Re: [Qemu-devel] [PATCH v6 00/25] Fixing record/replay and adding reverse debugging

[dovgaluk <dovgaluk@ispras.ru>]

Artem Pisarenko писал 2018-09-30 14:01:
> Feature still broken :(

Thanks for testing.

> 
> Brief description of my tests.
> 
> Guest image is Linux, which just powers off after kernel boots
> (instead of proceeding to user-space /init or /sbin/init).
> Base cmdline:
> qemu-system-x86_64 -nodefaults -machine pc,accel=tcg -m 2048 -cpu
> qemu64 -rtc clock=vm,base=2000-01-01T00:00:00 -kernel bzImage -initrd
> rootfs -append 'nokaslr console=ttyS0 rdinit=/init_poweroff'
> -nographic -serial SERIAL_VALUE -icount
> 1,sleep=off,rr=RR_VALUE,rrfile=icount_rr_capture.bin

I've never tried it with sleep=off. Can you remove it and try again?

We also seen a problem with '-nographic'. When we remove this option and 
QEMU runs with SDL
window, everything is ok. There is some problem with main loop which may 
sleep when there
is no GUI to update, or something like that. We couldn't fix it yet.

> 
> Test 1. When SERIAL_VALUE=none
> Running with RR_VALUE=record completes successfully.
> Running with RR_VALUE=replay doesn't completes. qemu process just
> eating ~100% cpu and memory usage doesn't grow after some moment. I
> don't see what happens because of problem no.2 (see below).

Try 'info replay' monitor command. Does instruction counter increases?

> 
> Test 2. When SERIAL_VALUE=stdio
> Running with RR_VALUE=record completes successfully.
> 
> Running with RR_VALUE=replay caues exit with error:
> 
> "qemu-system-x86_64: Missing character write event in the replay log"
> 
> These problems are same with qemu 2.12 (both vanilla and with previous
> versions of these patches applied). Furthemore, I consider whole
> icount mode broken and determinism isn't achievable.
> The irony is that I actually don't need record/replay feature. I've
> tried to use it only as instrument to debug failing determinism in
> qemu code. But since replay/record feature itself relies on
> determinism, which is broken, it's no wonder why it fails also (I just
> hoped to bypass it).
> 
> Contact me if you need more details. I just tired a lot trying to get
> all these things working... Hope is leaving me...

Can you share the kernel in case the icount still broken?


Pavel Dovgalyuk