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Re: My OS does not boot in real hardware
Posted: Mon Feb 18, 2019 3:22 pm
by deleted8917
If I remember correctly, GRUB enables the protected mode, A20 and GDT?
Re: My OS does not boot in real hardware
Posted: Mon Feb 18, 2019 3:30 pm
by Octocontrabass
The CPU will be in protected mode. The A20 line will be enabled. The GDT will not be set up, so you must set up your own GDT before you can load any segment registers.
That's all explained in the
multiboot specification in section 3.3, "I386 machine state". You should search the specification before asking here; otherwise you'll just get a lot of answers telling you to look in the spec.
Re: My OS does not boot in real hardware
Posted: Mon Feb 18, 2019 3:32 pm
by MichaelPetch
GRUB enables A20, enters 32-bit Protected mode with its own GDT. However, this is important - you should be establishing your own GDT because The Multiboot spec makes it clear the GDT record that gets loaded with LGDT should be considered invalid. You also don't know which selectors GRUB will use for code and data. The first time you attempt to load/reload a selector it could cause a crash. This is a real possibility if you enable your Interrupt Descriptor table and establish your own interrupt handlers. The documentation for Multiboot (legacy) is here:
https://www.gnu.org/software/grub/manua ... iboot.html
Re: My OS does not boot in real hardware
Posted: Mon Feb 18, 2019 3:35 pm
by deleted8917
Thanks for the info. I'm gonna to port my OS to use GRUB.
Re: My OS does not boot in real hardware
Posted: Mon Feb 18, 2019 4:46 pm
by deleted8917
Hi, again here (as expected). I ported almost successfully my OS to GRUB, but I get this error:
I already searched the error in Google, but I find no solution. (that can help me)
Here is bootg.asm:
Code: Select all
bits 32
%include "gdt.inc"
%include "idt.inc"
global start
extern kernelmain
start:
mov esp, _sys_stack
jmp stublet
ALIGN 4
mboot:
MULTIBOOT_PAGE_ALIGN equ 1<<0
MULTIBOOT_MEMORY_INFO equ 1<<1
MULTIBOOT_AOUT_KLUDGE equ 1<<16
MULTIBOOT_HEADER_MAGIC equ 0x1BADB002
MULTIBOOT_HEADER_FLAGS equ MULTIBOOT_PAGE_ALIGN | MULTIBOOT_MEMORY_INFO | MULTIBOOT_AOUT_KLUDGE
MULTIBOOT_CHECKSUM equ -(MULTIBOOT_HEADER_MAGIC + MULTIBOOT_HEADER_FLAGS)
EXTERN code, bss, end
dd MULTIBOOT_HEADER_MAGIC
dd MULTIBOOT_HEADER_FLAGS
dd MULTIBOOT_CHECKSUM
call InstallGDT
call kernelmain
stublet:
jmp $
SECTION .bss
resb 8192
_sys_stack:
The linker script is the same that can be finded in
Bare bones
Re: My OS does not boot in real hardware
Posted: Tue Feb 19, 2019 12:20 am
by zity
I'm not entirely sure this is the reason you get "no multiboot header found", but your header is incomplete. When using the MULTIBOOT_AOUT_KLUDGE you need to specify information about the layout of your binary file. Have a look here
https://www.gnu.org/software/grub/manua ... der-layout
For example, in my own loader I have the following header:
Code: Select all
mboot:
dd MULTIBOOT_HEADER_MAGIC
dd MULTIBOOT_HEADER_FLAGS
dd MULTIBOOT_CHECKSUM
dd mboot ; Location of this descriptor
dd code ; Start of the .text (code) section (defined in linker script)
dd bss ; End of the .data section (defined in linker script)
dd end ; End of loader (defined in linker script)
dd start ; Entry point below
Re: My OS does not boot in real hardware
Posted: Tue Feb 19, 2019 7:18 am
by deleted8917
zity wrote:I'm not entirely sure this is the reason you get "no multiboot header found"
Also, I don't know, just bad luck I think. Using the bare bones NASM bootloader I get "invalid arch dependent elf magic" error.
