Multiboot 2 Specification

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iocoder
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Multiboot 2 Specification

Post by iocoder »

Hello Again!
I would like my kernel to run with 'multiboot2' command of GRUB2. but can't find any specification online that standards MULTIBOOT2. i made a multiboot2 header in my kernel (at the start of text section), but GRUB2 says: "multiboot header not found". here is my header:

Code: Select all 

asm(".long	0xe85250d6			"); // Magic Number.
asm(".long	0x00000000			"); // Architecture = 32-bit Intel PMode.
asm(".long	0x00000010			"); // Header Length
asm(".long	-(0x10+0xe85250d6)		"); // Checksum
Any help would be appreciated.
Regards.
gerryg400
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Re: Multiboot 2 Specification

Post by gerryg400 »

Are you sure that the multiboot 2 header looks like that ? The following code is from the file multiboot2.h in the latest Grub2 release.

Code: Select all 

 ...
/* The magic field should contain this. */
#define MULTIBOOT2_HEADER_MAGIC			0xe85250d6
 ...
struct multiboot_header
{
 /* Must be MULTIBOOT_MAGIC - see above. */
 multiboot_uint32_t magic;
 /* Feature flags. */
 multiboot_uint32_t flags;
 /* The above fields plus this one must equal 0 mod 2^32. */
 multiboot_uint32_t checksum;
 ...
};
Where did you get the information for the new header format ?
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iocoder
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Re: Multiboot 2 Specification

Post by iocoder »

Wow it works fine now!
Thanks gerryg400, but could i know from where i can get multiboot2.h?
I searched for it online with no result...
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Re: Multiboot 2 Specification

Post by gerryg400 »

It's in the Grub 1.98 source.
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Re: Multiboot 2 Specification

Post by iocoder »

thanks, i got the file and included it in my kernel.
right now, is there any way to know the size of the kernel from GRUB or the boot loader?? i need the kernel to know the size of itself every time it boots in order to mark its memory space as used in an implemented memory map. this will help allocating free memory space in an accurate way. do u have any idea, plz???
Regards,
gerryg400
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Re: Multiboot 2 Specification

Post by gerryg400 »

mostafazizo wrote:thanks, i got the file and included it in my kernel.
right now, is there any way to know the size of the kernel from GRUB or the boot loader?? i need the kernel to know the size of itself every time it boots in order to mark its memory space as used in an implemented memory map. this will help allocating free memory space in an accurate way. do u have any idea, plz???
Regards,
I don't know how to get it from Grub. I feel the best way is to define a variable in your linker script that marks the end of the loadable image. I think this will probably work.

Code: Select all 

SECTIONS
{
	.text 0x100000 : 
	 ALIGN (0x1000)
	 { *(.text) } 
	.data :
	 ALIGN (0x1000)
	 { *(.data) } 
	
	.bss :
	 ALIGN (0x1000)
	 { *(.bss) }
	 
	.unused_section :
	 ALIGN (0x1000)
	 { kernel_end = . ; }
}
You can refer to kernel_end from within your code.

Code: Select all 

	extern uint32_t kernel_end;
	/* Get the physical address of the end of the image */
	pfree = (uint32_t)&kernel_end;
It's a little messy ( == there is probably a better way ) but it should work.
Last edited by gerryg400 on Thu Sep 02, 2010 9:08 pm, edited 1 time in total.
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Hangin10
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Re: Multiboot 2 Specification

Post by Hangin10 »

It doesn't need to be in a section, just inside the SECTIONS block.
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Re: Multiboot 2 Specification

Post by iocoder »

thanks gerryg400! thanks Hangin10!
the code works fine!
Here is my ld script:

Code: Select all 

ENTRY (init)
SECTIONS {
	. = 0x100000;
	ld_kernel_start = . ;
	
	.text	: {	*(.text )	}
	.bss	: {	*(.bss )	}
	.data	: {	*(.data )	}
	.rodata	: {	*(.rodata)	}
	
	ld_kernel_end = . ;
	
}
I wonder if i could know the boot device path (PCI bus/dev/func and so on) from GRUB2. do u have any idea? any help is appreciated...
sorry for the large quantity of questions, but this is only because i stayed months developing my kernel neglecting this part of it, cause it is full of obstacles.
Regards,
gerryg400
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Re: Multiboot 2 Specification

Post by gerryg400 »

mostafazizo wrote:I wonder if i could know the boot device path (PCI bus/dev/func and so on) from GRUB2. do u have any idea? any help is appreciated...
sorry for the large quantity of questions, but this is only because i stayed months developing my kernel neglecting this part of it, cause it is full of obstacles.
Regards,
You can get the bios drive number and the partition numbers from the multiboot_info struct.
If a trainstation is where trains stop, what is a workstation ?
iocoder
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Re: Multiboot 2 Specification

Post by iocoder »

gerryg400 wrote:
mostafazizo wrote:I wonder if i could know the boot device path (PCI bus/dev/func and so on) from GRUB2. do u have any idea? any help is appreciated...
sorry for the large quantity of questions, but this is only because i stayed months developing my kernel neglecting this part of it, cause it is full of obstacles.
Regards,
You can get the bios drive number and the partition numbers from the multiboot_info struct.
I know well :D but the BIOS Drive Number is not enough for a kernel that supports ATA/SATA HDDs, CD-ROMs, USB Mass Storage Devices and USB CD-ROMs to know which of those devices is the boot device...
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Re: Multiboot 2 Specification

Post by gerryg400 »

mostafazizo wrote:I know well :D but the BIOS Drive Number is not enough for a kernel that supports ATA/SATA HDDs, CD-ROMs, USB Mass Storage Devices and USB CD-ROMs to know which of those devices is the boot device...
I don't think there is one easy way. This thread may help.
If a trainstation is where trains stop, what is a workstation ?
Love4Boobies
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Re: Multiboot 2 Specification

Post by Love4Boobies »

Multiboot 2. You're welcome! :)
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gerryg400
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Re: Multiboot 2 Specification

Post by gerryg400 »

Love4Boobies wrote:Multiboot 2. You're welcome! :)
The problem with that document is that it doesn't match the current version of Grub (1.98). The version of multiboot2.h in the Grub distro and the version in the multiboot documentation are quite different. Oddly the magic numbers are the same. I'm not sure what the Grub guys are doing.

I think Grub 1.98 (and multiboot2.h in particular) are not Multiboot 2 compliant.
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Love4Boobies
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Re: Multiboot 2 Specification

Post by Love4Boobies »

They are obviously being uber-awesome again... :roll: Better build the PDF from http://bzr.savannah.gnu.org/r/grub/branches/multiboot2/ instead (you'll need the Bazaar versioning system).
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Re: Multiboot 2 Specification

Post by Kevin »

gerryg400 wrote:extern uint32_t kernel_end;
You don't actually want to refer to a value in the first 32 bit of the kernel, so I prefer to declare it as what it really is:

Code: Select all 

extern const void kernel_end;
Doesn't work in C++, though, as far as I know.
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