[Bug corefiles/16092] New: The 'gdb' 'gcore' command ignores coredump_filter, and 'madvise(,,MADV_DONTDUMP)'.

["jbyers.sf at gmail dot com" <sourceware-bugzilla at sourceware dot org>]

http://sourceware.org/bugzilla/show_bug.cgi?id=16092

            Bug ID: 16092
           Summary: The 'gdb' 'gcore' command ignores coredump_filter, and
                    'madvise(,,MADV_DONTDUMP)'.
           Product: gdb
           Version: 7.6
            Status: NEW
          Severity: normal
          Priority: P2
         Component: corefiles
          Assignee: unassigned at sourceware dot org
          Reporter: jbyers.sf at gmail dot com

The 'gdb' 'gcore' command ignores coredump_filter, and
'madvise(,,MADV_DONTDUMP)'.

On Linux x86_64, using 'gdb' version:

  GNU gdb (GDB) Red Hat Enterprise Linux (7.2-60.el6_4.1)

and also the latest version of 'gdb' '7.6.1' built from
source, the 'gcore' command used to take a "live" core of a
process ignores the Linux '/proc/PID/coredump_filter' bit
settings, and also 'mmap'ed memory madvise(,,MADV_DONTDUMP)'
settings and always dumps all of the address space
regardless of attempts to limit it.

Note that crash cores do not do this, and obey the filter
and madvise settings.

This is a real problem when the memory allocations are
large, and especially when there are large files mapped, but
sparsely accessed. Using 'gdb' and 'gcore' caused the
complete file to be read in and included it is also included
in the core.

There may be cases where overriding the coredump_filter and
'madvise(,,MADV_DONTDUMP)' are useful, but there should also
be a way to obey these settings and not have monstrously
huge 'gcore' generated core files.

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