So you've built the kernel. Now what can you do with it?
The main missing ingredient now is a root filesystem.
Some options:
- https://github.com/ivandavidov/minimal. Educational mostly. BusyBox + glibc init and shell, syslinux bootloader, no GCC cross compile.
- https://buildroot.org/. Professional stuff.
For x86 (TODO why only x86?), you can generate a bootable ISO with:
make isoimage FDINITRD=rootfs.cpio.gz
where FINITRD points to a previously constructed initrd that will be used to initialize the system.
This was used by Minimal Linux Live, which produces a nice little rootfs.cpio.gz with BusyBox.
The output file generated is:
build/arch/x86/boot/image.iso
You can then feed the generated ISO directly to QEMU with either:
qemu-system-x86_64 -cdrom image.iso
qemu-system-x86_64 -hda image.iso
or burn it to either an USB or CD with:
sudo dd if=image.iso of=/dev/sdX
Internally in 4.2, it is coded at arch/x86/boot/Makefile, and syslinux, mkisofs to make a ISO, and then isohybrid to make it bootable either from ISO or USB.