[lldb-server] Add setting to force 'g' packet use

Following up on https://reviews.llvm.org/D62221, this change introduces
the settings plugin.process.gdb-remote.use-g-packet-for-reading.  When
they are on, 'g' packets are used for reading registers.

Using 'g' packets can improve performance by reducing the number of
packets exchanged between client and server when a large number of
registers needs to be fetched.

Differential revision: https://reviews.llvm.org/D62931

1 files changed, 15 insertions, 12 deletions

diff --git a/lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationClient.cpp b/lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationClient.cpp
index feb9f0589ce..905ebe24a68 100644
--- a/lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationClient.cpp
+++ b/lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationClient.cpp
@@ -543,21 +543,24 @@ GDBRemoteCommunicationClient::SendThreadSpecificPacketAndWaitForResponse(
 //
 // Takes a valid thread ID because p needs to apply to a thread.
 bool GDBRemoteCommunicationClient::GetpPacketSupported(lldb::tid_t tid) {
-  if (m_supports_p == eLazyBoolCalculate) {
-    m_supports_p = eLazyBoolNo;
-    StreamString payload;
-    payload.PutCString("p0");
-    StringExtractorGDBRemote response;
-    if (SendThreadSpecificPacketAndWaitForResponse(tid, std::move(payload),
-                                                   response, false) ==
-            PacketResult::Success &&
-        response.IsNormalResponse()) {
-      m_supports_p = eLazyBoolYes;
-    }
-  }
+  if (m_supports_p == eLazyBoolCalculate)
+    m_supports_p = GetThreadPacketSupported(tid, "p0");
   return m_supports_p;
 }
 
+LazyBool GDBRemoteCommunicationClient::GetThreadPacketSupported(
+    lldb::tid_t tid, llvm::StringRef packetStr) {
+  StreamString payload;
+  payload.PutCString(packetStr);
+  StringExtractorGDBRemote response;
+  if (SendThreadSpecificPacketAndWaitForResponse(
+          tid, std::move(payload), response, false) == PacketResult::Success &&
+      response.IsNormalResponse()) {
+    return eLazyBoolYes;
+  }
+  return eLazyBoolNo;
+}
+
 StructuredData::ObjectSP GDBRemoteCommunicationClient::GetThreadsInfo() {
   // Get information on all threads at one using the "jThreadsInfo" packet
   StructuredData::ObjectSP object_sp;