feat(kernel): load tss

kernel/dev/at/cga.inc

@@ -111,7 +111,7 @@ cga_putc:
 	; scroll up
 	push esi
 	push edi
-	mov ecx, CGA_COLUMNS*(CGA_LINES)*2
+	mov ecx, CGA_COLUMNS*(CGA_LINES)
 	mov edi, CGA_MEMORY
 	mov esi, CGA_MEMORY+80*2
 	rep movsw

kernel/gdt.inc

@@ -23,8 +23,12 @@ gdt:
 
 	; Tss
 .tss:
-	dw ?
-	dd ?
+	.limit  dw ?
+	.base   dw ?
+	.baseh0 db ? 
+	.access db ?
+	.flags  db ?
+	.baseh1 db ?
 
 .end:
 	
@@ -33,5 +37,32 @@ pGDT:
 	dd gdt
 
 gdt_set_tss:
-	
+	mov ecx, sizeof.TSS
+	mov [gdt.limit], cx
+	mov [gdt.base], ax
+
+	shr ecx, 16
+	shr eax, 16
+
+	mov [gdt.baseh0], al
+	mov [gdt.baseh1], ah
+	mov al, 0x89
+	mov [gdt.access], al
+
+	and cl, 0xF
+	or cl, 0x40
+	mov [gdt.flags], cl
+	ret
+
+gdt_flush:
+	; load kernel gdt 
+	lgdt [pGDT]
+	jmp 0x08:@f
+@@:
+	mov ax, 0x10
+	mov ds, ax
+	mov es, ax
+	mov fs, ax
+	mov gs, ax
+	mov ss, ax
 	ret

kernel/kernel.asm

@@ -58,9 +58,18 @@ kmain:
 
 	call pic_init
 
-	; load kernel gdt 
-	lgdt [pGDT]
-	; I don't think i need to reload segment cuz their value are already correct
+	; clear tss
+	mov ecx, sizeof.TSS
+	xor ax, ax
+	mov edi, kTSS
+	rep movsb
+
+	mov cx, 0xdfff
+	mov eax, kTSS
+	mov [eax + TSS.iomap], cx
+
+	call gdt_set_tss
+	call gdt_flush
 
 	call idt_setup
 

kernel/sys/cpu.inc

@@ -87,6 +87,7 @@ struc TSS {
 	.trap     dw ?
 	.iomap    dw ?
 }
+DEFN TSS
 
 struc GDTGate {