Dynamic loading and execution of programs

         The kernel cannot be placed in the primary boot sector , Because it's big . The computer should start from the main boot program , The main boot program is responsible for loading the kernel , And transfer control . The kernel is responsible for loading user programs , And provide various routines for the user program to call . The routines provided to user program calls are called application program interfaces .

         Learning objectives in this chapter ：

        1. Understand that protected mode is a technology for the operating system , It does not burden the programming of ordinary applications .

        2. Learn the general principles of operating system loading and relocating applications in protected mode . Learn simple memory allocation , Understand the application program interface API Simple principle of .

        3. Learn some x86 New instructions for the processor , Include bswap,cupid,cmovcc,sgdt,movzx,movsx,cmpsb,cmpsw,cmpsd and xlat etc. .

13.1. Code list of this chapter

13.2. The structure of the kernel , Function and load

13.2.1. The structure of the kernel

         The kernel is divided into four parts , They are the initialization code , Kernel code snippet , Kernel data segment , Common routine segment , The main bootstrap is also part of the initialization code .

         The initialization code is used to start from BIOS It takes control of the processor and computer hardware , Install the most basic segment descriptor , Initialize the initial execution environment . then , Read and load the rest of the kernel from the hard disk , Create the memory segments that make up the kernel .

        Pseudo instruction equ We are only allowed to substitute symbols for specific values , But declared values do not take up space .

13.2.2. Kernel loading