FIXADDR_USER_* may not be constant

[PATCH] Put fixmaps into /proc/pid/maps via a pseudo-vma

From: David Mosberger <[email protected]>

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.