wslで、最小のカーネルをコンパイル その23

概要

wslで、kernel.elfのコンパイル、やってみた。
GDTを作りたい。

GDTとは。

サンプルコード

#include <stdio.h>


#define D_LDT   0x200   /* LDT segment        */
#define D_TASK  0x500   /* Task gate          */
#define D_TSS   0x900   /* TSS                */
#define D_CALL  0x0C00  /* 386 call gate      */
#define D_INT   0x0E00  /* 386 interrupt gate */
#define D_TRAP  0x0F00  /* 386 trap gate      */
#define D_DATA  0x1000  /* Data segment       */
#define D_CODE  0x1800  /* Code segment       */
#define D_DPL3         0x6000   /* DPL3 or mask for DPL                    */
#define D_DPL2         0x4000   /* DPL2 or mask for DPL                    */
#define D_DPL1         0x2000   /* DPL1 or mask for DPL                    */
#define D_PRESENT      0x8000   /* Present                                 */
#define D_NOT_PRESENT  0x8000   /* Not Present                             */
#define D_ACC      0x100  /* Accessed (Data or Code)          */
#define D_WRITE    0x200  /* Writable (Data segments only)    */
#define D_READ     0x200  /* Readable (Code segments only)    */
#define D_BUSY     0x200  /* Busy (TSS only)                  */
#define D_EXDOWN   0x400  /* Expand down (Data segments only) */
#define D_CONFORM  0x400  /* Conforming (Code segments only)  */
#define D_BIG      0x40	  /* Default to 32 bit mode           */
#define D_BIG_LIM  0x80	  /* Limit is in 4K units             */
struct x86_desc {
   unsigned short limit_low;     /* limit 0..15    */
   unsigned short base_low;      /* base  0..15    */
   unsigned char base_med;       /* base  16..23   */
   unsigned char access;         /* access byte    */
   unsigned int limit_high:4;    /* limit 16..19   */
   unsigned int granularity:4;   /* granularity    */
   unsigned char base_high;      /* base 24..31    */
} __attribute__ ((packed));
struct x86_gate {
   unsigned short offset_low;   /* offset 0..15    */
   unsigned short selector;     /* selector        */	
   unsigned short access;       /* access flags    */
   unsigned short offset_high;  /* offset 16..31   */
} __attribute__ ((packed));
union DT_entry {
   struct x86_desc desc;     /* Normal descriptor */
   struct x86_gate gate;     /* Gate descriptor   */
   unsigned long long dummy; /* Any other info    */
};
#define desc_table(name, length)    union DT_entry name[length] = 
#define stnd_desc(base, limit, control)     {desc: {(limit & 0xffff), (base & 0xffff), ((base >> 16) & 0xff), ((control+D_PRESENT) >> 8), (limit >> 16), ((control & 0xff) >> 4), (base >> 24)}}
desc_table(GDT, 3) {
	{dummy:0},
	stnd_desc(0, 0xFFFFF, (D_CODE + D_READ + D_BIG + D_BIG_LIM)),
	stnd_desc(0, 0xFFFFF, (D_DATA + D_WRITE + D_BIG + D_BIG_LIM)),
};
struct {
	unsigned short limit __attribute__ ((packed));
	union DT_entry *idt __attribute__ ((packed));
} loadgdt = { (3 * sizeof(union DT_entry) - 1), GDT };

int main(void){
    
    printf("ok");
}

以上。