From: Chris Torek <chris.torek@xxxxxxxxxxxxx> Date: Sat, 14 Mar 2009 12:53:52 -0600 > (PS: I have not thought nearly enough about this, but: in the > ultrasparc code I did in another lifetime, I did not bother fiddling > %cwp in the task-switch code, because we know the register windows > are empty both before and after, so %cwp does not really matter: > we are going to fault in all the "above" windows as usual, and in > that system, nothing ever let you peek at the %cwp value. It may > be possible to do the same in the linux code. In which case the > switch code has many more registers available to it, plus this > saves you one whole "wrpr" instruction. :-) Something for those > better-versed than I to consider, anyway.) Oh, CWP _does_ matter. You have to specifically use the saved CWP in the task switch because when we later get to the trap return into userspace we'll restore the %tstate register from the trap stack and that has a very specific CWP encoded into it. So it all has to line up properly. I suppose we could mask out the CWP in the pt_regs we restore in trap return, but that seems like more work than the CWP writes here :-) I'll address the rest of your email soon. -- To unsubscribe from this list: send the line "unsubscribe sparclinux" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
