GPF happening when loading kernel

HitmanYesman · **Joined:** Fri Apr 23, 2010 8:27 am **Posts:** 47

So, I have my kernel which is Kernel.c. I have my second bootloader which loads my kernel and copies it to the 1 MB after i enter Protected Mode. Bochs has a GPF and infinitely reboots. It's not that it can't find the file because I added in a way to display a message if the file didn't exist. So if you guys could take a look at it I'd be grateful.

These are the variables that I use and I show what they are so you guys can get a better understanding of it.:

Code:

CODE_DESC = 0x08
DATA_DESC = 0x10
IMAGE_RMODE_BASE = 0x3000
IMAGE_PMODE_BASE = 0x100000

Kernel.c:

Code:

void ClrScr();

int main(void)
{
   ClrScr();
   
   for (;;);
}

void ClrScr()
{
   char *vidmem = (char*)0xB8000;
   unsigned int i;
   
   for (i = 0; i < (80*25); i++) {
      *vidmem++ = 0;
      *vidmem++ = 0xF;
   }
}

From when I enter PMode from second bootloader:

Setup.asm:

Code:

Loader:
   mov   ax, DATA_DESC
   mov   ds, ax
   mov   ss, ax
   mov   es, ax
   mov   esp, 0x90000
   
Copy_Image:
   mov eax, DWORD [ImageSize]
   movzx ebx, WORD [bpbBytesPerSector]
   mul ebx
   mov ebx, 4
   div ebx
   cld
   mov esi, IMAGE_RMODE_BASE
   mov edi, IMAGE_PMODE_BASE
   mov ecx, eax
   rep movsd
   
   jmp   CODE_DESC:IMAGE_PMODE_BASE
   
   cli
   hlt

And this is how I'm compiling the Kernel.c file if it matters at all. By the way Setup.asm looks for the file called "KRNL32.BIN".

GCC Code:

Code:

gcc -ffreestanding -c Kernel.c -o KRNL32.BIN

Thanks for taking the time to read this and help me.

Combuster · **Posted:** Mon Apr 26, 2010 2:12 pm

Quote:

gcc -ffreestanding -c Kernel.c -o KRNL32.BIN

Care to explain to us what those flags do, and why you use them?

HitmanYesman · **Joined:** Fri Apr 23, 2010 8:27 am **Posts:** 47

Well, I've read a few tutorials on compiling with gcc and some have -ffreestanding some don't. As for -c if I don't put that it says no input files were listed and -o is the output file name.

Combuster · **Posted:** Mon Apr 26, 2010 2:29 pm

So you don't know what you are doing? :roll:

That needs fixing. I suggest you start with gcc's manuals.

HitmanYesman · **Joined:** Fri Apr 23, 2010 8:27 am **Posts:** 47

I just don't know what -ffreestanding does but I can find that out quickly. But any idea as to why it causes a GPF?

Combuster · **Posted:** Mon Apr 26, 2010 2:33 pm

Apparently you don't know what -c does either.

Also, why didn't you look up -ffreestanding before posting?

HitmanYesman · **Joined:** Fri Apr 23, 2010 8:27 am **Posts:** 47

Yeah I do. It compiles and assembles the file I specify. -o then can rename it.

Combuster · **Posted:** Mon Apr 26, 2010 2:36 pm

What then, does the absence of -c do?

Also, why didn't you look up -ffreestanding yet?

HitmanYesman · **Joined:** Fri Apr 23, 2010 8:27 am **Posts:** 47

Without -c it would link the file as well as compile. I'm searching for -ffreestanding at the moment.

Combuster · **Posted:** Mon Apr 26, 2010 2:40 pm

Would linking be the correct behaviour?

What would be the reasons that you would you linking over?

Also, why didn't you look up -ffreestanding before posting?

Why did I have to ask that three times?

HitmanYesman · **Joined:** Fri Apr 23, 2010 8:27 am **Posts:** 47

I'm not sure if linking would be the correct behaviour or not.

I didn't look it up because honestly I didn't think it was that important at the time and I really just want the kernel to be able to clear the screen at the moment.

Combuster · **Posted:** Mon Apr 26, 2010 2:45 pm

How would you try to find out if linking is correct or wrong?
What does linking do?
Why would you skip linking?
Also, why didn't you look up -ffreestanding before posting?
Why did I have to ask that four times?
Why do I keep asking questions?

HitmanYesman · **Joined:** Fri Apr 23, 2010 8:27 am **Posts:** 47

Quote:

How would you try to find out if linking is correct or wrong?

Read the GCC user's manual

Quote:

What does linking do?

Gathers multiple files and puts them all into one file

Quote:

Why would you skip linking?

Didn't think it was needed

Quote:

Also, why didn't you look up -ffreestanding before posting?

"I didn't look it up because honestly I didn't think it was that important at the time and I really just want the kernel to be able to clear the screen at the moment."

Quote:

Why did I have to ask that four times?

Because I posted right away to answer your initial question and failed to see you asked that.

Quote:

Why do I keep asking questions?

To let me know I need to read up on the compiler manual more...

Combuster · **Posted:** Mon Apr 26, 2010 2:56 pm

Then why didn't you look linking up in the GCC manual?
Does linking do anything else?
Why would you make a decision based on something you didn't know for sure?
Why didn't you explain -ffreestanding yet?
Why did I have to ask that three times after you saw it?
Why am I still asking this question?
Why are you still replying if you think you should be reading the manual first?

HitmanYesman · **Joined:** Fri Apr 23, 2010 8:27 am **Posts:** 47

Sorry, had to do something. And no I haven't read my manual yet.

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GPF happening when loading kernel

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