Hi Maneesh, Thanks for making the things more clear. Now I got the point that in case of bzImage kernel is loaded at 0x1000 only, but as soon as you have loaded 64k of it, it will be moved to high mem [i.e. 0x100000]... tell me if I am wrong. So bzImage is never placed at physical location 0x1000. It means that now uncompression routines are loaded at 0x100000 [instead of 0x10000 with zImage] and then head.S and misc.c [which have been moved to 0x100000] will then uncompress the kernel at 0x100000 again ?? Please clear these points also... TIA. Sumit Sharma. On Mon, 20 Sep 2004 manish regmi wrote : >>Hi, >>I would like to know about the memory layout of kernel when it boots with >>bzImage [i.e Big kernel]. I understand the following things :- >> >>1. Boot loader code [512 bytes] is loaded at 07c0:0000 address [i.e. 0x7c00 >>Physical address] using int 0x19 by the BIOS after POST thing. >>2. Boot loader code [here I assume that it's Linux Kernel Legacy bootloader and not >>any other LILO or Grub] then moves itself to location 0x90000. >>3. Then it loades the setup code at 0x90200 location. >>4. After this, bool loader loades compressed kernel image [zImage] at address >>0x10000 and then jumps to address 0x90200 [i.e at setup code]. >>5. Setup code then moves kernel from 0x10000 to 0x1000 location overwriting >>firmware code previously present there. Now setup code changes real mode to >>protected mode and transfers control to 0x1000. >>6. Now, you have compressed kernel Image at location 0x1000 whose intial code is >>head.S code. This code uncompresses the kernel at location 0x100000 and starts >>executing from there. >> >>FYI the above explaination is about zImage whose size can't be more than 512 KB. >>Can anyone tell me what happens in case of bzImage. >> >>What I understand is bzImage can't be loaded at location 0x10000 by the bootloader >>code [Explained in step 4], as we have limited space available only from 0x10000 to >>0x90000 [i.e 512 KB], but generally the size of bzImage is > 512 KB. So it can't be >>loaded there completely. >>Moreover, bootloader can't load kernel at high memory [0x100000] because CPU is >>running in real mode. >> >>Is bzImage partially loaded at 0x10000 and then this partial bzImage is moved to >>0x100000 instead of 0x1000 by setup code [after changing to real mode] ? If it is >>so, then there should be some code in head.S or misc.c [Which are the heads of >>bzImage] to load the rest portion of the bzImage, but I don't see this. >> >>Anyone please clear this doubt related to booting with bzImage. >> >>Thanks in advance. >>Sumit Sharma. > >Hi, >While loading bzImage the kernel does memory transfer from low memory to high memory (64K chunks) . >see setup.S line 836 > >also see 2.4 kernel internals > http://www.faqs.org/docs/kernel_2_4/lki-1.html#ss1.2 > >>Moreover, bootloader can't load kernel at high memory [0x100000] because CPU is >>running in real mode. > NOTE: In real mode we can access the 4G address space . It in known as Unreal Mode. >and grub runs in Protected mode. It contains code to switch itself to protected mode and switch back when reqd. > >regards manish > >_________________________________________________________________ >Help STOP SPAM with the new MSN 8 and get 2 months FREE* http://join.msn.com/?page=features/junkmail >
