On 12/05/2011 8.21, Sudheer Divakaran wrote:
On Thu, May 12, 2011 at 10:02 AM, Sudheer Divakaran <inbox1.sudheer@gmail.com> wrote:
Hi Vikram,
On Thu, May 12, 2011 at 9:02 AM, Vikram Narayanan<vikram186@gmail.com> wrote:
On Thu, May 12, 2011 at 1:51 AM, Mulyadi Santosa <mulyadi.santosa@gmail.com> wrote:
On Thu, May 12, 2011 at 03:11, Vikram Narayanan<vikram186@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.
One more info I want to clarify is, vmlinux.bin mentioned in the above snippet contains the compressed binary image and some other routines. Just go through the 'make V=1' output, you can see that the build process is actually compressing binary file extracted from the vmlinux elf image, which is again combined with some object files, creates another elf and again extracts the binary and finally combined with the setup.bin to create the final bzImage. So, elf interpretation doesn't happen on the uncompressed code.
Let's put some order here. The image that almost all bootloaders use is arch/x86/boot/bzImage which is made of a setup binary file (executable) joined with some compressed code (the real kernel) which is uncompressed in memory by the setup binary. The big suggestion I can give is to check the hidden files which end with .cmd. There is one of these for every object created by the compilation process. For example there is a file called .bzImage.cmd which tell you how bzImage was made: arch/x86/boot/tools/build -b arch/x86/boot/setup.bin arch/x86/boot/vmlinux.bin CURRENT > arch/x86/boot/bzImage NOTE: I refer to a quite old kernel here, it's likely that the compilation process has changed somehow. You can proceed now in reverse order to find how bzImage was made (if I understand correctly that is the one you are interested in). Here is how is made on my kernel tree: bzImage: arch/x86/boot/tools/build -b arch/x86/boot/setup.bin arch/x86/boot/vmlinux.bin CURRENT > arch/x86/boot/bzImage arch/x86/boot/vmlinux.bin: objcopy -O binary -R .note -R .comment -S arch/x86/boot/compressed/vmlinux arch/x86/boot/vmlinux.bin arch/x86/boot/compressed/vmlinux: ld -m elf_i386 -T arch/x86/boot/compressed/vmlinux_32.lds arch/x86/boot/compressed/head_32.o arch/x86/boot/compressed/misc.o arch/x86/boot/compressed/piggy.o -o arch/x86/boot/compressed/vmlinux arch/x86/boot/compressed/piggy.o: ld -m elf_i386 -r --format binary --oformat elf32-i386 -T arch/x86/boot/compressed/vmlinux.scr arch/x86/boot/compressed/vmlinux.bin.gz -o arch/x86/boot/compressed/piggy.o arch/x86/boot/compressed/vmlinux.bin.gz: gzip -f -9 < arch/x86/boot/compressed/vmlinux.bin > arch/x86/boot/compressed/vmlinux.bin.gz arch/x86/boot/compressed/vmlinux.bin: objcopy -O binary -R .note -R .comment -S vmlinux arch/x86/boot/compressed/vmlinux.bin vmlinux: ld -m elf_i386 --build-id -o vmlinux -T arch/x86/kernel/vmlinux.lds arch/x86/kernel/head_32.o arch/x86/kernel/init_task.o init/built-in.o --start-group usr/built-in.o arch/x86/kernel/built-in.o arch/x86/mm/built-in.o arch/x86/mach-default/built-in.o arch/x86/crypto/built-in.o arch/x86/vdso/built-in.o kernel/built-in.o mm/built-in.o fs/built-in.o ipc/built-in.o security/built-in.o crypto/built-in.o block/built-in.o lib/lib.a arch/x86/lib/lib.a lib/built-in.o arch/x86/lib/built-in.o drivers/built-in.o sound/built-in.o arch/x86/math-emu/built-in.o arch/x86/pci/built-in.o arch/x86/power/built-in.o net/built-in.o --end-group .tmp_kallsyms2.o NOTE: there are 2 vmlinux (vmlinux and arch\x86\boot\compressed\vmlinux) and 2 vmlinux.bin (arch\x86\boot\compressed\vmlinux.bin and arch\x86\boot\vmlinux.bin) which are not the same Hope this helps Regards Luca Ellero