[Patch 5/6] Scheduler support for HARDWARE_WATCHPOINTS.

[Patch 5/6] Scheduler support for HARDWARE_WATCHPOINTS.

[David Daney]

This is the meat of the patch.  Here we install the watch register values when we
schedule a new thread.

The implemtation of __restore_watch() is in asm/watch.h.  In the case where there
are no watch registers to install (the normal case) the overhead is 5 machine
instructions with gcc-3.4.3.

Signed-off-by: David Daney <ddaney@avtrex.com>
---
 include/asm-mips/system.h |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/include/asm-mips/system.h b/include/asm-mips/system.h
index a944eda..cd30f83 100644
--- a/include/asm-mips/system.h
+++ b/include/asm-mips/system.h
@@ -20,6 +20,7 @@
 #include <asm/cmpxchg.h>
 #include <asm/cpu-features.h>
 #include <asm/dsp.h>
+#include <asm/watch.h>
 #include <asm/war.h>
 
 
@@ -76,6 +77,7 @@ do {									\
 		__restore_dsp(current);					\
 	if (cpu_has_userlocal)						\
 		write_c0_userlocal(current_thread_info()->tp_value);	\
+	__restore_watch();						\
 } while (0)
 
 static inline unsigned long __xchg_u32(volatile int * m, unsigned int val)
-- 
1.5.5

[Patch 0/6] MIPS Hardware watchpoint support for gdb (version 2).

[David Daney]

This is my second take at MIPS watch register support.

Changes from the previous version include:

* Change layout of structures used by ptrace to eliminate holes.

* Use [set|clear]_tsk_thread_flag() and friends instead of racy direct 
access.

* mips64 support (untested).

* Fix sparse warnings.

For this version of the patch you will need the corresponding gdb patch 
which can be found here:

http://sourceware.org/ml/gdb-patches/2008-04/msg00642.html

David Daney

[PATCH 1/6] Add HARDWARE_WATCHPOINTS configure option.

[David Daney]

Add HARDWARE_WATCHPOINTS configure option.

This is automatically set for all MIPS32 and MIPS64 processors.

Signed-off-by: David Daney <ddaney@avtrex.com>
---
 arch/mips/Kconfig |    7 +++++++
 1 files changed, 7 insertions(+), 0 deletions(-)

diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
index 8724ed3..a52d3a8 100644
--- a/arch/mips/Kconfig
+++ b/arch/mips/Kconfig
@@ -1344,6 +1344,13 @@ config CPU_SUPPORTS_32BIT_KERNEL
 config CPU_SUPPORTS_64BIT_KERNEL
 	bool
 
+#
+# Set to y for ptrace access to watch registers.
+#
+config HARDWARE_WATCHPOINTS
+       bool
+       default y if CPU_MIPS32 || CPU_MIPS64
+
 menu "Kernel type"
 
 choice
-- 
1.5.5

[PATCH 2/6] Add HARDWARE_WATCHPOINTS definitions and support code.

[David Daney]

Add HARDWARE_WATCHPOINTS definitions and support code.

Signed-off-by: David Daney <ddaney@avtrex.com>
---
 arch/mips/kernel/Makefile      |    1 +
 arch/mips/kernel/watch.c       |  158 ++++++++++++++++++++++++++++++++++++++++
 include/asm-mips/cpu-info.h    |    5 +
 include/asm-mips/processor.h   |   32 ++++++++
 include/asm-mips/thread_info.h |    2 +
 include/asm-mips/watch.h       |   32 ++++++++
 6 files changed, 230 insertions(+), 0 deletions(-)
 create mode 100644 arch/mips/kernel/watch.c
 create mode 100644 include/asm-mips/watch.h

diff --git a/arch/mips/kernel/Makefile b/arch/mips/kernel/Makefile
index ed3d160..fdd59cd 100644
--- a/arch/mips/kernel/Makefile
+++ b/arch/mips/kernel/Makefile
@@ -72,6 +72,7 @@ obj-$(CONFIG_MIPS32_O32)	+= binfmt_elfo32.o scall64-o32.o
 
 obj-$(CONFIG_KGDB)		+= gdb-low.o gdb-stub.o
 obj-$(CONFIG_PROC_FS)		+= proc.o
+obj-$(CONFIG_HARDWARE_WATCHPOINTS) += watch.o
 
 obj-$(CONFIG_64BIT)		+= cpu-bugs64.o
 
diff --git a/arch/mips/kernel/watch.c b/arch/mips/kernel/watch.c
new file mode 100644
index 0000000..9eb7c4f
--- /dev/null
+++ b/arch/mips/kernel/watch.c
@@ -0,0 +1,158 @@
+/*
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License.  See the file "COPYING" in the main directory of this archive
+ * for more details.
+ *
+ * Copyright (C) 2008 David Daney
+ */
+
+#include <linux/sched.h>
+
+#include <asm/watch.h>
+
+void mips_install_watch_registers(void)
+{
+	struct mips3264_watch_reg_state *watches =
+		&current->thread.watch.mips3264;
+	switch (current_cpu_data.watch_reg_count) {
+	default:
+		BUG();
+	case 8:
+		write_c0_watchlo7(watches->watchlo[7]);
+		/* Write 1 to the I, R, and W bits to clear them. */
+		write_c0_watchhi7(watches->watchhi[7] | 7);
+	case 7:
+		write_c0_watchlo6(watches->watchlo[6]);
+		write_c0_watchhi6(watches->watchhi[6] | 7);
+	case 6:
+		write_c0_watchlo5(watches->watchlo[5]);
+		write_c0_watchhi5(watches->watchhi[5] | 7);
+	case 5:
+		write_c0_watchlo4(watches->watchlo[4]);
+		write_c0_watchhi4(watches->watchhi[4] | 7);
+	case 4:
+		write_c0_watchlo3(watches->watchlo[3]);
+		write_c0_watchhi3(watches->watchhi[3] | 7);
+	case 3:
+		write_c0_watchlo2(watches->watchlo[2]);
+		write_c0_watchhi2(watches->watchhi[2] | 7);
+	case 2:
+		write_c0_watchlo1(watches->watchlo[1]);
+		write_c0_watchhi1(watches->watchhi[1] | 7);
+	case 1:
+		write_c0_watchlo0(watches->watchlo[0]);
+		write_c0_watchhi0(watches->watchhi[0] | 7);
+	}
+}
+
+/*
+ * Read back the watchhi registers so the user space debugger has
+ * access to the I, R, and W bits.
+ */
+void mips_read_watch_registers(void)
+{
+	struct mips3264_watch_reg_state *watches =
+		&current->thread.watch.mips3264;
+	switch (current_cpu_data.watch_reg_count) {
+	default:
+		BUG();
+	case 8:
+		watches->watchhi[7] = read_c0_watchhi7();
+	case 7:
+		watches->watchhi[6] = read_c0_watchhi6();
+	case 6:
+		watches->watchhi[5] = read_c0_watchhi5();
+	case 5:
+		watches->watchhi[4] = read_c0_watchhi4();
+	case 4:
+		watches->watchhi[3] = read_c0_watchhi3();
+	case 3:
+		watches->watchhi[2] = read_c0_watchhi2();
+	case 2:
+		watches->watchhi[1] = read_c0_watchhi1();
+	case 1:
+		watches->watchhi[0] = read_c0_watchhi0();
+	}
+}
+
+void mips_clear_watch_registers(void)
+{
+	switch (current_cpu_data.watch_reg_count) {
+	default:
+		BUG();
+	case 8:
+		write_c0_watchlo7(0);
+	case 7:
+		write_c0_watchlo6(0);
+	case 6:
+		write_c0_watchlo5(0);
+	case 5:
+		write_c0_watchlo4(0);
+	case 4:
+		write_c0_watchlo3(0);
+	case 3:
+		write_c0_watchlo2(0);
+	case 2:
+		write_c0_watchlo1(0);
+	case 1:
+		write_c0_watchlo0(0);
+	}
+}
+
+__init void mips_probe_watch_registers(struct cpuinfo_mips *c)
+{
+	unsigned int t;
+
+	if ((c->options & MIPS_CPU_WATCH) == 0)
+		return;
+	/*
+	 * Check which of the I,R and W bits are supported, then
+	 * disable the register.
+	 */
+	write_c0_watchlo0(7);
+	t = read_c0_watchlo0();
+	write_c0_watchlo0(0);
+	c->watch_reg_irw = t & 7;
+
+	/* Write the mask bits and read them back to determine which
+	 * can be used. */
+	c->watch_reg_count = 1;
+	t = read_c0_watchhi0();
+	write_c0_watchhi0(t | 0xff8);
+	t = read_c0_watchhi0();
+	c->watch_reg_mask = t & 0xff8;
+	if ((t & 0x80000000) == 0)
+		return;
+
+	c->watch_reg_count = 2;
+	t = read_c0_watchhi1();
+	if ((t & 0x80000000) == 0)
+		return;
+
+	c->watch_reg_count = 3;
+	t = read_c0_watchhi2();
+	if ((t & 0x80000000) == 0)
+		return;
+
+	c->watch_reg_count = 4;
+	t = read_c0_watchhi3();
+	if ((t & 0x80000000) == 0)
+		return;
+
+	c->watch_reg_count = 5;
+	t = read_c0_watchhi4();
+	if ((t & 0x80000000) == 0)
+		return;
+
+	c->watch_reg_count = 6;
+	t = read_c0_watchhi5();
+	if ((t & 0x80000000) == 0)
+		return;
+
+	c->watch_reg_count = 7;
+	t = read_c0_watchhi6();
+	if ((t & 0x80000000) == 0)
+		return;
+
+	c->watch_reg_count = 8;
+}
diff --git a/include/asm-mips/cpu-info.h b/include/asm-mips/cpu-info.h
index 0c5a358..7d3a093 100644
--- a/include/asm-mips/cpu-info.h
+++ b/include/asm-mips/cpu-info.h
@@ -49,6 +49,11 @@ struct cpuinfo_mips {
 	unsigned int		fpu_id;
 	unsigned int		cputype;
 	int			isa_level;
+#if defined(CONFIG_HARDWARE_WATCHPOINTS)
+	unsigned int		watch_reg_count;
+	unsigned int		watch_reg_mask;
+	unsigned int		watch_reg_irw;
+#endif
 	int			tlbsize;
 	struct cache_desc	icache;	/* Primary I-cache */
 	struct cache_desc	dcache;	/* Primary D or combined I/D cache */
diff --git a/include/asm-mips/processor.h b/include/asm-mips/processor.h
index 58cbac5..0ae418a 100644
--- a/include/asm-mips/processor.h
+++ b/include/asm-mips/processor.h
@@ -105,6 +105,29 @@ struct mips_dsp_state {
 	{0,} \
 }
 
+#ifdef CONFIG_HARDWARE_WATCHPOINTS
+
+#define NUM_WATCH_REGS 8
+
+struct mips3264_watch_reg_state {
+	/* The width of watchlo is 32 in a 32 bit kernel and 64 in a
+	   64 bit kernel.  We use unsiged long as it has the same
+	   property. */
+	unsigned long watchlo[NUM_WATCH_REGS];
+	/* The width of watchhi is always 32 bits. */
+	__u32 watchhi[NUM_WATCH_REGS]; };
+
+union mips_watch_reg_state {
+	struct mips3264_watch_reg_state mips3264;
+};
+
+#define INIT_WATCH .watch = {{{0,},},}
+
+#define OPTIONAL_INIT_WATCH INIT_WATCH,
+#else
+#define OPTIONAL_INIT_WATCH
+#endif
+
 typedef struct {
 	unsigned long seg;
 } mm_segment_t;
@@ -137,6 +160,11 @@ struct thread_struct {
 	/* Saved state of the DSP ASE, if available. */
 	struct mips_dsp_state dsp;
 
+#ifdef CONFIG_HARDWARE_WATCHPOINTS
+	/* Saved watch register state, if available. */
+	union mips_watch_reg_state watch;
+#endif
+
 	/* Other stuff associated with the thread. */
 	unsigned long cp0_badvaddr;	/* Last user fault */
 	unsigned long cp0_baduaddr;	/* Last kernel fault accessing USEG */
@@ -193,6 +221,10 @@ struct thread_struct {
 		.dspcontrol	= 0,				\
 	},							\
 	/*							\
+	 * saved watch register stuff				\
+	 */							\
+	OPTIONAL_INIT_WATCH					\
+	/*							\
 	 * Other stuff associated with the process		\
 	 */							\
 	.cp0_badvaddr		= 0,				\
diff --git a/include/asm-mips/thread_info.h b/include/asm-mips/thread_info.h
index b2772df..e31de4b 100644
--- a/include/asm-mips/thread_info.h
+++ b/include/asm-mips/thread_info.h
@@ -122,6 +122,7 @@ register struct thread_info *__current_thread_info __asm__("$28");
 #define TIF_32BIT_REGS		22	/* also implies 16/32 fprs */
 #define TIF_32BIT_ADDR		23	/* 32-bit address space (o32/n32) */
 #define TIF_FPUBOUND		24	/* thread bound to FPU-full CPU set */
+#define TIF_LOAD_WATCH		25	/* If set, load watch registers */
 #define TIF_SYSCALL_TRACE	31	/* syscall trace active */
 
 #define _TIF_SYSCALL_TRACE	(1<<TIF_SYSCALL_TRACE)
@@ -138,6 +139,7 @@ register struct thread_info *__current_thread_info __asm__("$28");
 #define _TIF_32BIT_REGS		(1<<TIF_32BIT_REGS)
 #define _TIF_32BIT_ADDR		(1<<TIF_32BIT_ADDR)
 #define _TIF_FPUBOUND		(1<<TIF_FPUBOUND)
+#define _TIF_LOAD_WATCH		(1<<TIF_LOAD_WATCH)
 
 /* work to do on interrupt/exception return */
 #define _TIF_WORK_MASK		(0x0000ffef & ~_TIF_SECCOMP)
diff --git a/include/asm-mips/watch.h b/include/asm-mips/watch.h
new file mode 100644
index 0000000..ca79f5a
--- /dev/null
+++ b/include/asm-mips/watch.h
@@ -0,0 +1,32 @@
+/*
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License.  See the file "COPYING" in the main directory of this archive
+ * for more details.
+ *
+ * Copyright (C) 2008 David Daney
+ */
+#ifndef _ASM_WATCH_H
+#define _ASM_WATCH_H
+
+#include <linux/bitops.h>
+
+#include <asm/mipsregs.h>
+
+#ifdef CONFIG_HARDWARE_WATCHPOINTS
+void mips_install_watch_registers(void);
+void mips_read_watch_registers(void);
+void mips_clear_watch_registers(void);
+void mips_probe_watch_registers(struct cpuinfo_mips *c);
+
+#define __restore_watch() do {						\
+	if (unlikely(test_bit(TIF_LOAD_WATCH,				\
+			      &current_thread_info()->flags))) {	\
+		mips_install_watch_registers();				\
+	}								\
+} while (0)
+
+#else
+#define __restore_watch() do {} while (0)
+#endif
+
+#endif /* _ASM_WATCH_H */
-- 
1.5.5

[PATCH 3/6] Probe watch registers and report configuration.

[David Daney]

Probe watch registers and report configuration.

Probe for watch register characteristics, and report them in /proc/cpuinfo.

Signed-off-by: David Daney <ddaney@avtrex.com>
---
 arch/mips/kernel/cpu-probe.c |    4 ++++
 arch/mips/kernel/proc.c      |   10 ++++++++++
 2 files changed, 14 insertions(+), 0 deletions(-)

diff --git a/arch/mips/kernel/cpu-probe.c b/arch/mips/kernel/cpu-probe.c
index 89c3304..1563049 100644
--- a/arch/mips/kernel/cpu-probe.c
+++ b/arch/mips/kernel/cpu-probe.c
@@ -21,6 +21,7 @@
 #include <asm/fpu.h>
 #include <asm/mipsregs.h>
 #include <asm/system.h>
+#include <asm/watch.h>
 
 /*
  * Not all of the MIPS CPUs have the "wait" instruction available. Moreover,
@@ -678,6 +679,9 @@ static void __cpuinit decode_configs(struct cpuinfo_mips *c)
 static inline void cpu_probe_mips(struct cpuinfo_mips *c)
 {
 	decode_configs(c);
+#if defined(CONFIG_HARDWARE_WATCHPOINTS)
+	mips_probe_watch_registers(c);
+#endif
 	switch (c->processor_id & 0xff00) {
 	case PRID_IMP_4KC:
 		c->cputype = CPU_4KC;
diff --git a/arch/mips/kernel/proc.c b/arch/mips/kernel/proc.c
index 36f0653..e2f716c 100644
--- a/arch/mips/kernel/proc.c
+++ b/arch/mips/kernel/proc.c
@@ -50,8 +50,18 @@ static int show_cpuinfo(struct seq_file *m, void *v)
 	seq_printf(m, "tlb_entries\t\t: %d\n", cpu_data[n].tlbsize);
 	seq_printf(m, "extra interrupt vector\t: %s\n",
 	              cpu_has_divec ? "yes" : "no");
+#ifdef CONFIG_HARDWARE_WATCHPOINTS
+	seq_printf(m, "hardware watchpoint\t: %s",
+		   cpu_has_watch ? "yes" : "no\n");
+	if (cpu_has_watch)
+		seq_printf(m, ", count: %d, address mask: 0x%04x, irw mask 0x%02x\n",
+			   cpu_data[n].watch_reg_count,
+			   cpu_data[n].watch_reg_mask,
+			   cpu_data[n].watch_reg_irw);
+#else
 	seq_printf(m, "hardware watchpoint\t: %s\n",
 	              cpu_has_watch ? "yes" : "no");
+#endif
 	seq_printf(m, "ASEs implemented\t:%s%s%s%s%s%s\n",
 		      cpu_has_mips16 ? " mips16" : "",
 		      cpu_has_mdmx ? " mdmx" : "",
-- 
1.5.5

[PATCH 4/6] Watch exception handling for HARDWARE_WATCHPOINTS.

[David Daney]

Watch exception handling for HARDWARE_WATCHPOINTS.

Here we hook up the watch exception handler so that it sends SIGTRAP when
the hardware watch registers are triggered.

Signed-off-by: David Daney <ddaney@avtrex.com>
---
 arch/mips/kernel/genex.S |    4 ++++
 arch/mips/kernel/traps.c |   14 ++++++++++++++
 2 files changed, 18 insertions(+), 0 deletions(-)

diff --git a/arch/mips/kernel/genex.S b/arch/mips/kernel/genex.S
index c6ada98..15a9bde 100644
--- a/arch/mips/kernel/genex.S
+++ b/arch/mips/kernel/genex.S
@@ -416,7 +416,11 @@ NESTED(nmi_handler, PT_SIZE, sp)
 	BUILD_HANDLER tr tr sti silent			/* #13 */
 	BUILD_HANDLER fpe fpe fpe silent		/* #15 */
 	BUILD_HANDLER mdmx mdmx sti silent		/* #22 */
+#ifdef 	CONFIG_HARDWARE_WATCHPOINTS
+	BUILD_HANDLER watch watch sti silent		/* #23 */
+#else
 	BUILD_HANDLER watch watch sti verbose		/* #23 */
+#endif
 	BUILD_HANDLER mcheck mcheck cli verbose		/* #24 */
 	BUILD_HANDLER mt mt sti silent			/* #25 */
 	BUILD_HANDLER dsp dsp sti silent		/* #26 */
diff --git a/arch/mips/kernel/traps.c b/arch/mips/kernel/traps.c
index 824b187..22bb053 100644
--- a/arch/mips/kernel/traps.c
+++ b/arch/mips/kernel/traps.c
@@ -39,6 +39,7 @@
 #include <asm/tlbdebug.h>
 #include <asm/traps.h>
 #include <asm/uaccess.h>
+#include <asm/watch.h>
 #include <asm/mmu_context.h>
 #include <asm/types.h>
 #include <asm/stacktrace.h>
@@ -871,6 +872,18 @@ asmlinkage void do_mdmx(struct pt_regs *regs)
 
 asmlinkage void do_watch(struct pt_regs *regs)
 {
+#ifdef CONFIG_HARDWARE_WATCHPOINTS
+	/*
+	 * If the current thread has the watch registers loaded, save
+	 * their values and send SIGTRAP.  Otherwise another thread
+	 * left the registers set, clear them and continue.
+	 */
+	if (test_tsk_thread_flag(current, TIF_LOAD_WATCH)) {
+		mips_read_watch_registers();
+		force_sig(SIGTRAP, current);
+	} else
+		mips_clear_watch_registers();
+#else
 	if (board_watchpoint_handler) {
 		(*board_watchpoint_handler)(regs);
 		return;
@@ -883,6 +896,7 @@ asmlinkage void do_watch(struct pt_regs *regs)
 	dump_tlb_all();
 	show_regs(regs);
 	panic("Caught WATCH exception - probably caused by stack overflow.");
+#endif
 }
 
 asmlinkage void do_mcheck(struct pt_regs *regs)
-- 
1.5.5

[PATCH 5/6] Scheduler support for HARDWARE_WATCHPOINTS.

[David Daney]

Scheduler support for HARDWARE_WATCHPOINTS.

Here we hook up the scheduler.  Whenever we switch to a new process,
we check to see if the watch registers should be installed, and do it
if needed.

Signed-off-by: David Daney <ddaney@avtrex.com>
---
 include/asm-mips/system.h |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/include/asm-mips/system.h b/include/asm-mips/system.h
index a944eda..cd30f83 100644
--- a/include/asm-mips/system.h
+++ b/include/asm-mips/system.h
@@ -20,6 +20,7 @@
 #include <asm/cmpxchg.h>
 #include <asm/cpu-features.h>
 #include <asm/dsp.h>
+#include <asm/watch.h>
 #include <asm/war.h>
 
 
@@ -76,6 +77,7 @@ do {									\
 		__restore_dsp(current);					\
 	if (cpu_has_userlocal)						\
 		write_c0_userlocal(current_thread_info()->tp_value);	\
+	__restore_watch();						\
 } while (0)
 
 static inline unsigned long __xchg_u32(volatile int * m, unsigned int val)
-- 
1.5.5

[PATCH 6/6] Ptrace support for HARDWARE_WATCHPOINTS.

[David Daney]

Ptrace support for HARDWARE_WATCHPOINTS

This is the final part of the watch register patch.  Here we hook up
ptrace so that the user space debugger (gdb), can set and read the
registers.

Signed-off-by: David Daney <ddaney@avtrex.com>
---
 arch/mips/kernel/ptrace.c |   93 +++++++++++++++++++++++++++++++++++++++++++++
 include/asm-mips/ptrace.h |   31 +++++++++++++++
 2 files changed, 124 insertions(+), 0 deletions(-)

diff --git a/arch/mips/kernel/ptrace.c b/arch/mips/kernel/ptrace.c
index 35234b9..8e86134 100644
--- a/arch/mips/kernel/ptrace.c
+++ b/arch/mips/kernel/ptrace.c
@@ -46,7 +46,12 @@
  */
 void ptrace_disable(struct task_struct *child)
 {
+#ifdef CONFIG_HARDWARE_WATCHPOINTS
+	/* Don't load the watchpoint registers for the ex-child. */
+	clear_tsk_thread_flag(child, TIF_LOAD_WATCH);
+#else
 	/* Nothing to do.. */
+#endif
 }
 
 /*
@@ -167,6 +172,84 @@ int ptrace_setfpregs(struct task_struct *child, __u32 __user *data)
 	return 0;
 }
 
+#ifdef CONFIG_HARDWARE_WATCHPOINTS
+static int ptrace_get_watch_regs(struct task_struct *child,
+				 struct pt_watch_regs __user *addr)
+{
+	enum pt_watch_style style;
+	int i;
+
+	if (!cpu_has_watch)
+		return -EIO;
+	if (!access_ok(VERIFY_WRITE, addr, sizeof(struct pt_watch_regs)))
+		return -EIO;
+
+#ifdef CONFIG_32BIT
+	style = pt_watch_style_mips32;
+#define WATCH_STYLE mips32
+#else
+	style = pt_watch_style_mips64;
+#define WATCH_STYLE mips64
+#endif
+
+	__put_user(style, &addr->style);
+	__put_user(current_cpu_data.watch_reg_count,
+		   &addr->WATCH_STYLE.num_valid);
+	__put_user(current_cpu_data.watch_reg_mask,
+		   &addr->WATCH_STYLE.reg_mask);
+	__put_user(current_cpu_data.watch_reg_irw,
+		   &addr->WATCH_STYLE.irw_mask);
+	for (i = 0; i < current_cpu_data.watch_reg_count; i++) {
+		__put_user(child->thread.watch.mips3264.watchlo[i],
+			   &addr->WATCH_STYLE.watchlo[i]);
+		__put_user(child->thread.watch.mips3264.watchhi[i] & 0xfff,
+			   &addr->WATCH_STYLE.watchhi[i]);
+	}
+
+	return 0;
+}
+
+static int ptrace_set_watch_regs(struct task_struct *child,
+				 struct pt_watch_regs __user *addr)
+{
+	int i;
+	int watch_active = 0;
+	unsigned long lt[NUM_WATCH_REGS];
+	unsigned int ht[NUM_WATCH_REGS];
+
+	if (!cpu_has_watch)
+		return -EIO;
+	if (!access_ok(VERIFY_READ, addr, sizeof(struct pt_watch_regs)))
+		return -EIO;
+	/* Check the values. */
+	for (i = 0; i < NUM_WATCH_REGS; i++) {
+		__get_user(lt[i], &addr->WATCH_STYLE.watchlo[i]);
+		if (lt[i] & __UA_LIMIT)
+			return -EINVAL;
+
+		__get_user(ht[i], &addr->WATCH_STYLE.watchhi[i]);
+		if (ht[i] & ~0xff8)
+			return -EINVAL;
+	}
+	/* Install them. */
+	for (i = 0; i < NUM_WATCH_REGS; i++) {
+		if (lt[i] & 7)
+			watch_active = 1;
+		child->thread.watch.mips3264.watchlo[i] = lt[i];
+		/* Set the G bit. */
+		child->thread.watch.mips3264.watchhi[i] = ht[i] | 0x40000000;
+	}
+
+	if (watch_active)
+		set_tsk_thread_flag(child, TIF_LOAD_WATCH);
+	else
+		clear_tsk_thread_flag(child, TIF_LOAD_WATCH);
+
+	return 0;
+}
+
+#endif /* CONFIG_HARDWARE_WATCHPOINTS */
+
 long arch_ptrace(struct task_struct *child, long request, long addr, long data)
 {
 	int ret;
@@ -439,7 +522,17 @@ long arch_ptrace(struct task_struct *child, long request, long addr, long data)
 		ret = put_user(task_thread_info(child)->tp_value,
 				(unsigned long __user *) data);
 		break;
+#ifdef CONFIG_HARDWARE_WATCHPOINTS
+	case PTRACE_GET_WATCH_REGS:
+		ret = ptrace_get_watch_regs(child,
+					(struct pt_watch_regs __user *) addr);
+		break;
 
+	case PTRACE_SET_WATCH_REGS:
+		ret = ptrace_set_watch_regs(child,
+					(struct pt_watch_regs __user *) addr);
+		break;
+#endif
 	default:
 		ret = ptrace_request(child, request, addr, data);
 		break;
diff --git a/include/asm-mips/ptrace.h b/include/asm-mips/ptrace.h
index 786f7e3..d8d821d 100644
--- a/include/asm-mips/ptrace.h
+++ b/include/asm-mips/ptrace.h
@@ -71,6 +71,37 @@ struct pt_regs {
 #define PTRACE_POKEDATA_3264	0xc3
 #define PTRACE_GET_THREAD_AREA_3264	0xc4
 
+/* Read and write watchpoint registers.  */
+enum pt_watch_style {
+	pt_watch_style_mips32,
+	pt_watch_style_mips64
+};
+struct mips32_watch_regs {
+	uint32_t watchlo[8];
+	uint32_t watchhi[8];
+	uint32_t num_valid;
+	uint32_t reg_mask;
+	uint32_t irw_mask;
+};
+struct mips64_watch_regs {
+	uint64_t watchlo[8];
+	uint32_t watchhi[8];
+	uint32_t num_valid;
+	uint32_t reg_mask;
+	uint32_t irw_mask;
+};
+
+struct pt_watch_regs {
+	enum pt_watch_style style;
+	union {
+		struct mips32_watch_regs mips32;
+		struct mips32_watch_regs mips64;
+	};
+};
+
+#define PTRACE_GET_WATCH_REGS	0xd0
+#define PTRACE_SET_WATCH_REGS	0xd1
+
 #ifdef __KERNEL__
 
 #include <linux/linkage.h>
-- 
1.5.5