modify mk/qemu.mk
I think there's a bug in this file
at line 12, it should be
-kernel $(OUTDIR)/$(TARGET).bin > /dev/null 2>&1 & \
not -kernel $(OUTDIR)/$(TARGET).bin > 2>&1>/dev/null & \
I got an error in the original version while using the make qemudbg command
and fixed it by modifying line 12
Anyway, I can use gdb to track the code now