from calculating register
+	 * based addresses.
+	 *
+	 * For the time being, we only report 1 watchpoint register so we
+	 * always know which watchpoint fired. In the future we can either
+	 * add a disassembler and address generation emulator, or we can
+	 * insert a check to see if the DFAR is set on watchpoint exception
+	 * entry [the ARM ARM states that the DFAR is UNPREDICTABLE, but
+	 * experience shows that it is set on some implementations].
+	 */
+
+#if 0
+	u32 didr, wrps;
+	ARM_DBG_READ(c0, 0, didr);
+	return ((didr >> 28) & 0xf) + 1;
+#endif
+
+	return 1;
+}
+
+int hw_breakpoint_slots(int type)
+{
+	switch (type) {
+	case TYPE_INST:
+		return core_num_brps;
+	case TYPE_DATA:
+		return core_num_wrps;
+	default:
+		pr_warning("unknown slot type: %d\n", type);
+		return 0;
+	}
+}
+
+/* Determine debug architecture. */
+static u8 get_debug_arch(void)
+{
+	u32 didr;
+
+	/* Do we implement the extended CPUID interface? */
+	if (((read_cpuid_id() >> 16) & 0xf) != 0xf) {
+		pr_warning("CPUID feature registers not supported. "
+				"Assuming v6 debug is present.\n");
+		return ARM_DEBUG_ARCH_V6;
+	}
+
+	ARM_DBG_READ(c0, 0, didr);
+	return ((didr >> 16) & 0xf);
+}
+
+u8 arch_get_debug_arch(void)
+{
+	return debug_arch;
+}
+
+#define READ_WB_REG_CASE(OP2, M, VAL)		\
+	case ((OP2 << 4) + M):			\
+		ARM_DBG_READ(c ## M, OP2, VAL); \
+		break
+
+#define WRITE_WB_REG_CASE(OP2, M, VAL)		\
+	case ((OP2 << 4) + M):			\
+		ARM_DBG_WRITE(c ## M, OP2, VAL);\
+		break
+
+#define GEN_READ_WB_REG_CASES(OP2, VAL)		\
+	READ_WB_REG_CASE(OP2, 0, VAL);		\
+	READ_WB_REG_CASE(OP2, 1, VAL);		\
+	READ_WB_REG_CASE(OP2, 2, VAL);		\
+	READ_WB_REG_CASE(OP2, 3, VAL);		\
+	READ_WB_REG_CASE(OP2, 4, VAL);		\
+	READ_WB_REG_CASE(OP2, 5, VAL);		\
+	READ_WB_REG_CASE(OP2, 6, VAL);		\
+	READ_WB_REG_CASE(OP2, 7, VAL);		\
+	READ_WB_REG_CASE(OP2, 8, VAL);		\
+	READ_WB_REG_CASE(OP2, 9, VAL);		\
+	READ_WB_REG_CASE(OP2, 10, VAL);		\
+	READ_WB_REG_CASE(OP2, 11, VAL);		\
+	READ_WB_REG_CASE(OP2, 12, VAL);		\
+	READ_WB_REG_CASE(OP2, 13, VAL);		\
+	READ_WB_REG_CASE(OP2, 14, VAL);		\
+	READ_WB_REG_CASE(OP2, 15, VAL)
+
+#define GEN_WRITE_WB_REG_CASES(OP2, VAL)	\
+	WRITE_WB_REG_CASE(OP2, 0, VAL);		\
+	WRITE_WB_REG_CASE(OP2, 1, VAL);		\
+	WRITE_WB_REG_CASE(OP2, 2, VAL);		\
+	WRITE_WB_REG_CASE(OP2, 3, VAL);		\
+	WRITE_WB_REG_CASE(OP2, 4, VAL);		\
+	WRITE_WB_REG_CASE(OP2, 5, VAL);		\
+	WRITE_WB_REG_CASE(OP2, 6, VAL);		\
+	WRITE_WB_REG_CASE(OP2, 7, VAL);		\
+	WRITE_WB_REG_CASE(OP2, 8, VAL);		\
+	WRITE_WB_REG_CASE(OP2, 9, VAL);		\
+	WRITE_WB_REG_CASE(OP2, 10, VAL);	\
+	WRITE_WB_REG_CASE(OP2, 11, VAL);	\
+	WRITE_WB_REG_CASE(OP2, 12, VAL);	\
+	WRITE_WB_REG_CASE(OP2, 13, VAL);	\
+	WRITE_WB_REG_CASE(OP2, 14, VAL);	\
+	WRITE_WB_REG_CASE(OP2, 15, VAL)
+
+static u32 read_wb_reg(int n)
+{
+	u32 val = 0;
+
+	switch (n) {
+	GEN_READ_WB_REG_CASES(ARM_OP2_BVR, val);
+	GEN_READ_WB_REG_CASES(ARM_OP2_BCR, val);
+	GEN_READ_WB_REG_CASES(ARM_OP2_WVR, val);
+	GEN_READ_WB_REG_CASES(ARM_OP2_WCR, val);
+	default:
+		pr_warning("attempt to read from unknown breakpoint "
+				"register %d\n", n);
+	}
+
+	return val;
+}
+
+static void write_wb_reg(int n, u32 val)
+{
+	switch (n) {
+	GEN_WRITE_WB_REG_CASES(ARM_OP2_BVR, val);
+	GEN_WRITE_WB_REG_CASES(ARM_OP2_BCR, val);
+	GEN_WRITE_WB_REG_CASES(ARM_OP2_WVR, val);
+	GEN_WRITE_WB_REG_CASES(ARM_OP2_WCR, val);
+	default:
+		pr_warning("attempt to write to unknown breakpoint "
+				"register %d\n", n);
+	}
+}
+
+/*
+ * In order to access the breakpoint/watchpoint control registers,
+ * we must be running in debug monitor mode. Unfortunately, we can
+ * be put into halting debug mode@any time by an external debugger
+ * but there is nothing we can do to prevent that.
+ */
+static int enable_monitor_mode(void)
+{
+	u32 dscr;
+	int ret = 0;
+
+	ARM_DBG_READ(c1, 0, dscr);
+
+	/* Ensure that halting mode is disabled. */
+	if (dscr & ARM_DSCR_HDBGEN) {
+		pr_info("halting debug mode enabled. Unable to access "
+				"hardware resources.\n");
+		ret = -EPERM;
+		goto out;
+	}
+
+	/* Write to the corresponding DSCR. */
+	switch (debug_arch) {
+	case ARM_DEBUG_ARCH_V6:
+	case ARM_DEBUG_ARCH_V6_1:
+		ARM_DBG_WRITE(c1, 0, (dscr | ARM_DSCR_MDBGEN));
+		break;
+	case ARM_DEBUG_ARCH_V7_ECP14:
+		ARM_DBG_WRITE(c2, 2, (dscr | ARM_DSCR_MDBGEN));
+		break;
+	default:
+		ret = -ENODEV;
+		goto out;
+	}
+
+	/* Check that the write made it through. */
+	ARM_DBG_READ(c1, 0, dscr);
+	if (!(dscr & ARM_DSCR_MDBGEN)) {
+		pr_info("failed to enable monitor mode.");
+		ret = -EPERM;
+	}
+
+out:
+	return ret;
+}
+
+/*
+ * Check if 8-bit byte-address select is available.
+ * This clobbers WRP 0.
+ */
+static u8 get_max_wp_len(void)
+{
+	u32 ctrl_reg;
+	struct arch_hw_breakpoint_ctrl ctrl;
+	u8 size = 4;
+
+	if (debug_arch < ARM_DEBUG_ARCH_V7_ECP14)
+		goto out;
+
+	if (enable_monitor_mode())
+		goto out;
+
+	memset(&ctrl, 0, sizeof(ctrl));
+	ctrl.len = ARM_BREAKPOINT_LEN_8;
+	ctrl_reg = encode_ctrl_reg(ctrl);
+
+	write_wb_reg(ARM_BASE_WVR, 0);
+	write_wb_reg(ARM_BASE_WCR, ctrl_reg);
+	if ((read_wb_reg(ARM_BASE_WCR) & ctrl_reg) == ctrl_reg)
+		size = 8;
+
+out:
+	return size;
+}
+
+u8 arch_get_max_wp_len(void)
+{
+	return max_watchpoint_len;
+}
+
+/*
+ * Install a perf counter breakpoint.
+ */
+int arch_install_hw_breakpoint(struct perf_event *bp)
+{
+	struct arch_hw_breakpoint *info = counter_arch_bp(bp);
+	struct perf_event **slot, **slots;
+	int i, max_slots, ctrl_base, val_base, ret = 0;
+
+	/* Ensure that we are in monitor mode and halting mode is disabled. */
+	ret = enable_monitor_mode();
+	if (ret)
+		goto out;
+
+	if (info->ctrl.type == ARM_BREAKPOINT_EXECUTE) {
+		/* Breakpoint */
+		ctrl_base = ARM_BASE_BCR;
+		val_base = ARM_BASE_BVR;
+		slots = __get_cpu_var(bp_on_reg);
+		max_slots = core_num_brps;
+	} else {
+		/* Watchpoint */
+		ctrl_base = ARM_BASE_WCR;
+		val_base = ARM_BASE_WVR;
+		slots = __get_cpu_var(wp_on_reg);
+		max_slots = core_num_wrps;
+	}
+
+	for (i = 0; i < max_slots; ++i) {
+		slot = &slots[i];
+
+		if (!*slot) {
+			*slot = bp;
+			break;
+		}
+	}
+
+	if (WARN_ONCE(i == max_slots, "Can't find any breakpoint slot")) {
+		ret = -EBUSY;
+		goto out;
+	}
+
+	/* Setup the address register. */
+	write_wb_reg(val_base + i, info->address);
+
+	/* Setup the control register. */
+	write_wb_reg(ctrl_base + i, encode_ctrl_reg(info->ctrl));
+
+out:
+	return ret;
+}
+
+void arch_uninstall_hw_breakpoint(struct perf_event *bp)
+{
+	struct arch_hw_breakpoint *info = counter_arch_bp(bp);
+	struct perf_event **slot, **slots;
+	int i, max_slots, base;
+
+	if (info->ctrl.type == ARM_BREAKPOINT_EXECUTE) {
+		/* Breakpoint */
+		base = ARM_BASE_BCR;
+		slots = __get_cpu_var(bp_on_reg);
+		max_slots = core_num_brps;
+	} else {
+		/* Watchpoint */
+		base = ARM_BASE_WCR;
+		slots = __get_cpu_var(wp_on_reg);
+		max_slots = core_num_wrps;
+	}
+
+	/* Remove the breakpoint. */
+	for (i = 0; i < max_slots; ++i) {
+		slot = &slots[i];
+
+		if (*slot == bp) {
+			*slot = NULL;
+			break;
+		}
+	}
+
+	if (WARN_ONCE(i == max_slots, "Can't find any breakpoint slot"))
+		return;
+
+	/* Reset the control register. */
+	write_wb_reg(base + i, 0);
+}
+
+static int get_hbp_len(u8 hbp_len)
+{
+	unsigned int len_in_bytes = 0;
+
+	switch (hbp_len) {
+	case ARM_BREAKPOINT_LEN_1:
+		len_in_bytes = 1;
+		break;
+	case ARM_BREAKPOINT_LEN_2:
+		len_in_bytes = 2;
+		break;
+	case ARM_BREAKPOINT_LEN_4:
+		len_in_bytes = 4;
+		break;
+	case ARM_BREAKPOINT_LEN_8:
+		len_in_bytes = 8;
+		break;
+	}
+
+	return len_in_bytes;
+}
+
+/*
+ * Check whether bp virtual address is in kernel space.
+ */
+int arch_check_bp_in_kernelspace(struct perf_event *bp)
+{
+	unsigned int len;
+	unsigned long va;
+	struct arch_hw_breakpoint *info = counter_arch_bp(bp);
+
+	va = info->address;
+	len = get_hbp_len(info->ctrl.len);
+
+	return (va >= TASK_SIZE) && ((va + len - 1) >= TASK_SIZE);
+}
+
+/*
+ * Extract generic type and length encodings from an arch_hw_breakpoint_ctrl.
+ * Hopefully this will disappear when ptrace can bypass the conversion
+ * to generic breakpoint descriptions.
+ */
+int arch_bp_generic_fields(struct arch_hw_breakpoint_ctrl ctrl,
+			   int *gen_len, int *gen_type)
+{
+	/* Type */
+	switch (ctrl.type) {
+	case ARM_BREAKPOINT_EXECUTE:
+		*gen_type = HW_BREAKPOINT_X;
+		break;
+	case ARM_BREAKPOINT_LOAD:
+		*gen_type = HW_BREAKPOINT_R;
+		break;
+	case ARM_BREAKPOINT_STORE:
+		*gen_type = HW_BREAKPOINT_W;
+		break;
+	case ARM_BREAKPOINT_LOAD | ARM_BREAKPOINT_STORE:
+		*gen_type = HW_BREAKPOINT_RW;
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	/* Len */
+	switch (ctrl.len) {
+	case ARM_BREAKPOINT_LEN_1:
+		*gen_len = HW_BREAKPOINT_LEN_1;
+		break;
+	case ARM_BREAKPOINT_LEN_2:
+		*gen_len = HW_BREAKPOINT_LEN_2;
+		break;
+	case ARM_BREAKPOINT_LEN_4:
+		*gen_len = HW_BREAKPOINT_LEN_4;
+		break;
+	case ARM_BREAKPOINT_LEN_8:
+		*gen_len = HW_BREAKPOINT_LEN_8;
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+/*
+ * Construct an arch_hw_breakpoint from a perf_event.
+ */
+static int arch_build_bp_info(struct perf_event *bp)
+{
+	struct arch_hw_breakpoint *info = counter_arch_bp(bp);
+
+	/* Type */
+	switch (bp->attr.bp_type) {
+	case HW_BREAKPOINT_X:
+		info->ctrl.type = ARM_BREAKPOINT_EXECUTE;
+		break;
+	case HW_BREAKPOINT_R:
+		info->ctrl.type = ARM_BREAKPOINT_LOAD;
+		break;
+	case HW_BREAKPOINT_W:
+		info->ctrl.type = ARM_BREAKPOINT_STORE;
+		break;
+	case HW_BREAKPOINT_RW:
+		info->ctrl.type = ARM_BREAKPOINT_LOAD | ARM_BREAKPOINT_STORE;
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	/* Len */
+	switch (bp->attr.bp_len) {
+	case HW_BREAKPOINT_LEN_1:
+		info->ctrl.len = ARM_BREAKPOINT_LEN_1;
+		break;
+	case HW_BREAKPOINT_LEN_2:
+		info->ctrl.len = ARM_BREAKPOINT_LEN_2;
+		break;
+	case HW_BREAKPOINT_LEN_4:
+		info->ctrl.len = ARM_BREAKPOINT_LEN_4;
+		break;
+	case HW_BREAKPOINT_LEN_8:
+		info->ctrl.len = ARM_BREAKPOINT_LEN_8;
+		if ((info->ctrl.type != ARM_BREAKPOINT_EXECUTE)
+			&& max_watchpoint_len == 8)
+			break;
+	default:
+		return -EINVAL;
+	}
+
+	/* Privilege */
+	info->ctrl.privilege = ARM_BREAKPOINT_USER | ARM_BREAKPOINT_PRIV;
+
+	/* Address */
+	info->address = bp->attr.bp_addr;
+
+	/* Enabled? */
+	info->ctrl.enabled = ~bp->attr.disabled;
+
+	return 0;
+}
+
+/*
+ * Validate the arch-specific HW Breakpoint register settings.
+ */
+int arch_validate_hwbkpt_settings(struct perf_event *bp)
+{
+	struct arch_hw_breakpoint *info = counter_arch_bp(bp);
+	int ret = 0;
+	u32 alignment_mask = 0x3;
+
+	/* Build the arch_hw_breakpoint. */
+	ret = arch_build_bp_info(bp);
+	if (ret)
+		goto out;
+
+	/* Check address alignment. */
+	if (info->ctrl.len == ARM_BREAKPOINT_LEN_8)
+		alignment_mask = 0x7;
+	if (info->address & alignment_mask) {
+		ret = -EINVAL;
+		goto out;
+	}
+
+	/*
+	 * Currently we rely on an overflow handler to take
+	 * care of single-stepping the breakpoint when it fires.
+	 */
+	if (WARN_ONCE(!bp->overflow_handler,
+			"overflow handler required but none found")) {
+		ret = -EINVAL;
+		goto out;
+	}
+
+out:
+	return ret;
+}
+
+static void watchpoint_handler(unsigned long unpredictable,
+				struct pt_regs *regs)
+{
+	int i;
+	struct perf_event **slots = __get_cpu_var(wp_on_reg);
+	struct arch_hw_breakpoint *info;
+
+	for (i = 0; i < core_num_wrps; ++i) {
+		rcu_read_lock();
+
+		if (slots[i] == NULL) {
+			rcu_read_unlock();
+			break;
+		}
+
+		/* TODO: Check if this watchpoint actually fired. */
+
+		/*
+		 * The DFAR is unpredictable. Since we only allow a
+		 * single watchpoint, we can set the trigger to the lowest
+		 * possible faulting address.
+		 */
+		info = counter_arch_bp(slots[i]);
+		info->trigger = info->address;
+		perf_bp_event(slots[i], regs);
+
+		rcu_read_unlock();
+	}
+}
+
+static void breakpoint_handler(unsigned long unpredictable,
+				struct pt_regs *regs)
+{
+	int i;
+	u32 ctrl_reg, val, addr;
+	struct perf_event **slots = __get_cpu_var(bp_on_reg);
+	struct arch_hw_breakpoint *info;
+	struct arch_hw_breakpoint_ctrl ctrl;
+
+	/* The exception entry code places the amended lr in the PC. */
+	addr = regs->ARM_pc;
+
+	for (i = 0; i < core_num_brps; ++i) {
+		rcu_read_lock();
+
+		if (slots[i] == NULL) {
+			rcu_read_unlock();
+			break;
+		}
+
+		/* Check if the breakpoint value matches. */
+		val = read_wb_reg(ARM_BASE_BVR + i);
+		if (val != (addr & ~0x3)) {
+			rcu_read_unlock();
+			continue;
+		}
+
+		/* Possible match, check the byte address select to confirm. */
+		ctrl_reg = read_wb_reg(ARM_BASE_BCR + i);
+		decode_ctrl_reg(ctrl_reg, &ctrl);
+
+		if ((1 << (addr & 0x3)) & ctrl.len) {
+			info = counter_arch_bp(slots[i]);
+			info->trigger = addr;
+			perf_bp_event(slots[i], regs);
+		}
+
+		rcu_read_unlock();
+	}
+}
+
+/*
+ * Called from either the Data Abort Handler [watchpoint] or the
+ * Prefetch Abort Handler [breakpoint].
+ */
+static int hw_breakpoint_pending(unsigned long addr, unsigned int fsr,
+					struct pt_regs *regs)
+{
+	int ret = 1; /* Unhandled fault. */
+	u32 dscr;
+
+	/* We only handle watchpoints and hardware breakpoints. */
+	ARM_DBG_READ(c1, 0, dscr);
+
+	/* Perform perf callbacks. */
+	switch (ARM_DSCR_MOE(dscr)) {
+	case ARM_ENTRY_BREAKPOINT:
+		breakpoint_handler(addr, regs);
+		break;
+	case ARM_ENTRY_ASYNC_WATCHPOINT:
+	case ARM_ENTRY_SYNC_WATCHPOINT:
+		watchpoint_handler(addr, regs);
+		break;
+	default:
+		goto out;
+	}
+
+	ret = 0;
+out:
+	return ret;
+}
+
+/*
+ * One-time initialisation.
+ */
+static int __init arch_hw_breakpoint_init(void)
+{
+	int ret = 0, i;
+	u32 dscr;
+
+	debug_arch = get_debug_arch();
+
+	if (debug_arch > ARM_DEBUG_ARCH_V7_ECP14) {
+		pr_info("debug architecture 0x%x unsupported.\n", debug_arch);
+		ret = -ENODEV;
+		goto out;
+	}
+
+	/* Determine how many BRPs/WRPs are available. */
+	core_num_brps = get_num_brps();
+	core_num_wrps = get_num_wrps();
+
+	pr_info("found %d breakpoint and %d watchpoint registers.\n",
+			core_num_brps, core_num_wrps);
+
+	ARM_DBG_READ(c1, 0, dscr);
+	if (dscr & ARM_DSCR_HDBGEN) {
+		pr_warning("halting debug mode enabled. Assuming maximum "
+				"watchpoint size of 4 bytes.");
+	} else {
+		/* Work out the maximum supported watchpoint length. */
+		max_watchpoint_len = get_max_wp_len();
+		pr_info("maximum watchpoint size is %u bytes.\n",
+				max_watchpoint_len);
+
+		/*
+		 * Reset the breakpoint resources. We assume that a halting
+		 * debugger will leave the world in a nice state for us.
+		 */
+		for (i = 0; i < core_num_brps; ++i) {
+			write_wb_reg(ARM_BASE_BCR + i, 0UL);
+			write_wb_reg(ARM_BASE_BVR + i, 0UL);
+		}
+
+		for (i = 0; i < core_num_wrps; ++i) {
+			write_wb_reg(ARM_BASE_WCR + i, 0UL);
+			write_wb_reg(ARM_BASE_WVR + i, 0UL);
+		}
+	}
+
+	/* Register thread flush notifier. */
+	thread_register_notifier(&hw_breakpoint_thread_notifier_block);
+
+	/* Register debug fault handler. */
+	hook_fault_code(2, hw_breakpoint_pending, SIGTRAP, "debug exception");
+	hook_ifault_code(2, hw_breakpoint_pending, SIGTRAP, "debug exception");
+
+out:
+	return ret;
+}
+arch_initcall(arch_hw_breakpoint_init);
+
+void hw_breakpoint_pmu_read(struct perf_event *bp)
+{
+}
+
+/*
+ * Dummy function to register with die_notifier.
+ */
+int hw_breakpoint_exceptions_notify(struct notifier_block *unused,
+					unsigned long val, void *data)
+{
+	return NOTIFY_DONE;
+}
-- 
1.6.3.3

[PATCH 3/4] ARM: hw-breakpoint: add new ptrace requests for hw-breakpoint interaction

[Will Deacon]

For debuggers to take advantage of the hw-breakpoint framework in the kernel,
it is necessary to expose the API calls via a ptrace interface.

This patch exposes the hardware breakpoints framework as a collection of
virtual registers, accesible using PTRACE_SETHBPREGS and PTRACE_GETHBPREGS
requests. The breakpoints are stored in the debug_info struct of the running
thread.

Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: S. Karthikeyan <informkarthik@gmail.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
---
 arch/arm/include/asm/processor.h |    4 +
 arch/arm/include/asm/ptrace.h    |    2 +
 arch/arm/kernel/hw_breakpoint.c  |   13 +++
 arch/arm/kernel/ptrace.c         |  196 ++++++++++++++++++++++++++++++++++++++
 4 files changed, 215 insertions(+), 0 deletions(-)

diff --git a/arch/arm/include/asm/processor.h b/arch/arm/include/asm/processor.h
index 6a89567..dbd33c3 100644
--- a/arch/arm/include/asm/processor.h
+++ b/arch/arm/include/asm/processor.h
@@ -19,6 +19,7 @@
 
 #ifdef __KERNEL__
 
+#include <asm/hw_breakpoint.h>
 #include <asm/ptrace.h>
 #include <asm/types.h>
 
@@ -41,6 +42,9 @@ struct debug_entry {
 struct debug_info {
 	int			nsaved;
 	struct debug_entry	bp[2];
+#ifdef CONFIG_HAVE_HW_BREAKPOINT
+	struct perf_event	*hbp[ARM_MAX_HBP_SLOTS];
+#endif
 };
 
 struct thread_struct {
diff --git a/arch/arm/include/asm/ptrace.h b/arch/arm/include/asm/ptrace.h
index 9dcb11e..21560e4 100644
--- a/arch/arm/include/asm/ptrace.h
+++ b/arch/arm/include/asm/ptrace.h
@@ -29,6 +29,8 @@
 #define PTRACE_SETCRUNCHREGS	26
 #define PTRACE_GETVFPREGS	27
 #define PTRACE_SETVFPREGS	28
+#define PTRACE_GETHBPREGS	29
+#define PTRACE_SETHBPREGS	30
 
 /*
  * PSR bits
diff --git a/arch/arm/kernel/hw_breakpoint.c b/arch/arm/kernel/hw_breakpoint.c
index b249cd7..5d5faec 100644
--- a/arch/arm/kernel/hw_breakpoint.c
+++ b/arch/arm/kernel/hw_breakpoint.c
@@ -647,6 +647,19 @@ out:
 	return ret;
 }
 
+static int hw_breakpoint_thread_notify(struct notifier_block *self,
+				       unsigned long cmd, void *t)
+{
+	if (cmd == THREAD_NOTIFY_FLUSH)
+		flush_ptrace_hw_breakpoint(current);
+
+	return NOTIFY_DONE;
+}
+
+static struct notifier_block hw_breakpoint_thread_notifier_block = {
+	.notifier_call = hw_breakpoint_thread_notify,
+};
+
 /*
  * One-time initialisation.
  */
diff --git a/arch/arm/kernel/ptrace.c b/arch/arm/kernel/ptrace.c
index 3f562a7..51b9931 100644
--- a/arch/arm/kernel/ptrace.c
+++ b/arch/arm/kernel/ptrace.c
@@ -19,6 +19,8 @@
 #include <linux/init.h>
 #include <linux/signal.h>
 #include <linux/uaccess.h>
+#include <linux/perf_event.h>
+#include <linux/hw_breakpoint.h>
 
 #include <asm/pgtable.h>
 #include <asm/system.h>
@@ -751,6 +753,189 @@ static int ptrace_setvfpregs(struct task_struct *tsk, void __user *data)
 }
 #endif
 
+#ifdef CONFIG_HAVE_HW_BREAKPOINT
+/*
+ * Handle hitting a HW-breakpoint.
+ */
+static void ptrace_hbptriggered(struct perf_event *bp, int unused,
+				     struct perf_sample_data *data,
+				     struct pt_regs *regs)
+{
+	struct arch_hw_breakpoint *bkpt = counter_arch_bp(bp);
+	siginfo_t info;
+
+	info.si_signo	= SIGTRAP;
+	info.si_errno	= bkpt->ctrl.type;
+	info.si_code	= TRAP_HWBKPT;
+	info.si_addr	= (void __user *)(bkpt->trigger);
+
+	force_sig_info(SIGTRAP, &info, current);
+}
+
+void flush_ptrace_hw_breakpoint(struct task_struct *tsk)
+{
+	int i;
+	struct thread_struct *t = &tsk->thread;
+
+	for (i = 0; i < ARM_MAX_HBP_SLOTS; i++) {
+		unregister_hw_breakpoint(t->debug.hbp[i]);
+		t->debug.hbp[i] = NULL;
+	}
+}
+
+static u32 ptrace_get_hbp_resource_info(void)
+{
+	u8 num_brps, num_wrps, debug_arch, wp_len;
+	u32 reg = 0;
+
+	num_brps	= hw_breakpoint_slots(TYPE_INST);
+	num_wrps	= hw_breakpoint_slots(TYPE_DATA);
+	debug_arch	= arch_get_debug_arch();
+	wp_len		= arch_get_max_wp_len();
+
+	reg		|= debug_arch;
+	reg		<<= 8;
+	reg		|= wp_len;
+	reg		<<= 8;
+	reg		|= num_wrps;
+	reg		<<= 8;
+	reg		|= num_brps;
+
+	return reg;
+}
+
+/*
+ * Convert a virtual register number into an index for a thread_info
+ * breakpoint array. Breakpoints are identified using positive numbers
+ * whilst watchpoints are negative. The registers are laid out as pairs
+ * of (address, control), each pair mapping to a unique hw_breakpoint struct.
+ * Register 0 is reserved for describing resource information.
+ */
+static int ptrace_hbp_num_to_idx(long num)
+{
+	if (num < 0)
+		num = (ARM_MAX_BRP << 1) - num;
+	return (num - 1) >> 1;
+}
+
+static struct perf_event *ptrace_hbp_create(struct task_struct *tsk, int type)
+{
+	struct perf_event_attr attr;
+
+	hw_breakpoint_init(&attr);
+
+	/* Initialise fields to sane defaults. */
+	attr.bp_addr	= 0;
+	attr.bp_len	= HW_BREAKPOINT_LEN_4;
+	attr.type	= type;
+	attr.disabled	= 1;
+
+	return register_user_hw_breakpoint(&attr, ptrace_hbptriggered, tsk);
+}
+
+static int ptrace_gethbpregs(struct task_struct *tsk, long num,
+			     unsigned long  __user *data)
+{
+	u32 reg;
+	int idx, ret = 0;
+	struct perf_event *bp;
+	struct arch_hw_breakpoint *arch_bp;
+
+	if (num == 0) {
+		reg = ptrace_get_hbp_resource_info();
+	} else {
+		idx = ptrace_hbp_num_to_idx(num);
+		if (idx < 0 || idx >= ARM_MAX_HBP_SLOTS) {
+			ret = -EINVAL;
+			goto out;
+		}
+
+		bp = tsk->thread.debug.hbp[idx];
+		if (!bp) {
+			reg = 0;
+			goto put;
+		}
+
+		arch_bp = counter_arch_bp(bp);
+		if (idx & 0x1)
+			reg = encode_ctrl_reg(arch_bp->ctrl);
+		else
+			reg = arch_bp->address;
+	}
+
+put:
+	if (put_user(reg, data))
+		ret = -EFAULT;
+
+out:
+	return ret;
+}
+
+static int ptrace_sethbpregs(struct task_struct *tsk, long num,
+			     unsigned long __user *data)
+{
+	int idx, gen_len, gen_type, implied_type, ret = 0;
+	u32 user_val;
+	struct perf_event *bp;
+	struct arch_hw_breakpoint_ctrl ctrl;
+	struct perf_event_attr attr;
+
+	if (num == 0)
+		goto out;
+	else if (num < 0)
+		implied_type = HW_BREAKPOINT_RW;
+	else
+		implied_type = HW_BREAKPOINT_X;
+
+	idx = ptrace_hbp_num_to_idx(num);
+	if (idx < 0 || idx >= ARM_MAX_HBP_SLOTS) {
+		ret = -EINVAL;
+		goto out;
+	}
+
+	if (get_user(user_val, data)) {
+		ret = -EFAULT;
+		goto out;
+	}
+
+	bp = tsk->thread.debug.hbp[idx];
+	if (!bp) {
+		bp = ptrace_hbp_create(tsk, implied_type);
+		if (IS_ERR(bp)) {
+			ret = PTR_ERR(bp);
+			goto out;
+		}
+		tsk->thread.debug.hbp[idx] = bp;
+	}
+
+	attr = bp->attr;
+
+	if (idx & 0x1) {
+		/* Control */
+		decode_ctrl_reg(user_val, &ctrl);
+		ret = arch_bp_generic_fields(ctrl, &gen_len, &gen_type);
+		if (ret)
+			goto out;
+
+		if ((gen_type & implied_type) != gen_type) {
+				ret = -EINVAL;
+				goto out;
+		}
+
+		attr.bp_len	= gen_len;
+		attr.bp_type	= gen_type;
+		attr.disabled	= ~ctrl.enabled;
+	} else {
+		/* Address */
+		attr.bp_addr	= user_val;
+	}
+
+	ret = modify_user_hw_breakpoint(bp, &attr);
+out:
+	return ret;
+}
+#endif
+
 long arch_ptrace(struct task_struct *child, long request, long addr, long data)
 {
 	int ret;
@@ -820,6 +1005,17 @@ long arch_ptrace(struct task_struct *child, long request, long addr, long data)
 			break;
 #endif
 
+#ifdef CONFIG_HAVE_HW_BREAKPOINT
+		case PTRACE_GETHBPREGS:
+			ret = ptrace_gethbpregs(child, addr,
+						(unsigned long __user *)data);
+			break;
+		case PTRACE_SETHBPREGS:
+			ret = ptrace_sethbpregs(child, addr,
+						(unsigned long __user *)data);
+			break;
+#endif
+
 		default:
 			ret = ptrace_request(child, request, addr, data);
 			break;
-- 
1.6.3.3

[PATCH 4/4] ARM: hw-breakpoint: add HAVE_HW_BREAKPOINT to Kconfig

[Will Deacon]

If we're targetting a v6 or v7 core and have at least software perf events
available, then automatically add support for hardware breakpoints.

Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: S. Karthikeyan <informkarthik@gmail.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
---
 arch/arm/Kconfig         |    1 +
 arch/arm/kernel/Makefile |    1 +
 2 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index e57cb24..7ed4d58 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -24,6 +24,7 @@ config ARM
 	select HAVE_KERNEL_LZMA
 	select HAVE_PERF_EVENTS
 	select PERF_USE_VMALLOC
+	select HAVE_HW_BREAKPOINT if (PERF_EVENTS && (CPU_V6 || CPU_V7))
 	help
 	  The ARM series is a line of low-power-consumption RISC chip designs
 	  licensed by ARM Ltd and targeted at embedded applications and
diff --git a/arch/arm/kernel/Makefile b/arch/arm/kernel/Makefile
index 26d302c..e679fb0 100644
--- a/arch/arm/kernel/Makefile
+++ b/arch/arm/kernel/Makefile
@@ -39,6 +39,7 @@ obj-$(CONFIG_ARM_THUMBEE)	+= thumbee.o
 obj-$(CONFIG_KGDB)		+= kgdb.o
 obj-$(CONFIG_ARM_UNWIND)	+= unwind.o
 obj-$(CONFIG_HAVE_TCM)		+= tcm.o
+obj-$(CONFIG_HAVE_HW_BREAKPOINT)	+= hw_breakpoint.o
 
 obj-$(CONFIG_CRUNCH)		+= crunch.o crunch-bits.o
 AFLAGS_crunch-bits.o		:= -Wa,-mcpu=ep9312
-- 
1.6.3.3

[RFC PATCH 0/4] ARM: add support for hw-breakpoints [v3]

[Will Deacon]

Hello,

> This is version 3 of the RFC patches originally posted at:
> 
> v1.) http://lists.infradead.org/pipermail/linux-arm-kernel/2010-February/009084.html
> v2.) http://lists.infradead.org/pipermail/linux-arm-kernel/2010-March/011170.html
> 
> Changes from v2 include:
> 	- Based on 2.6.35-rc2
> 	- Updated to use new hw-breakpoint API features
> 	- Addressed some comments from Frederic on LKML
> 	- Complete redesign of the ptrace interface so that it
> 	  follows the ARM ARM (v7) register structure more closely.
> 
> Unfortunately, I've only managed to compile-test this and check that the
> resulting image boots. The main reasons for posting are (a) to support
> current GDB development and (b) to attract comments on the code.

I've managed to do some preliminary testing using the GDB work
in progress and found a few coding howlers. Rather than submit
a new patchset, I'll keep an up-to-date patch series, rebased
against the latest mainline tag here:

http://www.linux-arm.org/git?p=linux-2.6-wd.git;a=shortlog;h=refs/heads/hw-breakpoint

Once the GDB work is complete, I'll submit v4 to this list.

Cheers,

Will

[PATCH 2/4] ARM: hw-breakpoint: add ARM backend for the hw-breakpoint framework

[Will Deacon]

The hw-breakpoint framework in the kernel requires architecture-specific
support in order to install, remove, validate and manage hardware
breakpoints.

This patch adds preliminary support for this framework to the ARM
architecture, but restricts the number of watchpoints to a single resource
to get around the fact that the Data Fault Address Register is unpredictable
when a watchpoint debug exception is taken.

Currently, clients must handle synchronous breakpoint exceptions.
This requires the ability to single-step over the causative instruction to
avoid getting stuck in an infinite loop.

The memory-mapped extended debug interface is unsupported due to its
unreliability in real implementations.

Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: S. Karthikeyan <informkarthik@gmail.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
---
 arch/arm/include/asm/hw_breakpoint.h |  117 ++++++
 arch/arm/kernel/hw_breakpoint.c      |  747 ++++++++++++++++++++++++++++++++++
 2 files changed, 864 insertions(+), 0 deletions(-)
 create mode 100644 arch/arm/include/asm/hw_breakpoint.h
 create mode 100644 arch/arm/kernel/hw_breakpoint.c

diff --git a/arch/arm/include/asm/hw_breakpoint.h b/arch/arm/include/asm/hw_breakpoint.h
new file mode 100644
index 0000000..c995219
--- /dev/null
+++ b/arch/arm/include/asm/hw_breakpoint.h
@@ -0,0 +1,117 @@
+#ifndef _ARM_HW_BREAKPOINT_H
+#define _ARM_HW_BREAKPOINT_H
+
+#ifdef __KERNEL__
+struct arch_hw_breakpoint_ctrl {
+		u32 __reserved	: 19,
+		len		: 8,
+		type		: 2,
+		privilege	: 2,
+		enabled		: 1;
+};
+
+struct arch_hw_breakpoint {
+	u32	address;
+	u32	trigger;
+	struct arch_hw_breakpoint_ctrl ctrl;
+};
+
+static inline u32 encode_ctrl_reg(struct arch_hw_breakpoint_ctrl ctrl)
+{
+	return (ctrl.len << 5) | (ctrl.type << 3) |
+		(ctrl.privilege << 1) | ctrl.enabled;
+}
+
+static inline void decode_ctrl_reg(u32 reg,
+				   struct arch_hw_breakpoint_ctrl *ctrl)
+{
+	ctrl->enabled	= reg & 0x1;
+	reg >>= 1;
+	ctrl->privilege	= reg & 0x3;
+	reg >>= 2;
+	ctrl->type	= reg & 0x3;
+	reg >>= 2;
+	ctrl->len	= reg & 0xff;
+}
+
+/* Debug architecture numbers. */
+#define ARM_DEBUG_ARCH_V6	1
+#define ARM_DEBUG_ARCH_V6_1	2
+#define ARM_DEBUG_ARCH_V7_ECP14	3
+#define ARM_DEBUG_ARCH_V7_MM	4
+
+/* Breakpoint */
+#define ARM_BREAKPOINT_EXECUTE	0
+
+/* Watchpoints */
+#define ARM_BREAKPOINT_LOAD	1
+#define ARM_BREAKPOINT_STORE	2
+
+/* Privilege Levels */
+#define ARM_BREAKPOINT_PRIV	1
+#define ARM_BREAKPOINT_USER	2
+
+/* Lengths */
+#define ARM_BREAKPOINT_LEN_1	0x1
+#define ARM_BREAKPOINT_LEN_2	0x3
+#define ARM_BREAKPOINT_LEN_4	0xf
+#define ARM_BREAKPOINT_LEN_8	0xff
+
+/* Limits */
+#define ARM_MAX_BRP		16
+#define ARM_MAX_WRP		16
+#define ARM_MAX_HBP_SLOTS	(ARM_MAX_BRP + ARM_MAX_WRP)
+
+/* DSCR method of entry bits. */
+#define ARM_DSCR_MOE(x)			((x >> 2) & 0xf)
+#define ARM_ENTRY_BREAKPOINT		0x1
+#define ARM_ENTRY_ASYNC_WATCHPOINT	0x2
+#define ARM_ENTRY_SYNC_WATCHPOINT	0xa
+
+/* DSCR monitor/halting bits. */
+#define ARM_DSCR_HDBGEN		(1 << 14)
+#define ARM_DSCR_MDBGEN		(1 << 15)
+
+/* opcode2 numbers for the co-processor instructions. */
+#define ARM_OP2_BVR		4
+#define ARM_OP2_BCR		5
+#define ARM_OP2_WVR		6
+#define ARM_OP2_WCR		7
+
+/* Base register numbers for the debug registers. */
+#define ARM_BASE_BVR		64
+#define ARM_BASE_BCR		80
+#define ARM_BASE_WVR		96
+#define ARM_BASE_WCR		112
+
+/* Accessor macros for the debug registers. */
+#define ARM_DBG_READ(M, OP2, VAL) do {\
+	asm volatile("mrc p14, 0, %0, c0," #M ", " #OP2 : "=r" (VAL));\
+} while (0)
+
+#define ARM_DBG_WRITE(M, OP2, VAL) do {\
+	asm volatile("mcr p14, 0, %0, c0," #M ", " #OP2 : : "r" (VAL));\
+} while (0)
+
+struct notifier_block;
+struct perf_event;
+struct pmu;
+struct task_struct;
+
+extern struct pmu perf_ops_bp;
+extern int arch_bp_generic_fields(struct arch_hw_breakpoint_ctrl ctrl,
+				  int *gen_len, int *gen_type);
+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,
+					   unsigned long val, void *data);
+extern u8 arch_get_debug_arch(void);
+extern u8 arch_get_max_wp_len(void);
+
+int arch_install_hw_breakpoint(struct perf_event *bp);
+void arch_uninstall_hw_breakpoint(struct perf_event *bp);
+void hw_breakpoint_pmu_read(struct perf_event *bp);
+int hw_breakpoint_slots(int type);
+
+#endif	/* __KERNEL__ */
+#endif	/* _ARM_HW_BREAKPOINT_H */
diff --git a/arch/arm/kernel/hw_breakpoint.c b/arch/arm/kernel/hw_breakpoint.c
new file mode 100644
index 0000000..ab13e33
--- /dev/null
+++ b/arch/arm/kernel/hw_breakpoint.c
@@ -0,0 +1,747 @@
+/*
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * 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.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ *
+ * Copyright (C) 2009, 2010 ARM Limited
+ *
+ * Author: Will Deacon <will.deacon@arm.com>
+ */
+
+/*
+ * HW_breakpoint: a unified kernel/user-space hardware breakpoint facility,
+ * using the CPU's debug registers.
+ */
+
+#define pr_fmt(fmt) "hw-breakpoint: " fmt
+
+#include <linux/errno.h>
+#include <linux/perf_event.h>
+#include <linux/hw_breakpoint.h>
+#include <linux/smp.h>
+
+#include <asm/cacheflush.h>
+#include <asm/cputype.h>
+#include <asm/current.h>
+#include <asm/hw_breakpoint.h>
+#include <asm/kdebug.h>
+#include <asm/system.h>
+#include <asm/thread_notify.h>
+#include <asm/traps.h>
+
+/* Breakpoint currently in use for each BRP. */
+static DEFINE_PER_CPU(struct perf_event *, bp_on_reg[ARM_MAX_BRP]);
+
+/* Watchpoint currently in use for each WRP. */
+static DEFINE_PER_CPU(struct perf_event *, wp_on_reg[ARM_MAX_WRP]);
+
+/* Number of BRP/WRP registers on this CPU. */
+static int core_num_brps;
+static int core_num_wrps;
+
+/* Debug architecture version. */
+static u8 debug_arch;
+
+/* Maximum supported watchpoint length. */
+static u8 max_watchpoint_len;
+
+/* Determine number of BRP registers available. */
+static int get_num_brps(void)
+{
+	u32 didr;
+	ARM_DBG_READ(c0, 0, didr);
+	return ((didr >> 24) & 0xf) + 1;
+}
+
+/* Determine number of WRP registers available. */
+static int get_num_wrps(void)
+{
+	/*
+	 * FIXME: When a watchpoint fires, the only way to work out which
+	 * watchpoint it was is by disassembling the faulting instruction
+	 * and working out the address of the memory access.
+	 *
+	 * Furthermore, we can only do this if the watchpoint was precise
+	 * since imprecise watchpoints prevent us from calculating register
+	 * based addresses.
+	 *
+	 * For the time being, we only report 1 watchpoint register so we
+	 * always know which watchpoint fired. In the future we can either
+	 * add a disassembler and address generation emulator, or we can
+	 * insert a check to see if the DFAR is set on watchpoint exception
+	 * entry [the ARM ARM states that the DFAR is UNPREDICTABLE, but
+	 * experience shows that it is set on some implementations].
+	 */
+
+#if 0
+	u32 didr, wrps;
+	ARM_DBG_READ(c0, 0, didr);
+	return ((didr >> 28) & 0xf) + 1;
+#endif
+
+	return 1;
+}
+
+int hw_breakpoint_slots(int type)
+{
+	/*
+	 * We can be called early, so don't rely on
+	 * our static variables being initialised.
+	 */
+	switch (type) {
+	case TYPE_INST:
+		return get_num_brps();
+	case TYPE_DATA:
+		return get_num_wrps();
+	default:
+		pr_warning("unknown slot type: %d\n", type);
+		return 0;
+	}
+}
+
+/* Determine debug architecture. */
+static u8 get_debug_arch(void)
+{
+	u32 didr;
+
+	/* Do we implement the extended CPUID interface? */
+	if (((read_cpuid_id() >> 16) & 0xf) != 0xf) {
+		pr_warning("CPUID feature registers not supported. "
+				"Assuming v6 debug is present.\n");
+		return ARM_DEBUG_ARCH_V6;
+	}
+
+	ARM_DBG_READ(c0, 0, didr);
+	return ((didr >> 16) & 0xf);
+}
+
+u8 arch_get_debug_arch(void)
+{
+	return debug_arch;
+}
+
+#define READ_WB_REG_CASE(OP2, M, VAL)		\
+	case ((OP2 << 4) + M):			\
+		ARM_DBG_READ(c ## M, OP2, VAL); \
+		break
+
+#define WRITE_WB_REG_CASE(OP2, M, VAL)		\
+	case ((OP2 << 4) + M):			\
+		ARM_DBG_WRITE(c ## M, OP2, VAL);\
+		break
+
+#define GEN_READ_WB_REG_CASES(OP2, VAL)		\
+	READ_WB_REG_CASE(OP2, 0, VAL);		\
+	READ_WB_REG_CASE(OP2, 1, VAL);		\
+	READ_WB_REG_CASE(OP2, 2, VAL);		\
+	READ_WB_REG_CASE(OP2, 3, VAL);		\
+	READ_WB_REG_CASE(OP2, 4, VAL);		\
+	READ_WB_REG_CASE(OP2, 5, VAL);		\
+	READ_WB_REG_CASE(OP2, 6, VAL);		\
+	READ_WB_REG_CASE(OP2, 7, VAL);		\
+	READ_WB_REG_CASE(OP2, 8, VAL);		\
+	READ_WB_REG_CASE(OP2, 9, VAL);		\
+	READ_WB_REG_CASE(OP2, 10, VAL);		\
+	READ_WB_REG_CASE(OP2, 11, VAL);		\
+	READ_WB_REG_CASE(OP2, 12, VAL);		\
+	READ_WB_REG_CASE(OP2, 13, VAL);		\
+	READ_WB_REG_CASE(OP2, 14, VAL);		\
+	READ_WB_REG_CASE(OP2, 15, VAL)
+
+#define GEN_WRITE_WB_REG_CASES(OP2, VAL)	\
+	WRITE_WB_REG_CASE(OP2, 0, VAL);		\
+	WRITE_WB_REG_CASE(OP2, 1, VAL);		\
+	WRITE_WB_REG_CASE(OP2, 2, VAL);		\
+	WRITE_WB_REG_CASE(OP2, 3, VAL);		\
+	WRITE_WB_REG_CASE(OP2, 4, VAL);		\
+	WRITE_WB_REG_CASE(OP2, 5, VAL);		\
+	WRITE_WB_REG_CASE(OP2, 6, VAL);		\
+	WRITE_WB_REG_CASE(OP2, 7, VAL);		\
+	WRITE_WB_REG_CASE(OP2, 8, VAL);		\
+	WRITE_WB_REG_CASE(OP2, 9, VAL);		\
+	WRITE_WB_REG_CASE(OP2, 10, VAL);	\
+	WRITE_WB_REG_CASE(OP2, 11, VAL);	\
+	WRITE_WB_REG_CASE(OP2, 12, VAL);	\
+	WRITE_WB_REG_CASE(OP2, 13, VAL);	\
+	WRITE_WB_REG_CASE(OP2, 14, VAL);	\
+	WRITE_WB_REG_CASE(OP2, 15, VAL)
+
+static u32 read_wb_reg(int n)
+{
+	u32 val = 0;
+
+	switch (n) {
+	GEN_READ_WB_REG_CASES(ARM_OP2_BVR, val);
+	GEN_READ_WB_REG_CASES(ARM_OP2_BCR, val);
+	GEN_READ_WB_REG_CASES(ARM_OP2_WVR, val);
+	GEN_READ_WB_REG_CASES(ARM_OP2_WCR, val);
+	default:
+		pr_warning("attempt to read from unknown breakpoint "
+				"register %d\n", n);
+	}
+
+	return val;
+}
+
+static void write_wb_reg(int n, u32 val)
+{
+	switch (n) {
+	GEN_WRITE_WB_REG_CASES(ARM_OP2_BVR, val);
+	GEN_WRITE_WB_REG_CASES(ARM_OP2_BCR, val);
+	GEN_WRITE_WB_REG_CASES(ARM_OP2_WVR, val);
+	GEN_WRITE_WB_REG_CASES(ARM_OP2_WCR, val);
+	default:
+		pr_warning("attempt to write to unknown breakpoint "
+				"register %d\n", n);
+	}
+}
+
+/*
+ * In order to access the breakpoint/watchpoint control registers,
+ * we must be running in debug monitor mode. Unfortunately, we can
+ * be put into halting debug mode@any time by an external debugger
+ * but there is nothing we can do to prevent that.
+ */
+static int enable_monitor_mode(void)
+{
+	u32 dscr;
+	int ret = 0;
+
+	ARM_DBG_READ(c1, 0, dscr);
+
+	/* Ensure that halting mode is disabled. */
+	if (WARN_ONCE(dscr & ARM_DSCR_HDBGEN, "halting debug mode enabled."
+				"Unable to access hardware resources.")) {
+		ret = -EPERM;
+		goto out;
+	}
+
+	/* Write to the corresponding DSCR. */
+	switch (debug_arch) {
+	case ARM_DEBUG_ARCH_V6:
+	case ARM_DEBUG_ARCH_V6_1:
+		ARM_DBG_WRITE(c1, 0, (dscr | ARM_DSCR_MDBGEN));
+		break;
+	case ARM_DEBUG_ARCH_V7_ECP14:
+		ARM_DBG_WRITE(c2, 2, (dscr | ARM_DSCR_MDBGEN));
+		break;
+	default:
+		ret = -ENODEV;
+		goto out;
+	}
+
+	/* Check that the write made it through. */
+	ARM_DBG_READ(c1, 0, dscr);
+	if (WARN_ONCE(!(dscr & ARM_DSCR_MDBGEN),
+				"failed to enable monitor mode.")) {
+		ret = -EPERM;
+	}
+
+out:
+	return ret;
+}
+
+/*
+ * Check if 8-bit byte-address select is available.
+ * This clobbers WRP 0.
+ */
+static u8 get_max_wp_len(void)
+{
+	u32 ctrl_reg;
+	struct arch_hw_breakpoint_ctrl ctrl;
+	u8 size = 4;
+
+	if (debug_arch < ARM_DEBUG_ARCH_V7_ECP14)
+		goto out;
+
+	if (enable_monitor_mode())
+		goto out;
+
+	memset(&ctrl, 0, sizeof(ctrl));
+	ctrl.len = ARM_BREAKPOINT_LEN_8;
+	ctrl_reg = encode_ctrl_reg(ctrl);
+
+	write_wb_reg(ARM_BASE_WVR, 0);
+	write_wb_reg(ARM_BASE_WCR, ctrl_reg);
+	if ((read_wb_reg(ARM_BASE_WCR) & ctrl_reg) == ctrl_reg)
+		size = 8;
+
+out:
+	return size;
+}
+
+u8 arch_get_max_wp_len(void)
+{
+	return max_watchpoint_len;
+}
+
+/*
+ * Install a perf counter breakpoint.
+ */
+int arch_install_hw_breakpoint(struct perf_event *bp)
+{
+	struct arch_hw_breakpoint *info = counter_arch_bp(bp);
+	struct perf_event **slot, **slots;
+	int i, max_slots, ctrl_base, val_base, ret = 0;
+
+	/* Ensure that we are in monitor mode and halting mode is disabled. */
+	ret = enable_monitor_mode();
+	if (ret)
+		goto out;
+
+	if (info->ctrl.type == ARM_BREAKPOINT_EXECUTE) {
+		/* Breakpoint */
+		ctrl_base = ARM_BASE_BCR;
+		val_base = ARM_BASE_BVR;
+		slots = __get_cpu_var(bp_on_reg);
+		max_slots = core_num_brps;
+	} else {
+		/* Watchpoint */
+		ctrl_base = ARM_BASE_WCR;
+		val_base = ARM_BASE_WVR;
+		slots = __get_cpu_var(wp_on_reg);
+		max_slots = core_num_wrps;
+	}
+
+	for (i = 0; i < max_slots; ++i) {
+		slot = &slots[i];
+
+		if (!*slot) {
+			*slot = bp;
+			break;
+		}
+	}
+
+	if (WARN_ONCE(i == max_slots, "Can't find any breakpoint slot")) {
+		ret = -EBUSY;
+		goto out;
+	}
+
+	/* Setup the address register. */
+	write_wb_reg(val_base + i, info->address);
+
+	/* Setup the control register. */
+	write_wb_reg(ctrl_base + i, encode_ctrl_reg(info->ctrl) | 0x1);
+
+out:
+	return ret;
+}
+
+void arch_uninstall_hw_breakpoint(struct perf_event *bp)
+{
+	struct arch_hw_breakpoint *info = counter_arch_bp(bp);
+	struct perf_event **slot, **slots;
+	int i, max_slots, base;
+
+	if (info->ctrl.type == ARM_BREAKPOINT_EXECUTE) {
+		/* Breakpoint */
+		base = ARM_BASE_BCR;
+		slots = __get_cpu_var(bp_on_reg);
+		max_slots = core_num_brps;
+	} else {
+		/* Watchpoint */
+		base = ARM_BASE_WCR;
+		slots = __get_cpu_var(wp_on_reg);
+		max_slots = core_num_wrps;
+	}
+
+	/* Remove the breakpoint. */
+	for (i = 0; i < max_slots; ++i) {
+		slot = &slots[i];
+
+		if (*slot == bp) {
+			*slot = NULL;
+			break;
+		}
+	}
+
+	if (WARN_ONCE(i == max_slots, "Can't find any breakpoint slot"))
+		return;
+
+	/* Reset the control register. */
+	write_wb_reg(base + i, 0);
+}
+
+static int get_hbp_len(u8 hbp_len)
+{
+	unsigned int len_in_bytes = 0;
+
+	switch (hbp_len) {
+	case ARM_BREAKPOINT_LEN_1:
+		len_in_bytes = 1;
+		break;
+	case ARM_BREAKPOINT_LEN_2:
+		len_in_bytes = 2;
+		break;
+	case ARM_BREAKPOINT_LEN_4:
+		len_in_bytes = 4;
+		break;
+	case ARM_BREAKPOINT_LEN_8:
+		len_in_bytes = 8;
+		break;
+	}
+
+	return len_in_bytes;
+}
+
+/*
+ * Check whether bp virtual address is in kernel space.
+ */
+int arch_check_bp_in_kernelspace(struct perf_event *bp)
+{
+	unsigned int len;
+	unsigned long va;
+	struct arch_hw_breakpoint *info = counter_arch_bp(bp);
+
+	va = info->address;
+	len = get_hbp_len(info->ctrl.len);
+
+	return (va >= TASK_SIZE) && ((va + len - 1) >= TASK_SIZE);
+}
+
+/*
+ * Extract generic type and length encodings from an arch_hw_breakpoint_ctrl.
+ * Hopefully this will disappear when ptrace can bypass the conversion
+ * to generic breakpoint descriptions.
+ */
+int arch_bp_generic_fields(struct arch_hw_breakpoint_ctrl ctrl,
+			   int *gen_len, int *gen_type)
+{
+	/* Type */
+	switch (ctrl.type) {
+	case ARM_BREAKPOINT_EXECUTE:
+		*gen_type = HW_BREAKPOINT_X;
+		break;
+	case ARM_BREAKPOINT_LOAD:
+		*gen_type = HW_BREAKPOINT_R;
+		break;
+	case ARM_BREAKPOINT_STORE:
+		*gen_type = HW_BREAKPOINT_W;
+		break;
+	case ARM_BREAKPOINT_LOAD | ARM_BREAKPOINT_STORE:
+		*gen_type = HW_BREAKPOINT_RW;
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	/* Len */
+	switch (ctrl.len) {
+	case ARM_BREAKPOINT_LEN_1:
+		*gen_len = HW_BREAKPOINT_LEN_1;
+		break;
+	case ARM_BREAKPOINT_LEN_2:
+		*gen_len = HW_BREAKPOINT_LEN_2;
+		break;
+	case ARM_BREAKPOINT_LEN_4:
+		*gen_len = HW_BREAKPOINT_LEN_4;
+		break;
+	case ARM_BREAKPOINT_LEN_8:
+		*gen_len = HW_BREAKPOINT_LEN_8;
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+/*
+ * Construct an arch_hw_breakpoint from a perf_event.
+ */
+static int arch_build_bp_info(struct perf_event *bp)
+{
+	struct arch_hw_breakpoint *info = counter_arch_bp(bp);
+
+	/* Type */
+	switch (bp->attr.bp_type) {
+	case HW_BREAKPOINT_X:
+		info->ctrl.type = ARM_BREAKPOINT_EXECUTE;
+		break;
+	case HW_BREAKPOINT_R:
+		info->ctrl.type = ARM_BREAKPOINT_LOAD;
+		break;
+	case HW_BREAKPOINT_W:
+		info->ctrl.type = ARM_BREAKPOINT_STORE;
+		break;
+	case HW_BREAKPOINT_RW:
+		info->ctrl.type = ARM_BREAKPOINT_LOAD | ARM_BREAKPOINT_STORE;
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	/* Len */
+	switch (bp->attr.bp_len) {
+	case HW_BREAKPOINT_LEN_1:
+		info->ctrl.len = ARM_BREAKPOINT_LEN_1;
+		break;
+	case HW_BREAKPOINT_LEN_2:
+		info->ctrl.len = ARM_BREAKPOINT_LEN_2;
+		break;
+	case HW_BREAKPOINT_LEN_4:
+		info->ctrl.len = ARM_BREAKPOINT_LEN_4;
+		break;
+	case HW_BREAKPOINT_LEN_8:
+		info->ctrl.len = ARM_BREAKPOINT_LEN_8;
+		if ((info->ctrl.type != ARM_BREAKPOINT_EXECUTE)
+			&& max_watchpoint_len >= 8)
+			break;
+	default:
+		return -EINVAL;
+	}
+
+	/* Privilege */
+	info->ctrl.privilege = ARM_BREAKPOINT_USER | ARM_BREAKPOINT_PRIV;
+
+	/* Address */
+	info->address = bp->attr.bp_addr;
+
+	/* Enabled? */
+	info->ctrl.enabled = !bp->attr.disabled;
+
+	return 0;
+}
+
+/*
+ * Validate the arch-specific HW Breakpoint register settings.
+ */
+int arch_validate_hwbkpt_settings(struct perf_event *bp)
+{
+	struct arch_hw_breakpoint *info = counter_arch_bp(bp);
+	int ret = 0;
+	u32 bytelen, max_len, offset, alignment_mask = 0x3;
+
+	/* Build the arch_hw_breakpoint. */
+	ret = arch_build_bp_info(bp);
+	if (ret)
+		goto out;
+
+	/* Check address alignment. */
+	if (info->ctrl.len == ARM_BREAKPOINT_LEN_8)
+		alignment_mask = 0x7;
+	if (info->address & alignment_mask) {
+		/*
+		 * Try to fix the alignment. This may result in a length
+		 * that is too large, so we must check for that.
+		 */
+		bytelen = get_hbp_len(info->ctrl.len);
+		max_len = info->ctrl.type == ARM_BREAKPOINT_EXECUTE ? 4 :
+				max_watchpoint_len;
+
+		if (max_len >= 8)
+			offset = info->address & 0x7;
+		else
+			offset = info->address & 0x3;
+
+		if (bytelen > (1 << ((max_len - (offset + 1)) >> 1))) {
+			ret = -EFBIG;
+			goto out;
+		}
+
+		info->ctrl.len <<= offset;
+		info->address &= ~offset;
+
+		pr_debug("breakpoint alignment fixup: length = 0x%x, "
+			"address = 0x%x\n", info->ctrl.len, info->address);
+	}
+
+	/*
+	 * Currently we rely on an overflow handler to take
+	 * care of single-stepping the breakpoint when it fires.
+	 */
+	if (WARN_ONCE(!bp->overflow_handler,
+			"overflow handler required but none found")) {
+		ret = -EINVAL;
+		goto out;
+	}
+
+out:
+	return ret;
+}
+
+static void watchpoint_handler(unsigned long unpredictable,
+				struct pt_regs *regs)
+{
+	int i;
+	struct perf_event **slots = __get_cpu_var(wp_on_reg);
+	struct arch_hw_breakpoint *info;
+
+	for (i = 0; i < core_num_wrps; ++i) {
+		rcu_read_lock();
+
+		if (slots[i] == NULL) {
+			rcu_read_unlock();
+			break;
+		}
+
+		/* TODO: Check if this watchpoint actually fired. */
+
+		/*
+		 * The DFAR is unpredictable. Since we only allow a
+		 * single watchpoint, we can set the trigger to the lowest
+		 * possible faulting address.
+		 */
+		info = counter_arch_bp(slots[i]);
+		info->trigger = slots[i]->attr.bp_addr;
+		pr_debug("watchpoint fired: address = 0x%x\n", info->trigger);
+		perf_bp_event(slots[i], regs);
+
+		rcu_read_unlock();
+	}
+}
+
+static void breakpoint_handler(unsigned long unpredictable,
+				struct pt_regs *regs)
+{
+	int i;
+	u32 ctrl_reg, val, addr;
+	struct perf_event **slots = __get_cpu_var(bp_on_reg);
+	struct arch_hw_breakpoint *info;
+	struct arch_hw_breakpoint_ctrl ctrl;
+
+	/* The exception entry code places the amended lr in the PC. */
+	addr = regs->ARM_pc;
+
+	for (i = 0; i < core_num_brps; ++i) {
+		rcu_read_lock();
+
+		if (slots[i] == NULL) {
+			rcu_read_unlock();
+			break;
+		}
+
+		/* Check if the breakpoint value matches. */
+		val = read_wb_reg(ARM_BASE_BVR + i);
+		if (val != (addr & ~0x3)) {
+			rcu_read_unlock();
+			continue;
+		}
+
+		/* Possible match, check the byte address select to confirm. */
+		ctrl_reg = read_wb_reg(ARM_BASE_BCR + i);
+		decode_ctrl_reg(ctrl_reg, &ctrl);
+
+		if ((1 << (addr & 0x3)) & ctrl.len) {
+			info = counter_arch_bp(slots[i]);
+			info->trigger = addr;
+			pr_debug("breakpoint fired: address = 0x%x\n", addr);
+			perf_bp_event(slots[i], regs);
+		}
+
+		rcu_read_unlock();
+	}
+}
+
+/*
+ * Called from either the Data Abort Handler [watchpoint] or the
+ * Prefetch Abort Handler [breakpoint].
+ */
+static int hw_breakpoint_pending(unsigned long addr, unsigned int fsr,
+					struct pt_regs *regs)
+{
+	int ret = 1; /* Unhandled fault. */
+	u32 dscr;
+
+	/* We only handle watchpoints and hardware breakpoints. */
+	ARM_DBG_READ(c1, 0, dscr);
+
+	/* Perform perf callbacks. */
+	switch (ARM_DSCR_MOE(dscr)) {
+	case ARM_ENTRY_BREAKPOINT:
+		breakpoint_handler(addr, regs);
+		break;
+	case ARM_ENTRY_ASYNC_WATCHPOINT:
+	case ARM_ENTRY_SYNC_WATCHPOINT:
+		watchpoint_handler(addr, regs);
+		break;
+	default:
+		goto out;
+	}
+
+	ret = 0;
+out:
+	return ret;
+}
+
+/*
+ * One-time initialisation.
+ */
+static int __init arch_hw_breakpoint_init(void)
+{
+	int ret = 0, i;
+	u32 dscr;
+
+	debug_arch = get_debug_arch();
+
+	if (debug_arch > ARM_DEBUG_ARCH_V7_ECP14) {
+		pr_info("debug architecture 0x%x unsupported.\n", debug_arch);
+		ret = -ENODEV;
+		goto out;
+	}
+
+	/* Determine how many BRPs/WRPs are available. */
+	core_num_brps = get_num_brps();
+	core_num_wrps = get_num_wrps();
+
+	pr_info("found %d breakpoint and %d watchpoint registers.\n",
+			core_num_brps, core_num_wrps);
+
+	ARM_DBG_READ(c1, 0, dscr);
+	if (dscr & ARM_DSCR_HDBGEN) {
+		pr_warning("halting debug mode enabled. Assuming maximum "
+				"watchpoint size of 4 bytes.");
+	} else {
+		/* Work out the maximum supported watchpoint length. */
+		max_watchpoint_len = get_max_wp_len();
+		pr_info("maximum watchpoint size is %u bytes.\n",
+				max_watchpoint_len);
+
+		/*
+		 * Reset the breakpoint resources. We assume that a halting
+		 * debugger will leave the world in a nice state for us.
+		 */
+		for (i = 0; i < core_num_brps; ++i) {
+			write_wb_reg(ARM_BASE_BCR + i, 0UL);
+			write_wb_reg(ARM_BASE_BVR + i, 0UL);
+		}
+
+		for (i = 0; i < core_num_wrps; ++i) {
+			write_wb_reg(ARM_BASE_WCR + i, 0UL);
+			write_wb_reg(ARM_BASE_WVR + i, 0UL);
+		}
+	}
+
+	/* Register thread flush notifier. */
+	thread_register_notifier(&hw_breakpoint_thread_notifier_block);
+
+	/* Register debug fault handler. */
+	hook_fault_code(2, hw_breakpoint_pending, SIGTRAP, "debug exception");
+	hook_ifault_code(2, hw_breakpoint_pending, SIGTRAP, "debug exception");
+
+out:
+	return ret;
+}
+arch_initcall(arch_hw_breakpoint_init);
+
+void hw_breakpoint_pmu_read(struct perf_event *bp)
+{
+}
+
+/*
+ * Dummy function to register with die_notifier.
+ */
+int hw_breakpoint_exceptions_notify(struct notifier_block *unused,
+					unsigned long val, void *data)
+{
+	return NOTIFY_DONE;
+}
-- 
1.6.3.3

[PATCH 2/4] ARM: hw-breakpoint: add ARM backend for the hw-breakpoint framework

[Will Deacon]

The hw-breakpoint framework in the kernel requires architecture-specific
support in order to install, remove, validate and manage hardware
breakpoints.

This patch adds preliminary support for this framework to the ARM
architecture, but restricts the number of watchpoints to a single resource
to get around the fact that the Data Fault Address Register is unpredictable
when a watchpoint debug exception is taken.

Currently, clients must handle synchronous breakpoint exceptions.
This requires the ability to single-step over the causative instruction to
avoid getting stuck in an infinite loop.

The memory-mapped extended debug interface is unsupported due to its
unreliability in real implementations.

Cc: Russell King - ARM Linux <linux@arm.linux.org.uk>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: S. Karthikeyan <informkarthik@gmail.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
---
 arch/arm/include/asm/hw_breakpoint.h |  117 ++++++
 arch/arm/kernel/hw_breakpoint.c      |  748 ++++++++++++++++++++++++++++++++++
 2 files changed, 865 insertions(+), 0 deletions(-)
 create mode 100644 arch/arm/include/asm/hw_breakpoint.h
 create mode 100644 arch/arm/kernel/hw_breakpoint.c

diff --git a/arch/arm/include/asm/hw_breakpoint.h b/arch/arm/include/asm/hw_breakpoint.h
new file mode 100644
index 0000000..c995219
--- /dev/null
+++ b/arch/arm/include/asm/hw_breakpoint.h
@@ -0,0 +1,117 @@
+#ifndef _ARM_HW_BREAKPOINT_H
+#define _ARM_HW_BREAKPOINT_H
+
+#ifdef __KERNEL__
+struct arch_hw_breakpoint_ctrl {
+		u32 __reserved	: 19,
+		len		: 8,
+		type		: 2,
+		privilege	: 2,
+		enabled		: 1;
+};
+
+struct arch_hw_breakpoint {
+	u32	address;
+	u32	trigger;
+	struct arch_hw_breakpoint_ctrl ctrl;
+};
+
+static inline u32 encode_ctrl_reg(struct arch_hw_breakpoint_ctrl ctrl)
+{
+	return (ctrl.len << 5) | (ctrl.type << 3) |
+		(ctrl.privilege << 1) | ctrl.enabled;
+}
+
+static inline void decode_ctrl_reg(u32 reg,
+				   struct arch_hw_breakpoint_ctrl *ctrl)
+{
+	ctrl->enabled	= reg & 0x1;
+	reg >>= 1;
+	ctrl->privilege	= reg & 0x3;
+	reg >>= 2;
+	ctrl->type	= reg & 0x3;
+	reg >>= 2;
+	ctrl->len	= reg & 0xff;
+}
+
+/* Debug architecture numbers. */
+#define ARM_DEBUG_ARCH_V6	1
+#define ARM_DEBUG_ARCH_V6_1	2
+#define ARM_DEBUG_ARCH_V7_ECP14	3
+#define ARM_DEBUG_ARCH_V7_MM	4
+
+/* Breakpoint */
+#define ARM_BREAKPOINT_EXECUTE	0
+
+/* Watchpoints */
+#define ARM_BREAKPOINT_LOAD	1
+#define ARM_BREAKPOINT_STORE	2
+
+/* Privilege Levels */
+#define ARM_BREAKPOINT_PRIV	1
+#define ARM_BREAKPOINT_USER	2
+
+/* Lengths */
+#define ARM_BREAKPOINT_LEN_1	0x1
+#define ARM_BREAKPOINT_LEN_2	0x3
+#define ARM_BREAKPOINT_LEN_4	0xf
+#define ARM_BREAKPOINT_LEN_8	0xff
+
+/* Limits */
+#define ARM_MAX_BRP		16
+#define ARM_MAX_WRP		16
+#define ARM_MAX_HBP_SLOTS	(ARM_MAX_BRP + ARM_MAX_WRP)
+
+/* DSCR method of entry bits. */
+#define ARM_DSCR_MOE(x)			((x >> 2) & 0xf)
+#define ARM_ENTRY_BREAKPOINT		0x1
+#define ARM_ENTRY_ASYNC_WATCHPOINT	0x2
+#define ARM_ENTRY_SYNC_WATCHPOINT	0xa
+
+/* DSCR monitor/halting bits. */
+#define ARM_DSCR_HDBGEN		(1 << 14)
+#define ARM_DSCR_MDBGEN		(1 << 15)
+
+/* opcode2 numbers for the co-processor instructions. */
+#define ARM_OP2_BVR		4
+#define ARM_OP2_BCR		5
+#define ARM_OP2_WVR		6
+#define ARM_OP2_WCR		7
+
+/* Base register numbers for the debug registers. */
+#define ARM_BASE_BVR		64
+#define ARM_BASE_BCR		80
+#define ARM_BASE_WVR		96
+#define ARM_BASE_WCR		112
+
+/* Accessor macros for the debug registers. */
+#define ARM_DBG_READ(M, OP2, VAL) do {\
+	asm volatile("mrc p14, 0, %0, c0," #M ", " #OP2 : "=r" (VAL));\
+} while (0)
+
+#define ARM_DBG_WRITE(M, OP2, VAL) do {\
+	asm volatile("mcr p14, 0, %0, c0," #M ", " #OP2 : : "r" (VAL));\
+} while (0)
+
+struct notifier_block;
+struct perf_event;
+struct pmu;
+struct task_struct;
+
+extern struct pmu perf_ops_bp;
+extern int arch_bp_generic_fields(struct arch_hw_breakpoint_ctrl ctrl,
+				  int *gen_len, int *gen_type);
+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,
+					   unsigned long val, void *data);
+extern u8 arch_get_debug_arch(void);
+extern u8 arch_get_max_wp_len(void);
+
+int arch_install_hw_breakpoint(struct perf_event *bp);
+void arch_uninstall_hw_breakpoint(struct perf_event *bp);
+void hw_breakpoint_pmu_read(struct perf_event *bp);
+int hw_breakpoint_slots(int type);
+
+#endif	/* __KERNEL__ */
+#endif	/* _ARM_HW_BREAKPOINT_H */
diff --git a/arch/arm/kernel/hw_breakpoint.c b/arch/arm/kernel/hw_breakpoint.c
new file mode 100644
index 0000000..9fe8843
--- /dev/null
+++ b/arch/arm/kernel/hw_breakpoint.c
@@ -0,0 +1,748 @@
+/*
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * 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.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ *
+ * Copyright (C) 2009, 2010 ARM Limited
+ *
+ * Author: Will Deacon <will.deacon@arm.com>
+ */
+
+/*
+ * HW_breakpoint: a unified kernel/user-space hardware breakpoint facility,
+ * using the CPU's debug registers.
+ */
+
+#define pr_fmt(fmt) "hw-breakpoint: " fmt
+
+#include <linux/errno.h>
+#include <linux/perf_event.h>
+#include <linux/hw_breakpoint.h>
+#include <linux/smp.h>
+
+#include <asm/cacheflush.h>
+#include <asm/cputype.h>
+#include <asm/current.h>
+#include <asm/hw_breakpoint.h>
+#include <asm/kdebug.h>
+#include <asm/system.h>
+#include <asm/thread_notify.h>
+#include <asm/traps.h>
+
+/* Breakpoint currently in use for each BRP. */
+static DEFINE_PER_CPU(struct perf_event *, bp_on_reg[ARM_MAX_BRP]);
+
+/* Watchpoint currently in use for each WRP. */
+static DEFINE_PER_CPU(struct perf_event *, wp_on_reg[ARM_MAX_WRP]);
+
+/* Number of BRP/WRP registers on this CPU. */
+static int core_num_brps;
+static int core_num_wrps;
+
+/* Debug architecture version. */
+static u8 debug_arch;
+
+/* Maximum supported watchpoint length. */
+static u8 max_watchpoint_len;
+
+/* Determine number of BRP registers available. */
+static int get_num_brps(void)
+{
+	u32 didr;
+	ARM_DBG_READ(c0, 0, didr);
+	return ((didr >> 24) & 0xf) + 1;
+}
+
+/* Determine number of WRP registers available. */
+static int get_num_wrps(void)
+{
+	/*
+	 * FIXME: When a watchpoint fires, the only way to work out which
+	 * watchpoint it was is by disassembling the faulting instruction
+	 * and working out the address of the memory access.
+	 *
+	 * Furthermore, we can only do this if the watchpoint was precise
+	 * since imprecise watchpoints prevent us from calculating register
+	 * based addresses.
+	 *
+	 * For the time being, we only report 1 watchpoint register so we
+	 * always know which watchpoint fired. In the future we can either
+	 * add a disassembler and address generation emulator, or we can
+	 * insert a check to see if the DFAR is set on watchpoint exception
+	 * entry [the ARM ARM states that the DFAR is UNPREDICTABLE, but
+	 * experience shows that it is set on some implementations].
+	 */
+
+#if 0
+	u32 didr, wrps;
+	ARM_DBG_READ(c0, 0, didr);
+	return ((didr >> 28) & 0xf) + 1;
+#endif
+
+	return 1;
+}
+
+int hw_breakpoint_slots(int type)
+{
+	/*
+	 * We can be called early, so don't rely on
+	 * our static variables being initialised.
+	 */
+	switch (type) {
+	case TYPE_INST:
+		return get_num_brps();
+	case TYPE_DATA:
+		return get_num_wrps();
+	default:
+		pr_warning("unknown slot type: %d\n", type);
+		return 0;
+	}
+}
+
+/* Determine debug architecture. */
+static u8 get_debug_arch(void)
+{
+	u32 didr;
+
+	/* Do we implement the extended CPUID interface? */
+	if (((read_cpuid_id() >> 16) & 0xf) != 0xf) {
+		pr_warning("CPUID feature registers not supported. "
+				"Assuming v6 debug is present.\n");
+		return ARM_DEBUG_ARCH_V6;
+	}
+
+	ARM_DBG_READ(c0, 0, didr);
+	return ((didr >> 16) & 0xf);
+}
+
+u8 arch_get_debug_arch(void)
+{
+	return debug_arch;
+}
+
+#define READ_WB_REG_CASE(OP2, M, VAL)		\
+	case ((OP2 << 4) + M):			\
+		ARM_DBG_READ(c ## M, OP2, VAL); \
+		break
+
+#define WRITE_WB_REG_CASE(OP2, M, VAL)		\
+	case ((OP2 << 4) + M):			\
+		ARM_DBG_WRITE(c ## M, OP2, VAL);\
+		break
+
+#define GEN_READ_WB_REG_CASES(OP2, VAL)		\
+	READ_WB_REG_CASE(OP2, 0, VAL);		\
+	READ_WB_REG_CASE(OP2, 1, VAL);		\
+	READ_WB_REG_CASE(OP2, 2, VAL);		\
+	READ_WB_REG_CASE(OP2, 3, VAL);		\
+	READ_WB_REG_CASE(OP2, 4, VAL);		\
+	READ_WB_REG_CASE(OP2, 5, VAL);		\
+	READ_WB_REG_CASE(OP2, 6, VAL);		\
+	READ_WB_REG_CASE(OP2, 7, VAL);		\
+	READ_WB_REG_CASE(OP2, 8, VAL);		\
+	READ_WB_REG_CASE(OP2, 9, VAL);		\
+	READ_WB_REG_CASE(OP2, 10, VAL);		\
+	READ_WB_REG_CASE(OP2, 11, VAL);		\
+	READ_WB_REG_CASE(OP2, 12, VAL);		\
+	READ_WB_REG_CASE(OP2, 13, VAL);		\
+	READ_WB_REG_CASE(OP2, 14, VAL);		\
+	READ_WB_REG_CASE(OP2, 15, VAL)
+
+#define GEN_WRITE_WB_REG_CASES(OP2, VAL)	\
+	WRITE_WB_REG_CASE(OP2, 0, VAL);		\
+	WRITE_WB_REG_CASE(OP2, 1, VAL);		\
+	WRITE_WB_REG_CASE(OP2, 2, VAL);		\
+	WRITE_WB_REG_CASE(OP2, 3, VAL);		\
+	WRITE_WB_REG_CASE(OP2, 4, VAL);		\
+	WRITE_WB_REG_CASE(OP2, 5, VAL);		\
+	WRITE_WB_REG_CASE(OP2, 6, VAL);		\
+	WRITE_WB_REG_CASE(OP2, 7, VAL);		\
+	WRITE_WB_REG_CASE(OP2, 8, VAL);		\
+	WRITE_WB_REG_CASE(OP2, 9, VAL);		\
+	WRITE_WB_REG_CASE(OP2, 10, VAL);	\
+	WRITE_WB_REG_CASE(OP2, 11, VAL);	\
+	WRITE_WB_REG_CASE(OP2, 12, VAL);	\
+	WRITE_WB_REG_CASE(OP2, 13, VAL);	\
+	WRITE_WB_REG_CASE(OP2, 14, VAL);	\
+	WRITE_WB_REG_CASE(OP2, 15, VAL)
+
+static u32 read_wb_reg(int n)
+{
+	u32 val = 0;
+
+	switch (n) {
+	GEN_READ_WB_REG_CASES(ARM_OP2_BVR, val);
+	GEN_READ_WB_REG_CASES(ARM_OP2_BCR, val);
+	GEN_READ_WB_REG_CASES(ARM_OP2_WVR, val);
+	GEN_READ_WB_REG_CASES(ARM_OP2_WCR, val);
+	default:
+		pr_warning("attempt to read from unknown breakpoint "
+				"register %d\n", n);
+	}
+
+	return val;
+}
+
+static void write_wb_reg(int n, u32 val)
+{
+	switch (n) {
+	GEN_WRITE_WB_REG_CASES(ARM_OP2_BVR, val);
+	GEN_WRITE_WB_REG_CASES(ARM_OP2_BCR, val);
+	GEN_WRITE_WB_REG_CASES(ARM_OP2_WVR, val);
+	GEN_WRITE_WB_REG_CASES(ARM_OP2_WCR, val);
+	default:
+		pr_warning("attempt to write to unknown breakpoint "
+				"register %d\n", n);
+	}
+	isb();
+}
+
+/*
+ * In order to access the breakpoint/watchpoint control registers,
+ * we must be running in debug monitor mode. Unfortunately, we can
+ * be put into halting debug mode@any time by an external debugger
+ * but there is nothing we can do to prevent that.
+ */
+static int enable_monitor_mode(void)
+{
+	u32 dscr;
+	int ret = 0;
+
+	ARM_DBG_READ(c1, 0, dscr);
+
+	/* Ensure that halting mode is disabled. */
+	if (WARN_ONCE(dscr & ARM_DSCR_HDBGEN, "halting debug mode enabled."
+				"Unable to access hardware resources.")) {
+		ret = -EPERM;
+		goto out;
+	}
+
+	/* Write to the corresponding DSCR. */
+	switch (debug_arch) {
+	case ARM_DEBUG_ARCH_V6:
+	case ARM_DEBUG_ARCH_V6_1:
+		ARM_DBG_WRITE(c1, 0, (dscr | ARM_DSCR_MDBGEN));
+		break;
+	case ARM_DEBUG_ARCH_V7_ECP14:
+		ARM_DBG_WRITE(c2, 2, (dscr | ARM_DSCR_MDBGEN));
+		break;
+	default:
+		ret = -ENODEV;
+		goto out;
+	}
+
+	/* Check that the write made it through. */
+	ARM_DBG_READ(c1, 0, dscr);
+	if (WARN_ONCE(!(dscr & ARM_DSCR_MDBGEN),
+				"failed to enable monitor mode.")) {
+		ret = -EPERM;
+	}
+
+out:
+	return ret;
+}
+
+/*
+ * Check if 8-bit byte-address select is available.
+ * This clobbers WRP 0.
+ */
+static u8 get_max_wp_len(void)
+{
+	u32 ctrl_reg;
+	struct arch_hw_breakpoint_ctrl ctrl;
+	u8 size = 4;
+
+	if (debug_arch < ARM_DEBUG_ARCH_V7_ECP14)
+		goto out;
+
+	if (enable_monitor_mode())
+		goto out;
+
+	memset(&ctrl, 0, sizeof(ctrl));
+	ctrl.len = ARM_BREAKPOINT_LEN_8;
+	ctrl_reg = encode_ctrl_reg(ctrl);
+
+	write_wb_reg(ARM_BASE_WVR, 0);
+	write_wb_reg(ARM_BASE_WCR, ctrl_reg);
+	if ((read_wb_reg(ARM_BASE_WCR) & ctrl_reg) == ctrl_reg)
+		size = 8;
+
+out:
+	return size;
+}
+
+u8 arch_get_max_wp_len(void)
+{
+	return max_watchpoint_len;
+}
+
+/*
+ * Install a perf counter breakpoint.
+ */
+int arch_install_hw_breakpoint(struct perf_event *bp)
+{
+	struct arch_hw_breakpoint *info = counter_arch_bp(bp);
+	struct perf_event **slot, **slots;
+	int i, max_slots, ctrl_base, val_base, ret = 0;
+
+	/* Ensure that we are in monitor mode and halting mode is disabled. */
+	ret = enable_monitor_mode();
+	if (ret)
+		goto out;
+
+	if (info->ctrl.type == ARM_BREAKPOINT_EXECUTE) {
+		/* Breakpoint */
+		ctrl_base = ARM_BASE_BCR;
+		val_base = ARM_BASE_BVR;
+		slots = __get_cpu_var(bp_on_reg);
+		max_slots = core_num_brps;
+	} else {
+		/* Watchpoint */
+		ctrl_base = ARM_BASE_WCR;
+		val_base = ARM_BASE_WVR;
+		slots = __get_cpu_var(wp_on_reg);
+		max_slots = core_num_wrps;
+	}
+
+	for (i = 0; i < max_slots; ++i) {
+		slot = &slots[i];
+
+		if (!*slot) {
+			*slot = bp;
+			break;
+		}
+	}
+
+	if (WARN_ONCE(i == max_slots, "Can't find any breakpoint slot")) {
+		ret = -EBUSY;
+		goto out;
+	}
+
+	/* Setup the address register. */
+	write_wb_reg(val_base + i, info->address);
+
+	/* Setup the control register. */
+	write_wb_reg(ctrl_base + i, encode_ctrl_reg(info->ctrl) | 0x1);
+
+out:
+	return ret;
+}
+
+void arch_uninstall_hw_breakpoint(struct perf_event *bp)
+{
+	struct arch_hw_breakpoint *info = counter_arch_bp(bp);
+	struct perf_event **slot, **slots;
+	int i, max_slots, base;
+
+	if (info->ctrl.type == ARM_BREAKPOINT_EXECUTE) {
+		/* Breakpoint */
+		base = ARM_BASE_BCR;
+		slots = __get_cpu_var(bp_on_reg);
+		max_slots = core_num_brps;
+	} else {
+		/* Watchpoint */
+		base = ARM_BASE_WCR;
+		slots = __get_cpu_var(wp_on_reg);
+		max_slots = core_num_wrps;
+	}
+
+	/* Remove the breakpoint. */
+	for (i = 0; i < max_slots; ++i) {
+		slot = &slots[i];
+
+		if (*slot == bp) {
+			*slot = NULL;
+			break;
+		}
+	}
+
+	if (WARN_ONCE(i == max_slots, "Can't find any breakpoint slot"))
+		return;
+
+	/* Reset the control register. */
+	write_wb_reg(base + i, 0);
+}
+
+static int get_hbp_len(u8 hbp_len)
+{
+	unsigned int len_in_bytes = 0;
+
+	switch (hbp_len) {
+	case ARM_BREAKPOINT_LEN_1:
+		len_in_bytes = 1;
+		break;
+	case ARM_BREAKPOINT_LEN_2:
+		len_in_bytes = 2;
+		break;
+	case ARM_BREAKPOINT_LEN_4:
+		len_in_bytes = 4;
+		break;
+	case ARM_BREAKPOINT_LEN_8:
+		len_in_bytes = 8;
+		break;
+	}
+
+	return len_in_bytes;
+}
+
+/*
+ * Check whether bp virtual address is in kernel space.
+ */
+int arch_check_bp_in_kernelspace(struct perf_event *bp)
+{
+	unsigned int len;
+	unsigned long va;
+	struct arch_hw_breakpoint *info = counter_arch_bp(bp);
+
+	va = info->address;
+	len = get_hbp_len(info->ctrl.len);
+
+	return (va >= TASK_SIZE) && ((va + len - 1) >= TASK_SIZE);
+}
+
+/*
+ * Extract generic type and length encodings from an arch_hw_breakpoint_ctrl.
+ * Hopefully this will disappear when ptrace can bypass the conversion
+ * to generic breakpoint descriptions.
+ */
+int arch_bp_generic_fields(struct arch_hw_breakpoint_ctrl ctrl,
+			   int *gen_len, int *gen_type)
+{
+	/* Type */
+	switch (ctrl.type) {
+	case ARM_BREAKPOINT_EXECUTE:
+		*gen_type = HW_BREAKPOINT_X;
+		break;
+	case ARM_BREAKPOINT_LOAD:
+		*gen_type = HW_BREAKPOINT_R;
+		break;
+	case ARM_BREAKPOINT_STORE:
+		*gen_type = HW_BREAKPOINT_W;
+		break;
+	case ARM_BREAKPOINT_LOAD | ARM_BREAKPOINT_STORE:
+		*gen_type = HW_BREAKPOINT_RW;
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	/* Len */
+	switch (ctrl.len) {
+	case ARM_BREAKPOINT_LEN_1:
+		*gen_len = HW_BREAKPOINT_LEN_1;
+		break;
+	case ARM_BREAKPOINT_LEN_2:
+		*gen_len = HW_BREAKPOINT_LEN_2;
+		break;
+	case ARM_BREAKPOINT_LEN_4:
+		*gen_len = HW_BREAKPOINT_LEN_4;
+		break;
+	case ARM_BREAKPOINT_LEN_8:
+		*gen_len = HW_BREAKPOINT_LEN_8;
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+/*
+ * Construct an arch_hw_breakpoint from a perf_event.
+ */
+static int arch_build_bp_info(struct perf_event *bp)
+{
+	struct arch_hw_breakpoint *info = counter_arch_bp(bp);
+
+	/* Type */
+	switch (bp->attr.bp_type) {
+	case HW_BREAKPOINT_X:
+		info->ctrl.type = ARM_BREAKPOINT_EXECUTE;
+		break;
+	case HW_BREAKPOINT_R:
+		info->ctrl.type = ARM_BREAKPOINT_LOAD;
+		break;
+	case HW_BREAKPOINT_W:
+		info->ctrl.type = ARM_BREAKPOINT_STORE;
+		break;
+	case HW_BREAKPOINT_RW:
+		info->ctrl.type = ARM_BREAKPOINT_LOAD | ARM_BREAKPOINT_STORE;
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	/* Len */
+	switch (bp->attr.bp_len) {
+	case HW_BREAKPOINT_LEN_1:
+		info->ctrl.len = ARM_BREAKPOINT_LEN_1;
+		break;
+	case HW_BREAKPOINT_LEN_2:
+		info->ctrl.len = ARM_BREAKPOINT_LEN_2;
+		break;
+	case HW_BREAKPOINT_LEN_4:
+		info->ctrl.len = ARM_BREAKPOINT_LEN_4;
+		break;
+	case HW_BREAKPOINT_LEN_8:
+		info->ctrl.len = ARM_BREAKPOINT_LEN_8;
+		if ((info->ctrl.type != ARM_BREAKPOINT_EXECUTE)
+			&& max_watchpoint_len >= 8)
+			break;
+	default:
+		return -EINVAL;
+	}
+
+	/* Privilege */
+	info->ctrl.privilege = ARM_BREAKPOINT_USER | ARM_BREAKPOINT_PRIV;
+
+	/* Address */
+	info->address = bp->attr.bp_addr;
+
+	/* Enabled? */
+	info->ctrl.enabled = !bp->attr.disabled;
+
+	return 0;
+}
+
+/*
+ * Validate the arch-specific HW Breakpoint register settings.
+ */
+int arch_validate_hwbkpt_settings(struct perf_event *bp)
+{
+	struct arch_hw_breakpoint *info = counter_arch_bp(bp);
+	int ret = 0;
+	u32 bytelen, max_len, offset, alignment_mask = 0x3;
+
+	/* Build the arch_hw_breakpoint. */
+	ret = arch_build_bp_info(bp);
+	if (ret)
+		goto out;
+
+	/* Check address alignment. */
+	if (info->ctrl.len == ARM_BREAKPOINT_LEN_8)
+		alignment_mask = 0x7;
+	if (info->address & alignment_mask) {
+		/*
+		 * Try to fix the alignment. This may result in a length
+		 * that is too large, so we must check for that.
+		 */
+		bytelen = get_hbp_len(info->ctrl.len);
+		max_len = info->ctrl.type == ARM_BREAKPOINT_EXECUTE ? 4 :
+				max_watchpoint_len;
+
+		if (max_len >= 8)
+			offset = info->address & 0x7;
+		else
+			offset = info->address & 0x3;
+
+		if (bytelen > (1 << ((max_len - (offset + 1)) >> 1))) {
+			ret = -EFBIG;
+			goto out;
+		}
+
+		info->ctrl.len <<= offset;
+		info->address &= ~offset;
+
+		pr_debug("breakpoint alignment fixup: length = 0x%x, "
+			"address = 0x%x\n", info->ctrl.len, info->address);
+	}
+
+	/*
+	 * Currently we rely on an overflow handler to take
+	 * care of single-stepping the breakpoint when it fires.
+	 */
+	if (WARN_ONCE(!bp->overflow_handler,
+			"overflow handler required but none found")) {
+		ret = -EINVAL;
+		goto out;
+	}
+
+out:
+	return ret;
+}
+
+static void watchpoint_handler(unsigned long unpredictable,
+				struct pt_regs *regs)
+{
+	int i;
+	struct perf_event **slots = __get_cpu_var(wp_on_reg);
+	struct arch_hw_breakpoint *info;
+
+	for (i = 0; i < core_num_wrps; ++i) {
+		rcu_read_lock();
+
+		if (slots[i] == NULL) {
+			rcu_read_unlock();
+			break;
+		}
+
+		/* TODO: Check if this watchpoint actually fired. */
+
+		/*
+		 * The DFAR is unpredictable. Since we only allow a
+		 * single watchpoint, we can set the trigger to the lowest
+		 * possible faulting address.
+		 */
+		info = counter_arch_bp(slots[i]);
+		info->trigger = slots[i]->attr.bp_addr;
+		pr_debug("watchpoint fired: address = 0x%x\n", info->trigger);
+		perf_bp_event(slots[i], regs);
+
+		rcu_read_unlock();
+	}
+}
+
+static void breakpoint_handler(unsigned long unpredictable,
+				struct pt_regs *regs)
+{
+	int i;
+	u32 ctrl_reg, val, addr;
+	struct perf_event **slots = __get_cpu_var(bp_on_reg);
+	struct arch_hw_breakpoint *info;
+	struct arch_hw_breakpoint_ctrl ctrl;
+
+	/* The exception entry code places the amended lr in the PC. */
+	addr = regs->ARM_pc;
+
+	for (i = 0; i < core_num_brps; ++i) {
+		rcu_read_lock();
+
+		if (slots[i] == NULL) {
+			rcu_read_unlock();
+			break;
+		}
+
+		/* Check if the breakpoint value matches. */
+		val = read_wb_reg(ARM_BASE_BVR + i);
+		if (val != (addr & ~0x3)) {
+			rcu_read_unlock();
+			continue;
+		}
+
+		/* Possible match, check the byte address select to confirm. */
+		ctrl_reg = read_wb_reg(ARM_BASE_BCR + i);
+		decode_ctrl_reg(ctrl_reg, &ctrl);
+
+		if ((1 << (addr & 0x3)) & ctrl.len) {
+			info = counter_arch_bp(slots[i]);
+			info->trigger = addr;
+			pr_debug("breakpoint fired: address = 0x%x\n", addr);
+			perf_bp_event(slots[i], regs);
+		}
+
+		rcu_read_unlock();
+	}
+}
+
+/*
+ * Called from either the Data Abort Handler [watchpoint] or the
+ * Prefetch Abort Handler [breakpoint].
+ */
+static int hw_breakpoint_pending(unsigned long addr, unsigned int fsr,
+					struct pt_regs *regs)
+{
+	int ret = 1; /* Unhandled fault. */
+	u32 dscr;
+
+	/* We only handle watchpoints and hardware breakpoints. */
+	ARM_DBG_READ(c1, 0, dscr);
+
+	/* Perform perf callbacks. */
+	switch (ARM_DSCR_MOE(dscr)) {
+	case ARM_ENTRY_BREAKPOINT:
+		breakpoint_handler(addr, regs);
+		break;
+	case ARM_ENTRY_ASYNC_WATCHPOINT:
+	case ARM_ENTRY_SYNC_WATCHPOINT:
+		watchpoint_handler(addr, regs);
+		break;
+	default:
+		goto out;
+	}
+
+	ret = 0;
+out:
+	return ret;
+}
+
+/*
+ * One-time initialisation.
+ */
+static int __init arch_hw_breakpoint_init(void)
+{
+	int ret = 0, i;
+	u32 dscr;
+
+	debug_arch = get_debug_arch();
+
+	if (debug_arch > ARM_DEBUG_ARCH_V7_ECP14) {
+		pr_info("debug architecture 0x%x unsupported.\n", debug_arch);
+		ret = -ENODEV;
+		goto out;
+	}
+
+	/* Determine how many BRPs/WRPs are available. */
+	core_num_brps = get_num_brps();
+	core_num_wrps = get_num_wrps();
+
+	pr_info("found %d breakpoint and %d watchpoint registers.\n",
+			core_num_brps, core_num_wrps);
+
+	ARM_DBG_READ(c1, 0, dscr);
+	if (dscr & ARM_DSCR_HDBGEN) {
+		pr_warning("halting debug mode enabled. Assuming maximum "
+				"watchpoint size of 4 bytes.");
+	} else {
+		/* Work out the maximum supported watchpoint length. */
+		max_watchpoint_len = get_max_wp_len();
+		pr_info("maximum watchpoint size is %u bytes.\n",
+				max_watchpoint_len);
+
+		/*
+		 * Reset the breakpoint resources. We assume that a halting
+		 * debugger will leave the world in a nice state for us.
+		 */
+		for (i = 0; i < core_num_brps; ++i) {
+			write_wb_reg(ARM_BASE_BCR + i, 0UL);
+			write_wb_reg(ARM_BASE_BVR + i, 0UL);
+		}
+
+		for (i = 0; i < core_num_wrps; ++i) {
+			write_wb_reg(ARM_BASE_WCR + i, 0UL);
+			write_wb_reg(ARM_BASE_WVR + i, 0UL);
+		}
+	}
+
+	/* Register thread flush notifier. */
+	thread_register_notifier(&hw_breakpoint_thread_notifier_block);
+
+	/* Register debug fault handler. */
+	hook_fault_code(2, hw_breakpoint_pending, SIGTRAP, "debug exception");
+	hook_ifault_code(2, hw_breakpoint_pending, SIGTRAP, "debug exception");
+
+out:
+	return ret;
+}
+arch_initcall(arch_hw_breakpoint_init);
+
+void hw_breakpoint_pmu_read(struct perf_event *bp)
+{
+}
+
+/*
+ * Dummy function to register with die_notifier.
+ */
+int hw_breakpoint_exceptions_notify(struct notifier_block *unused,
+					unsigned long val, void *data)
+{
+	return NOTIFY_DONE;
+}
-- 
1.6.3.3

[PATCH 2/4] ARM: hw-breakpoint: add ARM backend for the hw-breakpoint framework

[Will Deacon]

The hw-breakpoint framework in the kernel requires architecture-specific
support in order to install, remove, validate and manage hardware
breakpoints.

This patch adds initial support for this framework to the ARM architecture,
but restricts the number of watchpoints to a single resource to get around
the fact that the Data Fault Address Register is unknown when a watchpoint
debug exception is taken.

On cores with v7 debug, the Kernel can handle breakpoint and watchpoint
exceptions occuring from userspace. Older cores require clients to handle
the exception themselves by registering an appropriate overflow handler
or, in the case of ptrace, handling the raised SIGTRAP.

The memory-mapped extended debug interface is unsupported due to its
unreliability in real implementations.

Cc: Russell King - ARM Linux <linux@arm.linux.org.uk>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: S. Karthikeyan <informkarthik@gmail.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
---
 arch/arm/include/asm/hw_breakpoint.h |  122 +++++
 arch/arm/kernel/hw_breakpoint.c      |  849 ++++++++++++++++++++++++++++++++++
 2 files changed, 971 insertions(+), 0 deletions(-)
 create mode 100644 arch/arm/include/asm/hw_breakpoint.h
 create mode 100644 arch/arm/kernel/hw_breakpoint.c

diff --git a/arch/arm/include/asm/hw_breakpoint.h b/arch/arm/include/asm/hw_breakpoint.h
new file mode 100644
index 0000000..576ec04
--- /dev/null
+++ b/arch/arm/include/asm/hw_breakpoint.h
@@ -0,0 +1,122 @@
+#ifndef _ARM_HW_BREAKPOINT_H
+#define _ARM_HW_BREAKPOINT_H
+
+#ifdef __KERNEL__
+struct arch_hw_breakpoint_ctrl {
+		u32 __reserved	: 9,
+		mismatch	: 1,
+				: 9,
+		len		: 8,
+		type		: 2,
+		privilege	: 2,
+		enabled		: 1;
+};
+
+struct arch_hw_breakpoint {
+	u32	address;
+	u32	trigger;
+	struct perf_event *suspended_wp;
+	struct arch_hw_breakpoint_ctrl ctrl;
+};
+
+static inline u32 encode_ctrl_reg(struct arch_hw_breakpoint_ctrl ctrl)
+{
+	return (ctrl.mismatch << 22) | (ctrl.len << 5) | (ctrl.type << 3) |
+		(ctrl.privilege << 1) | ctrl.enabled;
+}
+
+static inline void decode_ctrl_reg(u32 reg,
+				   struct arch_hw_breakpoint_ctrl *ctrl)
+{
+	ctrl->enabled	= reg & 0x1;
+	reg >>= 1;
+	ctrl->privilege	= reg & 0x3;
+	reg >>= 2;
+	ctrl->type	= reg & 0x3;
+	reg >>= 2;
+	ctrl->len	= reg & 0xff;
+	reg >>= 17;
+	ctrl->mismatch	= reg & 0x1;
+}
+
+/* Debug architecture numbers. */
+#define ARM_DEBUG_ARCH_V6	1
+#define ARM_DEBUG_ARCH_V6_1	2
+#define ARM_DEBUG_ARCH_V7_ECP14	3
+#define ARM_DEBUG_ARCH_V7_MM	4
+
+/* Breakpoint */
+#define ARM_BREAKPOINT_EXECUTE	0
+
+/* Watchpoints */
+#define ARM_BREAKPOINT_LOAD	1
+#define ARM_BREAKPOINT_STORE	2
+
+/* Privilege Levels */
+#define ARM_BREAKPOINT_PRIV	1
+#define ARM_BREAKPOINT_USER	2
+
+/* Lengths */
+#define ARM_BREAKPOINT_LEN_1	0x1
+#define ARM_BREAKPOINT_LEN_2	0x3
+#define ARM_BREAKPOINT_LEN_4	0xf
+#define ARM_BREAKPOINT_LEN_8	0xff
+
+/* Limits */
+#define ARM_MAX_BRP		16
+#define ARM_MAX_WRP		16
+#define ARM_MAX_HBP_SLOTS	(ARM_MAX_BRP + ARM_MAX_WRP)
+
+/* DSCR method of entry bits. */
+#define ARM_DSCR_MOE(x)			((x >> 2) & 0xf)
+#define ARM_ENTRY_BREAKPOINT		0x1
+#define ARM_ENTRY_ASYNC_WATCHPOINT	0x2
+#define ARM_ENTRY_SYNC_WATCHPOINT	0xa
+
+/* DSCR monitor/halting bits. */
+#define ARM_DSCR_HDBGEN		(1 << 14)
+#define ARM_DSCR_MDBGEN		(1 << 15)
+
+/* opcode2 numbers for the co-processor instructions. */
+#define ARM_OP2_BVR		4
+#define ARM_OP2_BCR		5
+#define ARM_OP2_WVR		6
+#define ARM_OP2_WCR		7
+
+/* Base register numbers for the debug registers. */
+#define ARM_BASE_BVR		64
+#define ARM_BASE_BCR		80
+#define ARM_BASE_WVR		96
+#define ARM_BASE_WCR		112
+
+/* Accessor macros for the debug registers. */
+#define ARM_DBG_READ(M, OP2, VAL) do {\
+	asm volatile("mrc p14, 0, %0, c0," #M ", " #OP2 : "=r" (VAL));\
+} while (0)
+
+#define ARM_DBG_WRITE(M, OP2, VAL) do {\
+	asm volatile("mcr p14, 0, %0, c0," #M ", " #OP2 : : "r" (VAL));\
+} while (0)
+
+struct notifier_block;
+struct perf_event;
+struct pmu;
+struct task_struct;
+
+extern struct pmu perf_ops_bp;
+extern int arch_bp_generic_fields(struct arch_hw_breakpoint_ctrl ctrl,
+				  int *gen_len, int *gen_type);
+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,
+					   unsigned long val, void *data);
+extern u8 arch_get_debug_arch(void);
+extern u8 arch_get_max_wp_len(void);
+
+int arch_install_hw_breakpoint(struct perf_event *bp);
+void arch_uninstall_hw_breakpoint(struct perf_event *bp);
+void hw_breakpoint_pmu_read(struct perf_event *bp);
+int hw_breakpoint_slots(int type);
+
+#endif	/* __KERNEL__ */
+#endif	/* _ARM_HW_BREAKPOINT_H */
diff --git a/arch/arm/kernel/hw_breakpoint.c b/arch/arm/kernel/hw_breakpoint.c
new file mode 100644
index 0000000..54593b0
--- /dev/null
+++ b/arch/arm/kernel/hw_breakpoint.c
@@ -0,0 +1,849 @@
+/*
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * 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.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ *
+ * Copyright (C) 2009, 2010 ARM Limited
+ *
+ * Author: Will Deacon <will.deacon@arm.com>
+ */
+
+/*
+ * HW_breakpoint: a unified kernel/user-space hardware breakpoint facility,
+ * using the CPU's debug registers.
+ */
+#define pr_fmt(fmt) "hw-breakpoint: " fmt
+
+#include <linux/errno.h>
+#include <linux/perf_event.h>
+#include <linux/hw_breakpoint.h>
+#include <linux/smp.h>
+
+#include <asm/cacheflush.h>
+#include <asm/cputype.h>
+#include <asm/current.h>
+#include <asm/hw_breakpoint.h>
+#include <asm/kdebug.h>
+#include <asm/system.h>
+#include <asm/traps.h>
+
+/* Breakpoint currently in use for each BRP. */
+static DEFINE_PER_CPU(struct perf_event *, bp_on_reg[ARM_MAX_BRP]);
+
+/* Watchpoint currently in use for each WRP. */
+static DEFINE_PER_CPU(struct perf_event *, wp_on_reg[ARM_MAX_WRP]);
+
+/* Number of BRP/WRP registers on this CPU. */
+static int core_num_brps;
+static int core_num_wrps;
+
+/* Debug architecture version. */
+static u8 debug_arch;
+
+/* Maximum supported watchpoint length. */
+static u8 max_watchpoint_len;
+
+/* Determine number of BRP registers available. */
+static int get_num_brps(void)
+{
+	u32 didr;
+	ARM_DBG_READ(c0, 0, didr);
+	return ((didr >> 24) & 0xf) + 1;
+}
+
+/* Determine number of WRP registers available. */
+static int get_num_wrps(void)
+{
+	/*
+	 * FIXME: When a watchpoint fires, the only way to work out which
+	 * watchpoint it was is by disassembling the faulting instruction
+	 * and working out the address of the memory access.
+	 *
+	 * Furthermore, we can only do this if the watchpoint was precise
+	 * since imprecise watchpoints prevent us from calculating register
+	 * based addresses.
+	 *
+	 * For the time being, we only report 1 watchpoint register so we
+	 * always know which watchpoint fired. In the future we can either
+	 * add a disassembler and address generation emulator, or we can
+	 * insert a check to see if the DFAR is set on watchpoint exception
+	 * entry [the ARM ARM states that the DFAR is UNKNOWN, but
+	 * experience shows that it is set on some implementations].
+	 */
+
+#if 0
+	u32 didr, wrps;
+	ARM_DBG_READ(c0, 0, didr);
+	return ((didr >> 28) & 0xf) + 1;
+#endif
+
+	return 1;
+}
+
+int hw_breakpoint_slots(int type)
+{
+	/*
+	 * We can be called early, so don't rely on
+	 * our static variables being initialised.
+	 */
+	switch (type) {
+	case TYPE_INST:
+		return get_num_brps();
+	case TYPE_DATA:
+		return get_num_wrps();
+	default:
+		pr_warning("unknown slot type: %d\n", type);
+		return 0;
+	}
+}
+
+/* Determine debug architecture. */
+static u8 get_debug_arch(void)
+{
+	u32 didr;
+
+	/* Do we implement the extended CPUID interface? */
+	if (((read_cpuid_id() >> 16) & 0xf) != 0xf) {
+		pr_warning("CPUID feature registers not supported. "
+				"Assuming v6 debug is present.\n");
+		return ARM_DEBUG_ARCH_V6;
+	}
+
+	ARM_DBG_READ(c0, 0, didr);
+	return (didr >> 16) & 0xf;
+}
+
+/* Does this core support mismatch breakpoints? */
+static int core_has_mismatch_bps(void)
+{
+	return debug_arch >= ARM_DEBUG_ARCH_V7_ECP14 && core_num_brps > 1;
+}
+
+u8 arch_get_debug_arch(void)
+{
+	return debug_arch;
+}
+
+#define READ_WB_REG_CASE(OP2, M, VAL)		\
+	case ((OP2 << 4) + M):			\
+		ARM_DBG_READ(c ## M, OP2, VAL); \
+		break
+
+#define WRITE_WB_REG_CASE(OP2, M, VAL)		\
+	case ((OP2 << 4) + M):			\
+		ARM_DBG_WRITE(c ## M, OP2, VAL);\
+		break
+
+#define GEN_READ_WB_REG_CASES(OP2, VAL)		\
+	READ_WB_REG_CASE(OP2, 0, VAL);		\
+	READ_WB_REG_CASE(OP2, 1, VAL);		\
+	READ_WB_REG_CASE(OP2, 2, VAL);		\
+	READ_WB_REG_CASE(OP2, 3, VAL);		\
+	READ_WB_REG_CASE(OP2, 4, VAL);		\
+	READ_WB_REG_CASE(OP2, 5, VAL);		\
+	READ_WB_REG_CASE(OP2, 6, VAL);		\
+	READ_WB_REG_CASE(OP2, 7, VAL);		\
+	READ_WB_REG_CASE(OP2, 8, VAL);		\
+	READ_WB_REG_CASE(OP2, 9, VAL);		\
+	READ_WB_REG_CASE(OP2, 10, VAL);		\
+	READ_WB_REG_CASE(OP2, 11, VAL);		\
+	READ_WB_REG_CASE(OP2, 12, VAL);		\
+	READ_WB_REG_CASE(OP2, 13, VAL);		\
+	READ_WB_REG_CASE(OP2, 14, VAL);		\
+	READ_WB_REG_CASE(OP2, 15, VAL)
+
+#define GEN_WRITE_WB_REG_CASES(OP2, VAL)	\
+	WRITE_WB_REG_CASE(OP2, 0, VAL);		\
+	WRITE_WB_REG_CASE(OP2, 1, VAL);		\
+	WRITE_WB_REG_CASE(OP2, 2, VAL);		\
+	WRITE_WB_REG_CASE(OP2, 3, VAL);		\
+	WRITE_WB_REG_CASE(OP2, 4, VAL);		\
+	WRITE_WB_REG_CASE(OP2, 5, VAL);		\
+	WRITE_WB_REG_CASE(OP2, 6, VAL);		\
+	WRITE_WB_REG_CASE(OP2, 7, VAL);		\
+	WRITE_WB_REG_CASE(OP2, 8, VAL);		\
+	WRITE_WB_REG_CASE(OP2, 9, VAL);		\
+	WRITE_WB_REG_CASE(OP2, 10, VAL);	\
+	WRITE_WB_REG_CASE(OP2, 11, VAL);	\
+	WRITE_WB_REG_CASE(OP2, 12, VAL);	\
+	WRITE_WB_REG_CASE(OP2, 13, VAL);	\
+	WRITE_WB_REG_CASE(OP2, 14, VAL);	\
+	WRITE_WB_REG_CASE(OP2, 15, VAL)
+
+static u32 read_wb_reg(int n)
+{
+	u32 val = 0;
+
+	switch (n) {
+	GEN_READ_WB_REG_CASES(ARM_OP2_BVR, val);
+	GEN_READ_WB_REG_CASES(ARM_OP2_BCR, val);
+	GEN_READ_WB_REG_CASES(ARM_OP2_WVR, val);
+	GEN_READ_WB_REG_CASES(ARM_OP2_WCR, val);
+	default:
+		pr_warning("attempt to read from unknown breakpoint "
+				"register %d\n", n);
+	}
+
+	return val;
+}
+
+static void write_wb_reg(int n, u32 val)
+{
+	switch (n) {
+	GEN_WRITE_WB_REG_CASES(ARM_OP2_BVR, val);
+	GEN_WRITE_WB_REG_CASES(ARM_OP2_BCR, val);
+	GEN_WRITE_WB_REG_CASES(ARM_OP2_WVR, val);
+	GEN_WRITE_WB_REG_CASES(ARM_OP2_WCR, val);
+	default:
+		pr_warning("attempt to write to unknown breakpoint "
+				"register %d\n", n);
+	}
+	isb();
+}
+
+/*
+ * In order to access the breakpoint/watchpoint control registers,
+ * we must be running in debug monitor mode. Unfortunately, we can
+ * be put into halting debug mode@any time by an external debugger
+ * but there is nothing we can do to prevent that.
+ */
+static int enable_monitor_mode(void)
+{
+	u32 dscr;
+	int ret = 0;
+
+	ARM_DBG_READ(c1, 0, dscr);
+
+	/* Ensure that halting mode is disabled. */
+	if (WARN_ONCE(dscr & ARM_DSCR_HDBGEN, "halting debug mode enabled."
+				"Unable to access hardware resources.")) {
+		ret = -EPERM;
+		goto out;
+	}
+
+	/* Write to the corresponding DSCR. */
+	switch (debug_arch) {
+	case ARM_DEBUG_ARCH_V6:
+	case ARM_DEBUG_ARCH_V6_1:
+		ARM_DBG_WRITE(c1, 0, (dscr | ARM_DSCR_MDBGEN));
+		break;
+	case ARM_DEBUG_ARCH_V7_ECP14:
+		ARM_DBG_WRITE(c2, 2, (dscr | ARM_DSCR_MDBGEN));
+		break;
+	default:
+		ret = -ENODEV;
+		goto out;
+	}
+
+	/* Check that the write made it through. */
+	ARM_DBG_READ(c1, 0, dscr);
+	if (WARN_ONCE(!(dscr & ARM_DSCR_MDBGEN),
+				"failed to enable monitor mode.")) {
+		ret = -EPERM;
+	}
+
+out:
+	return ret;
+}
+
+/*
+ * Check if 8-bit byte-address select is available.
+ * This clobbers WRP 0.
+ */
+static u8 get_max_wp_len(void)
+{
+	u32 ctrl_reg;
+	struct arch_hw_breakpoint_ctrl ctrl;
+	u8 size = 4;
+
+	if (debug_arch < ARM_DEBUG_ARCH_V7_ECP14)
+		goto out;
+
+	if (enable_monitor_mode())
+		goto out;
+
+	memset(&ctrl, 0, sizeof(ctrl));
+	ctrl.len = ARM_BREAKPOINT_LEN_8;
+	ctrl_reg = encode_ctrl_reg(ctrl);
+
+	write_wb_reg(ARM_BASE_WVR, 0);
+	write_wb_reg(ARM_BASE_WCR, ctrl_reg);
+	if ((read_wb_reg(ARM_BASE_WCR) & ctrl_reg) == ctrl_reg)
+		size = 8;
+
+out:
+	return size;
+}
+
+u8 arch_get_max_wp_len(void)
+{
+	return max_watchpoint_len;
+}
+
+/*
+ * Handler for reactivating a suspended watchpoint when the single
+ * step `mismatch' breakpoint is triggered.
+ */
+static void wp_single_step_handler(struct perf_event *bp, int unused,
+				   struct perf_sample_data *data,
+				   struct pt_regs *regs)
+{
+	perf_event_enable(counter_arch_bp(bp)->suspended_wp);
+	unregister_hw_breakpoint(bp);
+}
+
+static int bp_is_single_step(struct perf_event *bp)
+{
+	return bp->overflow_handler == wp_single_step_handler;
+}
+
+/*
+ * Install a perf counter breakpoint.
+ */
+int arch_install_hw_breakpoint(struct perf_event *bp)
+{
+	struct arch_hw_breakpoint *info = counter_arch_bp(bp);
+	struct perf_event **slot, **slots;
+	int i, max_slots, ctrl_base, val_base, ret = 0;
+
+	/* Ensure that we are in monitor mode and halting mode is disabled. */
+	ret = enable_monitor_mode();
+	if (ret)
+		goto out;
+
+	if (info->ctrl.type == ARM_BREAKPOINT_EXECUTE) {
+		/* Breakpoint */
+		ctrl_base = ARM_BASE_BCR;
+		val_base = ARM_BASE_BVR;
+		slots = __get_cpu_var(bp_on_reg);
+		max_slots = core_num_brps - 1;
+
+		if (bp_is_single_step(bp)) {
+			info->ctrl.mismatch = 1;
+			i = max_slots;
+			slots[i] = bp;
+			goto setup;
+		}
+	} else {
+		/* Watchpoint */
+		ctrl_base = ARM_BASE_WCR;
+		val_base = ARM_BASE_WVR;
+		slots = __get_cpu_var(wp_on_reg);
+		max_slots = core_num_wrps;
+	}
+
+	for (i = 0; i < max_slots; ++i) {
+		slot = &slots[i];
+
+		if (!*slot) {
+			*slot = bp;
+			break;
+		}
+	}
+
+	if (WARN_ONCE(i == max_slots, "Can't find any breakpoint slot")) {
+		ret = -EBUSY;
+		goto out;
+	}
+
+setup:
+	/* Setup the address register. */
+	write_wb_reg(val_base + i, info->address);
+
+	/* Setup the control register. */
+	write_wb_reg(ctrl_base + i, encode_ctrl_reg(info->ctrl) | 0x1);
+
+out:
+	return ret;
+}
+
+void arch_uninstall_hw_breakpoint(struct perf_event *bp)
+{
+	struct arch_hw_breakpoint *info = counter_arch_bp(bp);
+	struct perf_event **slot, **slots;
+	int i, max_slots, base;
+
+	if (info->ctrl.type == ARM_BREAKPOINT_EXECUTE) {
+		/* Breakpoint */
+		base = ARM_BASE_BCR;
+		slots = __get_cpu_var(bp_on_reg);
+		max_slots = core_num_brps - 1;
+
+		if (bp_is_single_step(bp)) {
+			i = max_slots;
+			slots[i] = NULL;
+			goto reset;
+		}
+	} else {
+		/* Watchpoint */
+		base = ARM_BASE_WCR;
+		slots = __get_cpu_var(wp_on_reg);
+		max_slots = core_num_wrps;
+	}
+
+	/* Remove the breakpoint. */
+	for (i = 0; i < max_slots; ++i) {
+		slot = &slots[i];
+
+		if (*slot == bp) {
+			*slot = NULL;
+			break;
+		}
+	}
+
+	if (WARN_ONCE(i == max_slots, "Can't find any breakpoint slot"))
+		return;
+
+reset:
+	/* Reset the control register. */
+	write_wb_reg(base + i, 0);
+}
+
+static int get_hbp_len(u8 hbp_len)
+{
+	unsigned int len_in_bytes = 0;
+
+	switch (hbp_len) {
+	case ARM_BREAKPOINT_LEN_1:
+		len_in_bytes = 1;
+		break;
+	case ARM_BREAKPOINT_LEN_2:
+		len_in_bytes = 2;
+		break;
+	case ARM_BREAKPOINT_LEN_4:
+		len_in_bytes = 4;
+		break;
+	case ARM_BREAKPOINT_LEN_8:
+		len_in_bytes = 8;
+		break;
+	}
+
+	return len_in_bytes;
+}
+
+/*
+ * Check whether bp virtual address is in kernel space.
+ */
+int arch_check_bp_in_kernelspace(struct perf_event *bp)
+{
+	unsigned int len;
+	unsigned long va;
+	struct arch_hw_breakpoint *info = counter_arch_bp(bp);
+
+	va = info->address;
+	len = get_hbp_len(info->ctrl.len);
+
+	return (va >= TASK_SIZE) && ((va + len - 1) >= TASK_SIZE);
+}
+
+/*
+ * Extract generic type and length encodings from an arch_hw_breakpoint_ctrl.
+ * Hopefully this will disappear when ptrace can bypass the conversion
+ * to generic breakpoint descriptions.
+ */
+int arch_bp_generic_fields(struct arch_hw_breakpoint_ctrl ctrl,
+			   int *gen_len, int *gen_type)
+{
+	/* Type */
+	switch (ctrl.type) {
+	case ARM_BREAKPOINT_EXECUTE:
+		*gen_type = HW_BREAKPOINT_X;
+		break;
+	case ARM_BREAKPOINT_LOAD:
+		*gen_type = HW_BREAKPOINT_R;
+		break;
+	case ARM_BREAKPOINT_STORE:
+		*gen_type = HW_BREAKPOINT_W;
+		break;
+	case ARM_BREAKPOINT_LOAD | ARM_BREAKPOINT_STORE:
+		*gen_type = HW_BREAKPOINT_RW;
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	/* Len */
+	switch (ctrl.len) {
+	case ARM_BREAKPOINT_LEN_1:
+		*gen_len = HW_BREAKPOINT_LEN_1;
+		break;
+	case ARM_BREAKPOINT_LEN_2:
+		*gen_len = HW_BREAKPOINT_LEN_2;
+		break;
+	case ARM_BREAKPOINT_LEN_4:
+		*gen_len = HW_BREAKPOINT_LEN_4;
+		break;
+	case ARM_BREAKPOINT_LEN_8:
+		*gen_len = HW_BREAKPOINT_LEN_8;
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+/*
+ * Construct an arch_hw_breakpoint from a perf_event.
+ */
+static int arch_build_bp_info(struct perf_event *bp)
+{
+	struct arch_hw_breakpoint *info = counter_arch_bp(bp);
+
+	/* Type */
+	switch (bp->attr.bp_type) {
+	case HW_BREAKPOINT_X:
+		info->ctrl.type = ARM_BREAKPOINT_EXECUTE;
+		break;
+	case HW_BREAKPOINT_R:
+		info->ctrl.type = ARM_BREAKPOINT_LOAD;
+		break;
+	case HW_BREAKPOINT_W:
+		info->ctrl.type = ARM_BREAKPOINT_STORE;
+		break;
+	case HW_BREAKPOINT_RW:
+		info->ctrl.type = ARM_BREAKPOINT_LOAD | ARM_BREAKPOINT_STORE;
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	/* Len */
+	switch (bp->attr.bp_len) {
+	case HW_BREAKPOINT_LEN_1:
+		info->ctrl.len = ARM_BREAKPOINT_LEN_1;
+		break;
+	case HW_BREAKPOINT_LEN_2:
+		info->ctrl.len = ARM_BREAKPOINT_LEN_2;
+		break;
+	case HW_BREAKPOINT_LEN_4:
+		info->ctrl.len = ARM_BREAKPOINT_LEN_4;
+		break;
+	case HW_BREAKPOINT_LEN_8:
+		info->ctrl.len = ARM_BREAKPOINT_LEN_8;
+		if ((info->ctrl.type != ARM_BREAKPOINT_EXECUTE)
+			&& max_watchpoint_len >= 8)
+			break;
+	default:
+		return -EINVAL;
+	}
+
+	/* Address */
+	info->address = bp->attr.bp_addr;
+
+	/* Privilege */
+	info->ctrl.privilege = ARM_BREAKPOINT_USER;
+	if (arch_check_bp_in_kernelspace(bp) && !bp_is_single_step(bp))
+		info->ctrl.privilege |= ARM_BREAKPOINT_PRIV;
+
+	/* Enabled? */
+	info->ctrl.enabled = !bp->attr.disabled;
+
+	/* Mismatch */
+	info->ctrl.mismatch = 0;
+
+	return 0;
+}
+
+/*
+ * Validate the arch-specific HW Breakpoint register settings.
+ */
+int arch_validate_hwbkpt_settings(struct perf_event *bp)
+{
+	struct arch_hw_breakpoint *info = counter_arch_bp(bp);
+	int ret = 0;
+	u32 bytelen, max_len, offset, alignment_mask = 0x3;
+
+	/* Build the arch_hw_breakpoint. */
+	ret = arch_build_bp_info(bp);
+	if (ret)
+		goto out;
+
+	/* Check address alignment. */
+	if (info->ctrl.len == ARM_BREAKPOINT_LEN_8)
+		alignment_mask = 0x7;
+	if (info->address & alignment_mask) {
+		/*
+		 * Try to fix the alignment. This may result in a length
+		 * that is too large, so we must check for that.
+		 */
+		bytelen = get_hbp_len(info->ctrl.len);
+		max_len = info->ctrl.type == ARM_BREAKPOINT_EXECUTE ? 4 :
+				max_watchpoint_len;
+
+		if (max_len >= 8)
+			offset = info->address & 0x7;
+		else
+			offset = info->address & 0x3;
+
+		if (bytelen > (1 << ((max_len - (offset + 1)) >> 1))) {
+			ret = -EFBIG;
+			goto out;
+		}
+
+		info->ctrl.len <<= offset;
+		info->address &= ~offset;
+
+		pr_debug("breakpoint alignment fixup: length = 0x%x, "
+			"address = 0x%x\n", info->ctrl.len, info->address);
+	}
+
+	/*
+	 * Currently we rely on an overflow handler to take
+	 * care of single-stepping the breakpoint when it fires.
+	 * In the case of userspace breakpoints on a core with V7 debug,
+	 * we can use the mismatch feature as a poor-man's hardware single-step.
+	 */
+	if (WARN_ONCE(!bp->overflow_handler &&
+		(arch_check_bp_in_kernelspace(bp) || !core_has_mismatch_bps()),
+			"overflow handler required but none found")) {
+		ret = -EINVAL;
+		goto out;
+	}
+out:
+	return ret;
+}
+
+static void update_mismatch_flag(int idx, int flag)
+{
+	struct perf_event *bp = __get_cpu_var(bp_on_reg[idx]);
+	struct arch_hw_breakpoint *info;
+
+	if (bp == NULL)
+		return;
+
+	info = counter_arch_bp(bp);
+
+	/* Update the mismatch field to enter/exit `single-step' mode */
+	if (!bp->overflow_handler && info->ctrl.mismatch != flag) {
+		info->ctrl.mismatch = flag;
+		write_wb_reg(ARM_BASE_BCR + idx, encode_ctrl_reg(info->ctrl) | 0x1);
+	}
+}
+
+static void watchpoint_handler(unsigned long unknown, struct pt_regs *regs)
+{
+	int i;
+	struct perf_event *bp, **slots = __get_cpu_var(wp_on_reg);
+	struct arch_hw_breakpoint *info;
+	struct perf_event_attr attr;
+
+	/* Without a disassembler, we can only handle 1 watchpoint. */
+	BUG_ON(core_num_wrps > 1);
+
+	hw_breakpoint_init(&attr);
+	attr.bp_addr	= regs->ARM_pc & ~0x3;
+	attr.bp_len	= HW_BREAKPOINT_LEN_4;
+	attr.bp_type	= HW_BREAKPOINT_X;
+
+	for (i = 0; i < core_num_wrps; ++i) {
+		rcu_read_lock();
+
+		if (slots[i] == NULL) {
+			rcu_read_unlock();
+			continue;
+		}
+
+		/*
+		 * The DFAR is an unknown value. Since we only allow a
+		 * single watchpoint, we can set the trigger to the lowest
+		 * possible faulting address.
+		 */
+		info = counter_arch_bp(slots[i]);
+		info->trigger = slots[i]->attr.bp_addr;
+		pr_debug("watchpoint fired: address = 0x%x\n", info->trigger);
+		perf_bp_event(slots[i], regs);
+
+		/*
+		 * If no overflow handler is present, insert a temporary
+		 * mismatch breakpoint so we can single-step over the
+		 * watchpoint trigger.
+		 */
+		if (!slots[i]->overflow_handler) {
+			bp = register_user_hw_breakpoint(&attr,
+							 wp_single_step_handler,
+							 current);
+			counter_arch_bp(bp)->suspended_wp = slots[i];
+			perf_event_disable(slots[i]);
+		}
+
+		rcu_read_unlock();
+	}
+}
+
+static void breakpoint_handler(unsigned long unknown, struct pt_regs *regs)
+{
+	int i;
+	int mismatch;
+	u32 ctrl_reg, val, addr;
+	struct perf_event *bp, **slots = __get_cpu_var(bp_on_reg);
+	struct arch_hw_breakpoint *info;
+	struct arch_hw_breakpoint_ctrl ctrl;
+
+	/* The exception entry code places the amended lr in the PC. */
+	addr = regs->ARM_pc;
+
+	for (i = 0; i < core_num_brps; ++i) {
+		rcu_read_lock();
+
+		bp = slots[i];
+
+		if (bp == NULL) {
+			rcu_read_unlock();
+			continue;
+		}
+
+		mismatch = 0;
+
+		/* Check if the breakpoint value matches. */
+		val = read_wb_reg(ARM_BASE_BVR + i);
+		if (val != (addr & ~0x3))
+			goto unlock;
+
+		/* Possible match, check the byte address select to confirm. */
+		ctrl_reg = read_wb_reg(ARM_BASE_BCR + i);
+		decode_ctrl_reg(ctrl_reg, &ctrl);
+		if ((1 << (addr & 0x3)) & ctrl.len) {
+			mismatch = 1;
+			info = counter_arch_bp(bp);
+			info->trigger = addr;
+		}
+
+unlock:
+		if ((mismatch && !info->ctrl.mismatch) || bp_is_single_step(bp)) {
+			pr_debug("breakpoint fired: address = 0x%x\n", addr);
+			perf_bp_event(bp, regs);
+		}
+
+		update_mismatch_flag(i, mismatch);
+		rcu_read_unlock();
+	}
+}
+
+/*
+ * Called from either the Data Abort Handler [watchpoint] or the
+ * Prefetch Abort Handler [breakpoint].
+ */
+static int hw_breakpoint_pending(unsigned long addr, unsigned int fsr,
+				 struct pt_regs *regs)
+{
+	int ret = 1; /* Unhandled fault. */
+	u32 dscr;
+
+	/* We only handle watchpoints and hardware breakpoints. */
+	ARM_DBG_READ(c1, 0, dscr);
+
+	/* Perform perf callbacks. */
+	switch (ARM_DSCR_MOE(dscr)) {
+	case ARM_ENTRY_BREAKPOINT:
+		breakpoint_handler(addr, regs);
+		break;
+	case ARM_ENTRY_ASYNC_WATCHPOINT:
+		WARN_ON("Asynchronous watchpoint exception taken. "
+			"Debugging results may be unreliable");
+	case ARM_ENTRY_SYNC_WATCHPOINT:
+		watchpoint_handler(addr, regs);
+		break;
+	default:
+		goto out;
+	}
+
+	ret = 0;
+out:
+	return ret;
+}
+
+/*
+ * One-time initialisation.
+ */
+static void __init reset_ctrl_regs(void *unused)
+{
+	int i;
+
+	if (enable_monitor_mode())
+		return;
+
+	for (i = 0; i < core_num_brps; ++i) {
+		write_wb_reg(ARM_BASE_BCR + i, 0UL);
+		write_wb_reg(ARM_BASE_BVR + i, 0UL);
+	}
+
+	for (i = 0; i < core_num_wrps; ++i) {
+		write_wb_reg(ARM_BASE_WCR + i, 0UL);
+		write_wb_reg(ARM_BASE_WVR + i, 0UL);
+	}
+}
+
+static int __init arch_hw_breakpoint_init(void)
+{
+	int ret = 0;
+	u32 dscr;
+
+	debug_arch = get_debug_arch();
+
+	if (debug_arch > ARM_DEBUG_ARCH_V7_ECP14) {
+		pr_info("debug architecture 0x%x unsupported.\n", debug_arch);
+		ret = -ENODEV;
+		goto out;
+	}
+
+	/* Determine how many BRPs/WRPs are available. */
+	core_num_brps = get_num_brps();
+	core_num_wrps = get_num_wrps();
+
+	pr_info("found %d breakpoint and %d watchpoint registers.\n",
+			core_num_brps, core_num_wrps);
+
+	if (core_has_mismatch_bps())
+		pr_info("1 breakpoint reserved for watchpoint single-step.\n");
+
+	ARM_DBG_READ(c1, 0, dscr);
+	if (dscr & ARM_DSCR_HDBGEN) {
+		pr_warning("halting debug mode enabled. Assuming maximum "
+				"watchpoint size of 4 bytes.");
+	} else {
+		/* Work out the maximum supported watchpoint length. */
+		max_watchpoint_len = get_max_wp_len();
+		pr_info("maximum watchpoint size is %u bytes.\n",
+				max_watchpoint_len);
+
+		/*
+		 * Reset the breakpoint resources. We assume that a halting
+		 * debugger will leave the world in a nice state for us.
+		 */
+		smp_call_function(reset_ctrl_regs, NULL, 1);
+		reset_ctrl_regs(NULL);
+	}
+
+	/* Register debug fault handler. */
+	hook_fault_code(2, hw_breakpoint_pending, SIGTRAP, TRAP_HWBKPT,
+			"watchpoint debug exception");
+	hook_ifault_code(2, hw_breakpoint_pending, SIGTRAP, TRAP_HWBKPT,
+			"breakpoint debug exception");
+
+out:
+	return ret;
+}
+arch_initcall(arch_hw_breakpoint_init);
+
+void hw_breakpoint_pmu_read(struct perf_event *bp)
+{
+}
+
+/*
+ * Dummy function to register with die_notifier.
+ */
+int hw_breakpoint_exceptions_notify(struct notifier_block *unused,
+					unsigned long val, void *data)
+{
+	return NOTIFY_DONE;
+}
-- 
1.6.3.3