On 06.05.2011, at 01:50, Rob Landley wrote: > On 05/05/2011 06:26 PM, Alexander Graf wrote: >>> As an aside: I think QEMU should have an option which is "just load >>> a plain ELF or raw binary, with no funny Linux-kernel-specific >>> behaviour" rather than overloading -kernel to mean "if it's a raw >>> image it's Linux and if it's an ELF file it's not". >> >> Traditionally, -bios has been that one. -kernel is more of a real >> bootloader replacement, including all the weirdness a bootloader does >> :). > > Except that neither "qemu-system-x86_64 -bios vmlinux" nor > qemu-system-x86_64 -kernel vmlinux" will load an ELF kernel on x86-64. > > The code to do this _exists_ within qemu, it's just not hooked up > consistently on all targets. We have a universal cross-platform image > format, and we have support in qemu for loading that format, and for > some reason it's only enabled on certain targets. I've never understood > why...
Unfortunately, booting isn't that easy :). The kernel needs some more data than just itself and an entry point to properly load. On some architectures, it requires a device tree (and pointer to it in a register), it might require page tables / TLB entries to be set up, if you want -initrd and -append to work you also need to tell the kernel where to find those. So while ELF is a nice container for binaries, there are still some pieces missing to actually make it a kernel loader. But that's what multiboot was invented for. I haven't seen too much effort going on around multiboot on non-x86, but it basically fills exactly the gap you're wondering about. It uses ELF and adds a simple boot protocol for all the other fancy stuff a kernel needs. Alex
