Re: [Qemu-devel] [RFC PATCH v5 00/31] Deterministic replay and reverse execution

[Pavel Dovgaluk]

> From: Artyom Tarasenko [mailto:address@hidden
> On Wed, Nov 26, 2014 at 11:47 AM, Pavel Dovgaluk
> <address@hidden> wrote:
> > That covermail was wrong. Here is the correct one:
> >
> > This set of patches is related to the reverse execution and deterministic
> > replay of qemu execution  This implementation of deterministic replay can
> > be used for deterministic debugging of guest code through gdb remote
> > interface.
> >
> > These patches include only core function of the replay,
> > excluding the support for replaying serial, audio, network, and USB devices'
> > operations. Reverse debugging and monitor commands were also excluded to
> > be submitted later as separate patches.
> >
> > Execution recording writes non-deterministic events log, which can be later
> > used for replaying the execution anywhere and for unlimited number of times.
> > It also supports checkpointing for faster rewinding during reverse 
> > debugging.
> > Execution replaying reads the log and replays all non-deterministic events
> > including external input, hardware clocks, and interrupts.
> >
> > Deterministic replay has the following features:
> >  * Deterministically replays whole system execution and all contents of the 
> > memory,
> >    state of the hadrware devices, clocks, and screen of the VM.
> >  * Writes execution log into the file for latter replaying for multiple 
> > times
> >    on different machines.
> >  * Supports i386, x86_64, and ARM hardware platforms.
> 
> This patch series is really impressive, hats off!
> 
> I wonder what would have to be done to add support for SPARC-64? Since
> has a PCI bus, I guess the support in atapi and usb devices is already
> there. Is anything beyond translate.c has to be adjusted?

This implementation of replay does not requires changing the translation.
But there could be some issues anyway:
 - icount can have some bugs for this CPU
 - there could be translation non-determinism when it crosses pages boundary
 - virtual devices can create non-synchronized bottom halves that will bring 
non-determinism
 - clocks and timers can be incorrectly used by virtual devices

It will be great if you can try replay for SPARC and report about your 
experience.

Pavel Dovgalyuk