Add a very trivial example for scripted stepping.

llvm-svn: 218650

lldb/examples/python/scripted_step.py

@@ -0,0 +1,130 @@
+#############################################################################
+# This script contains two trivial examples of simple "scripted step" classes.
+# To fully understand how the lldb "Thread Plan" architecture works, read the
+# comments at the beginning of ThreadPlan.h in the lldb sources.  The python
+# interface is a reduced version of the full internal mechanism, but captures
+# most of the power with a much simpler interface.
+#
+# But I'll attempt a brief summary here.  
+# Stepping in lldb is done independently for each thread.  Moreover, the stepping
+# operations are stackable.  So for instance if you did a "step over", and in 
+# the course of stepping over you hit a breakpoint, stopped and stepped again,
+# the first "step-over" would be suspended, and the new step operation would
+# be enqueued.  Then if that step over caused the program to hit another breakpoint,
+# lldb would again suspend the second step and return control to the user, so
+# now there are two pending step overs.  Etc. with all the other stepping 
+# operations.  Then if you hit "continue" the bottom-most step-over would complete, 
+# and another continue would complete the first "step-over".
+#
+# lldb represents this system with a stack of "Thread Plans".  Each time a new
+# stepping operation is requested, a new plan is pushed on the stack.  When the
+# operation completes, it is pushed off the stack.
+#
+# The bottom-most plan in the stack is the immediate controller of stepping,
+# most importantly, when the process resumes, the bottom most plan will get
+# asked whether to set the program running freely, or to instruction-single-step
+# the current thread.  In the scripted interface, you indicate this by returning
+# False or True respectively from the should_step method.
+#
+# Each time the process stops the thread plan stack for each thread that stopped 
+# "for a reason", Ii.e. a single-step completed on that thread, or a breakpoint
+# was hit), is queried to determine how to proceed, starting from the most 
+# recently pushed plan, in two stages:
+#
+# 1) Each plan is asked if it "explains" the stop.  The first plan to claim the
+#    stop wins.  In scripted Thread Plans, this is done by returning True from
+#    the "explains_stop method.  This is how, for instance, control is returned
+#    to the User when the "step-over" plan hits a breakpoint.  The step-over 
+#    plan doesn't explain the breakpoint stop, so it returns false, and the 
+#    breakpoint hit is propagated up the stack to the "base" thread plan, which
+#    is the one that handles random breakpoint hits.
+#
+# 2) Then the plan that won the first round is asked if the process should stop.
+#    This is done in the "should_stop" method.  The scripted plans actually do
+#    three jobs in should_stop:
+#      a) They determine if they have completed their job or not.  If they have
+#         they indicate that by calling SetPlanComplete on their thread plan.
+#      b) They decide whether they want to return control to the user or not.
+#         They do this by returning True or False respectively.
+#      c) If they are not done, they set up whatever machinery they will use
+#         the next time the thread continues.
+#
+#    Note that deciding to return control to the user, and deciding your plan
+#    is done, are orthgonal operations.  You could set up the next phase of 
+#    stepping, and then return True from should_stop, and when the user next
+#    "continued" the process your plan would resume control.  Of course, the
+#    user might also "step-over" or some other operation that would push a 
+#    different plan, which would take control till it was done.
+#
+#    One other detail you should be aware of, if the plan below you on the
+#    stack was done, then it will be popped and the next plan will take control
+#    and its "should_stop" will be called.
+#
+#    Note also, there should be another method called when your plan is popped,
+#    to allow you to do whatever cleanup is required.  I haven't gotten to that
+#    yet.  For now you should do that at the same time you mark your plan complete.
+#
+# Both examples show stepping through an address range for 20 bytes from the
+# current PC.  The first one does it by single stepping and checking a condition.
+# It doesn't, however handle the case where you step into another frame while
+# still in the current range in the starting frame.  
+#
+# That is better handled in the second example by using the built-in StepOverRange
+# thread plan.
+#
+# To use these stepping modes, you would do:
+#
+#     (lldb) command script import scripted_step.py
+#     (lldb) thread step-scripted -C scripted_step.SimpleStep
+# or
+#
+#     (lldb) thread step-scripted -C scripted_step.StepWithPlan
+
+import lldb
+
+class SimpleStep:
+    def __init__ (self, thread_plan, dict):
+        self.thread_plan = thread_plan
+        self.start_address = thread_plan.GetThread().GetFrameAtIndex(0).GetPC()
+
+    def explains_stop (self, event):
+        # We are stepping, so if we stop for any other reason, it isn't
+        # because of us.
+        if self.thread_plan.GetThread().GetStopReason()== lldb.eStopReasonTrace:
+            return True
+        else:
+            return False
+
+    def should_stop (self, event):
+        cur_pc = self.thread_plan.GetThread().GetFrameAtIndex(0).GetPC()
+
+        if cur_pc < self.start_address or cur_pc >= self.start_address + 20:
+            self.thread_plan.SetPlanComplete(True)
+                return True
+        else:
+            return False
+
+    def should_step (self):
+        return True
+
+class StepWithPlan:
+    def__init__ (self,thread_plan, dict):
+    self.thread_plan = thread_plan
+    self.start_address = thread_plan.GetThread().GetFrameAtIndex(0).GetPCAddress()
+    self.step_thread_plan =thread_plan.QueueThreadPlanForStepOverRange(self.start_address, 20);
+
+    defexplains_stop (self, event):
+    # Since all I'm doing is running a plan, I will only ever get askedthis
+    # if myplan doesn't explain the stop, and in that caseI don'teither.
+        return False
+
+defshould_stop (self, event):
+if self.step_thread_plan.IsPlanComplete():
+            self.thread_plan.SetPlanComplete(True)
+            return True
+else:
+        return False
+
+defshould_step (self):
+return False
+