Binary package “libc6-xen” in ubuntu precise

Embedded GNU C Library: Shared libraries [Xen version]

 Contains the standard libraries that are used by nearly all programs on
 the system. This package includes shared versions of the standard C
 library and the standard math library, as well as many others.
 This set of libraries is optimized for the Xen hypervisor, and will be
 selected instead when running under Xen.