[lldb] Add support for gdb-style 'x' packet (#124733)

See also
https://discourse.llvm.org/t/rfc-fixing-incompatibilties-of-the-x-packet-w-r-t-gdb/84288
and https://sourceware.org/pipermail/gdb/2025-January/051705.html

1 files changed, 13 insertions, 9 deletions

diff --git a/lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationClient.cpp b/lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationClient.cpp
index b3f1c6f..581dd8f 100644
--- a/lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationClient.cpp
+++ b/lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationClient.cpp
@@ -275,7 +275,6 @@ void GDBRemoteCommunicationClient::ResetDiscoverableSettings(bool did_exec) {
     m_supports_vCont_s = eLazyBoolCalculate;
     m_supports_vCont_S = eLazyBoolCalculate;
     m_supports_p = eLazyBoolCalculate;
-    m_supports_x = eLazyBoolCalculate;
     m_supports_QSaveRegisterState = eLazyBoolCalculate;
     m_qHostInfo_is_valid = eLazyBoolCalculate;
     m_curr_pid_is_valid = eLazyBoolCalculate;
@@ -295,6 +294,7 @@ void GDBRemoteCommunicationClient::ResetDiscoverableSettings(bool did_exec) {
     m_supports_qXfer_siginfo_read = eLazyBoolCalculate;
     m_supports_augmented_libraries_svr4_read = eLazyBoolCalculate;
     m_uses_native_signals = eLazyBoolCalculate;
+    m_x_packet_state.reset();
     m_supports_qProcessInfoPID = true;
     m_supports_qfProcessInfo = true;
     m_supports_qUserName = true;
@@ -348,6 +348,7 @@ void GDBRemoteCommunicationClient::GetRemoteQSupported() {
   m_supports_memory_tagging = eLazyBoolNo;
   m_supports_qSaveCore = eLazyBoolNo;
   m_uses_native_signals = eLazyBoolNo;
+  m_x_packet_state.reset();
 
   m_max_packet_size = UINT64_MAX; // It's supposed to always be there, but if
                                   // not, we assume no limit
@@ -401,6 +402,8 @@ void GDBRemoteCommunicationClient::GetRemoteQSupported() {
         m_supports_qSaveCore = eLazyBoolYes;
       else if (x == "native-signals+")
         m_uses_native_signals = eLazyBoolYes;
+      else if (x == "binary-upload+")
+        m_x_packet_state = xPacketState::Prefixed;
       // Look for a list of compressions in the features list e.g.
       // qXfer:features:read+;PacketSize=20000;qEcho+;SupportedCompressions=zlib-
       // deflate,lzma
@@ -715,19 +718,20 @@ Status GDBRemoteCommunicationClient::WriteMemoryTags(
   return status;
 }
 
-bool GDBRemoteCommunicationClient::GetxPacketSupported() {
-  if (m_supports_x == eLazyBoolCalculate) {
+GDBRemoteCommunicationClient::xPacketState
+GDBRemoteCommunicationClient::GetxPacketState() {
+  if (!m_x_packet_state)
+    GetRemoteQSupported();
+  if (!m_x_packet_state) {
     StringExtractorGDBRemote response;
-    m_supports_x = eLazyBoolNo;
-    char packet[256];
-    snprintf(packet, sizeof(packet), "x0,0");
-    if (SendPacketAndWaitForResponse(packet, response) ==
+    m_x_packet_state = xPacketState::Unimplemented;
+    if (SendPacketAndWaitForResponse("x0,0", response) ==
         PacketResult::Success) {
       if (response.IsOKResponse())
-        m_supports_x = eLazyBoolYes;
+        m_x_packet_state = xPacketState::Bare;
     }
   }
-  return m_supports_x;
+  return *m_x_packet_state;
 }
 
 lldb::pid_t GDBRemoteCommunicationClient::GetCurrentProcessID(bool allow_lazy) {