QEMU debugging techniques

Capture everything

qemu-system-x86_64 -m 512 -cdrom build/opencube.iso \
    -serial file:boot.log -display none \
    -netdev user,id=n1 -device e1000,netdev=n1

The serial log IS the boot narrative - one OK per subsystem.

Watch the machine, not just the guest

-d int,cpu_reset,guest_errors -D qemu.log    (interrupts/resets/errors)
-monitor stdio                               (QEMU monitor alongside)

GDB into the kernel

qemu-system-x86_64 ... -s -S        # gdb stub, frozen at reset
gdb build/opencube_base.elf          # the pre-strip ELF has symbols
(gdb) target remote localhost:1234
(gdb) break kmain
(gdb) continue

build/opencube_base.elf is kept by make kernel precisely for this - the final build/opencube.elf is stripped.

Deterministic replays

The build is reproducible - the same tree produces byte-identical ELFs, so a crash you can reproduce twice is the same bytes both times. Combine with QEMU's own -icount for timing stability in network tests.

Device matrix at a glance

The QEMU flags that light up each driver family are tabulated in the driver manuals - attach exactly the device you're debugging.