Messages in this thread | | | Date | Thu, 22 May 2008 17:33:30 -0700 | From | "H. Peter Anvin" <> | Subject | Re: [RFC] x86: xsave/xrstor support, ucontext_t extensions |
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Mikael Pettersson wrote: > > > > While restoring from the user, kernel also need to find out what layout > > > the user is passing. So it's bi-directional. I prefer the same mechanism > > > (using cookies/magic numbers etc inaddition to uc_flags or cpuid checks) to > > > interpret the fpstate for both user/kernel. > > > > No, it really doesn't: the kernel only needs to be able to read the same > > format as it itself wrote. > > The kernel needs to accept one(*) of the formats it can produce, which > is not necessarily what it last produced. It's not inconceivable that > user-space will construct sigframes on the fly (to emulate setcontext), > or that it will mangle sigframes (e.g. to map non-rt to rt before sigreturn). > > (*) The format is determined by which version of sys_sigreturn the > user invokes. >
No. You CANNOT restore from a frame that doesn't have the full state - you don't have enough information to do so!
-hpa
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