PREEMPTIBLE_HANDLER_KERNEL needs to spill uspace windows to uspace wbuf

[Jakub Jermář]

PREEMPTIBLE_HANDLER_KERNEL checks the value of the CANSAVE register to see whether the imminent SAVE instruction would generate a window spill trap or not. If CANSAVE is zero, it uses the INLINE_SPILL macro to spill a register window without generating the spill trap. INLINE_SPILL assumes a kernel window, but it is also possible to have a uspace window at this point. In this case, INLINE_SPILL will wrongly interpret the window's uspace stack address as a kernel stack address, leading to a random memory corruption.

It is therefore necessary to also check the value in the OTHERWIN register to see whether the spilled window would be a uspace window. In such case, INLINE_SPILL_TO_WBUF needs to be used instead of INLINE_SPILL to spill the uspace window to the uspace window buffer.

[Jakub Jermář]

There is an unmerged fix for this in the CHT pre-integration branch:

​http://bazaar.launchpad.net/~jakub/helenos/cht-preintegration/revision/2290

[Jakub Jermář]

Fix merged in mainline,2297.