[lldb-dev] Continue misfiring after expression evaluation

Jim Ingham jingham at apple.com
Wed Dec 5 15:49:37 PST 2012

I don't see this happening on Mac OS X.  That test succeeds, and I don't see the behavior you describe.

You should not need to clear the completed plan stack.  The way it is supposed to work is as follows:

Running functions is always done by Process::RunThreadPlan.  After the ThreadPlanCallFunction gets done running in that function, we do this
bit of code:

        // Restore the thread state if we are going to discard the plan execution.
        if (return_value == eExecutionCompleted || discard_on_error)
That should set the StopInfo that was squirreled away in Thread::CheckpointThreadState back as the current StopInfo for the thread.  Is that getting called?  If not, why not?  If it is getting called, why isn't it succeeding in resetting the thread's StopInfo back to the old reason?

Note, up till a couple of weeks ago this work was done in the DoTakedown method of ThreadPlanCallFunction, but I moved resetting the StopInfo out of that function (which gets called while the stop event for the function call is still being processed) to here, because otherwise it might trigger the original StopInfo's PerformAction while you are in the middle of handing the ThreadPlanCallFunction's execution, which isn't right.

Hope that helps.


On Dec 5, 2012, at 3:28 PM, "Kaylor, Andrew" <andrew.kaylor at intel.com> wrote:

> Hi all,
> I’ve been debugging a problem on Linux where if you hit a breakpoint, then evaluate an expression that requires JITing, then continue LLDB will break at the line you were already on.  I don’t know if this problem is specific to Linux, but that’s where I’m debugging it.  This problem appears in the ‘lang/c/setvalues/TestSetValues.py’ test case, but can also be reproduced manually.
> What I’m seeing is that when the ‘continue’ handling calls Thread::SetupForResume() the current Thread reports its stop reason as ‘eStopReasonPlanComplete’ because the ThreadPlan for evaluating the expression is still on the completed plans stack.  As a result, the ThreadPlanStepOverBreakpoint plan doesn’t get queued.  If I add calls to ‘m_completed_plan_stack.clear()’ and ‘m_discarded_plan_stack.clear()’ at the top of the ‘if (GetResumeState() == eStateSuspended)’ block in Thread::SetupForResume() then everything works as expected.
> Obviously, that feels like a pretty risky thing to do, at best.  It seems like the expression command handling should have done something to clear the completed plan stack when it was finished, but as of yet I haven’t found a place where that is appropriate.
> Can anyone give me guidance on this issue?
> Thanks,
> Andy
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