Qemu booting raw kernel image (not ELF)

Issue

is there a way to convince qemu (qemu-system-mipsel v4.1.0, if it matters) to load a binary (non-elf) image built for (ancient) u-boot?

I tried both my uImage and vmlinux.bin, but I always get "The image is not ELF"

Full command-line is:

qemu-system-mipsel -M malta -kernel output/images/vmlinux.bin -serial stdio -drive file=output/images/rootfs.ext2,format=raw -append "rootwait root=/dev/hda" -net nic,model=pcnet -net user

Error is:

qemu-system-mipsel: could not load kernel 'output/images/vmlinux.bin': The image is not ELF

... which is absolutely true! That image (its uImage counter-part, actually) works fine on a real target (very similar to Malta, but that's beyond point; a failing kernel would be a completely different problem) using (in u-boot) something like:

usb reset; fatload usb 0 85000000 uImage; fatload usb 0 86000000 initram.cpio.xz; setenv bootargs rd_start=0x86000000 rd_size=15000000 USE=usb; bootm 85000000

As said: my problem is qemu doesn't even try to load the image, not that it fails at run-time.

What is the right spell to use?

Solution

You may have to use the -bios flag to provide the U-boot image and then set up the environment yourself to do the hand-off to the kernel. From my understanding, QEMU requires ELF-formatted images to be provided to the -kernel flag, presumably (heavy emphasis on this word) because the data contained in the ELF headers is necessary to configure the environment in lieu of a true bootloader (since you're effectively bypassing that boot stage and jumping straight to kernel execution). -bios does not have these requirements, as you're probably not going to see a first-stage binary using ELF headers.

If you know the entry point to the kernel image, which it seems like you do based off of that uboot command, you could use the -bios flag in conjunction with the -device loader,addr=[entry point],cpu-num=0. However, if there's any MMU, TLB, or other arch-specific addressing going on in your hardware, you might run into problems with that.

Take all of this with a dose of a skepticism, as I'm only working off of knowledge I've acquired by doing something similar to you. There may be a better way of doing it.

Answered By - SwarthyMantooth