[Bug preprocessor/58379] New: default mmap based implementation (mmap_gt_pch_get_address/mmap_gt_pch_use_address) is useless

["martin at netbsd dot org" <gcc-bugzilla@gcc.gnu.org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58379

            Bug ID: 58379
           Summary: default mmap based implementation
                    (mmap_gt_pch_get_address/mmap_gt_pch_use_address) is
                    useless
           Product: gcc
           Version: 4.8.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: preprocessor
          Assignee: unassigned at gcc dot gnu.org
          Reporter: martin at netbsd dot org

I may be misunderstanding the interface - but it looks to me like it lets the
kernel chose an arbitrary mapping address for different compiler invocations
but relies on the assumption that the returned address will be the same. If
not, the compiler fails with a fatal_error when trying to read a precompiled
header file ("had to relocate PCH").

I can not imagine a host system where this would work reliably (or even
typically twice in a row).

Please tell me I misunderstood, or consider disabling PCH support for host
platforms without host_hooks overriding this function.