Add GDB scheduler-locking control to the Debugger-agnostic API (#2409)

* Add GDB scheduler-locking control to the Debugger-agnostic API

* Add back uses of scheduler-locking where they'd been removed

pwndbg/aglib/tls.py

@@ -16,7 +16,11 @@ def __call_pthread_self() -> int:
     if pwndbg.dbg.selected_inferior().symbol_address_from_name("pthread_self") is None:
         return 0
     try:
-        return int(pwndbg.dbg.selected_frame().evaluate_expression("(void *)pthread_self()"))
+        return int(
+            pwndbg.dbg.selected_frame().evaluate_expression(
+                "(void *)pthread_self()", lock_scheduler=True
+            )
+        )
     except pwndbg.dbg_mod.Error:
         return 0
 

pwndbg/dbg/__init__.py

@@ -154,10 +154,17 @@ class Registers:
 
 
 class Frame:
-    def evaluate_expression(self, expression: str) -> Value:
+    def evaluate_expression(self, expression: str, lock_scheduler: bool = False) -> Value:
         """
         Evaluate the given expression in the context of this frame, and
         return a `Value`.
+
+        # `lock_scheduler`
+        Additionally, callers of this function might specify that they want to
+        enable scheduler locking during the evaluation of this expression. This
+        is a GDB-only option, and is intended for cases in which the result
+        would be incorrect without it enabled, when running in GDB. Other
+        debuggers should ignore this parameter.
         """
         raise NotImplementedError()
 

pwndbg/dbg/gdb.py

@@ -2,6 +2,7 @@ from __future__ import annotations
 
 import re
 import signal
+from contextlib import nullcontext
 from typing import Any
 from typing import Generator
 from typing import List
@@ -86,10 +87,12 @@ class GDBFrame(pwndbg.dbg_mod.Frame):
         self.inner = inner
 
     @override
-    def evaluate_expression(self, expression: str) -> pwndbg.dbg_mod.Value:
+    def evaluate_expression(
-        from pwndbg.gdblib.scheduler import lock_scheduler
+        self, expression: str, lock_scheduler: bool = False
+    ) -> pwndbg.dbg_mod.Value:
+        from pwndbg.gdblib.scheduler import lock_scheduler as do_lock_scheduler
 
-        with lock_scheduler():
+        with do_lock_scheduler() if lock_scheduler else nullcontext():
             with selection(self.inner, lambda: gdb.selected_frame(), lambda f: f.select()):
                 try:
                     value = parse_and_eval(expression, global_context=False)

pwndbg/dbg/lldb/__init__.py

@@ -97,7 +97,9 @@ class LLDBFrame(pwndbg.dbg_mod.Frame):
         self.proc = proc
 
     @override
-    def evaluate_expression(self, expression: str) -> pwndbg.dbg_mod.Value:
+    def evaluate_expression(
+        self, expression: str, lock_scheduler: bool = False
+    ) -> pwndbg.dbg_mod.Value:
         value = self.inner.EvaluateExpression(expression)
         opt_out = _is_optimized_out(value)