reptar | static sites that roar | Static Site Generator library

if jq is not a strict requirement, alternatively you could do it using a unix walk-path utility jtc

QEMU will use host CPU when the guest CPU is doing something, even if that "something" is "spin around in a tight loop". If the guest code uses the CPU instruction WFI ("wait for interrupt") in its idle loop, QEMU will handle that by stopping until a guest interrupt occurs. (WFI is an Arm instruction; for other guest architectures there is generally an equivalent instruction, like x86's HLT.)

So whether QEMU uses 100% CPU when the guest is "idle" depends on what exactly the guest's idle loop does. The idle loop in a "real OS" like Linux will use WFI (which on real hardware is useful for reducing power consumption) and so will idle at very low host CPU usage. CPU usage sitting at a u-boot prompt will depend on how u-boot is coded; CPU usage in your assembly code will depend on what it does.