[Qemu-devel] [Qemu devel] qemu fpu state in synch with hw fpu state

[Mehul Chadha]

Hello,

We are working on a record replaying tool in qemu and kvm.
 We have successfully implemented record replaying individually in both 
the systems. So, we can record executions of VM in qemu and replay it in
 qemu and similarly in kvm. The next interesting stuff would be to 
implement a cross system where we can record execution in kvm and 
asynchronously replay it in qemu. There are some interesting 
applications of being able to do this (eg. asynchronous taint analysis).

We maintain a record log where we record non deterministic 
information during record and while replaying, the record log is used. 
For eg. we store interrupt info, IO in this record log.

For cross
 record replay to work, it is important that the entire state of the 
system remains same across all instructions in both qemu and kvm (HW). 
We have done most of this work, but it seems still much is left. We are 
facing issues to get the floating point state consistent across all 
floating point instructions. Any pointers here will be appreciated. We 
find that floating point status word and floating point control word are
 not consistent with the actual hardware state. We also tried the new 
patch where i386 is made compatible with softfloat, but there still 
seems to be issues with it. 

What would be the likely effort required to get qemu fpu in synch with hw fpu?

Thanks,
Mehul