Bran's OS tutorial Exception handling

[Chocrates]

Hey All,

Im going through the Bran Os tutorials and i cannot seem to get the idt set up to handle the exceptions.

Im a bit at a loss as to why its not working. The question is, what are some good ways to debug this early boot code, and are there any "normal" mistakes people usually make when trying to install these?

I can post the source, but for the most part its straight from the tutorials.

I am running this in qemu, and my physical cpu is an amd, which from what i can find doesn't seem like it has a GDT, which could be an issue.

[Nessphoro]

Eh, all x86 CPU have GDT,
and you're running QEMU which simulates the CPU, and in turn GDT,
Plus if you're booting via GRUB, it sets up a GDT for you.

But yeah, check if you're loading the LIDT with proper values.

[gerryg400]

and my physical cpu is an amd, which from what i can find doesn't seem like it has a GDT, which could be an issue.

What do you mean by this ? All 386 compatible CPUs need a GDT. Remember you must build the GDT.

[Chocrates]

and my physical cpu is an amd, which from what i can find doesn't seem like it has a GDT, which could be an issue.

What do you mean by this ? All 386 compatible CPUs need a GDT. Remember you must build the GDT.

Wiki and a few other places say that GDT is intel specific.

Plus if you're booting via GRUB, it sets up a GDT for you.

But yeah, check if you're loading the LIDT with proper values.

Not using grub, letting qemu boot the kernel for me....

i will go back through the LIDT code
thanks!

[gerryg400]

Plus if you're booting via GRUB, it sets up a GDT for you.

Grub tells you not to rely on its GDT. It does load some values into the segment regs but you must not try to reload them without your own GDT.

[gerryg400]

Wiki and a few other places say that GDT is intel specific.

And your AMD is an Intel clone. Rest assured it needs a GDT.

[Nessphoro]

Plus if you're booting via GRUB, it sets up a GDT for you.

Grub tells you not to rely on its GDT. It does load some values into the segment regs but you must not try to reload them without your own GDT.

Nevertheless it works,

And by GRUB I meant Multiboot compliant bootloader - aka QEMU's

[Chocrates]

No dice.

in the link.ld file i had to change phys = 0x00100000; to phys = 0x00001000; to allow qemu to load the kernel image

when compiling the the source from the tutorial, with the only modifcations being removing the underscores from function names in the asm file, and the link.ld file change, the exception handlers dont work.

Any ideas as to why the link.ld change is presumably causing this?

[Nessphoro]

Can we see your LD script.

[Chocrates]

OUTPUT_FORMAT("binary")
ENTRY(_start)
phys = 0x00001000;
SECTIONS
{
.text phys : AT(phys) {
code = .;
*(.text)
*(.rodata)
. = ALIGN(4096);
}
.data : AT(phys + (data - code))
{
data = .;
*(.data)
. = ALIGN(4096);
}
.bss : AT(phys + (bss - code))
{
bss = .;
*(.bss)
. = ALIGN(4096);
}
end = .;
}

[Bietje]

Can you give us some more information of the errors you get..

The only thing I can think of right now is that you are overwriting you own code at some point.

[Chocrates]

Aha!

turns out it was working flawlessly, except that my puts function doesn't like strings, but instead likes an array of chars....

I will look into that and post here if i fix it, for completeness.

I appologize for wasiting your time!

Edit:

apparently i should have looked harder as well:

http://wiki.osdev.org/Bran%27s_Known_Bugs