4 files changed, 96 insertions, 1 deletions

diff --git a/samples/Kconfig b/samples/Kconfig
index 04be681a3ded..8924f72f0629 100644
--- a/samples/Kconfig
+++ b/samples/Kconfig
@@ -38,4 +38,10 @@ config SAMPLE_KRETPROBES
         default m
         depends on SAMPLE_KPROBES && KRETPROBES
 
+config SAMPLE_HW_BREAKPOINT
+        tristate "Build kernel hardware breakpoint examples -- loadable module only"
+        depends on HAVE_HW_BREAKPOINT && m
+        help
+          This builds kernel hardware breakpoint example modules.
+
 endif # SAMPLES
diff --git a/samples/Makefile b/samples/Makefile
index 43343a03b1f4..0f15e6d77fd6 100644
--- a/samples/Makefile
+++ b/samples/Makefile
@@ -1,3 +1,4 @@
 # Makefile for Linux samples code
 
-obj-$(CONFIG_SAMPLES)   += kobject/ kprobes/ tracepoints/ trace_events/
+obj-$(CONFIG_SAMPLES)   += kobject/ kprobes/ tracepoints/ trace_events/ \
+                           hw_breakpoint/
diff --git a/samples/hw_breakpoint/Makefile b/samples/hw_breakpoint/Makefile
new file mode 100644
index 000000000000..0f5c31c2fc47
--- /dev/null
+++ b/samples/hw_breakpoint/Makefile
@@ -0,0 +1 @@
+obj-$(CONFIG_SAMPLE_HW_BREAKPOINT) += data_breakpoint.o
diff --git a/samples/hw_breakpoint/data_breakpoint.c b/samples/hw_breakpoint/data_breakpoint.c
new file mode 100644
index 000000000000..29525500df00
--- /dev/null
+++ b/samples/hw_breakpoint/data_breakpoint.c
@@ -0,0 +1,87 @@
+/*
+ * data_breakpoint.c - Sample HW Breakpoint file to watch kernel data address
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * 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.
+ *
+ * usage: insmod data_breakpoint.ko ksym=<ksym_name>
+ *
+ * This file is a kernel module that places a breakpoint over ksym_name kernel
+ * variable using Hardware Breakpoint register. The corresponding handler which
+ * prints a backtrace is invoked everytime a write operation is performed on
+ * that variable.
+ *
+ * Copyright (C) IBM Corporation, 2009
+ *
+ * Author: K.Prasad <prasad@linux.vnet.ibm.com>
+ */
+#include <linux/module.h>       /* Needed by all modules */
+#include <linux/kernel.h>       /* Needed for KERN_INFO */
+#include <linux/init.h>         /* Needed for the macros */
+#include <linux/kallsyms.h>
+
+#include <linux/perf_event.h>
+#include <linux/hw_breakpoint.h>
+
+struct perf_event **sample_hbp;
+
+static char ksym_name[KSYM_NAME_LEN] = "pid_max";
+module_param_string(ksym, ksym_name, KSYM_NAME_LEN, S_IRUGO);
+MODULE_PARM_DESC(ksym, "Kernel symbol to monitor; this module will report any"
+                        " write operations on the kernel symbol");
+
+static void sample_hbp_handler(struct perf_event *temp, void *data)
+{
+        printk(KERN_INFO "%s value is changed\n", ksym_name);
+        dump_stack();
+        printk(KERN_INFO "Dump stack from sample_hbp_handler\n");
+}
+
+static int __init hw_break_module_init(void)
+{
+        int ret;
+        DEFINE_BREAKPOINT_ATTR(attr);
+
+        attr.bp_addr = kallsyms_lookup_name(ksym_name);
+        attr.bp_len = HW_BREAKPOINT_LEN_4;
+        attr.bp_type = HW_BREAKPOINT_W | HW_BREAKPOINT_R;
+
+        sample_hbp = register_wide_hw_breakpoint(&attr, sample_hbp_handler);
+        if (IS_ERR(sample_hbp)) {
+                ret = PTR_ERR(sample_hbp);
+                goto fail;
+        }
+
+        printk(KERN_INFO "HW Breakpoint for %s write installed\n", ksym_name);
+
+        return 0;
+
+fail:
+        printk(KERN_INFO "Breakpoint registration failed\n");
+
+        return ret;
+}
+
+static void __exit hw_break_module_exit(void)
+{
+        unregister_wide_hw_breakpoint(sample_hbp);
+        printk(KERN_INFO "HW Breakpoint for %s write uninstalled\n", ksym_name);
+}
+
+module_init(hw_break_module_init);
+module_exit(hw_break_module_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("K.Prasad");
+MODULE_DESCRIPTION("ksym breakpoint");