[lldb-dap] Support inspecting memory

Adds support for the `readMemory` request which allows VS-Code to
inspect memory. Also, add `memoryReference` to variablesa and `evaluate`
responses, such that the binary view can be opened from the variables
view and from the "watch" pane.

Author: vogelsgesang

lldb/packages/Python/lldbsuite/test/tools/lldb-dap/dap_server.py

@@ -691,6 +691,21 @@ def request_disassemble(
         for inst in instructions:
             self.disassembled_instructions[inst["address"]] = inst
 
+    def request_read_memory(
+        self, memoryReference, offset, count
+    ):
+        args_dict = {
+            "memoryReference": memoryReference,
+            "offset": offset,
+            "count": count,
+        }
+        command_dict = {
+            "command": "readMemory",
+            "type": "request",
+            "arguments": args_dict,
+        }
+        return self.send_recv(command_dict)
+
     def request_evaluate(self, expression, frameIndex=0, threadId=None, context=None):
         stackFrame = self.get_stackFrame(frameIndex=frameIndex, threadId=threadId)
         if stackFrame is None:

lldb/test/API/tools/lldb-dap/memory/Makefile

@@ -0,0 +1,3 @@
+CXX_SOURCES := main.cpp
+
+include Makefile.rules

lldb/test/API/tools/lldb-dap/memory/TestDAP_memory.py

@@ -0,0 +1,121 @@
+"""
+Test lldb-dap memory support
+"""
+
+
+from base64 import b64decode
+import dap_server
+from lldbsuite.test.decorators import *
+from lldbsuite.test.lldbtest import *
+from lldbsuite.test import lldbutil
+import lldbdap_testcase
+import os
+
+
+class TestDAP_memory(lldbdap_testcase.DAPTestCaseBase):
+    def test_read_memory(self):
+        """
+        Tests the 'read_memory' request
+        """
+        program = self.getBuildArtifact("a.out")
+        self.build_and_launch(program)
+        source = "main.cpp"
+        self.source_path = os.path.join(os.getcwd(), source)
+        self.set_source_breakpoints(
+            source,
+            [
+                line_number(source, "// Breakpoint"),
+            ],
+        )
+        self.continue_to_next_stop()
+
+        locals = {l['name']: l for l in self.dap_server.get_local_variables()}
+        rawptr_ref = locals['rawptr']['memoryReference']
+
+        # We can read the complete string
+        mem = self.dap_server.request_read_memory(rawptr_ref, 0, 5)["body"]
+        self.assertEqual(mem["unreadableBytes"], 0);
+        self.assertEqual(b64decode(mem["data"]), b"dead\0")
+
+        # Use an offset
+        mem = self.dap_server.request_read_memory(rawptr_ref, 2, 3)["body"]
+        self.assertEqual(b64decode(mem["data"]), b"ad\0")
+
+        # Use a negative offset
+        mem = self.dap_server.request_read_memory(rawptr_ref, -1, 6)["body"]
+        self.assertEqual(b64decode(mem["data"])[1:], b"dead\0")
+
+        # Reads of size 0 are successful
+        # VS-Code sends those in order to check if a `memoryReference` can actually be dereferenced.
+        mem = self.dap_server.request_read_memory(rawptr_ref, 0, 0)
+        self.assertEqual(mem["success"], True)
+        self.assertEqual(mem["body"]["data"], "")
+
+        # Reads at offset 0x0 fail
+        mem = self.dap_server.request_read_memory("0x0", 0, 6)
+        self.assertEqual(mem["success"], False)
+        self.assertTrue(mem["message"].startswith("Unable to read memory: "))
+
+
+    def test_memory_refs_variables(self):
+        """
+        Tests memory references for evaluate
+        """
+        program = self.getBuildArtifact("a.out")
+        self.build_and_launch(program)
+        source = "main.cpp"
+        self.source_path = os.path.join(os.getcwd(), source)
+        self.set_source_breakpoints(
+            source, [line_number(source, "// Breakpoint")],
+        )
+        self.continue_to_next_stop()
+
+        locals = {l['name']: l for l in self.dap_server.get_local_variables()}
+
+        # Pointers should have memory-references
+        self.assertIn("memoryReference", locals['rawptr'].keys())
+        # Smart-pointers also have memory-references
+        self.assertIn("memoryReference", self.dap_server.get_local_variable_child("smartptr", "pointer").keys())
+        # Non-pointers should not have memory-references
+        self.assertNotIn("memoryReference", locals['not_a_ptr'].keys())
+
+
+    def test_memory_refs_evaluate(self):
+        """
+        Tests memory references for evaluate
+        """
+        program = self.getBuildArtifact("a.out")
+        self.build_and_launch(program)
+        source = "main.cpp"
+        self.source_path = os.path.join(os.getcwd(), source)
+        self.set_source_breakpoints(
+            source, [line_number(source, "// Breakpoint")],
+        )
+        self.continue_to_next_stop()
+
+        # Pointers contain memory references
+        self.assertIn("memoryReference", self.dap_server.request_evaluate("rawptr + 1")["body"].keys())
+
+        # Non-pointer expressions don't include a memory reference
+        self.assertNotIn("memoryReference", self.dap_server.request_evaluate("1 + 3")["body"].keys())
+
+
+    def test_memory_refs_set_variable(self):
+        """
+        Tests memory references for `setVariable`
+        """
+        program = self.getBuildArtifact("a.out")
+        self.build_and_launch(program)
+        source = "main.cpp"
+        self.source_path = os.path.join(os.getcwd(), source)
+        self.set_source_breakpoints(
+            source, [line_number(source, "// Breakpoint")],
+        )
+        self.continue_to_next_stop()
+
+        # Pointers contain memory references
+        ptr_value = self.get_local_as_int("rawptr")
+        self.assertIn("memoryReference", self.dap_server.request_setVariable(1, "rawptr", ptr_value + 2)["body"].keys())
+
+        # Non-pointer expressions don't include a memory reference
+        self.assertNotIn("memoryReference", self.dap_server.request_setVariable(1, "not_a_ptr", 42)["body"].keys())

lldb/test/API/tools/lldb-dap/memory/main.cpp

@@ -0,0 +1,10 @@
+#include <memory>
+#include <iostream>
+
+int main() {
+    int not_a_ptr = 666;
+    const char* rawptr = "dead";
+    std::unique_ptr<int> smartptr(new int(42));
+    // Breakpoint
+    return 0;
+}

lldb/tools/lldb-dap/JSONUtils.cpp

@@ -1085,6 +1085,19 @@ std::string VariableDescription::GetResult(llvm::StringRef context) {
   return description.trim().str();
 }
 
+lldb::addr_t GetMemoryReference(lldb::SBValue v) {
+  if (!v.GetType().IsPointerType() && !v.GetType().IsArrayType()) {
+    return LLDB_INVALID_ADDRESS;
+  }
+
+  lldb::SBValue deref = v.Dereference();
+  if (!deref.IsValid()) {
+    return LLDB_INVALID_ADDRESS;
+  }
+
+  return deref.GetLoadAddress();
+}
+
 // "Variable": {
 //   "type": "object",
 //   "description": "A Variable is a name/value pair. Optionally a variable
@@ -1144,8 +1157,16 @@ std::string VariableDescription::GetResult(llvm::StringRef context) {
 //                       can use this optional information to present the
 //                       children in a paged UI and fetch them in chunks."
 //     }
-//
-//
+//     "memoryReference": {
+//        "type": "string",
+//        "description": "A memory reference associated with this variable.
+//                        For pointer type variables, this is generally a
+//                        reference to the memory address contained in the
+//                        pointer. For executable data, this reference may later
+//                        be used in a `disassemble` request. This attribute may
+//                        be returned by a debug adapter if corresponding
+//                        capability `supportsMemoryReferences` is true."
+//      },
 //     "$__lldb_extensions": {
 //       "description": "Unofficial extensions to the protocol",
 //       "properties": {
@@ -1253,6 +1274,11 @@ llvm::json::Value CreateVariable(lldb::SBValue v, int64_t variablesReference,
   else
     object.try_emplace("variablesReference", (int64_t)0);
 
+  
+  if (lldb::addr_t addr = GetMemoryReference(v); addr != LLDB_INVALID_ADDRESS) {
+    object.try_emplace("memoryReference", "0x" + llvm::utohexstr(addr));
+  }
+
   object.try_emplace("$__lldb_extensions", desc.GetVariableExtensionsJSON());
   return llvm::json::Value(std::move(object));
 }

lldb/tools/lldb-dap/JSONUtils.h

@@ -411,6 +411,12 @@ struct VariableDescription {
   std::string GetResult(llvm::StringRef context);
 };
 
+/// Get the corresponding `memoryReference` for a value.
+///
+/// According to the DAP documentation, the `memoryReference` should
+/// refer to the pointee, not to the address of the pointer itself.
+lldb::addr_t GetMemoryReference(lldb::SBValue v);
+
 /// Create a "Variable" object for a LLDB thread object.
 ///
 /// This function will fill in the following keys in the returned