Deeper debugging of the loader requires poking around in the kernel loader. The easiest way to do that is to just build a custom kernel with calls to printk and run it in qemu.

cd $KERNEL_SOURCES
make ARCH=arm versatile_defconfig
make ARCH=arm CROSS_COMPILE=arm-linux-gnueabi- all -j10
cd arch/arm/boot

This builds a kernel. Rebuild as-needed with additional instrumentation. Next, we need a filesystem (or at least an init process) for the kernel to boot. We don’t actually need much here, so we can just set our test binary as init. The kernel will panic when the binary exits, but that is fine.

# Assume that the test binary is called 'init'
echo init | cpio -o --format=newc > initramfs

To run the image with the test binary, use

qemu-system-arm -M versatilepb -m 128M -kernel zImage -nographic -append "earlyprintk=vga,keep" -dtb ./dts/versatile-pb.dtb -initrd initramfs

• The -dtb argument provides an ARM device tree to qemu to tell it how to map various devices. We don’t bother to initialize graphics and just dump logs to the terminal we are running qemu in.
• To exit qemu after it crashes, hit C-a, c, q <enter>.