GRUB and Multiboot header Problem?

[amirsadig]

hi, I am tring to use GRUB to load some images in the memory.
as I read in Multiboot specification, I shlould set bit 3 so that Information about modules will be includes in the header information.

MULTIBOOT_PAGE_ALIGN   equ 1<<0
MULTIBOOT_MEMORY_INFO   equ 1<<1
MULTIBOOT_MODULE_INFO   equ 1<<3
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_MODULE_INFO
MULTIBOOT_CHECKSUM   equ -(MULTIBOOT_HEADER_MAGIC + MULTIBOOT_HEADER_FLAGS)


ALIGN 4
mboot:
   dd MULTIBOOT_HEADER_MAGIC
   dd MULTIBOOT_HEADER_FLAGS
   dd MULTIBOOT_CHECKSUM
; aout kludge. These must be PHYSICAL addresses
   dd mboot
   dd code
   dd bss
   dd end
   dd entry


then I receive this message when, GRUB try to load my kernel: "Unsupported Mutiboot features requested".

note that I use GRUB version 0.93

[Whatever5k]

You don't need so much stuff (actually, I'm too lazy to check what the MULTBOOT_MODULE_INFO is supposed to mean).
Just use this here:

Code: Select all

MULTIBOOT_PAGE_ALIGN   equ 1<<0
MULTIBOOT_MEMORY_INFO  equ 1<<1 MULTIBOOT_HEADER_MAGIC equ 0x1BADB002
MULTIBOOT_HEADER_FLAGS equ MULTIBOOT_PAGE_ALIGN | MULTIBOOT_MEMORY_INFO
CHECKSUM               equ -(MULTIBOOT_HEADER_MAGIC + MULTIBOOT_HEADER_FLAGS) ; The Multiboot header (in NASM syntax)
align 4
dd MULTIBOOT_HEADER_MAGIC
dd MULTIBOOT_HEADER_FLAGS
dd CHECKSUM

Now the Multiboot specification tells you that ebx contains the Multiboot info structure:

Code: Select all

/* The Multiboot information.  */
typedef struct multiboot_info
{
   unsigned long flags;
   unsigned long mem_lower;
   unsigned long mem_upper;
   unsigned long boot_device;
   unsigned long cmdline;
   unsigned long mods_count;
   unsigned long mods_addr;
   union
   {
      aout_symbol_table_t aout_sym;
      elf_section_header_table_t elf_sec;
    } u;
    unsigned long mmap_length;
    unsigned long mmap_addr;
} multiboot_info_t;

So in your assembly code, you just check if you are booted by GRUB (by a Multiboot boot loader respectively) and pass the multiboot info to a structure:

Code: Select all

cmp eax, 0x2BADB002 ; are we booted by GRUB?
jne no_multiboot 
mov [mboot_info], ebx
sete [mboot_valid]
jmp go_on

no_multiboot:
 ; do error handling or anything else here

go_on:
 ...

section .data
mboot_valid: dd 0
mboot_info: dd 0

Hope this helps...

[amirsadig]

thanks, it work.
I have supposed that I must the set bit 3, so that GruB write the information about the loaded modules.

[amirsadig]

still there something I don't understand. in the Multiboot header information I have set the begin of the code and the end of data and the end of my kernel as end of bss, so that it does not load modules before those address, but still it load it between them.

; these are in the linker script file
EXTERN _code, _bss, _end

ALIGN 4
mboot:
   dd MULTIBOOT_HEADER_MAGIC
   dd MULTIBOOT_HEADER_FLAGS
   dd MULTIBOOT_CHECKSUM
; aout kludge. These must be PHYSICAL addresses
   dd mboot
   dd _code // begin of text segment
   dd _bss // begin of bss is end of data segment
   dd _end // end of my kernel image
   dd entry

_code at 0x100000
_bss at 0x109000
_end at 0x119AE3

the module has been loaded at 0x10E000. normal it should load 0x11A000!!!