bt: gracefully handle FaultError for variable values

There's no reason to be confident that a variable value will be valid
when we're formatting it in the stack trace. It is possible that it will
contain stale values that may result in FaultErrors. Be sure to catch
this and simply print a message saying the FaultError happened. This
ensures bt does not crash in these exceptional cases.

Signed-off-by: Stephen Brennan <[email protected]>

Author: brenns10

drgn_tools/bt.py

@@ -373,7 +373,13 @@ def get_sp(frame: drgn.StackFrame) -> int:
                     raise
             if val.absent_ and not show_absent:
                 continue
-            val_str = val.format_(dereference=False).replace("\n", "\n     ")
+
+            try:
+                val_str = val.format_(dereference=False).replace(
+                    "\n", "\n     "
+                )
+            except FaultError:
+                val_str = "(FaultError occurred while formatting!)"
             print(pfx + " " * 5 + f"{local} = {val_str}")