From: David Mosberger <davidm@napali.hpl.hp.com>

This patch makes /proc/PID/maps report the range from FIXADDR_USER_START to
FIXADDR_USER_END as a final pseudo-vma.  This is consistent with the notion
that reading /proc/PID/maps tells you about every page containing data that
the process can in fact access, and with things such as ptrace allowing
access to this memory.  Without this, userland tools that want to look at all
of a process's accessible pages need special-case knowledge about things such
as the vsyscall DSO page.  With this change, existing code that iterates over
the /proc/PID/maps lines will cover those pages like any other.  For example,
this lets gdb's "gcore" command synthesize a core file from a live process
that contains the vsyscall DSO page as a real core dump would, using its
existing generic iterator code and no new special cases.