Write to QEMU guest system registers & memory?

Question

How do you write to the processor registers and specific memory addresses of a virtual system running in QEMU?

My desire would be to accomplish this from a user space program running outside of QEMU. This would be to induce interrupts and finely control execution of the processor and virtual hardware.

The QEMU Monitor is supposed to read parameters or do simple injects of mouse or keyboard events, but I haven't seen anything about writing.

Answer 1

GDB server within QEMU Monitor seems to be the best for your purpose. One of your options is implementing a gdb protocol, another one is driving gdb itself through its command line.

I've tested it a bit: attaching, reading and writing memory seems to work (I read what I write); jumping to another address seems to work too. (If you may call injected code, you can do anything, theoretically). Writing to text-mode video memory doesn't work (I don't even read what I wrote, and nothing changes on display).