[Bug libc/13425] New: Remove x86_64 Linux vsyscall page support

["luto at mit dot edu" <sourceware-bugzilla at sourceware dot org>]

http://sourceware.org/bugzilla/show_bug.cgi?id=13425

             Bug #: 13425
           Summary: Remove x86_64 Linux vsyscall page support
           Product: glibc
           Version: 2.14
            Status: NEW
          Severity: normal
          Priority: P2
         Component: libc
        AssignedTo: drepper.fsp@gmail.com
        ReportedBy: luto@mit.edu
    Classification: Unclassified


As of Linux 3.1, the vsyscall entry points (0xffffffffff600x00) are often
slower and never faster than real syscalls.  They are also somewhat fragile in
that they can confuse various binary tracing systems (e.g. the Chromium
sandbox) and they cause some problems with UML.

It would be nice to support the vdso in static binaries, but, failing that,
glibc should just stop using the vsyscall page.

(Note: for getcpu on older kernels without a real sys_getcpu syscall, the
vsyscall page or vdso support might be mandatory.  But the syscall should IMO
be preferred over the vsyscall entry.)

If this change is made, then vsyscall=none has a good chance of working :)

This is a continuation of bug 12813.

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