Re: [Qemu-devel] [RFC PATCH v3 15/49] softmmu: fixing usage of cpu_st/ld* from helpers

["Pavel Dovgaluk" <Pavel.Dovgaluk@ispras.ru>]

> From: Alex Bennée [mailto:alex.bennee@linaro.org]
> Pavel Dovgalyuk writes:
> 
> > MMU helper functions are called from generated code and other helper
> > functions. In both cases they try to get function's return address for
> > using it while restoring virtual CPU state.
> >
> > When MMU helper is called from some other helper function
> > (like helper_maskmov_xmm) through cpu_st* function, the return address
> > will point to that helper. That is why CPU state cannot be restored in
> > the case of MMU fault.
> >
> > This patch introduces several inline helpers to load return address
> > which points to the right place.
> >
> <snip>
> 
> OK I find it fairly hard to follow all the glue magic (not your fault
> ;-) we have in QEMU. However wouldn't it be simpler for the helper
> pre-amble code to ensure the subject pc is updated in the CPU
> environment?

Then I'll need to rewrite all helper calls or change their structure
by adding code which restores the PC.

> Can QEMU only rectify the processor state from a TranlationBlock tc address?

Current guest PC is not known during execution of the TB. When memory access
exception occurs, helpers have to evaluate guest PC using the host one.
Host PC should point to the translated block and this patch eliminates reading
wrong host PC value during such recovery.

Pavel Dovgalyuk