OSDev.org

Posted: **Fri Jan 30, 2009 5:06 pm**

Ok, before I start I would just like to say I spent a long time searching the forums and googling around before I considered posting. I then spent further time doing the same before I actually decided to click the button

So lets hope that will reduce the flaming

I'm new to the idea of OS development so I decided to follow the Wiki here http://wiki.osdev.org/Bare_bones as C is my language of choice. My code matches to that on the wiki and I have followed the instructions exactly. However, running Bochs I get a stream of "you suck messages":

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00000321341d[CPU0 ] UndefinedOpcode: ff causes exception 6
00000321341d[CPU0 ] exception(06 h)
00000321341d[CPU0 ] interrupt(): vector = 6, INT = 0, EXT = 1
00000321342i[CPU0 ] BxError: instruction with opcode=0xff
00000321342i[CPU0 ] mod was c0, nnn was 7, rm was 7
00000321342i[CPU0 ] WARNING: Encountered an unknown instruction (signalling illegal instruction)

I then played around some more and if I use the legacy BIOS for bochs or qemu there are no errors. It goes nicely to the grub screen (which is a nice start), and then obviously wants me to load the kernel and boot the OS. But there are no drives or anything mounted so I cannot point it to a kernel file or to anything. I'm loading it from floppy.img file (made using the instructions on the wiki above), and just wondered if someone could at the least point this noob in the right direction

Many thanks!

Posted: **Fri Jan 30, 2009 5:16 pm**

if you get into grub, it'll show the command prompt (if not, press c).

then, as per the wiki, type
kernel 200+18
boot

Posted: **Fri Jan 30, 2009 5:20 pm**

Oh my god. All I can say is thanks for not flaming me as I have read that wiki countless times and clearly missed something slapping me in the face. I do however get an error message, which I know is my fault but ...

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[multiboot-elf, <0x100000:0x38:0x4000>
Error 28: Selected Item cannot fit into memory

Ok I've read around and everywhere seems to point to rodata, but I can't see how this is my problem. This is the linker code:

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ENTRY (loader)

SECTIONS{
    . = 0x00100000;

    .text :{
        *(.text)
        *(.rodata)
    }

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

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

And here is the output from `objdump -h kernel.bin`

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kernel.bin:     file format elf32-i386

Sections:
Idx Name          Size      VMA       LMA       File off  Algn
  0 .text         00000038  00100000  00100000  00001000  2**4
                  CONTENTS, ALLOC, LOAD, READONLY, CODE
  1 .bss          00004000  00100038  00100038  00001038  2**2
                  ALLOC
  2 .comment      00000047  00000000  00000000  00001038  2**0
                  CONTENTS, READONLY

I can only guess that it's to do with .bss because of that output, but that's me making an uneducated guess

Any chance of an educated guess?

Edit: Wow I hate myself tonight. It was nothing to do with the code, all I needed to do was configure grub to have an amount of uppermemory.

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uppermem 64

Or however much you want, hope this helps someone

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