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The liner address of GDT should be $BOOTSEG<<4+gdt, is that right? Cause now the BOOTSEG is a segment address now.Hobbes wrote:You're welcome. Now can you calculate the linear address of the GDT?
Code: Select all
/* Boot file of nosdl;
* This file is loaded at 0x10000;
* Enter the protected mode and run init;
* The max size of this file is 8k;
*/
#define BOOTSEG 0x1000 /* where I am in; */
/* Generate a gdt with 32bits base, 20bits limit and 12bits flag;
* We use a 32bits limit (low 20bits available) and
* 16bits flag (lower 4bits of higher byte are always 0) here;
*/
.text
.code16
.globl _start
_start:
movl $0xB800,%eax
movl %eax,%gs
mov $'S',%al
mov $0x0C,%ah
movl %eax,%gs:((80*0+5)*2)
/* Prepare to enter the protected mode; */
__enter:
/* Reset registers; */
movl $BOOTSEG,%eax
movl %eax,%ds
/* Clear interrupt flags; */
cli
/* Load GDT; */
lgdt gdtptr
/* Open A20 Line; */
inb $0x92,%al
orb $0b00000010,%al
outb %al,$0x92
/* Set cr0, enter protected mode; */
movl %cr0,%eax
orl $0x01,%eax
movl %eax,%cr0
ljmp $0x10,$(__enter32)
/*
* Here we enter the 32bits world;
* The next step is init idt and other things;
*/
__enter32:
.code32
/* Display a P; */
xorl %eax,%eax
movl $sel_video,%eax
movl %eax,%gs
movl $((80*0+10)*2),%edi
mov $0x0F,%ah
mov $'P',%al
movl %eax,%gs:(%edi)
jmp .
/* GDT table; */
.code16
gdt: .quad 0x0000000000000000 /* Not used; */
gdt_kstack: .quad 0x00CF92000000FFFF /* Reserved for kernel stack; 0x08; */
gdt_kcode: .quad 0x00CF9A000000FFFF /* Kernel code segment; 0x10; */
gdt_kdata: .quad 0x00CF92000000FFFF /* Kernel data segment; 0x18; */
gdt_ustack: .quad 0x00CFF2000000FFFF /* Reserved for user stack; 0x20; */
gdt_ucode: .quad 0x00CFFA000000FFFF /* User code segment; 0x28; */
gdt_udata: .quad 0x00CFF2000000FFFF /* User data segment; 0x30; */
gdt_video: .quad 0x00CFF200B800FFFF /* Video buffer; 0x38; */
.quad 0x0000000000000000 /* Not used; */
.set gdtlen, (.-gdt) /* GDT Length; */
gdtptr: .2byte (gdtlen-1) /* GDT Limit; */
gdtbase: .4byte BOOTSEG<<4+gdt /* GDT Base address; */
/* Selectors; */
.set sel_kcode, gdt_kcode-gdt
.set sel_kdata, gdt_kdata-gdt
.set sel_ucode, gdt_ucode-gdt
.set sel_udata, gdt_udata-gdt
.set sel_video, gdt_video-gdt
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# Makefile of nosdl;
CC = gcc
LD = ld
OBJCPY = objcopy
DD = dd
RM = rm
MOUNT = mount
UMOUNT = umount
LDOPTS =-Ttext 0x7c00
LDOPTB =-Ttext 0x0000
OCOPT = -R .pdr -R .comment -R .note -S -O binary
MIDFILES = boot.o boot.elf boot secboot.bin secboot.o secboot.elf
MKFS = mkfs.ext2
YES = yes
all:boot.img
secoot.o:secboot.S
@$(CC) -c secboot.S
secboot.elf:secboot.o
@$(LD) secboot.o -o secboot.elf $(LDOPTS)
secboot.bin:secboot.elf
@$(OBJCPY) $(OCOPT) secboot.elf secboot.bin
boot.img:secboot.bin
@$(DD) if=/dev/zero of=boot.img bs=512 count=2880
@$(YES) | $(MKFS) boot.img
@$(DD) if=secboot.bin of=boot.img bs=512 count=2 conv=notrunc
boot.o:boot.S
@$(CC) -c boot.S -Iinclude
boot.elf:boot.o
@$(LD) boot.o -o boot.elf $(LDOPTB)
boot:boot.elf
@$(OBJCPY) $(OCOPT) boot.elf boot
clean:
@$(RM) -rf $(MIDFILES)
system:boot.img boot
@sudo mount -o loop boot.img /home/ley/floppy
@cp boot /home/ley/floppy
@sleep 3
@sudo umount /home/ley/floppy
it's "initialized", know your terminologyIs there any register that I should ritualized
(which begs the question, how often did you get corrected by the compiler's spelling?)What is the difference between a far jump (what ljmp does, stupid GAS confusing people) and a near jump (jmp)? Have you read the manual on the matter?And this jump... do I need a ljmp or just jmp?
Combuster wrote:it's "initialized", know your terminologyIs there any register that I should ritualized
What is the difference between a far jump (what ljmp does, stupid GAS confusing people) and a near jump (jmp)? Have you read the manual on the matter?And this jump... do I need a ljmp or just jmp?
wrong spell of the word...the limit of ljmp is 64kb, while jmp has the limit 256b?
In this case, I think "Whose code did you steal" would almost be more appropriateyou are only seconds from somebody to tell you to RTFM
You were wrong - it took Combuster 20 minutes from your post to his.Hobbes wrote:Leyley, you are only seconds from somebody to tell you to RTFM. Knowing the difference between near and far jumps is a prerequisite for OS development.
Thanks for the OP. As I said before, I am a rookie of this, I will collect the required knowledge before next post. As you said RTFM.Combuster wrote:the limit of ljmp is 64kb, while jmp has the limit 256b?In this case, I think "Whose code did you steal" would almost be more appropriateyou are only seconds from somebody to tell you to RTFM
@OP: Read the forum rules. In particular the "required knowledge" part.
Technically, I already posted a covert RTFM 25 minutes before hobbes suggested itJamesM wrote:You were wrong - it took Combuster 20 minutes from your post to his.Hobbes wrote:Leyley, you are only seconds from somebody to tell you to RTFM. Knowing the difference between near and far jumps is a prerequisite for OS development.
Maybe he was on lunch
Yep, definitely RTFM. Here's the link (1st google result for keywords "virtualbox debugger"): http://www.virtualbox.org/manual/ch12.html#idp6899568leyley wrote:And another thing, can I use VirtualBox to debug my program? I want to know the contents of registers.
Agreed. I've modified a bit (mostly printfs for more informative output, like RPL and IST when listing IDT), and now it's even more powerful.Nable wrote:IMHO, bochs internal debugger seems much better
Always the man we can count on!Combuster wrote:Technically, I already posted a covert RTFM 25 minutes before hobbes suggested it
