[lldb] Add Process::SupportsReverseDirection() method and use it

This allows `SBProcess::ContinueInDirection()` to error out early if the
target does not support any kind of reverse execution.

Author: rocallahan

lldb/include/lldb/Target/Process.h

@@ -1089,6 +1089,13 @@ class Process : public std::enable_shared_from_this<Process>,
   ///     Returns an error object.
   virtual Status WillResume() { return Status(); }
 
+  /// Reports whether this process supports reverse execution.
+  ///
+  /// \return
+  ///     Returns true if the process supports reverse execution (at least
+  /// under some circumstances).
+  virtual bool SupportsReverseDirection() { return false; }
+
   /// Resumes all of a process's threads as configured using the Thread run
   /// control functions.
   ///

lldb/source/API/SBProcess.cpp

@@ -584,8 +584,14 @@ SBError SBProcess::Continue() {
 }
 
 SBError SBProcess::ContinueInDirection(RunDirection direction) {
-  if (ProcessSP process_sp = GetSP())
+  if (ProcessSP process_sp = GetSP()) {
+    if (direction == RunDirection::eRunReverse &&
+        !process_sp->SupportsReverseDirection())
+      return Status::FromErrorStringWithFormatv(
+          "error: {0} does not support reverse execution of processes",
+          GetPluginName());
     process_sp->SetBaseDirection(direction);
+  }
   return Continue();
 }
 

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

@@ -1182,6 +1182,11 @@ Status ProcessGDBRemote::WillResume() {
   return Status();
 }
 
+bool ProcessGDBRemote::SupportsReverseDirection() {
+  return m_gdb_comm.GetReverseStepSupported() ||
+         m_gdb_comm.GetReverseContinueSupported();
+}
+
 Status ProcessGDBRemote::DoResume(RunDirection direction) {
   Status error;
   Log *log = GetLog(GDBRLog::Process);

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

@@ -111,6 +111,8 @@ class ProcessGDBRemote : public Process,
   // Process Control
   Status WillResume() override;
 
+  bool SupportsReverseDirection() override;
+
   Status DoResume(lldb::RunDirection direction) override;
 
   Status DoHalt(bool &caused_stop) override;

lldb/test/API/functionalities/reverse-execution/TestReverseContinueNotSupported.py

@@ -22,7 +22,9 @@ def test_reverse_continue_not_supported(self):
 
         # This will fail gracefully.
         status = process.ContinueInDirection(lldb.eRunReverse)
-        self.assertFailure(status, "target does not support reverse-continue")
+        self.assertFailure(
+            status, "error: gdb-remote does not support reverse execution of processes"
+        )
 
         status = process.ContinueInDirection(lldb.eRunForward)
         self.assertSuccess(status)