elf format, symbols and ld linker script

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FlashBurn

Joined: 06 Jan 2005
Posts: 87

FlashBurn 22 May 2006, 10:11

I´m about to move my kernel to the elf format, but as always this isn´t as easy as I thought Sad

1st problem is I use the addresses of labels for things like that:

Code:

foo1 dw bar and 0xffff
foo2 dw bar shr 16

2nd problem is that I defined a constant for the size of the kernel:

Code:

kernel_size= bss_end - init

section '.text' executable align 16
init:
...
mov ecx,(kernel_size shr 12) + 3
...
section '.data' writeable align 4096
...
mem_stack_4kb dd (kernel_size and 0xfffff000) + 0xc0012000
...
section '.bss' writeable align 4096
...
bss_end:

This wont work anymore! What have I to do to make it work again?

The next problem I have is the linker script for ld. I want to specifiy that the pma is 0x100000 and the vma is 0xc0000000. How can I do this? At the moment I use the org command for setting the address, but this doesn´t work right Sad

Maybe there is a tutorial for using linker scripts?

22 May 2006, 10:11

FlashBurn

Joined: 06 Jan 2005
Posts: 87

FlashBurn 22 May 2006, 10:47

Ok, I found a sample script and modified it a little bit for my needs!

Code:

/* Link.ld */
OUTPUT_FORMAT("elf32-i386")
OUTPUT(kernel.so)
ENTRY(init)
SECTIONS
{
    .text 0xc0100000 : AT ( 0x100000 )
    {
        _code = .;
        *(.text)
        . = ALIGN(4096);
    }

    .data : AT ( 0x100000 + ( ADDR(.data) - ADDR(.text) ) )
    {
        _data = .;
        *(.data)
        . = ALIGN(4096);
    }

    .bss : AT ( 0x100000 + ( ADDR(.bss) - ADDR(.text) ) )
    {
        _bss = .;
        *(.bss)
        . = ALIGN(4096);
    }

    _end = .;
}

I haven´t tested if the code works alright.

22 May 2006, 10:47

FlashBurn

Joined: 06 Jan 2005
Posts: 87

FlashBurn 22 May 2006, 12:13

Ok, the script and the kernel are working now Razz

I have only one problem left Wink

How can it be made that all sections except .text, .data and .bss come direct after the elf header and then these 3 section come?

22 May 2006, 12:13

MarcoAlves

Joined: 09 Jun 2006
Posts: 30

MarcoAlves 19 Jun 2006, 13:10

FlashBurn, I've tried to use your ld script but with no success. I'm using
djgpp under windows. When I try to link the linker says that it can't recognize elf32-i386 format.

Please, help me.
Thx in advance.

Best regards,
Marco Alves.

19 Jun 2006, 13:10

FlashBurn

Joined: 06 Jan 2005
Posts: 87

FlashBurn 19 Jun 2006, 14:36

Show me your kernel source and then maybe I can help you.

19 Jun 2006, 14:36

MarcoAlves

Joined: 09 Jun 2006
Posts: 30

MarcoAlves 19 Jun 2006, 14:44

The kernel is attached.

It's SO simple. I'm noob yet. Smile

Description:		Download
Filename:	main.rar
Filesize:	1.02 KB
Downloaded:	370 Time(s)

19 Jun 2006, 14:44

FlashBurn

Joined: 06 Jan 2005
Posts: 87

FlashBurn 19 Jun 2006, 19:11

1st thing is that you use djgpp and with this compiler you can´t compile for elf format! And my script isn´t something for someone who don´t have enough knowledge. I think you should use grub as bootloader and I don´t know but I think it should load coff files.

19 Jun 2006, 19:11

MarcoAlves

Joined: 09 Jun 2006
Posts: 30

MarcoAlves 19 Jun 2006, 19:38

FlashBurn, I've understood entirely your script. Smile

I'm new on asm, but senior C# .NET programmer, so I think that I can acquire the "enough knowlege" just reading, and reading and reading. Smile

I just didn't understood why the error happens because djgpp's ld was not linking. Now, i get it.

Nevertheless, thank you.

19 Jun 2006, 19:38

FlashBurn

Joined: 06 Jan 2005
Posts: 87

FlashBurn 21 Jun 2006, 18:01

Either you make yourself a crosscompiler or you use grub + coff kernel. djgpp isn´t the best solution for os deving!

21 Jun 2006, 18:01

MarcoAlves

Joined: 09 Jun 2006
Posts: 30

MarcoAlves 22 Jun 2006, 12:41

I'm downloading cygwin. Hope it help me.

22 Jun 2006, 12:41

FlashBurn

Joined: 06 Jan 2005
Posts: 87

FlashBurn 23 Jun 2006, 14:49

I don´t know if I used mingw or cygwin for creating my crosscompiler, but I think it was mingw and I also onyl needed ld for linking, because I´m only writing in asm.

23 Jun 2006, 14:49

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