centos 自定义内核模块 编译运行

简单记录一下 centos 自定义内核模块的一些编译运行记录，代码如下：

主要功能是通过rdtsc 指令直接从 CPU MSR 寄存器中获取时钟，尝试获取两次，两次之间会做一些赋值操作什么的，并记录一下时差。

#include <linux/hardirq.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/preempt.h>
#include <linux/sched.h>
void inline measured_function(volatile int *var) { (*var) = 1; }

static int __init hello_start(void) {
  unsigned long flags;
  uint64_t start, end;
  int variable = 0;
  unsigned cycles_low, cycles_high, cycles_low1, cycles_high1;
  printk(KERN_INFO "Loading test module...\n");
  preempt_disable();         /*we disable preemption on our CPU*/
  raw_local_irq_save(flags); /*we disable hard interrupts on our CPU*/
  /*at this stage we exclusively own the CPU*/
  asm volatile(
      "RDTSC\n\t"
      "mov %%edx, %0\n\t"
      "mov %%eax, %1\n\t"
      : "=r"(cycles_high), "=r"(cycles_low));
  measured_function(&variable);
  asm volatile(
      "RDTSC\n\t"
      "mov %%edx, %0\n\t"
      "mov %%eax, %1\n\t"
      : "=r"(cycles_high1), "=r"(cycles_low1));
  raw_local_irq_restore(flags);
  /*we enable hard interrupts on our CPU*/
  preempt_enable(); /*we enable preemption*/
  start = (((uint64_t)cycles_high << 32) | cycles_low);
  end = (((uint64_t)cycles_high1 << 32) | cycles_low1);
  printk(KERN_INFO "\n function execution time is %llu clock cycles",
         (end - start));
  return 0;
}

static void __exit hello_end(void) { printk(KERN_INFO "Goodbye Mr.\n"); }
module_init(hello_start);
module_exit(hello_end);      

编译方式，Makefile

# obj-m 必须存在，后面的 .o 文件可以是自己的文件名，其他无需更改
obj-m := rdtsc_mode.o 
KERNELBUILD :=/lib/modules/$(shell uname -r)/build
default:
        make -C $(KERNELBUILD) M=$(shell pwd) modules

clean:
        rm -rf *.o *.ko *.mod.c .*.cmd      

将源代码文件和 makefile 放在一个目录之下，

​​

​sudo make​

​ 执行即可，执行成功之后会在当前目录下生成一个 rdtsc_mode.ko 文件。

[Fri Jan 14 16:41:52 2022] Loading test module...
[Fri Jan 14 16:41:52 2022] function execution time is 3504353503 clock cycles
[Fri Jan 14 16:42:11 2022] Goodbye Mr.