Harden tests that deal with memory regions

Exercising aarch64-elf with a custom debug stub i noticed a few failures in
both gdb.base/breakpoint-in-ro-region.exp and gdb.base/memattr.exp:

FAIL: gdb.base/breakpoint-in-ro-region.exp: create read-only mem region covering main
FAIL: gdb.base/breakpoint-in-ro-region.exp: writing to read-only memory fails
FAIL: gdb.base/breakpoint-in-ro-region.exp: inserting software breakpoint in read-only memory fails

FAIL: gdb.base/memattr.exp: create mem region 1
FAIL: gdb.base/memattr.exp: create mem region 2
FAIL: gdb.base/memattr.exp: create mem region 3
FAIL: gdb.base/memattr.exp: create mem region 4
FAIL: gdb.base/memattr.exp: create mem region 5
FAIL: gdb.base/memattr.exp: info mem (1)
FAIL: gdb.base/memattr.exp: mem1 cannot be read
FAIL: gdb.base/memattr.exp: mem2 cannot be written
FAIL: gdb.base/memattr.exp: mem2 can be read
FAIL: gdb.base/memattr.exp: disable mem 1
FAIL: gdb.base/memattr.exp: mem 1 was disabled
FAIL: gdb.base/memattr.exp: enable mem 1
FAIL: gdb.base/memattr.exp: mem 1 was enabled
FAIL: gdb.base/memattr.exp: disable mem 2 4
FAIL: gdb.base/memattr.exp: mem 2 and 4 were disabled
FAIL: gdb.base/memattr.exp: enable mem 2-4
FAIL: gdb.base/memattr.exp: mem 2-4 were enabled
FAIL: gdb.base/memattr.exp: mem 1 to 5 were disabled
FAIL: gdb.base/memattr.exp: mem 1 to 5 were enabled
FAIL: gdb.base/memattr.exp: delete mem 1
FAIL: gdb.base/memattr.exp: mem 1 was deleted
FAIL: gdb.base/memattr.exp: delete mem 2 4
FAIL: gdb.base/memattr.exp: mem 2 and 4 were deleted
FAIL: gdb.base/memattr.exp: mem 2-4 were deleted

These failures don't show up with gdbserver or native gdb on Linux because
they don't export any memory maps, therefore the vector of memory regions is
empty.

Outside of that scenario, we can't guarantee the absence of memory regions
reported by the target upon a connection. In our particular target, we
provide a memory map and the memory regions vector ceases to be empty.

With a non-empty memory regions vector, manipulating memory regions will cause
gdb to be more verbose and output text. For example:

memattr.c:require_user_regions

  /* Otherwise, let the user know how to get back.  */
  if (from_tty)
    warning (_("Switching to manual control of memory regions; use "
	       "\"mem auto\" to fetch regions from the target again."));

memattr.c:create_mem_region

      if ((lo >= n->lo && (lo < n->hi || n->hi == 0))
	  || (hi > n->lo && (hi <= n->hi || n->hi == 0))
	  || (lo <= n->lo && ((hi >= n->hi && n->hi != 0) || hi == 0)))
	{
	  printf_unfiltered (_("overlapping memory region\n"));
	  return;
	}

In my particular case i got both of the above messages.

In order to fix this, i've moved the delete_memory proc from
gdb.base/memattr.exp to a new file lib/memory.exp and made lib/gdb.exp
load that file.

For both gdb.base/breakpoint-in-ro-region.exp and gdb.base/memattr.exp the
patch clears all existing memory regions after running to main. That way we
are guaranteed to have a clean state for memory regions so the tests can
exercise whatever they want and have an expected output pattern.

Regression checked on x86-64/Ubuntu 16.04.

gdb/testsuite/ChangeLog:

2017-01-26  Luis Machado  <lgustavo@codesourcery.com>

	* lib/memory.exp: New file.
	* lib/gdb.exp: Load memory.exp.
	* gdb.base/memattr.exp (delete_memory): Move proc to
	lib/memory.exp and rename to delete_memory_regions.
	Replace delete_memory with delete_memory_regions.
	Cleanup memory regions before tests.
	* gdb.base/breakpoint-in-ro-region.exp: Cleanup memory regions
	before tests.

2 files changed, 34 insertions, 0 deletions

diff --git a/gdb/testsuite/lib/gdb.exp b/gdb/testsuite/lib/gdb.exp
index 2ff5c22a1d..48bd7eefbd 100644
--- a/gdb/testsuite/lib/gdb.exp
+++ b/gdb/testsuite/lib/gdb.exp
@@ -28,6 +28,7 @@ if {$tool == ""} {
 load_lib libgloss.exp
 load_lib cache.exp
 load_lib gdb-utils.exp
+load_lib memory.exp
 
 global GDB
 
diff --git a/gdb/testsuite/lib/memory.exp b/gdb/testsuite/lib/memory.exp
new file mode 100644
index 0000000000..62dd8ada77
--- /dev/null
+++ b/gdb/testsuite/lib/memory.exp
@@ -0,0 +1,33 @@
+# Copyright 2012-2017 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# This file holds functions and data dealing with memory checks and other memory
+# manipulation routines.
+
+# Deletes all memory regions GDB currently knows about.
+
+proc delete_memory_regions {} {
+    global gdb_prompt
+
+    gdb_test_multiple "delete mem" "delete mem" {
+       -re "Delete all memory regions.*y or n.*$" {
+           send_gdb "y\n"
+           exp_continue
+       }
+       -re "$gdb_prompt $" { }
+    }
+}
+
+