How vmlinux is recognized?

[Sudheer Divakaran]

Hi Vikram,

On Thu, May 12, 2011 at 9:02 AM, Vikram Narayanan <vikram186 at gmail.com> wrote:
> On Thu, May 12, 2011 at 1:51 AM, Mulyadi Santosa
> <mulyadi.santosa at gmail.com> wrote:
>> On Thu, May 12, 2011 at 03:11, Vikram Narayanan <vikram186 at gmail.com> wrote:
>>> Yes. I agree. But how who converts the ELF binary to raw binary so
>>> that the processor understands. Or how is it actually done?
>>
>> OK I try my best to understand your question :)
>>
>> i think I got it...you probably guessed that vmlinux created first,
>> then vmlinuz... AFAIK, it's the other way around...or more precisely,
>> not both.
>
> I think you got it wrong. I will try to put my question more elaborately.
> 1) The system is on and BIOS code runs. It gives the control to the
> boot loader, say GRUB.
> 2) Grub picks up the kernel from the specific partition. (i.e a
> vmlinuz image), which denotes that it is compressed.
> 3) There are uncompression routines in the kernel itself, If I am not
> wrong. So the kernel uncompresses itself.
> 4) Now the uncompressed thing is the vmlinux image, right?
> 5) The vmlinux is in ELF format. Correct?
> 6) If the OS boots and if u try to run an ELF file, the loader knows
> how to load that in the RAM. (I mean it knows how to interpret the ELF
> format)
> 7) Coming back to the vmlinux image, Who takes care of the loading activity.?
> 8) Who recognizes that the image is ELF format and do the necessary
> things accordingly.?
>
> Hope I have my question clear now.
>



If understand your question correctly, you believe that the
uncompressed kernel is in elf format. correct?. it is in binary
format, so elf interpretation is not required, #5 is wrong.

You can see this by building the kernel using 'make V=1'  and note the
following line in the output,

"arch/x86/boot/tools/build arch/x86/boot/setup.bin
arch/x86/boot/vmlinux.bin CURRENT > arch/x86/boot/bzImage"

means bzImage is made out of two binary files extracted from the elf images.
-- 
Thanks
Sudheer