Add a missing null pointer check in CommandObjectThread.cpp.

[emaste]

LGTM, I think I had this same change in a local branch at one point.

[jingham]

How do you get a thread that has NO frame 0? That seems weird, we always have a register context to make frame 0...

Anyway, if you're going to do this, add it to the "thread == NULL" checks earlier on in the function so we can get out of the command with an appropriate error message. If we don't have a frame 0 we probably don't have registers so I'm not really sure how we're going to do any kind of stepping...

Jim

[sas]

This is a patch that I've been keeping in my branches for a while. I
hit a null pointer dereference there. Looks like Ed had the same
issue. I'll move the check to the beginning of the function as you
suggested though.

[emaste]

I encountered an issue like this early on while bringing up a new target (FreeBSD/mips64 I think), while the work was incomplete. Of course once I finished we always have frame 0, which is why I didn't commit it at the time.

But it (or, perhaps just an assert) presumably will be handy when someone else goes down the same path.

[jasonmolenda]

Not worth changing the patch but fwiw you could have added eFlagRequiresFrame to the CommandObjectParsed flags for this command to do the same thing. My main reaction echoes Jim's - I don't know what it means to have a thread and no frame 0. But given that two lldb devs have hit it, I guess early in the startup of a new platform you can get hit this.

[jingham]

Yes, I think there are a lot of places around in lldb where we assume that if you have a valid thread you have a valid frame 0. You're not going to get very far if you don't get that right.

Jim

source/Commands/CommandObjectThread.cpp

DoExecute (Args& command, CommandReturnObject &result)
             bool_stop_other_threads = true;
 
         ThreadPlanSP new_plan_sp;
         
         if (m_step_type == eStepTypeInto)
         {
             StackFrame *frame = thread->GetStackFrameAtIndex(0).get();
 
-            if (frame->HasDebugInformation ())
+            if (frame && frame->HasDebugInformation ())
             {
                 new_plan_sp = thread->QueueThreadPlanForStepInRange (abort_other_plans,
                                                                 frame->GetSymbolContext(eSymbolContextEverything).line_entry.range, 
                                                                 frame->GetSymbolContext(eSymbolContextEverything),
                                                                 m_options.m_step_in_target.c_str(),
                                                                 stop_other_threads,
                                                                 m_options.m_step_in_avoid_no_debug,
                                                                 m_options.m_step_out_avoid_no_debug);