Exception 13 ?

[Winter Jörg]

James: ([e-mail]): Thanks for the hint on loading a Kernel,
but:

Now I have a verified routine that loads the kernel (block by block) from my
ATA-Disk into memory (at whatever I like. Currently at 0x00010000). I´m
loading a zImage at 0x00010000, the bootsect at 0x9000, 
the setupsectors (4) at 0x9200. It´s just like the other loaders do it
...he?

I have the code like: static void (*v)() =(void *)KERNEL_START;

I start like: v();

and the machine (the openbios) throws me an exception 13. (general
Protection Fault errorcode 0).

I tried nearly any combination of stack-location, entry-adress and
kerneltype ... all fails ...
I now read alot about descriptors and segments and so cause I suspect the
problem is somewhere there ...

But I just dont get the point. What am I doing wrong now ?? I thought the
kernel would just set up and start?

I figured out that already the jump done with the   v();  is the one that
causes the exception, no matter if there is a kernel or just dummy code
(like: jmp $).

There must be something I misunderstood completely !!  Help, I´m lost ...

greetinx,  J.Winter

-
To unsubscribe: send mail to [e-mail]
with 'unsubscribe openbios' in the body of the message

[James]

As I understand it, the zImage has a whole lot of junk to boot the kernel
at the start and it is compressd, so you can't just read it and jump to
it.  You first have to uncompress zImage (just gunzip zImage, I
forget if you have to rename zImage zImage.gz).  You then must strip the
kernel's boot code.  I always did this in a script like:
  objcopy -O binary -R .note -R .comment -S vmlinux /tmp/$$-tmp-linux
You then must regunzip the image in a format that your gunzip program can
read:
  gzip -f -3 /tmp/$$-tmp-linux

You must then use some C code (like inflate.c provided with the linux
kernel (which is the same inflate.c from openbios)) to inflate the image.
This is kinda tricky.  I do it by first copying the image in at something
like 0x20000 and then uncompressing that image to 0x100000 and then
jumping to 0x100000.  Oh yeah;  the kernel won't just boot completely, it
will get to somewhere (I think the bogomips test) and die because it is
missing interrupts or something like that.

You may want to start more basically by taking the zImage, uncompressing
it, stripping it, and then copying the big, uncompressed image straight to
0x100000 and jumping there.

- James

On Sat, 12 Feb 2000, [iso-8859-1] Winter J�rg wrote:
> James: ([e-mail]): Thanks for the hint on loading a Kernel,
> but:
>
> Now I have a verified routine that loads the kernel (block by block) from my
> ATA-Disk into memory (at whatever I like. Currently at 0x00010000). I�m
> loading a zImage at 0x00010000, the bootsect at 0x9000, 
> the setupsectors (4) at 0x9200. It�s just like the other loaders do it
> ...he?
>
> I have the code like: static void (*v)() =(void *)KERNEL_START;
>
> I start like: v();
>
> and the machine (the openbios) throws me an exception 13. (general
> Protection Fault errorcode 0).
>
> I tried nearly any combination of stack-location, entry-adress and
> kerneltype ... all fails ...
> I now read alot about descriptors and segments and so cause I suspect the
> problem is somewhere there ...
>
> But I just dont get the point. What am I doing wrong now ?? I thought the
> kernel would just set up and start?
>
> I figured out that already the jump done with the   v();  is the one that
> causes the exception, no matter if there is a kernel or just dummy code
> (like: jmp $).
>
> There must be something I misunderstood completely !!  Help, I�m lost ...
>
> greetinx,  J.Winter
>
> To unsubscribe: send mail to [e-mail]
> with 'unsubscribe openbios' in the body of the message

-
To unsubscribe: send mail to [e-mail]
with 'unsubscribe openbios' in the body of the message

[Jeff Garzik]

James wrote:
> As I understand it, the zImage has a whole lot of junk to boot the kernel
> at the start and it is compressd, so you can't just read it and jump to
> it.

Sure you can, as long as the right boot code is attached.  The final
stage of the kernel build looks something like

make vmlinux
    make bootcode
    gzip -9 vmlinux
    cat bootcode vmlinux.gz > zImage

You can jump directly to zImage, which will trigger the uncompress code.

If you use the "make zdisk" target, Linux will boot straight from a
floppy:

dd if=zdisk of=/dev/fd0

Regards,

Jeff

[Ronald G. Minnich]

On Sat, 12 Feb 2000, Jeff Garzik wrote:
> Sure you can, as long as the right boot code is attached.  The final
> stage of the kernel build looks something like
>
> make vmlinux
>    make bootcode
>    gzip -9 vmlinux
>    cat bootcode vmlinux.gz > zImage

what a zimage is (in short): 
1) 512 bytes of floppy boot block
2) 2048 bytes of secondary boot block. 
3) linux kernel startup, with an uncompressed header and a compressed
image. The uncompressed header does the gunzip. Since we use openbios
gunzip, one of these two gunzips is useless and should be removed. For
linuxbios we opt to remove the linux kernel gunzip -- it's dead code after
boot, so why put it in? saves a few bytes.

startup: 
If you're on floppy, the first 512 bytes are read, which reads the second
2048 bytes, which reads the kernel. The start of the kernel is some setup
and the 'unzipper'.

If you're on hard drive the standard booters skip the first 512 bytes and
go for the secondary bootstrap.

When we build a kernel for bios, we just compress vmlinux itself, minus
all the unzippers. I'm going to put this tree on the web page tomorrow.

Sorry if this is too short, isdn is screwing me up again.

ron

-
To unsubscribe: send mail to [e-mail]
with 'unsubscribe openbios' in the body of the message