Add "target" parameter to DAP attach request

This adds a new "target" to the DAP attach request.  This is passed to
"target remote".  I thought "attach" made the most sense for this,
because in some sense gdb is attaching to a running process.  It's
worth noting that all DAP "attach" parameters are defined by the
implementation.

Reviewed-By: Eli Zaretskii <eliz@gnu.org>

4 files changed, 74 insertions, 4 deletions

diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index 5823bf2..fc3a330 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -39070,12 +39070,16 @@ If provided, this is a string that specifies the program to use.  This
 corresponds to the @code{file} command.  @xref{Files}.
 @end table
 
-@value{GDBN} defines a parameter that can be passed to the
-@code{attach} request:
+@value{GDBN} defines some parameters that can be passed to the
+@code{attach} request.  One of these must be specified.
 
 @table @code
 @item pid
 The process ID to which @value{GDBN} should attach.  @xref{Attach}.
+
+@item target
+The target to which @value{GDBN} should connect.  This is a string and
+is passed to the @code{target remote} command.  @xref{Connecting}.
 @end table
 
 @node JIT Interface
diff --git a/gdb/python/lib/gdb/dap/launch.py b/gdb/python/lib/gdb/dap/launch.py
index e187c31..2fec326 100644
--- a/gdb/python/lib/gdb/dap/launch.py
+++ b/gdb/python/lib/gdb/dap/launch.py
@@ -56,13 +56,19 @@ def launch(
 
 
 @request("attach")
-def attach(*, pid: int, **args):
+def attach(*, pid: Optional[int] = None, target: Optional[str] = None, **args):
     # Ensure configurationDone does not try to run.
     global _program
     _program = None
+    if pid is not None:
+        cmd = "attach " + str(pid)
+    elif target is not None:
+        cmd = "target remote " + target
+    else:
+        raise Exception("attach requires either 'pid' or 'target'")
     # Use send_gdb_with_response to ensure we get an error if the
     # attach fails.
-    send_gdb_with_response("attach " + str(pid))
+    send_gdb_with_response(cmd)
     return None
 
 
diff --git a/gdb/testsuite/gdb.dap/remote-dap.exp b/gdb/testsuite/gdb.dap/remote-dap.exp
new file mode 100644
index 0000000..3352408
--- /dev/null
+++ b/gdb/testsuite/gdb.dap/remote-dap.exp
@@ -0,0 +1,49 @@
+# Copyright 2023 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/>.
+
+# Test "attach" with a remote target in DAP.
+
+load_lib gdbserver-support.exp
+load_lib dap-support.exp
+
+require allow_dap_tests allow_gdbserver_tests
+# We want to have control over where we start gdbserver.
+require {!is_remote target}
+
+# This test is only for remote targets.
+if {[target_info exists gdb_protocol]
+    && [target_info gdb_protocol] != "remote"} {
+    unsupported "requires remote"
+    return
+}
+
+standard_testfile attach.c
+
+if {[build_executable ${testfile}.exp $testfile $srcfile] == -1} {
+    return
+}
+
+set target_exec [gdb_remote_download target [standard_output_file $testfile]]
+
+lassign [gdbserver_start "" $target_exec] protocol port
+# Really should have been caught up above.
+gdb_assert {$protocol == "remote"}
+
+# We just want to test that attaching works at all.
+if {[dap_target_remote $port] != ""} {
+    dap_shutdown true
+}
+
+close_gdbserver
diff --git a/gdb/testsuite/lib/dap-support.exp b/gdb/testsuite/lib/dap-support.exp
index 5c54748..e1fada8 100644
--- a/gdb/testsuite/lib/dap-support.exp
+++ b/gdb/testsuite/lib/dap-support.exp
@@ -283,6 +283,17 @@ proc dap_attach {pid} {
 		[format {o pid [i %s]} $pid]]
 }
 
+# Start gdb, send a DAP initialize request, and then an attach request
+# specifying TARGET as the remote target.  Returns the empty string on
+# failure, or the response object from the attach request.
+proc dap_target_remote {target} {
+    if {[_dap_initialize "startup - initialize"] == ""} {
+	return ""
+    }
+    return [dap_check_request_and_response "startup - target" attach \
+		[format {o target [s %s]} $target]]
+}
+
 # Cleanly shut down gdb.  TERMINATE is passed as the terminateDebuggee
 # parameter to the request.
 proc dap_shutdown {{terminate false}} {