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

    > The de-facto ABI for signal delivery and sigreturn is unfortunately
    > based on fairly fixed-layout structs on the stack (sigframes). The
    > only flexibility there that I've found is the sigcontext's fpstate
    > pointer which allows the fpstate to be located elsewhere.

    One sure 100% compatible way would be to only change the signal layout once
    the application used anything that needs XSAVE/XRSTOR. But implementing
    that would be likely complicated and I'm not sure it's worth it.

    I don't remember that much breakage when the FXSAVE support was
    introduced on i386. That already changed these data structures.

    > Another idea is that marking non-siginfo sigframes could be done
    > by adding a sys_xsave_sigreturn() and letting those sigframes
    > have a return address pointing to a vsyscall that invokes this
    > new syscall.

    That sounds easy enough. x86-64 right now doesn't use signal vsyscalls but
    there is no principle reason it can't.


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