[Lldb-commits] [lldb] [lldb] Parse qSupported MultiMemRead tag in GDB Remote Client (PR #163249)

[Felipe de Azevedo Piovezan via lldb-commits]

https://github.com/felipepiovezan updated https://github.com/llvm/llvm-project/pull/163249

>From 2c6aec5408fa3119da4f333819257f0557a08f97 Mon Sep 17 00:00:00 2001
From: Felipe de Azevedo Piovezan <fpiovezan at apple.com>
Date: Mon, 13 Oct 2025 12:15:14 -0700
Subject: [PATCH 1/2] [lldb] Parse qSupported MultiMemRead tag in GDB Remote
 Client

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
---
 .../gdb-remote/GDBRemoteCommunicationClient.cpp       | 10 ++++++++++
 .../Process/gdb-remote/GDBRemoteCommunicationClient.h |  3 +++
 .../gdb-remote/GDBRemoteCommunicationClientTest.cpp   | 11 +++++++++++
 3 files changed, 24 insertions(+)

diff --git a/lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationClient.cpp b/lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationClient.cpp
index 7d2bd452acca9..11f164c2426ce 100644
--- a/lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationClient.cpp
+++ b/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
diff --git a/lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationClient.h b/lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationClient.h
index a765e95bf9814..ad590a25d0f16 100644
--- a/lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationClient.h
+++ b/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,
diff --git a/lldb/unittests/Process/gdb-remote/GDBRemoteCommunicationClientTest.cpp b/lldb/unittests/Process/gdb-remote/GDBRemoteCommunicationClientTest.cpp
index f940229985887..ce042e5ddf422 100644
--- a/lldb/unittests/Process/gdb-remote/GDBRemoteCommunicationClientTest.cpp
+++ b/lldb/unittests/Process/gdb-remote/GDBRemoteCommunicationClientTest.cpp
@@ -639,3 +639,14 @@ 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();
+}

>From 40f67909cb3c12f984ec8140923f5eea50ca1509 Mon Sep 17 00:00:00 2001
From: Felipe de Azevedo Piovezan <fpiovezan at apple.com>
Date: Tue, 14 Oct 2025 13:59:45 -0700
Subject: [PATCH 2/2] fixup! Add negative test

---
 .../gdb-remote/GDBRemoteCommunicationClientTest.cpp   | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/lldb/unittests/Process/gdb-remote/GDBRemoteCommunicationClientTest.cpp b/lldb/unittests/Process/gdb-remote/GDBRemoteCommunicationClientTest.cpp
index ce042e5ddf422..012eae02d5857 100644
--- a/lldb/unittests/Process/gdb-remote/GDBRemoteCommunicationClientTest.cpp
+++ b/lldb/unittests/Process/gdb-remote/GDBRemoteCommunicationClientTest.cpp
@@ -650,3 +650,14 @@ TEST_F(GDBRemoteCommunicationClientTest, MultiMemReadSupported) {
   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();
+}