Re: [RFC] x86: xsave/xrstor support, ucontext_t extensions

[Mikael Pettersson]

H. Peter Anvin writes:
 > > But user can potentially change the _fpstate pointer in sigcontext struct.
 > 
 > If so, they get what they bargained for... I am not even sure the kernel 
 > will successfully clean up the stack frame if they do that.

Why would that be a problem? The stack is defined by the user's SP,
which is in the integer state part of the sigframe. We do a sigreturn(),
reload SP/PC/etc, and off we go. Where fpstate pointed to doesn't matter,
as long as it was NULL or a valid fpstate image.
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