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authorK.Prasad <prasad@linux.vnet.ibm.com>2009-06-01 14:16:20 -0400
committerFrederic Weisbecker <fweisbec@gmail.com>2009-06-02 16:47:00 -0400
commit432039933a16b8227b7b267f46ac1c1b9b3adf14 (patch)
tree9ca2b6af261a968e2c1cccaeb0a9c89b1cb701a0 /samples/hw_breakpoint
parent17f557e5b5d43a2af66c969f6560ac7105020672 (diff)
hw-breakpoints: sample HW breakpoint over kernel data address
This patch introduces a sample kernel module to demonstrate the use of Hardware Breakpoint feature. It places a breakpoint over the kernel variable 'pid_max' to monitor all write operations and emits a function-backtrace when done. Signed-off-by: K.Prasad <prasad@linux.vnet.ibm.com> Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Diffstat (limited to 'samples/hw_breakpoint')
-rw-r--r--samples/hw_breakpoint/Makefile1
-rw-r--r--samples/hw_breakpoint/data_breakpoint.c83
2 files changed, 84 insertions, 0 deletions
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..9cbdbb871b7a
--- /dev/null
+++ b/samples/hw_breakpoint/data_breakpoint.c
@@ -0,0 +1,83 @@
1/*
2 * data_breakpoint.c - Sample HW Breakpoint file to watch kernel data address
3 *
4 * This program is free software; you can redistribute it and/or modify
5 * it under the terms of the GNU General Public License as published by
6 * the Free Software Foundation; either version 2 of the License, or
7 * (at your option) any later version.
8 *
9 * This program is distributed in the hope that it will be useful,
10 * but WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12 * GNU General Public License for more details.
13 *
14 * You should have received a copy of the GNU General Public License
15 * along with this program; if not, write to the Free Software
16 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
17 *
18 * usage: insmod data_breakpoint.ko ksym=<ksym_name>
19 *
20 * This file is a kernel module that places a breakpoint over ksym_name kernel
21 * variable using Hardware Breakpoint register. The corresponding handler which
22 * prints a backtrace is invoked everytime a write operation is performed on
23 * that variable.
24 *
25 * Copyright (C) IBM Corporation, 2009
26 */
27#include <linux/module.h> /* Needed by all modules */
28#include <linux/kernel.h> /* Needed for KERN_INFO */
29#include <linux/init.h> /* Needed for the macros */
30
31#include <asm/hw_breakpoint.h>
32
33struct hw_breakpoint sample_hbp;
34
35static char ksym_name[KSYM_NAME_LEN] = "pid_max";
36module_param_string(ksym, ksym_name, KSYM_NAME_LEN, S_IRUGO);
37MODULE_PARM_DESC(ksym, "Kernel symbol to monitor; this module will report any"
38 " write operations on the kernel symbol");
39
40void sample_hbp_handler(struct hw_breakpoint *temp, struct pt_regs
41 *temp_regs)
42{
43 printk(KERN_INFO "%s value is changed\n", ksym_name);
44 dump_stack();
45 printk(KERN_INFO "Dump stack from sample_hbp_handler\n");
46}
47
48static int __init hw_break_module_init(void)
49{
50 int ret;
51
52#ifdef CONFIG_X86
53 sample_hbp.info.name = ksym_name;
54 sample_hbp.info.type = HW_BREAKPOINT_WRITE;
55 sample_hbp.info.len = HW_BREAKPOINT_LEN_4;
56#endif /* CONFIG_X86 */
57
58 sample_hbp.triggered = (void *)sample_hbp_handler;
59
60 ret = register_kernel_hw_breakpoint(&sample_hbp);
61
62 if (ret < 0) {
63 printk(KERN_INFO "Breakpoint registration failed\n");
64 return ret;
65 } else
66 printk(KERN_INFO "HW Breakpoint for %s write installed\n",
67 ksym_name);
68
69 return 0;
70}
71
72static void __exit hw_break_module_exit(void)
73{
74 unregister_kernel_hw_breakpoint(&sample_hbp);
75 printk(KERN_INFO "HW Breakpoint for %s write uninstalled\n", ksym_name);
76}
77
78module_init(hw_break_module_init);
79module_exit(hw_break_module_exit);
80
81MODULE_LICENSE("GPL");
82MODULE_AUTHOR("K.Prasad");
83MODULE_DESCRIPTION("ksym breakpoint");