On 12/13/2017 07:08 AM, Florian Weimer wrote: > Okay, this model is really quite different from x86. Is there a > good reason for the difference? Yes, both implementations are simple and take the "natural" behavior. x86 changes XSAVE-controlled register values on entering a signal, so we let them be changed (including PKRU). POWER hardware does not do this to its PKRU-equivalent, so we do not force it to. x86 didn't have to do this for *signals*. But, we kinda went on this trajectory when we decided to clear/restore FPU state on entering/exiting signals before XSAVE even existed. FWIW, I do *not* think we have to do this for future XSAVE states. But, if we do that, we probably need an interface for apps to tell us which states to save/restore and which state to set upon entering a signal handler. That's what I was trying to get you to consider instead of just a one-off hack to fix this for pkeys.
