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When using `SBFrame::EvaluateExpression` on a frame that's not the currently selected frame, we would sometimes run into errors such as: ``` error: error: The context has changed before we could JIT the expression! error: errored out in DoExecute, couldn't PrepareToExecuteJITExpression ``` During expression parsing, we call `RunStaticInitializers`. On our internal fork this happens quite frequently because any usage of, e.g., function pointers, will inject ptrauth fixup code into the expression. The static initializers are run using `RunThreadPlan`. The `ExecutionContext::m_frame_sp` going into the `RunThreadPlan` is the `SBFrame` that we called `EvaluateExpression` on. LLDB then tries to save this frame to restore it after the thread-plan ran (the restore occurs by unconditionally overwriting whatever is in `ExecutionContext::m_frame_sp`). However, if the `selected_frame_sp` is not the same as the `SBFrame`, then `RunThreadPlan` would set the `ExecutionContext`'s frame to a different frame than what we started with. When we `PrepareToExecuteJITExpression`, LLDB checks whether the `ExecutionContext` frame changed from when we initially `EvaluateExpression`, and if did, bails out with the error above. One such test-case is attached. This currently passes regardless of the fix because our ptrauth static initializers code isn't upstream yet. But the plan is to upstream it soon. This patch addresses the issue by saving/restoring the frame of the incoming `ExecutionContext`, if such frame exists. Otherwise, fall back to using the selected frame. rdar://147456589