OSDev.org

Posted: **Mon May 10, 2010 8:20 pm**

First off, quirky machine: Macbook Pro 5,4 (I /think/), running "Linux jagadai 2.6.32-22-generic #33-Ubuntu SMP Wed Apr 28 13:28:05 UTC 2010 x86_64 GNU/Linux"

I've been trying to set up the bare bones tutorial from the wiki, but with grub2 instead of normal grub. I created a qemu virtual system with a hard disk, booted using an ubuntu 10.04 livecd, installed grub onto an ext4 partition, and then booted the system with `qemu -hda hd.img -hdb fat:.`. Grub can see the virtual fat filesystem fine, but when I actually try to pass grub the image (exos.bin - but it's actually an ELF file) with `multiboot (hd1,1)/exos.bin` and `boot`, it just sits there. If I put those instructions in /boot/grub/grub.cfg on the ext4 filesystem, it clears the screen and then sits there.

I can boot the same image, with the same configuration, on the Grub2 actually installed on my computer, and it displays the glorious A to my screen.

Is this a problem with grub2? Or is this a problem with me compiling something wrong (see actual stuff below)? I seem to remember having a very similar (identical as far as I know - but what can you tell from a blank screen?) problem when I was setting stuff up with grub 1, the first time. (I lost those files by passing qemu /dev/sda3 as the disk image to use. "That's not a disk image - but I can fix that for ya!" Whoops.)

Ok, now the code I'm using. Makefile

Code: Select all

all: exos.bin

exos.bin: linker.ld loader.o kernel.o
        ld -melf_i386 -T linker.ld -o exos.bin loader.o kernel.o

loader.o: loader.s
        nasm -f elf -o loader.o loader.s 

kernel.o: kernel.c
        gcc -o kernel.o -c kernel.c -Wall -Wextra -nostdlib -nostartfiles -nodefaultlibs -m32 -march=i386

clean:
        rm -f *.bin *.o

export:
        cp exos.bin /boot

loader.s

Code: Select all

global loader           ; making entry point visible to linker
extern kmain
 
; setting up the Multiboot header - see GRUB docs for details
MODULEALIGN equ  1<<0                   ; align loaded modules on page boundaries
MEMINFO     equ  1<<1                   ; provide memory map
FLAGS       equ  MODULEALIGN | MEMINFO  ; this is the Multiboot 'flag' field
MAGIC       equ    0x1BADB002           ; 'magic number' lets bootloader find the header
CHECKSUM    equ -(MAGIC + FLAGS)        ; checksum required
 
section .text
align 4
MultiBootHeader:
   dd MAGIC
   dd FLAGS
   dd CHECKSUM
 
; reserve initial kernel stack space
STACKSIZE equ 0x4000                  ; that's 16k.
 
loader:
   mov esp, stack+STACKSIZE           ; set up the stack
   push eax                           ; pass Multiboot magic number
   push ebx                           ; pass Multiboot info structure
 
   call kmain
   cli
hang:
   hlt                                ; halt machine should kernel return
   jmp   hang
 
section .bss
align 4
stack:
   resb STACKSIZE                     ; reserve 16k stack on a doubleword boundary

kernel.c

Code: Select all

void kmain( void* mbd, unsigned int magic ) {
  if ( magic != 0x2BADB002 ) {
    /* Something went not according to specs. Print an error */
    /* message and halt, but do *not* rely on the multiboot */
    /* data structure. */
  }
 
  /* You could either use multiboot.h */
  /* (http://www.gnu.org/software/grub/manual/multiboot/multiboot.html#multiboot_002eh) */
  /* or do your offsets yourself. The following is merely an example. */ 
  char * boot_loader_name =(char*) ((long*)mbd)[16];
 
  /* Print a letter to screen to see everything is working: */
  unsigned char *videoram = (unsigned char *) 0xb8000;
  videoram[0] = 65; /* character 'A' */
  videoram[1] = 0x07; /* forground, background color. */
 
  /* Write your kernel here. */
}

linker.ld

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ENTRY (loader)

SECTIONS{
    . = 0x00100000;

    .text :{
        *(.text)
    }

    .rodata ALIGN (0x1000) : {
        *(.rodata)
    }

    .data ALIGN (0x1000) : {
        *(.data)
    }

    .bss : {
        sbss = .;
        *(COMMON)
        *(.bss)
        ebss = .;
    }
}

What did I do wrong?

Thanks in advance.

PS: since this is 32 bit code, I've tried it in both `qemu` (a 32-bit system) and `qemu-system-x86_64` - with identical results.

Posted: **Wed May 12, 2010 11:10 am**

Here's my GRUB2 config file, since I forgot it above:

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set default=0
set timeout=5
set root='(hd0,1)'

menu_color_normal=cyan/blue
menu_color_highlight=white/red

menuentry "ExOS" {
multiboot (hd0,1)/boot/exos.bin
boot
}

menuentry "ExOS-2" {
multiboot (hd1,1)/exos.bin
boot
}

Posted: **Sun May 30, 2010 10:20 am**

remove 'boot' from GRUB config file

Posted: **Sun May 30, 2010 10:46 am**

For all who wonder: I had to disable KVM. rmmod kvm_intel;rmmod kvm; and then it worked.

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grub2+qemu fails to boot image that boots with plain grub2

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Re: grub2+qemu fails to boot image that boots with plain gru

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