UCORE overview

brief introduction

In this paper, the knowledge of the operating system is roughly studied according to the Muke materials
ucore Course documentation
Course address
lab Answer address
Some answers have questions , But it can be used for reference

The first order

CPU Initialization will be carried out after power on , Then read the first instruction in memory . Part of the memory is ROM、 Part of it is RAM. After power failure RAM Information will disappear , however ROM The content is always .
The first instruction to read is CS:IP Address to （ The value should be the default ）, Just powered on CPU be in 16 In bit real mode , The addressing space size is 2 Of 20 Power （1MB）,CS、IP All are 16 Bit .CS*16+IP（0xFFFF0） Is the address of the first instruction , meanwhile CS:IP To be in 2 Of 20 In the addressing space of the power . The first instruction is at the bottom 1MB In space . This first instruction and its following instructions are BIOS, It should provide some services , then CPU To access disk devices .

BIOS

BIOS Read boot sector from disk （512 byte ） Loader in , Write it to memory 0x7c00, then CS:IP Jump there and execute the loader （bootloader）.
Say in detail ,BIOS Only run in real mode , It first checks the hardware , Perform device initialization . When repairing the computer , The display does not work , You can guess that there is a memory problem . because BIOS Check the memory first , It doesn't need to be checked later , Also don't start the system . Then check the inserted U disc 、 Disk or something . The information generated by inspection becomes BIOS data . although ROM The data will not disappear , But because the hardware inserted each time is different , therefore BIOS Will change these data . Finally, read the first sector of our disk .BIOS First read the main boot sector of the disk （512 byte ）. Because the information provided by this thing can help us choose which operating system in the boot disk . Select and read the active partition according to the information of the primary boot sector （ Partition boot sector ）. First execute the jump instruction of the partition boot sector , Jump to the startup code and start the loader .

Loader

The loader puts the disk's ucore Operating system data and code are loaded into memory , Jump to ucore Initial address . Give control to the operating system .
In detail , The loader will first read the boot configuration information from the file system , Based on this information, decide how to load the kernel , In this place, if we can get an option on the display （ Start menu ）, It's good to change the parameters . Finally, skip to the kernel .

Not detailed enough

It's still rough to know these , If you write an actual program , Also based on CPU manual 、BIOS standard （ Where to read the first , Above is 0xFFFF0）. So you still need to check a lot of information to write your own operating system .

System startup specification

BIOS

The hard disk partition table of the primary boot sector here has only four partition information , Information of each partition 16 byte （BIOS-MBR）.BIOS-GPT Support more than four partitions .PXE It's network startup , Download data from the server to the disk to start , here BIOS There should be network download function ,BIOS It's complicated . What I said earlier is to start on the local disk .

UEFI

Start the operating system consistently on all platforms . Boot any system on the disk . For the sake of safety , Check whether the boot record is credible . Only read the boot record that meets the signature .

Check information

You know BIOS And UEFI difference