[lldb][lldb-dap] Added support for "WriteMemory" request. (#131820)

Added debug adapter support for write memory.

---------

Co-authored-by: Santhosh Kumar Ellendula <sellendu@hu-sellendu-hyd.qualcomm.com>
Co-authored-by: Santhosh Kumar Ellendula <sellendu@hu-sellendu-lv.qualcomm.com>

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

@@ -831,6 +831,20 @@ class DebugCommunication(object):
         }
         return self.send_recv(command_dict)
 
+    def request_writeMemory(self, memoryReference, data, offset=0, allowPartial=True):
+        args_dict = {
+            "memoryReference": memoryReference,
+            "offset": offset,
+            "allowPartial": allowPartial,
+            "data": data,
+        }
+        command_dict = {
+            "command": "writeMemory",
+            "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/packages/Python/lldbsuite/test/tools/lldb-dap/lldbdap_testcase.py

@@ -8,6 +8,7 @@ from dap_server import Source
 from lldbsuite.test.lldbtest import *
 from lldbsuite.test import lldbplatformutil
 import lldbgdbserverutils
+import base64
 
 
 class DAPTestCaseBase(TestBase):
@@ -506,3 +507,20 @@ class DAPTestCaseBase(TestBase):
                 self.dap_server.request_disconnect(terminateDebuggee=True)
                 self.assertIsNotNone(server_tool, "debugserver not found.")
         return server_tool
+
+    def writeMemory(self, memoryReference, data=None, offset=None, allowPartial=None):
+        # This function accepts data in decimal and hexadecimal format,
+        # converts it to a Base64 string, and send it to the DAP,
+        # which expects Base64 encoded data.
+        encodedData = (
+            ""
+            if data is None
+            else base64.b64encode(
+                # (bit_length + 7 (rounding up to nearest byte) ) //8 = converts to bytes.
+                data.to_bytes((data.bit_length() + 7) // 8, "little")
+            ).decode()
+        )
+        response = self.dap_server.request_writeMemory(
+            memoryReference, encodedData, offset=offset, allowPartial=allowPartial
+        )
+        return response

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

@@ -125,3 +125,85 @@ class TestDAP_memory(lldbdap_testcase.DAPTestCaseBase):
         self.assertFalse(mem["success"], "expect fail on reading memory.")
 
         self.continue_to_exit()
+
+    def test_writeMemory(self):
+        """
+        Tests the 'writeMemory' 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()
+
+        # Get the 'not_a_ptr' writable variable reference address.
+        ptr_deref = self.dap_server.request_evaluate("not_a_ptr")["body"]
+        memref = ptr_deref["memoryReference"]
+
+        # Write the decimal value 50 (0x32 in hexadecimal) to memory.
+        # This corresponds to the ASCII character '2' and encodes to Base64 as "Mg==".
+        mem_response = self.writeMemory(memref, 50, 0, True)
+        self.assertEqual(mem_response["success"], True)
+        self.assertEqual(mem_response["body"]["bytesWritten"], 1)
+
+        # Read back the modified memory and verify that the written data matches
+        # the expected result.
+        mem_response = self.dap_server.request_readMemory(memref, 0, 1)
+        self.assertEqual(mem_response["success"], True)
+        self.assertEqual(mem_response["body"]["data"], "Mg==")
+
+        # Write the decimal value 100 (0x64 in hexadecimal) to memory.
+        # This corresponds to the ASCII character 'd' and encodes to Base64 as "ZA==".
+        # allowPartial=False
+        mem_response = self.writeMemory(memref, 100, 0, False)
+        self.assertEqual(mem_response["success"], True)
+        self.assertEqual(mem_response["body"]["bytesWritten"], 1)
+
+        # Read back the modified memory and verify that the written data matches
+        # the expected result.
+        mem_response = self.dap_server.request_readMemory(memref, 0, 1)
+        self.assertEqual(mem_response["success"], True)
+        self.assertEqual(mem_response["body"]["data"], "ZA==")
+
+        # Memory write failed for 0x0.
+        mem_response = self.writeMemory("0x0", 50, 0, True)
+        self.assertEqual(mem_response["success"], False)
+
+        # Malformed memory reference.
+        mem_response = self.writeMemory("12345", 50, 0, True)
+        self.assertEqual(mem_response["success"], False)
+
+        ptr_deref = self.dap_server.request_evaluate("nonWritable")["body"]
+        memref = ptr_deref["memoryReference"]
+
+        # Writing to non-writable region should return an appropriate error.
+        mem_response = self.writeMemory(memref, 50, 0, False)
+        self.assertEqual(mem_response["success"], False)
+        self.assertRegex(
+            mem_response["body"]["error"]["format"],
+            r"Memory " + memref + " region is not writable",
+        )
+
+        # Trying to write empty value; data=""
+        mem_response = self.writeMemory(memref)
+        self.assertEqual(mem_response["success"], False)
+        self.assertRegex(
+            mem_response["body"]["error"]["format"],
+            r"Data cannot be empty value. Provide valid data",
+        )
+
+        # Verify that large memory writes fail if the range spans non-writable
+        # or non -contiguous regions.
+        data = bytes([0xFF] * 8192)
+        mem_response = self.writeMemory(
+            memref, int.from_bytes(data, byteorder="little"), 0, False
+        )
+        self.assertEqual(mem_response["success"], False)
+        self.assertRegex(
+            mem_response["body"]["error"]["format"],
+            r"Memory " + memref + " region is not writable",
+        )

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

@@ -1,6 +1,8 @@
 int main() {
   int not_a_ptr = 666;
   const char *rawptr = "dead";
+  // Immutable variable, .rodata region.
+  static const int nonWritable = 100;
   // Breakpoint
   return 0;
 }

lldb/tools/lldb-dap/CMakeLists.txt

@@ -65,6 +65,7 @@ add_lldb_library(lldbDAP
   Handler/TestGetTargetBreakpointsRequestHandler.cpp
   Handler/ThreadsRequestHandler.cpp
   Handler/VariablesRequestHandler.cpp
+  Handler/WriteMemoryRequestHandler.cpp
   
   Protocol/ProtocolBase.cpp
   Protocol/ProtocolEvents.cpp

lldb/tools/lldb-dap/DAP.cpp

@@ -1554,6 +1554,7 @@ void DAP::RegisterRequests() {
   RegisterRequest<StepOutRequestHandler>();
   RegisterRequest<ThreadsRequestHandler>();
   RegisterRequest<VariablesRequestHandler>();
+  RegisterRequest<WriteMemoryRequestHandler>();
 
   // Custom requests
   RegisterRequest<CompileUnitsRequestHandler>();

lldb/tools/lldb-dap/Handler/RequestHandler.h

@@ -604,6 +604,19 @@ public:
   void operator()(const llvm::json::Object &request) const override;
 };
 
+class WriteMemoryRequestHandler final
+    : public RequestHandler<protocol::WriteMemoryArguments,
+                            llvm::Expected<protocol::WriteMemoryResponseBody>> {
+public:
+  using RequestHandler::RequestHandler;
+  static llvm::StringLiteral GetCommand() { return "writeMemory"; }
+  FeatureSet GetSupportedFeatures() const override {
+    return {protocol::eAdapterFeatureWriteMemoryRequest};
+  }
+  llvm::Expected<protocol::WriteMemoryResponseBody>
+  Run(const protocol::WriteMemoryArguments &args) const override;
+};
+
 } // namespace lldb_dap
 
 #endif

lldb/tools/lldb-dap/Handler/WriteMemoryRequestHandler.cpp

@@ -0,0 +1,100 @@
+//===-- WriteMemoryRequestHandler.cpp -------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "DAP.h"
+#include "JSONUtils.h"
+#include "RequestHandler.h"
+#include "lldb/API/SBMemoryRegionInfo.h"
+#include "llvm/ADT/StringExtras.h"
+#include "llvm/Support/Base64.h"
+
+namespace lldb_dap {
+
+// Writes bytes to memory at the provided location.
+//
+// Clients should only call this request if the corresponding capability
+//  supportsWriteMemoryRequest is true.
+llvm::Expected<protocol::WriteMemoryResponseBody>
+WriteMemoryRequestHandler::Run(
+    const protocol::WriteMemoryArguments &args) const {
+  const lldb::addr_t address = args.memoryReference + args.offset.value_or(0);
+  ;
+
+  lldb::SBProcess process = dap.target.GetProcess();
+  if (!lldb::SBDebugger::StateIsStoppedState(process.GetState()))
+    return llvm::make_error<NotStoppedError>();
+
+  if (args.data.empty()) {
+    return llvm::make_error<DAPError>(
+        "Data cannot be empty value. Provide valid data");
+  }
+
+  // The VSCode IDE or other DAP clients send memory data as a Base64 string.
+  // This function decodes it into raw binary before writing it to the target
+  // process memory.
+  std::vector<char> output;
+  auto decode_error = llvm::decodeBase64(args.data, output);
+
+  if (decode_error) {
+    return llvm::make_error<DAPError>(
+        llvm::toString(std::move(decode_error)).c_str());
+  }
+
+  lldb::SBError write_error;
+  uint64_t bytes_written = 0;
+
+  // Write the memory.
+  if (!output.empty()) {
+    lldb::SBProcess process = dap.target.GetProcess();
+    // If 'allowPartial' is false or missing, a debug adapter should attempt to
+    // verify the region is writable before writing, and fail the response if it
+    // is not.
+    if (!args.allowPartial.value_or(false)) {
+      // Start checking from the initial write address.
+      lldb::addr_t start_address = address;
+      // Compute the end of the write range.
+      lldb::addr_t end_address = start_address + output.size() - 1;
+
+      while (start_address <= end_address) {
+        // Get memory region info for the given address.
+        // This provides the region's base, end, and permissions
+        // (read/write/executable).
+        lldb::SBMemoryRegionInfo region_info;
+        lldb::SBError error =
+            process.GetMemoryRegionInfo(start_address, region_info);
+        // Fail if the region info retrieval fails, is not writable, or the
+        // range exceeds the region.
+        if (!error.Success() || !region_info.IsWritable()) {
+          return llvm::make_error<DAPError>(
+              "Memory 0x" + llvm::utohexstr(args.memoryReference) +
+              " region is not writable");
+        }
+        // If the current region covers the full requested range, stop futher
+        // iterations.
+        if (end_address <= region_info.GetRegionEnd()) {
+          break;
+        }
+        // Move to the start of the next memory region.
+        start_address = region_info.GetRegionEnd() + 1;
+      }
+    }
+
+    bytes_written =
+        process.WriteMemory(address, static_cast<void *>(output.data()),
+                            output.size(), write_error);
+  }
+
+  if (bytes_written == 0) {
+    return llvm::make_error<DAPError>(write_error.GetCString());
+  }
+  protocol::WriteMemoryResponseBody response;
+  response.bytesWritten = bytes_written;
+  return response;
+}
+
+} // namespace lldb_dap

lldb/tools/lldb-dap/Protocol/ProtocolRequests.cpp

@@ -531,4 +531,37 @@ json::Value toJSON(const ModulesResponseBody &MR) {
   return result;
 }
 
+bool fromJSON(const json::Value &Params, WriteMemoryArguments &WMA,
+              json::Path P) {
+  json::ObjectMapper O(Params, P);
+
+  const json::Object *wma_obj = Params.getAsObject();
+  constexpr llvm::StringRef ref_key = "memoryReference";
+  const std::optional<llvm::StringRef> memory_ref = wma_obj->getString(ref_key);
+  if (!memory_ref) {
+    P.field(ref_key).report("missing value");
+    return false;
+  }
+
+  const std::optional<lldb::addr_t> addr_opt =
+      DecodeMemoryReference(*memory_ref);
+  if (!addr_opt) {
+    P.field(ref_key).report("Malformed memory reference");
+    return false;
+  }
+
+  WMA.memoryReference = *addr_opt;
+
+  return O && O.mapOptional("allowPartial", WMA.allowPartial) &&
+         O.mapOptional("offset", WMA.offset) && O.map("data", WMA.data);
+}
+
+json::Value toJSON(const WriteMemoryResponseBody &WMR) {
+  json::Object result;
+
+  if (WMR.bytesWritten != 0)
+    result.insert({"bytesWritten", WMR.bytesWritten});
+  return result;
+}
+
 } // namespace lldb_dap::protocol

lldb/tools/lldb-dap/Protocol/ProtocolRequests.h

@@ -896,6 +896,38 @@ struct ModulesResponseBody {
 };
 llvm::json::Value toJSON(const ModulesResponseBody &);
 
+/// Arguments for `writeMemory` request.
+struct WriteMemoryArguments {
+  /// Memory reference to the base location to which data should be written.
+  lldb::addr_t memoryReference;
+
+  /// Offset (in bytes) to be applied to the reference location before writing
+  /// data. Can be negative.
+  std::optional<int64_t> offset;
+
+  /// Property to control partial writes. If true, the debug adapter should
+  /// attempt to write memory even if the entire memory region is not writable.
+  /// In such a case the debug adapter should stop after hitting the first byte
+  /// of memory that cannot be written and return the number of bytes written in
+  /// the response via the `offset` and `bytesWritten` properties.
+  /// If false or missing, a debug adapter should attempt to verify the region
+  /// is writable before writing, and fail the response if it is not.
+  std::optional<bool> allowPartial;
+
+  /// Bytes to write, encoded using base64.
+  std::string data;
+};
+bool fromJSON(const llvm::json::Value &, WriteMemoryArguments &,
+              llvm::json::Path);
+
+/// Response to writeMemory request.
+struct WriteMemoryResponseBody {
+  /// Property that should be returned when `allowPartial` is true to indicate
+  /// the number of bytes starting from address that were successfully written.
+  uint64_t bytesWritten = 0;
+};
+llvm::json::Value toJSON(const WriteMemoryResponseBody &);
+
 } // namespace lldb_dap::protocol
 
 #endif