[lldb] Implement basic support for reverse-continue (#99736)

This commit only adds support for the
`SBProcess::ReverseContinue()` API. A user-accessible command for this
will follow in a later commit.

This feature depends on a gdbserver implementation (e.g. `rr`) providing
support for the `bc` and `bs` packets. `lldb-server` does not support
those packets, and there is no plan to change that. So, for testing
purposes, `lldbreverse.py` wraps `lldb-server` with a Python
implementation of *very limited* record-and-replay functionality for use
by *tests only*.

The majority of this PR is test infrastructure (about 700 of the 950
lines added).

1 files changed, 22 insertions, 0 deletions

diff --git a/lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationClient.cpp b/lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationClient.cpp
index e42526c..fc792a4 100644
--- a/lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationClient.cpp
+++ b/lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationClient.cpp
@@ -199,6 +199,20 @@ uint64_t GDBRemoteCommunicationClient::GetRemoteMaxPacketSize() {
   return m_max_packet_size;
 }
 
+bool GDBRemoteCommunicationClient::GetReverseContinueSupported() {
+  if (m_supports_reverse_continue == eLazyBoolCalculate) {
+    GetRemoteQSupported();
+  }
+  return m_supports_reverse_continue == eLazyBoolYes;
+}
+
+bool GDBRemoteCommunicationClient::GetReverseStepSupported() {
+  if (m_supports_reverse_step == eLazyBoolCalculate) {
+    GetRemoteQSupported();
+  }
+  return m_supports_reverse_step == eLazyBoolYes;
+}
+
 bool GDBRemoteCommunicationClient::QueryNoAckModeSupported() {
   if (m_supports_not_sending_acks == eLazyBoolCalculate) {
     m_send_acks = true;
@@ -295,6 +309,8 @@ 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_supports_reverse_continue = eLazyBoolCalculate;
+    m_supports_reverse_step = eLazyBoolCalculate;
     m_supports_qProcessInfoPID = true;
     m_supports_qfProcessInfo = true;
     m_supports_qUserName = true;
@@ -348,6 +364,8 @@ void GDBRemoteCommunicationClient::GetRemoteQSupported() {
   m_supports_memory_tagging = eLazyBoolNo;
   m_supports_qSaveCore = eLazyBoolNo;
   m_uses_native_signals = eLazyBoolNo;
+  m_supports_reverse_continue = eLazyBoolNo;
+  m_supports_reverse_step = eLazyBoolNo;
 
   m_max_packet_size = UINT64_MAX; // It's supposed to always be there, but if
                                   // not, we assume no limit
@@ -401,6 +419,10 @@ void GDBRemoteCommunicationClient::GetRemoteQSupported() {
         m_supports_qSaveCore = eLazyBoolYes;
       else if (x == "native-signals+")
         m_uses_native_signals = eLazyBoolYes;
+      else if (x == "ReverseContinue+")
+        m_supports_reverse_continue = eLazyBoolYes;
+      else if (x == "ReverseStep+")
+        m_supports_reverse_step = eLazyBoolYes;
       // Look for a list of compressions in the features list e.g.
       // qXfer:features:read+;PacketSize=20000;qEcho+;SupportedCompressions=zlib-
       // deflate,lzma