Re: Booting Linux Kernel without bootloader

On 8/3/06, Milton Miller [off-list ref] wrote:

On Tue Aug  1 2006 11:17:41 PM CDT,  Grant Likely  wrote:

quoted

On 7/25/06, Clint Thomas [off-list ref] wrote:

quoted

Basically, the system I want linux running on does not require the
initialization of hardware that U-boot provides, or at least it does not
need it to boot the linux kernel. I want to load an uncompressed linux
kernel into memory and start the execution of the kernel, without using any
kind of bootloader. Is this possible? Or does linux need some kind of
firmware or other software to tell it to start executing? Thanks for any
info you might have.

Loading a kernel into memory and starting execution *is* a boot loader.  :)

If it's running on the cpu, then I agreee.   But he didn't say how he was loading
the image into memory, and if it is via an external agent then I would not
necessarly call that a boot loader, altough it is performing those tasks.
Actually, that may be too broad.  Is kexec a boot loader?

I would say it is.  :)

IMHO, even the basic tasks of correctly setting up the initial
conditions can be considered a bootloader.

quoted

You could use the bootwrapper that is in the kernel source tree
(zImage).  If a zImage's entry point is at the execution entry point,
then it will start the Linux kernel correctly.  However, it is still a
compressed image.

The boot wrapper is a reference implementation, not a required piece of the
boot sequence.  As I stated in my previous post, the kernel entry conditions
are documted and loading the vmlinux raw is reasonable, asssuming that
the other conditions can be met (registers and device  treee, and maybe
initrd).

I agree.  However, the original post sounded to me like he was looking
for a canned solution.  I know zImage isn't exactly what he asked for
because it is a compressed image, but it does achieve the *effect* he
asked for.

I am curious as to the source of his requirements.  ie. what is
loading the kernel into ram?  Where is it coming from?

I've got a similar situation on my Virtex-4 platform.  The FPGA takes
care of all device initialization.  However, the kernel is loaded of a
CF card via a *slow* JTAG interface.  Loading an uncompressed image is
more time consuming than loading a compressed image and uncompressing
it in software.

quoted

If you *really* need an uncompressed image, I would start with the
bootwrapper and hack it to work with an non-gzipped kernel image.
However, why do you want to do it this way?  You probably won't gain
much in boot time and it will be more difficult to maintain.

Actually, the code is aready there to just copy anything inthe kernel
section that is without the gzip header.

Perfect!

cheers,
g.

-- 
Grant Likely, B.Sc. P.Eng.
Secret Lab Technologies Ltd.
grant.likely@secretlab.ca
(403) 399-0195