0.487s-boot: access 4GB memory in real-mode

LINES

@@ -10,3 +10,5 @@
 
 2021-2-15 0.466: 466 lines, 5 files, rain
 
+2021-2-15 0.487: 487 lines, 5 files, rain
+

README.md

@@ -23,6 +23,14 @@ Cunix kernel
 `0.451s-boot`:  
 &#9`boot` can load 8 sectors (4KB) of loader (not 1 sector).  
 
-`0.466s-boot`:
+`0.466s-boot`:  
 &#9rebuild `boot`
+
+`0.487s-boot`:  
+&#9`loader` let FS can access 4GB memory in real-mode. because 
+&#9`loader` loaded GDT and load a data-segment to fs, then disable
+&#9protect-mode. 
+
 </pre>
+
+

boot/x86/loader.asm

@@ -20,6 +20,8 @@
 
 org 0x8000
 
+jmp _start
+
 %include "arch/x86/segment.inc"
 %include "arch/x86/paging.inc"
 
@@ -29,15 +31,34 @@ _start:
 	mov si, message
 	call print
 
-.to_protect_mode:
+; init segment register fs
+.init_fs:
 	; enable A20 address 20 line
-.open_a20
+.open_a20:
 	in al, 0x92
-	or al, 2
-	out  0x92, al
+	or al, 0x02
+	out 0x92, al
 
 	cli
 	lgdt [gdt32_descriptor]
+	mov eax, cr0
+	or eax, 0x01
+	mov cr0, eax
+	
+	mov ax, data32
+	mov fs, ax
+
+	mov eax, cr0
+	and eax, 11111111111111111111111111111110b
+	mov cr0, eax
+
+	; interrupt is disable
+	
+	; now, FS has addressing out of 1MB like protect-mode. 
+	
+
+.to_protect_mode:
+	; GDT is already load by .init_fs
 
 	mov eax, cr0
 	; set CR0.bit 1 (Protect-mode Enable)