初始化GDT和IDT

Author: yourtion

05_day/bootpack.c

@@ -38,6 +38,24 @@ struct BOOTINFO {
 	char *vram;
 };
 
+struct SEGMENT_DESCRIPTOR {
+	short limit_low, base_low;
+	char base_mid, access_right;
+	char limit_high, base_high;
+};
+
+struct GATE_DESCRIPTOR {
+	short offset_low, selector;
+	char dw_count, access_right;
+	short offset_high;
+};
+
+void init_gdtidt(void);
+void set_segmdesc(struct SEGMENT_DESCRIPTOR *sd, unsigned int limit, int base, int ar);
+void set_gatedesc(struct GATE_DESCRIPTOR *gd, int offset, int selector, int ar);
+void load_gdtr(int limit, int addr);
+void load_idtr(int limit, int addr);
+
 void HariMain(void)
 {
 	struct BOOTINFO *binfo = (struct BOOTINFO *) 0x0ff0;
@@ -217,4 +235,52 @@ void putblock8_8(char *vram, int vxsize, int pxsize,
 		}
 	}
 	return;
-}
+}
+
+void init_gdtidt(void)
+{
+	struct SEGMENT_DESCRIPTOR *gdt = (struct SEGMENT_DESCRIPTOR *) 0x00270000;
+	struct GATE_DESCRIPTOR    *idt = (struct GATE_DESCRIPTOR    *) 0x0026f800;
+	int i;
+
+	/* GDT初始化 */
+	for (i = 0; i < 8192; i++) {
+		set_segmdesc(gdt + i, 0, 0, 0);
+	}
+	set_segmdesc(gdt + 1, 0xffffffff, 0x00000000, 0x4092);
+	set_segmdesc(gdt + 2, 0x0007ffff, 0x00280000, 0x409a);
+	load_gdtr(0xffff, 0x00270000);
+
+	/* IDT初始化 */
+	for (i = 0; i < 256; i++) {
+		set_gatedesc(idt + i, 0, 0, 0);
+	}
+	load_idtr(0x7ff, 0x0026f800);
+
+	return;
+}
+
+void set_segmdesc(struct SEGMENT_DESCRIPTOR *sd, unsigned int limit, int base, int ar)
+{
+	if (limit > 0xfffff) {
+		ar |= 0x8000; /* G_bit = 1 */
+		limit /= 0x1000;
+	}
+	sd->limit_low    = limit & 0xffff;
+	sd->base_low     = base & 0xffff;
+	sd->base_mid     = (base >> 16) & 0xff;
+	sd->access_right = ar & 0xff;
+	sd->limit_high   = ((limit >> 16) & 0x0f) | ((ar >> 8) & 0xf0);
+	sd->base_high    = (base >> 24) & 0xff;
+	return;
+}
+
+void set_gatedesc(struct GATE_DESCRIPTOR *gd, int offset, int selector, int ar)
+{
+	gd->offset_low   = offset & 0xffff;
+	gd->selector     = selector;
+	gd->dw_count     = (ar >> 8) & 0xff;
+	gd->access_right = ar & 0xff;
+	gd->offset_high  = (offset >> 16) & 0xffff;
+	return;
+}

05_day/naskfunc.nas

@@ -10,6 +10,7 @@
 		GLOBAL	_io_in8,  _io_in16,  _io_in32
 		GLOBAL	_io_out8, _io_out16, _io_out32
 		GLOBAL	_io_load_eflags, _io_store_eflags
+		GLOBAL	_load_gdtr, _load_idtr
 
 [SECTION .text]
 
@@ -75,3 +76,15 @@ _io_store_eflags:	; void io_store_eflags(int eflags);
 		PUSH	EAX
 		POPFD		; POP EFLAGS 
 		RET
+		
+_load_gdtr:		; void load_gdtr(int limit, int addr);
+		MOV		AX,[ESP+4]		; limit
+		MOV		[ESP+6],AX
+		LGDT	[ESP+6]
+		RET
+
+_load_idtr:		; void load_idtr(int limit, int addr);
+		MOV		AX,[ESP+4]		; limit
+		MOV		[ESP+6],AX
+		LIDT	[ESP+6]
+		RET