Re: [Qemu-devel] [RFC PATCH v5 00/13] Reverse execution.

[Paolo Bonzini <pbonzini@redhat.com>]

Il 25/06/2014 17:19, fred.konrad@greensocs.com ha scritto:
> From: KONRAD Frederic <fred.konrad@greensocs.com>
>
> Hi everybody,
>
> This is the fifth version of this RFC (see the changes below).
>
> Those are the two first patch-set we have been worked on for reverse execution.
>
> The first part is fully reviewed except the "icount: introduce icount timer"
> patch maybe we can merge them?
>
> The first series:
>   icount: put icount variables into TimerState.
>   migration: migrate icount fields.
>   migration: make qemu_savevm_state public.
>   icount: introduce icount timer.
>   icount: check for icount clock deadline when cpu loop exits.
>   icount: make icount extra computed on icount clock as well.
>   timer: add cpu_icount_to_ns function.
>
> are various preparation patches for reverse execution.
>
> The last patches:
>   trace-events: add reverse-execution events.
>   introduce reverse execution mechanism.
>   gdbstub: allow reverse execution in gdb stub.
>   cpu-exec: trigger a debug request when rexec stops.
>   cexe: synchronize icount on the next event.
>   cexe: allow to enable reverse execution.
>
> are reverse execution introduction.
>
> They can be clone at: git://git.greensocs.com/qemu_cexe.git:cexe_2_3_v5
>
> The third series will be sent as soon as possible and have some issues with
> QEMU's thread as it use fork.
>
> This implementation of reverse execution works with instruction counting:
>
> A new clock is implemented which is icount clock. It grows each time an
> instruction is executed and is totally independant of host clock.
>
> Snapshots are taken regularly (based on icount clock) with help of migration
> code and written on the disk.
>
> When user wants to use reverse-stepi:
>  * Last snapshot is reloaded.
>  * A stop callback is created to be triggered at the previous instruction.
>
> This stop callback generates a debug exception so QEMU stops in debug mode.
>
> Command line:
>  * -cexe option is added to enable reverse execution, it needs icount 1.

What does -cexe stand for?

There was a patch on the list to convert -icount to QemuOpts, could you 
adopt that and add a cexe suboption?

Paolo