[lldb] Parse qSupported MultiMemRead tag in GDB Remote Client (llvm#163249)

This is in preparation for the new MultiMemRead packet discussed in the
RFC [1].

An alternative to using `qSupported` would be having clients send an
empty `MultiMemRead` packet. However, this is problematic because the
already-existing packet `M` is a prefix of `MultiMemRead`; an empty
reply would be ambiguous in this case. It is also risky that the stub
might interpret the `MultiMemRead` as a valid `M` packet.

Another advantage of `qSupported` is that this packet is already
exchanged, so parsing a new field is simpler than having to exchange one
extra packet.

[1]:
https://discourse.llvm.org/t/rfc-a-new-vectorized-memory-read-packet/88441

(cherry picked from commit ccf6e02)

Author: felipepiovezan

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

@@ -211,6 +211,12 @@ bool GDBRemoteCommunicationClient::GetReverseStepSupported() {
   return m_supports_reverse_step == eLazyBoolYes;
 }
 
+bool GDBRemoteCommunicationClient::GetMultiMemReadSupported() {
+  if (m_supports_multi_mem_read == eLazyBoolCalculate)
+    GetRemoteQSupported();
+  return m_supports_multi_mem_read == eLazyBoolYes;
+}
+
 bool GDBRemoteCommunicationClient::QueryNoAckModeSupported() {
   if (m_supports_not_sending_acks == eLazyBoolCalculate) {
     m_send_acks = true;
@@ -339,6 +345,7 @@ void GDBRemoteCommunicationClient::ResetDiscoverableSettings(bool did_exec) {
     m_supported_async_json_packets_is_valid = false;
     m_supported_async_json_packets_sp.reset();
     m_supports_jModulesInfo = true;
+    m_supports_multi_mem_read = eLazyBoolCalculate;
   }
 
   // These flags should be reset when we first connect to a GDB server and when
@@ -365,6 +372,7 @@ void GDBRemoteCommunicationClient::GetRemoteQSupported() {
   m_x_packet_state.reset();
   m_supports_reverse_continue = eLazyBoolNo;
   m_supports_reverse_step = eLazyBoolNo;
+  m_supports_multi_mem_read = eLazyBoolNo;
 
   m_max_packet_size = UINT64_MAX; // It's supposed to always be there, but if
                                   // not, we assume no limit
@@ -424,6 +432,8 @@ void GDBRemoteCommunicationClient::GetRemoteQSupported() {
         m_supports_reverse_continue = eLazyBoolYes;
       else if (x == "ReverseStep+")
         m_supports_reverse_step = eLazyBoolYes;
+      else if (x == "MultiMemRead+")
+        m_supports_multi_mem_read = eLazyBoolYes;
       // Look for a list of compressions in the features list e.g.
       // qXfer:features:read+;PacketSize=20000;qEcho+;SupportedCompressions=zlib-
       // deflate,lzma

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

@@ -342,6 +342,8 @@ class GDBRemoteCommunicationClient : public GDBRemoteClientBase {
 
   bool GetReverseStepSupported();
 
+  bool GetMultiMemReadSupported();
+
   LazyBool SupportsAllocDeallocMemory() // const
   {
     // Uncomment this to have lldb pretend the debug server doesn't respond to
@@ -574,6 +576,7 @@ class GDBRemoteCommunicationClient : public GDBRemoteClientBase {
   std::optional<xPacketState> m_x_packet_state;
   LazyBool m_supports_reverse_continue = eLazyBoolCalculate;
   LazyBool m_supports_reverse_step = eLazyBoolCalculate;
+  LazyBool m_supports_multi_mem_read = eLazyBoolCalculate;
 
   bool m_supports_qProcessInfoPID : 1, m_supports_qfProcessInfo : 1,
       m_supports_qUserName : 1, m_supports_qGroupName : 1,

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

@@ -639,3 +639,25 @@ TEST_F(GDBRemoteCommunicationClientTest, CalculateMD5) {
   EXPECT_EQ(expected_high, result->high());
 }
 #endif
+
+TEST_F(GDBRemoteCommunicationClientTest, MultiMemReadSupported) {
+  std::future<bool> async_result = std::async(std::launch::async, [&] {
+    StringExtractorGDBRemote qSupported_packet_request;
+    server.GetPacket(qSupported_packet_request);
+    server.SendPacket("MultiMemRead+;");
+    return true;
+  });
+  ASSERT_TRUE(client.GetMultiMemReadSupported());
+  async_result.wait();
+}
+
+TEST_F(GDBRemoteCommunicationClientTest, MultiMemReadNotSupported) {
+  std::future<bool> async_result = std::async(std::launch::async, [&] {
+    StringExtractorGDBRemote qSupported_packet_request;
+    server.GetPacket(qSupported_packet_request);
+    server.SendPacket(";");
+    return true;
+  });
+  ASSERT_FALSE(client.GetMultiMemReadSupported());
+  async_result.wait();
+}