一. 介绍

data breakpoint是一种特殊的断电，在处理检查到预设地址的值发生R/W操作时，发生断点中断。

二. 使用方法1

kernel有示例代码，在data_breakpoint.c中，在这里，kernel检查的是symbol的值发生变化，但是实际上测试发现直接使用寄存器地址也是可以的。
　　
　　看看.config里面，CONFIG_SAMPLES是否选中。
位置在Kernel Hacking/Sample kernel code。

samples目录好像不在缺省编译的范围内，自己手动编译就行了。
make M=samples即可。

aarch32 linux4.9

kernel 有breakpoint的编码实例data_breakpoint.c

相关函数:

register_wide_hw_breakpoint //kernel space 地址

register_user_hw_breakpoint //user space 地址

breakpoint 与 watchpoint 的原理需要查阅armv7_architecture_reference_manual

watchpoint：If the cause of the debug exception is a Watchpoint debug event, then a Data Abort exception is generated
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版权声明：本文为CSDN博主「shenhuxi_yu」的原创文章，遵循CC 4.0 BY-SA版权协议，转载请附上原文出处链接及本声明。
原文链接：https://blog.csdn.net/shenhuxi_yu/article/details/83155106
/*

• 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 every time a write operation is performed on
• that variable.
• Copyright IBM Corporation, 2009
• Author: K.Prasad [email protected]
  /
  #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 * __percpu *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 *bp,
struct perf_sample_data *data,
struct pt_regs *regs)
{
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;
struct perf_event_attr attr;

hw_breakpoint_init(&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, NULL);
if (IS_ERR((void __force *)sample_hbp)) {
    ret = PTR_ERR((void __force *)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”);

三. 使用方法2

上面是使用kernel的hw_breakpoint走watchpoint来注册的，实际上这里有一层封装，我们直接使用arch/arm下面的hw_breakpoint也是可以的。

这里直接给代码链接了：https://elixir.bootlin.com/linux/v4.6/source/arch/arm/kernel/hw_breakpoint.c

有很多操作寄存器的地方，比较底层了，不过便于理解。

三. 使用方法2

上面是使用kernel的hw_breakpoint走watchpoint来注册的，实际上这里有一层封装，我们直接使用arch/arm下面的hw_breakpoint也是可以的。

这里直接给代码链接了：https://elixir.bootlin.com/linux/v4.6/source/arch/arm/kernel/hw_breakpoint.c

有很多操作寄存器的地方，比较底层了，不过便于理解。
四. 第一种方法的结果

pid_max value is changed
CPU: 2 PID: 439 Comm: kworker/u8:3 Tainted: P W O 4.19.166 #2
Hardware name: xxxx (DT)
Workqueue: events_unbound call_usermodehelper_exec_work
Call trace:
dump_backtrace+0x0/0x164
show_stack+0x20/0x2c
dump_stack+0xb8/0xf0
sample_hbp_handler+0x28/0x3c [data_breakpoint]
__perf_event_overflow+0x94/0xe0
perf_swevent_event+0x98/0x104
perf_bp_event+0x6c/0x98
watchpoint_report+0x80/0x94
watchpoint_handler+0x100/0x208
do_debug_exception+0xe8/0x174
el1_dbg+0x18/0xa8
alloc_pid+0x80/0x284
copy_process+0xb48/0x1960
_do_fork+0xa0/0x434
kernel_thread+0x40/0x50
call_usermodehelper_exec_work+0x40/0xd8
process_one_work+0x210/0x3e8
worker_thread+0x228/0x3c4
kthread+0x13c/0x14c
ret_from_fork+0x10/0x18
Dump stack from sample_hbp_handler

六. 注意的地方

data breakpoint不同于breakpoint，发生异常后，因为寄存器中的值不会被清除，所以会一直循环中断
　　
一般的，我们通过调用单步执行，并且清掉异常寄存器的值，让程序可以继续执行，这样在下次发生异常的时候还可以继续进入data watchpoint