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

["H. Peter Anvin" <hpa@zytor.com>]

Suresh Siddha 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.

Either way, I find it somewhat surprising that the user would invoke a 
different sys_sigreturn especially if using a restorer function (which 
gcc always does.)

I really think I need to understand your application better, 
*especially* in the light of the fact you wouldn't at the moment know 
how even get the size of the frame.

	-hpa