Messages in this thread | | | Subject | Re: [RFC PATCH] x86/boot: make ELF kernel multiboot-able | From | Chao Peng <> | Date | Thu, 16 Feb 2017 10:12:10 +0800 |
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On Wed, 2017-02-15 at 17:42 +0100, Paolo Bonzini wrote: > > On 15/02/2017 15:41, Chao Peng wrote: > > > > Multiboot specification (http://git.savannah.gnu.org/cgit/grub.git/tree/doc/multiboot.texi?h=mul > > tiboot2) > > is an open standard that provides kernels with a uniform way to be booted > > by multiboot-compliant bootloaders (like grub). > > > > This patch is trying to make Linux ELF kernel image to be a > > multiboot-compliant OS so that it can be loaded by a multiboot-comliant > > bootloader. The benefit is eliminating the maintainance for realmode and > > decompression code and especially when the kernel is loaded in a virtual > > machine, the reducing for these code can greatly cuts down the boot time. > > > > However, the current version of multiboot spec doesn't support 64 bit > > well so for 64 bit kernel we need stub code to jump from 32 bit code to > > 64 bit code. Besides, there are still some other issues: > > 1). '-z max-page-size=0x1000' is used so the text segment start is in > > multiboot header search scope because GNU LD has default page size of > > 0x00200000 for ELF64, which will fail multiboot test. > > > > 2). The bootloader like grub has support for ELF kernel (even for ELF64) > > which makes the patch easier. However, the current grub implementaion > > thinks the entry address should be a VA. E.g. for 64 bit kernel, the entry > > address (0x1000000) is actually phiscial address, grub refuses to load it > > by saying: 'entry point isn't in a segment'. > > For kvm-unit-tests, we do "objcopy -O elf32-i386 dest.32bit dest.64bit" > and pass the resulting 32bit ELF file to grub. > > Out of curiosity, what happens if you pass the resulting multiboot file > to QEMU's -kernel option? >
The resulting kernel is a multiboot2 kernel. QEMU however supports loading multiboot v1 only.
Chao > Thanks, > > Paolo > > > > > This patch is sent out as RFC in case you have some ideas. > > > > Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
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