Kernel (1)

The last section has written to jump to the entry address of the kernel program, then let’s take a look at the code in the kernel

#include "type.h"
#include "const.h"
#include "protect.h"

PUBLIC  void*   memcpy(void* pDst, void* pSrc, int iSize);

PUBLIC  void    disp_str(char * pszInfo);

PUBLIC  u8      gdt_ptr[6]; /* 0~15:Limit  16~47:Base */
PUBLIC  DESCRIPTOR  gdt[GDT_SIZE];

PUBLIC void cstart()
{


    disp_str("\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n"
         "-----\"cstart\" begins-----\n");
    /* 将 LOADER 中的 GDT 复制到新的 GDT 中 */
    memcpy(&gdt,                   /* New GDT */
           (void*)(*((u32*)(&gdt_ptr[2]))),    /* Base  of Old GDT */
           *((u16*)(&gdt_ptr[0])) + 1      /* Limit of Old GDT */
        );
    /* gdt_ptr[6] 共 6 个字节：0~15:Limit  16~47:Base。用作 sgdt/lgdt 的参数。*/
    u16* p_gdt_limit = (u16*)(&gdt_ptr[0]);  //设置指针指向地址
    u32* p_gdt_base  = (u32*)(&gdt_ptr[2]);
    *p_gdt_limit = GDT_SIZE * sizeof(DESCRIPTOR) - 1;  //对该指针赋值
    *p_gdt_base  = (u32)&gdt;

    disp_str("-----\"cstart\" ends-----\n");

}

The content is very simple, switch the stack and GDT, the content is still the original content.