On 15/02/2017 15:41, Chao Peng wrote: > Multiboot specification > (http://git.savannah.gnu.org/cgit/grub.git/tree/doc/multiboot.texi?h=multiboot2) > 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? Thanks, Paolo > This patch is sent out as RFC in case you have some ideas. > > Signed-off-by: Chao Peng <chao.p.p...@linux.intel.com>
