Messages in this thread | | | Date | Thu, 22 May 2008 17:42:06 -0700 | From | Suresh Siddha <> | Subject | Re: [RFC] x86: xsave/xrstor support, ucontext_t extensions |
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On Thu, May 22, 2008 at 05:33:30PM -0700, H. Peter Anvin wrote: > 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!
What I was doing in the RFC is: restore the state what ever that was present and init the state that was not present in the stack frame.
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