Create a generic handler for Xfer packets

Summary:
This is the first of a few patches I have to improve the performance of dynamic module loading on Android.

In this first diff I'll describe the context of my main motivation and will then link to it in the other diffs to avoid repeating myself.

## Motivation
I have a few scenarios where opening a specific feature on an Android app takes around 40s when lldb is attached to it. The reason for that is because 40 modules are dynamicly loaded at that point in time and each one of them is taking ~1s.

## The problem
To learn about new modules we have a breakpoint on a linker function that is called twice whenever a module is loaded. One time just before it's loaded (so lldb can check which modules are loaded) and another right after it's loaded (so lldb can check again which ones are loaded and calculate the diference).
It's figuring out which modules are loaded that is taking quite some time. This is currently done by traversing the linked list of loaded shared libraries that the linker maintains in memory. Each item in the linked list requires its own `x` packet sent to the gdb server (this is android so the network also plays a part). In my scenario there are 400+ loaded libraries and even though we read 0x800 worth of bytes at a time we still make ~180 requests that end up taking 150-200ms.
We also do this twice, once before the module is loaded (state = eAdd) and another right after (state = eConsistent) which easly adds up to ~400ms per module.

## A solution

**Implement `xfer:libraries-svr4` in lldb-server:**
I noticed in the code that loads the new modules that it had support for the `xfer:libraries-svr4` packet (added ~4 years ago to support the ds2 debug server) but we didn't support it in lldb-server. This single packet returns an xml list of all the loaded modules by the process. The advantage is that there's no more need to make 180 requests to read the linked list. Additionally this new requests takes around 10ms.

**More efficient usage of the `xfer:libraries-svr4` packet in lldb:**
When `xfer:libraries-svr4` is available the Process class has a `LoadModules` function that requests this packet and then loads or unloads modules based on the current list of loaded modules by the process.
This is the function that is used by the DYLDRendezvous class to get the list of loaded modules before and after the module is loaded. However, this is really not needed since the LoadModules function already loaded or unloaded the modules accordingly. I changed this strategy to call LoadModules only once (after the process has loaded the module).

**Bugs**
I found a few issues in lldb while implementing this and have submitted independent patches for them.

I tried to devide this into multiple logical patches to make it easier to review and discuss.

## Tests

I wanted to put these set of diffs up before having all the tests up and running to start having them reviewed from a techical point of view. I'm also having some trouble making the tests running on linux so I need more time to make that happen.

# This diff

The `xfer` packages follow the same protocol, they are requested with `xfer:<object>:<read|write>:<annex>:<offset,length>` and a return that starts with `l` or `m` depending if the offset and length covers the entire data or not. Before implementing the `xfer:libraries-svr4` I refactored the `xfer:auxv` to generically handle xfer packets so we can easly add new ones.

The overall structure of the function ends up being:
* Parse the packet into its components: object, offset etc.
* Depending on the object do its own logic to generate the data.
* Return the data based on its size, the requested offset and length.

Reviewers: clayborg, xiaobai, labath

Reviewed By: labath

Subscribers: mgorny, krytarowski, lldb-commits

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D62499

llvm-svn: 362982

lldb/include/lldb/Utility/StringExtractorGDBRemote.h

@@ -128,7 +128,7 @@ class StringExtractorGDBRemote : public StringExtractor {
     eServerPacketType_qVAttachOrWaitSupported,
     eServerPacketType_qWatchpointSupportInfo,
     eServerPacketType_qWatchpointSupportInfoSupported,
-    eServerPacketType_qXfer_auxv_read,
+    eServerPacketType_qXfer,
 
     eServerPacketType_jSignalsInfo,
     eServerPacketType_jModulesInfo,

lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationServer.cpp

@@ -112,6 +112,22 @@ GDBRemoteCommunicationServer::SendErrorResponse(const Status &error) {
     return SendErrorResponse(error.GetError());
 }
 
+GDBRemoteCommunication::PacketResult
+GDBRemoteCommunicationServer::SendErrorResponse(llvm::Error error) {
+  std::unique_ptr<llvm::ErrorInfoBase> EIB;
+  std::unique_ptr<PacketUnimplementedError> PUE;
+  llvm::handleAllErrors(
+      std::move(error),
+      [&](std::unique_ptr<PacketUnimplementedError> E) { PUE = std::move(E); },
+      [&](std::unique_ptr<llvm::ErrorInfoBase> E) { EIB = std::move(E); });
+
+  if (EIB)
+    return SendErrorResponse(Status(llvm::Error(std::move(EIB))));
+  if (PUE)
+    return SendUnimplementedResponse(PUE->message().c_str());
+  return SendErrorResponse(Status("Unknown Error"));
+}
+
 GDBRemoteCommunication::PacketResult
 GDBRemoteCommunicationServer::Handle_QErrorStringEnable(
     StringExtractorGDBRemote &packet) {
@@ -138,3 +154,5 @@ GDBRemoteCommunicationServer::SendOKResponse() {
 bool GDBRemoteCommunicationServer::HandshakeWithClient() {
   return GetAck() == PacketResult::Success;
 }
+
+char PacketUnimplementedError::ID;

lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationServer.h

@@ -15,6 +15,9 @@
 #include "GDBRemoteCommunication.h"
 #include "lldb/lldb-private-forward.h"
 
+#include "llvm/Support/Errc.h"
+#include "llvm/Support/Error.h"
+
 class StringExtractorGDBRemote;
 
 namespace lldb_private {
@@ -59,6 +62,8 @@ class GDBRemoteCommunicationServer : public GDBRemoteCommunication {
 
   PacketResult SendErrorResponse(const Status &error);
 
+  PacketResult SendErrorResponse(llvm::Error error);
+
   PacketResult SendUnimplementedResponse(const char *packet);
 
   PacketResult SendErrorResponse(uint8_t error);
@@ -72,6 +77,18 @@ class GDBRemoteCommunicationServer : public GDBRemoteCommunication {
   DISALLOW_COPY_AND_ASSIGN(GDBRemoteCommunicationServer);
 };
 
+class PacketUnimplementedError
+    : public llvm::ErrorInfo<PacketUnimplementedError, llvm::StringError> {
+public:
+  static char ID;
+  using llvm::ErrorInfo<PacketUnimplementedError,
+                        llvm::StringError>::ErrorInfo; // inherit constructors
+  PacketUnimplementedError(const llvm::Twine &S)
+      : ErrorInfo(S, llvm::errc::not_supported) {}
+
+  PacketUnimplementedError() : ErrorInfo(llvm::errc::not_supported) {}
+};
+
 } // namespace process_gdb_remote
 } // namespace lldb_private
 

lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationServerLLGS.cpp

@@ -144,8 +144,8 @@ void GDBRemoteCommunicationServerLLGS::RegisterPacketHandlers() {
       StringExtractorGDBRemote::eServerPacketType_qWatchpointSupportInfo,
       &GDBRemoteCommunicationServerLLGS::Handle_qWatchpointSupportInfo);
   RegisterMemberFunctionHandler(
-      StringExtractorGDBRemote::eServerPacketType_qXfer_auxv_read,
-      &GDBRemoteCommunicationServerLLGS::Handle_qXfer_auxv_read);
+      StringExtractorGDBRemote::eServerPacketType_qXfer,
+      &GDBRemoteCommunicationServerLLGS::Handle_qXfer);
   RegisterMemberFunctionHandler(StringExtractorGDBRemote::eServerPacketType_s,
                                 &GDBRemoteCommunicationServerLLGS::Handle_s);
   RegisterMemberFunctionHandler(
@@ -2747,94 +2747,99 @@ GDBRemoteCommunicationServerLLGS::Handle_s(StringExtractorGDBRemote &packet) {
   return PacketResult::Success;
 }
 
-GDBRemoteCommunication::PacketResult
-GDBRemoteCommunicationServerLLGS::Handle_qXfer_auxv_read(
-    StringExtractorGDBRemote &packet) {
-// *BSD impls should be able to do this too.
-#if defined(__linux__) || defined(__NetBSD__)
-  Log *log(GetLogIfAnyCategoriesSet(LIBLLDB_LOG_PROCESS));
-
-  // Parse out the offset.
-  packet.SetFilePos(strlen("qXfer:auxv:read::"));
-  if (packet.GetBytesLeft() < 1)
-    return SendIllFormedResponse(packet,
-                                 "qXfer:auxv:read:: packet missing offset");
-
-  const uint64_t auxv_offset =
-      packet.GetHexMaxU64(false, std::numeric_limits<uint64_t>::max());
-  if (auxv_offset == std::numeric_limits<uint64_t>::max())
-    return SendIllFormedResponse(packet,
-                                 "qXfer:auxv:read:: packet missing offset");
-
-  // Parse out comma.
-  if (packet.GetBytesLeft() < 1 || packet.GetChar() != ',')
-    return SendIllFormedResponse(
-        packet, "qXfer:auxv:read:: packet missing comma after offset");
-
-  // Parse out the length.
-  const uint64_t auxv_length =
-      packet.GetHexMaxU64(false, std::numeric_limits<uint64_t>::max());
-  if (auxv_length == std::numeric_limits<uint64_t>::max())
-    return SendIllFormedResponse(packet,
-                                 "qXfer:auxv:read:: packet missing length");
-
-  // Grab the auxv data if we need it.
-  if (!m_active_auxv_buffer_up) {
+llvm::Expected<std::unique_ptr<llvm::MemoryBuffer>>
+GDBRemoteCommunicationServerLLGS::ReadXferObject(llvm::StringRef object,
+                                                 llvm::StringRef annex) {
+  if (object == "auxv") {
     // Make sure we have a valid process.
     if (!m_debugged_process_up ||
         (m_debugged_process_up->GetID() == LLDB_INVALID_PROCESS_ID)) {
-      if (log)
-        log->Printf(
-            "GDBRemoteCommunicationServerLLGS::%s failed, no process available",
-            __FUNCTION__);
-      return SendErrorResponse(0x10);
+      return llvm::createStringError(llvm::inconvertibleErrorCode(),
+                                     "No process available");
     }
 
     // Grab the auxv data.
     auto buffer_or_error = m_debugged_process_up->GetAuxvData();
-    if (!buffer_or_error) {
-      std::error_code ec = buffer_or_error.getError();
-      LLDB_LOG(log, "no auxv data retrieved: {0}", ec.message());
-      return SendErrorResponse(ec.value());
-    }
-    m_active_auxv_buffer_up = std::move(*buffer_or_error);
+    if (!buffer_or_error)
+      return llvm::errorCodeToError(buffer_or_error.getError());
+    return std::move(*buffer_or_error);
   }
 
+  return llvm::make_error<PacketUnimplementedError>(
+      "Xfer object not supported");
+}
+
+GDBRemoteCommunication::PacketResult
+GDBRemoteCommunicationServerLLGS::Handle_qXfer(
+    StringExtractorGDBRemote &packet) {
+  SmallVector<StringRef, 5> fields;
+  // The packet format is "qXfer:<object>:<action>:<annex>:offset,length"
+  StringRef(packet.GetStringRef()).split(fields, ':', 4);
+  if (fields.size() != 5)
+    return SendIllFormedResponse(packet, "malformed qXfer packet");
+  StringRef &xfer_object = fields[1];
+  StringRef &xfer_action = fields[2];
+  StringRef &xfer_annex = fields[3];
+  StringExtractor offset_data(fields[4]);
+  if (xfer_action != "read")
+    return SendUnimplementedResponse("qXfer action not supported");
+  // Parse offset.
+  const uint64_t xfer_offset =
+      offset_data.GetHexMaxU64(false, std::numeric_limits<uint64_t>::max());
+  if (xfer_offset == std::numeric_limits<uint64_t>::max())
+    return SendIllFormedResponse(packet, "qXfer packet missing offset");
+  // Parse out comma.
+  if (offset_data.GetChar() != ',')
+    return SendIllFormedResponse(packet,
+                                 "qXfer packet missing comma after offset");
+  // Parse out the length.
+  const uint64_t xfer_length =
+      offset_data.GetHexMaxU64(false, std::numeric_limits<uint64_t>::max());
+  if (xfer_length == std::numeric_limits<uint64_t>::max())
+    return SendIllFormedResponse(packet, "qXfer packet missing length");
+
+  // Get a previously constructed buffer if it exists or create it now.
+  std::string buffer_key = (xfer_object + xfer_action + xfer_annex).str();
+  auto buffer_it = m_xfer_buffer_map.find(buffer_key);
+  if (buffer_it == m_xfer_buffer_map.end()) {
+    auto buffer_up = ReadXferObject(xfer_object, xfer_annex);
+    if (!buffer_up)
+      return SendErrorResponse(buffer_up.takeError());
+    buffer_it = m_xfer_buffer_map
+                    .insert(std::make_pair(buffer_key, std::move(*buffer_up)))
+                    .first;
+  }
+
+  // Send back the response
   StreamGDBRemote response;
   bool done_with_buffer = false;
-
-  llvm::StringRef buffer = m_active_auxv_buffer_up->getBuffer();
-  if (auxv_offset >= buffer.size()) {
+  llvm::StringRef buffer = buffer_it->second->getBuffer();
+  if (xfer_offset >= buffer.size()) {
     // We have nothing left to send.  Mark the buffer as complete.
     response.PutChar('l');
     done_with_buffer = true;
   } else {
     // Figure out how many bytes are available starting at the given offset.
-    buffer = buffer.drop_front(auxv_offset);
-
+    buffer = buffer.drop_front(xfer_offset);
     // Mark the response type according to whether we're reading the remainder
-    // of the auxv data.
-    if (auxv_length >= buffer.size()) {
+    // of the data.
+    if (xfer_length >= buffer.size()) {
       // There will be nothing left to read after this
       response.PutChar('l');
       done_with_buffer = true;
     } else {
       // There will still be bytes to read after this request.
       response.PutChar('m');
-      buffer = buffer.take_front(auxv_length);
+      buffer = buffer.take_front(xfer_length);
     }
-
     // Now write the data in encoded binary form.
     response.PutEscapedBytes(buffer.data(), buffer.size());
   }
 
   if (done_with_buffer)
-    m_active_auxv_buffer_up.reset();
+    m_xfer_buffer_map.erase(buffer_it);
 
   return SendPacketNoLock(response.GetString());
-#else
-  return SendUnimplementedResponse("not implemented on this platform");
-#endif
 }
 
 GDBRemoteCommunication::PacketResult
@@ -3259,8 +3264,8 @@ uint32_t GDBRemoteCommunicationServerLLGS::GetNextSavedRegistersID() {
 void GDBRemoteCommunicationServerLLGS::ClearProcessSpecificData() {
   Log *log(GetLogIfAnyCategoriesSet(LIBLLDB_LOG_PROCESS));
 
-  LLDB_LOG(log, "clearing auxv buffer: {0}", m_active_auxv_buffer_up.get());
-  m_active_auxv_buffer_up.reset();
+  LLDB_LOG(log, "clearing {0} xfer buffers", m_xfer_buffer_map.size());
+  m_xfer_buffer_map.clear();
 }
 
 FileSpec

lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationServerLLGS.h

@@ -82,7 +82,7 @@ class GDBRemoteCommunicationServerLLGS
   MainLoop::ReadHandleUP m_stdio_handle_up;
 
   lldb::StateType m_inferior_prev_state = lldb::StateType::eStateInvalid;
-  std::unique_ptr<llvm::MemoryBuffer> m_active_auxv_buffer_up;
+  llvm::StringMap<std::unique_ptr<llvm::MemoryBuffer>> m_xfer_buffer_map;
   std::mutex m_saved_registers_mutex;
   std::unordered_map<uint32_t, lldb::DataBufferSP> m_saved_registers_map;
   uint32_t m_next_saved_registers_id = 1;
@@ -150,7 +150,7 @@ class GDBRemoteCommunicationServerLLGS
 
   PacketResult Handle_s(StringExtractorGDBRemote &packet);
 
-  PacketResult Handle_qXfer_auxv_read(StringExtractorGDBRemote &packet);
+  PacketResult Handle_qXfer(StringExtractorGDBRemote &packet);
 
   PacketResult Handle_QSaveRegisterState(StringExtractorGDBRemote &packet);
 
@@ -193,6 +193,9 @@ class GDBRemoteCommunicationServerLLGS
   FileSpec FindModuleFile(const std::string &module_path,
                           const ArchSpec &arch) override;
 
+  llvm::Expected<std::unique_ptr<llvm::MemoryBuffer>>
+  ReadXferObject(llvm::StringRef object, llvm::StringRef annex);
+
 private:
   void HandleInferiorState_Exited(NativeProcessProtocol *process);
 

lldb/source/Utility/StringExtractorGDBRemote.cpp

@@ -285,8 +285,8 @@ StringExtractorGDBRemote::GetServerPacketType() const {
       break;
 
     case 'X':
-      if (PACKET_STARTS_WITH("qXfer:auxv:read::"))
-        return eServerPacketType_qXfer_auxv_read;
+      if (PACKET_STARTS_WITH("qXfer:"))
+        return eServerPacketType_qXfer;
       break;
     }
     break;

lldb/unittests/Process/gdb-remote/CMakeLists.txt

@@ -1,6 +1,7 @@
 add_lldb_unittest(ProcessGdbRemoteTests
   GDBRemoteClientBaseTest.cpp
   GDBRemoteCommunicationClientTest.cpp
+  GDBRemoteCommunicationServerTest.cpp
   GDBRemoteCommunicationTest.cpp
   GDBRemoteTestUtils.cpp
 

lldb/unittests/Process/gdb-remote/GDBRemoteCommunicationServerTest.cpp

@@ -0,0 +1,73 @@
+//===-- GDBRemoteCommunicationServerTest.cpp --------------------*- C++ -*-===//
+//
+// 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 "gmock/gmock.h"
+#include "gtest/gtest.h"
+
+#include "GDBRemoteTestUtils.h"
+
+#include "Plugins/Process/gdb-remote/GDBRemoteCommunicationServer.h"
+#include "lldb/Utility/Connection.h"
+
+namespace lldb_private {
+namespace process_gdb_remote {
+
+TEST(GDBRemoteCommunicationServerTest, SendErrorResponse_ErrorNumber) {
+  MockServerWithMockConnection server;
+  server.SendErrorResponse(0x42);
+
+  EXPECT_THAT(server.GetPackets(), testing::ElementsAre("$E42#ab"));
+}
+
+TEST(GDBRemoteCommunicationServerTest, SendErrorResponse_Status) {
+  MockServerWithMockConnection server;
+  Status status;
+
+  status.SetError(0x42, lldb::eErrorTypeGeneric);
+  status.SetErrorString("Test error message");
+  server.SendErrorResponse(status);
+
+  EXPECT_THAT(
+      server.GetPackets(),
+      testing::ElementsAre("$E42;54657374206572726f72206d657373616765#ad"));
+}
+
+TEST(GDBRemoteCommunicationServerTest, SendErrorResponse_UnimplementedError) {
+  MockServerWithMockConnection server;
+
+  auto error =
+      llvm::make_error<PacketUnimplementedError>("Test unimplemented error");
+  server.SendErrorResponse(std::move(error));
+
+  EXPECT_THAT(server.GetPackets(), testing::ElementsAre("$#00"));
+}
+
+TEST(GDBRemoteCommunicationServerTest, SendErrorResponse_StringError) {
+  MockServerWithMockConnection server;
+
+  auto error = llvm::createStringError(llvm::inconvertibleErrorCode(),
+                                       "String error test");
+  server.SendErrorResponse(std::move(error));
+
+  EXPECT_THAT(
+      server.GetPackets(),
+      testing::ElementsAre("$Eff;537472696e67206572726f722074657374#b0"));
+}
+
+TEST(GDBRemoteCommunicationServerTest, SendErrorResponse_ErrorList) {
+  MockServerWithMockConnection server;
+
+  auto error = llvm::joinErrors(llvm::make_error<PacketUnimplementedError>(),
+                                llvm::make_error<PacketUnimplementedError>());
+
+  server.SendErrorResponse(std::move(error));
+  // Make sure only one packet is sent even when there are multiple errors.
+  EXPECT_EQ(server.GetPackets().size(), 1UL);
+}
+
+} // namespace process_gdb_remote
+} // namespace lldb_private