Make native gdbserver boards no longer be "remote" (in DejaGnu terms)

This commit finally clears the "isremote" flag in the native-gdbserver
and native-stdio-gdbserver boards.  The goal is to make all "native"
boards be considered not remote in DejaGnu terms, like the
native-extended-gdbserver board is too.

DejaGnu automatically considers boards remote if their names don't
match the local hostname.  That means that native-gdbserver and
native-extended-gdbserver are considered remote by default by DejaGnu,
even though they run locally.  native-extended-gdbserver, however,
overrides its isremote flag to force it to be not remote.  So we are
in that weird state where native-gdbserver is considered remote, and
native-extended-gdbserver is considered not remote.

A recent set of commits fixed all the problems (and some more) exposed
by testing with --target_board=native-gdbserver and
--target_board=native-stdio-gdbserver with isremote forced off on
x86-64 GNU/Linux.  I believe we're good to go now.

The native-stdio-gdbserver.exp/remote-stdio-gdbserver.exp boards
required deep non-obvious modifications unfortunately...  The problem
is that if a board is not remote, then DejaGnu doesn't call
${board}_spawn / ${board}_exec at all, and the
native-stdio-gdbserver.exp board relies on those procedures being
called.  To fix that, this commit redesigns how the stdio boards hook
into the testing framework to spawn gdbserver.  IMO, this is a good
change anyway, because the way its done currently is a bit of a hack,
and the result turns out to be simpler, even.  With this commit, they
now no longer load the "gdbserver" generic config, and hook at the
mi_gdb_target_load/gdb_reload level instead, making them more like
traditional board files.

To share code between native-stdio-gdbserver.exp and
remote-stdio-gdbserver.exp, a new shared stdio-gdbserver-base.exp file
is created.

Instead of having each native board clear isremote manually, boards
source the new "local-board.exp" file.

This also adds a new section to testsuite/README file discussing
local/remote/native, so that we can easily refer to it.

gdb/testsuite/ChangeLog:
2017-10-16  Pedro Alves  <palves@redhat.com>
	    Simon Marchi  <simon.marchi@polymtl.ca>

	* README (Local vs Remote vs Native): New section.
	* boards/local-board.exp: New file, with bits factored out from
	...
	* boards/native-extended-gdbserver.exp: ... here.  Load
	"local-board".
	* boards/native-gdbserver.exp: Load "local-board".
	(${board}_spawn, ${board}_exec): Delete.
	* boards/native-stdio-gdbserver.exp: Most contents factored out to
	...
	* boards/stdio-gdbserver-base.exp: ... this new file.
	* boards/native-stdio-gdbserver.exp: Reimplement, by loading
	"stdio-gdbserver-base" and defining a get_target_remote_pipe_cmd
	procedure.
	* boards/remote-stdio-gdbserver.exp: Load stdio-gdbserver-base
	instead of native-stdio-gdbserver.  Don't set gdb_server_prog nor
	stdio_gdbserver_command.
	(${board}_get_remote_address, ${board}_get_comm_port)
	(${board}_download, ${board}_upload): Delete.
	(get_target_remote_pipe_cmd): New.

1 files changed, 54 insertions, 0 deletions

diff --git a/gdb/testsuite/boards/stdio-gdbserver-base.exp b/gdb/testsuite/boards/stdio-gdbserver-base.exp
new file mode 100644
index 0000000..f3bf25c
--- /dev/null
+++ b/gdb/testsuite/boards/stdio-gdbserver-base.exp
@@ -0,0 +1,54 @@
+# Copyright 2011-2017 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 has common bits shared between other dejagnu "board files"
+# that are used to run the testsuite with gdbserver connected via
+# stdio.  Boards that source this must reimplement the
+# get_target_remote_pipe_address procedure.
+
+load_board_description "gdbserver-base"
+
+# Note this is loaded for gdb_target_cmd, not for making this board
+# use the generic "gdbserver" config.
+load_lib gdbserver-support.exp
+
+# This gdbserver can only run a process once per session.
+set_board_info gdb,do_reload_on_run 1
+
+# There's no support for argument-passing (yet).
+set_board_info noargs 1
+
+set_board_info use_gdb_stub 1
+set_board_info exit_is_reliable 1
+
+# We will be using the standard GDB remote protocol.
+set_board_info gdb_protocol "remote"
+
+# Return the CMD string in "target remote | CMD".
+proc get_target_remote_pipe_cmd {} {
+    error "must reimplement this procedure"
+}
+
+proc make_gdbserver_stdio_port {} {
+    return "| [get_target_remote_pipe_cmd]"
+}
+
+proc gdb_reload { } {
+    return [gdb_target_cmd "remote" [make_gdbserver_stdio_port]]
+}
+
+proc mi_gdb_target_load { } {
+    return [mi_gdb_target_cmd "remote" [make_gdbserver_stdio_port]]
+}