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    SubjectRe: [PATCH] linux-2.5.43_vsyscall_A0
    On Sat, Oct 19, 2002 at 06:10:19AM +0200, Andrea Arcangeli wrote:
    > On Fri, Oct 18, 2002 at 11:49:59PM -0500, Jeff Dike wrote:
    > > ak@muc.de said:
    > > > Guess you'll have some problems then with UML on x86-64, which always
    > > > uses vgettimeofday. But it's only used for gettimeofday() currently,
    > > > perhaps it's not that bad when the UML child runs with the host's
    > > > time.
    > >
    > > It's not horrible, but it's still broken. There are people who depend
    > > on UML being able to keep its own time separately from the host.
    > >
    > > > I guess it would be possible to add some support for UML to map own
    > > > code over the vsyscall reserved locations. UML would need to use the
    > > > syscalls then. But it'll be likely ugly.
    > >
    > > Yeah, it would be.
    > >
    > > My preferred solution would be for libc to ask the kernel where the vsyscall
    > > area is. That's reasonably clean and virtualizable. Andrea doesn't like it
    > > because it adds a few instructions to the vsyscall address calculation.
    >
    > yes, my preferred solution is still a runtime /proc entry that turns off
    > vsyscalls completely by root so you could trap gettimeofday/time via the
    > usual ptrace. That would be zero cost. Of course this would be needed

    Ok, a sysctl that modifies a variable in the vsyscall page and is
    tested by the code. That would be an option, I agree.

    For the locked TSC code we will need something like that anyways,
    so that locked TSC can force a syscall.

    -Andi
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