2019-2020-1 20199320 "Linux kernel principle and Analysis" in the fourth week of work

Chapter III MenuOS construction

Construct a simple Linux kernel

The first step in building a Linux system MenuOS

cd LinuxKernel/
qemu -kernel linux-3.18.6/arch/x86/boot/bzImage -initrd rootfs.img

Note: QEMU emulation kernel; bzImage is vnLinux after gzip compressed file is compressed kernel image; initrd root file system is memory; rootfs filesystem is compiled.

Run results shown in Figure:

The second step, to start the process of tracking the Linux kernel debugger (gdb using tracking)

1. Enter the following command to start the kernel:

   qemu -kernel linux-3.18.6/arch/x86/boot/bzImage -initrd rootfs.img -S -s

   Note:

   • -s: Create a gdb-server on port 1234, to set a breakpoint may be used to trace core after;
   • -S: the CPU initialization before freeze up.

   Start effect as shown below:

   

2. Start entering the following gdb load the kernel, to establish a connection

   file linux-3.18.6/vmlinux  //在gdb界面中target remote之前加载符号表
   target remote:1234  //用1234这个端口进行连接

3. Enter the following commands set a breakpoint at the gdb, start_kernel

   break start_kernel //可在target remote之前，也可在之后

   The effect is as:

   

   View strat_kernel Code:

   

   Analysis: strat_kernel is where it starts, for complete hardware system initialization, the code for the C runtime environment settings.

   Among them, the more important init_task PCB is manually created, it is the process descriptor, 0 process, that is the final idle process.

4. Enter the following command () to set a breakpoint in the rest_init gdb

   break rest_init

   View rest_init () Code:

   

   Analysis: By rest_init () New kernel_init and kthreadd kernel threads

   Note:

   • init_task (0 process) is not the only process that generated by the fork way;
   • All kernel threads are directly or indirectly a kthreadd parent process.

5. Summarize the process of creation

   • init_task () (PID 0) converted by calling cpu_idle () IDLE process , running in kernel space;
   • init_task () created kernel_init () (1 kernel thread) by calling do_execve can be converted to user mode 1 process the init , this is the first user mode kernel boot process;
   • init_task () created kthreadd () (No. 2 kernel threads) is always running in the kernel, it is responsible for all scheduling and management of kernel threads.

   The whole process as shown: