linux内存监控机制hwbp

调试代码大部分都是真的代码行进行运行时调式，可是有时候我们想知道某个变量的变化情况，对于庞大的代码，对每一个读写该变量的位置进行log不太现实，鉴于该问题x86体系就提出了hwbp机制，linux也整合了该机制。

代码说明一切：

#include <linux/module.h> /* Needed by all modules */^M
#include <linux/kernel.h> /* Needed for KERN_INFO */^M
#include <linux/init.h> /* Needed for the macros */^M
#include <linux/kallsyms.h>^M
^M
#include <linux/perf_event.h>^M
#include <linux/hw_breakpoint.h>^M
#include <asm/rwsem.h>^M
struct perf_event * __percpu *sample_hbp;^M
^M
/*static char ksym_name[KSYM_NAME_LEN] = "pid_max";^M
module_param_string(ksym, ksym_name, KSYM_NAME_LEN, S_IRUGO);^M
MODULE_PARM_DESC(ksym, "Kernel symbol to monitor; this module will report any"^M
                        " write operations on the kernel symbol");^M
*/^M
static int pid=0;^M
static struct task_struct *gtsk=NULL;^M
module_param(pid,int,S_IRUGO);^M
MODULE_PARM_DESC(pid,"pid of process to monitor mm rwsem");^M
^M
enum rwsem_waiter_type {^M
        RWSEM_WAITING_FOR_WRITE,^M
        RWSEM_WAITING_FOR_READ^M
};^M
^M
struct rwsem_waiter {^M
        struct list_head list;^M
        struct task_struct *task;^M
        enum rwsem_waiter_type type;^M
};^M
^M
static void sample_hbp_handler(struct perf_event *bp,^M
                               struct perf_sample_data *data,^M
                               struct pt_regs *regs)^M
{^M
        printk(KERN_INFO " value is changed\n");^M
        dump_stack();^M
        printk(KERN_INFO "Dump stack from sample_hbp_handler\n");^M
        struct rwsem_waiter *waiter;^M
        if (list_empty(&(gtsk->mm->mmap_sem.wait_list)))^M
                printk(KERN_INFO "sem list empty");^M
        list_for_each_entry(waiter,&(gtsk->mm->mmap_sem.wait_list),list)^M
                printk(KERN_INFO "sem list pid %d",waiter->task->pid);^M
}^M
^M
static int __init hw_break_module_init(void)^M
{^M
        int ret = 0;^M
        struct perf_event_attr attr;^M
^M
        struct task_struct *tsk = NULL;^M
        for_each_process(tsk)^M
        {^M
                if (tsk->pid == pid)^M
                {^M
                        gtsk = tsk;^M
                        break;^M
                }^M
        }^M
        if (tsk == &init_task)^M
                goto fail;^M
        ^M
        hw_breakpoint_init(&attr);^M
        /*attr.bp_addr = kallsyms_lookup_name(ksym_name);*/
        attr.bp_addr = (__u64)&(tsk->mm->mmap_sem.count);
        printk("addr of data is %p",&(tsk->mm->mmap_sem.count));
        attr.bp_len = HW_BREAKPOINT_LEN_4;^M
        attr.bp_type = HW_BREAKPOINT_W | HW_BREAKPOINT_R;
^M
        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;^M
        }^M
^M
        printk(KERN_INFO "HW Breakpoint for rwsem write installed\n");^M
^M
        return 0;^M
^M
fail:^M
        printk(KERN_INFO "Breakpoint registration failed\n");^M
^M
        return ret;^M
}^M
^M
static void __exit hw_break_module_exit(void)^M
{^M
        unregister_wide_hw_breakpoint(sample_hbp);^M
        printk(KERN_INFO "HW Breakpoint for rwsem %d write uninstalled\n", pid);^M
}^M
^M
module_init(hw_break_module_init);^M
module_exit(hw_break_module_exit);^M
^M
MODULE_LICENSE("GPL");^M
MODULE_AUTHOR("K.Prasad");^M
MODULE_DESCRIPTION("ksym breakpoint");