Add readMemory and writeMemory requests to DAP

This adds the DAP readMemory and writeMemory requests.  A small change
to the evaluation code is needed in order to test this -- this is one
of the few ways for a client to actually acquire a memory reference.

gdb/python/lib/gdb/dap/__init__.py

@@ -25,6 +25,7 @@ from . import bt
 from . import disassemble
 from . import evaluate
 from . import launch
+from . import memory
 from . import next
 from . import pause
 from . import scopes

gdb/python/lib/gdb/dap/memory.py

@@ -0,0 +1,51 @@
+# 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/>.
+
+import base64
+import gdb
+
+from .server import request, capability
+from .startup import send_gdb_with_response, in_gdb_thread
+
+
+@in_gdb_thread
+def _read_memory(addr, count):
+    buf = gdb.selected_inferior().read_memory(addr, count)
+    return base64.b64encode(buf).decode("ASCII")
+
+
+@request("readMemory")
+@capability("supportsReadMemoryRequest")
+def read_memory(*, memoryReference, offset=0, count, **extra):
+    addr = int(memoryReference, 0) + offset
+    buf = send_gdb_with_response(lambda: _read_memory(addr, count))
+    return {
+        "address": hex(addr),
+        "data": buf,
+    }
+
+
+@in_gdb_thread
+def _write_memory(addr, contents):
+    buf = base64.b64decode(contents)
+    gdb.selected_inferior().write_memory(addr, buf)
+
+
+@request("writeMemory")
+@capability("supportsWriteMemoryRequest")
+def write_memory(*, memoryReference, offset=0, data, **extra):
+    addr = int(memoryReference, 0) + offset
+    send_gdb_with_response(lambda: _write_memory(addr, data))
+    return {}

gdb/python/lib/gdb/dap/varref.py

@@ -116,6 +116,7 @@ class VariableReference(BaseReference):
         RESULT_NAME can be used to change how the simple string result
         is emitted in the result dictionary."""
         super().__init__(name)
+        self.value = value
         self.printer = gdb.printing.make_visualizer(value)
         self.result_name = result_name
         # We cache all the children we create.
@@ -160,6 +161,10 @@ class VariableReference(BaseReference):
                 result["indexedVariables"] = num_children
             else:
                 result["namedVariables"] = num_children
+        if self.value.type.code == gdb.TYPE_CODE_PTR:
+            result["memoryReference"] = hex(int(self.value))
+        elif self.value.address is not None:
+            result["memoryReference"] = hex(int(self.value.address))
         return result
 
     @in_gdb_thread