Initialize GDT and IDT

bootpack.c

@@ -4,6 +4,9 @@ void io_out8(int port, int data);
 int io_load_eflags(void);
 void io_store_eflags(int eflags);
 
+void load_gdtr(int limit, int addr);
+void load_idtr(int limit, int addr);
+
 const int COL8_BLACK = 0;
 const int COL8_WHITE = 7;
 const int COL8_GRAY = 8;
@@ -175,7 +178,59 @@ struct BOOTINFO {
   unsigned 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 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;
+}
+
+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;
+}
+
+void init_gdtidt(void) {
+  struct SEGMENT_DESCRIPTOR* gdt = (struct SEGMENT_DESCRIPTOR*)0x00270000;
+  struct GATE_DESCRIPTOR* idt = (struct GATE_DESCRIPTOR*)0x0026f800;
+
+  // Init GDT.
+  for (int 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);
+
+  // Init IDT.
+  for (int i = 0; i < 256; ++i)
+    set_gatedesc(idt + i, 0, 0, 0);
+  load_idtr(0x7ff, 0x0026f800);
+}
+
+
 void HariMain(void) {
+  init_gdtidt();
   init_palette();
 
   struct BOOTINFO* binfo = (struct BOOTINFO*)0x0ff0;

naskfunc.s

@@ -2,6 +2,7 @@
 .globl	io_in8, io_in16, io_in32
 .globl	io_out8, io_out16, io_out32
 .globl	io_load_eflags, io_store_eflags
+.globl	load_gdtr, load_idtr
 
 # void io_hlt(void)
 io_hlt:
@@ -77,3 +78,17 @@ io_store_eflags:
 	push	%eax
 	popfl			# pop eflags
 	ret
+
+# void load_gdtr(int limit, int addr)
+load_gdtr:
+        mov     4(%esp), %ax
+        mov     %ax, 6(%esp)
+        lgdt    6(%esp)
+        ret
+
+# void load_idtr(int limit, int addr)
+load_idtr:
+        mov     4(%esp), %ax
+        mov     %ax, 6(%esp)
+        lidt    6(%esp)
+        ret