On Fri, Aug 18, 2017 at 9:20 AM, Luc Van Oostenryck <luc.vanoostenryck@xxxxxxxxx> wrote: > Hi Josh, > > I was thinking lately about sparse's context checking. > I had an idea and I wondered if it hasn't already been > tried or discussed. > > The context checking essentially works with the instruction > OP_CONTEXT, that do nothing more than adding or subtracting > some constant value to 'the context'. Then, at checking time, > these instructions are interpreted along all the paths and if > there is a disagreement between values from different paths, > it emits a 'context imbalance' warning (there is also the > checks for the expected return value of the context). That is right. > > My idea/question is the following: this interpretation > is already done for all 'normal' values. So couldn't we > consider the context as a special kind of 'variable', > use a normal pseudo for it, use phi-nodes on them and Question. What syntax are you considering for declare this special pseudo? Does it automatically attach to the variable that has the context attribute? > let the normal simplification process act on them? > If the context is (proveably) well balanced, there > shouldn't be any phi-node left for this context. Assume you do the context pseudo attach to the lock variable. Then you will have to do the pointer alias properly. People might have different pointer point to that variable. > I'm not sure if there would be any significant advantage, > but it seems to me that what is currently done is > somehow redundant with the 'normal' processing. > It could also maybe help to have several independent > contexts. 'normal' process do you mean the context statement? > > [of course, we can't really use add/sub for the context > increase/decrease as we want to check if the context > don't become negative]. It can become negative for some helper function that wrap around the unclock function. I think the biggest problem with context right now is actually not able to inline or take into account for the function that change the context. We can add more context attribute to the function to describe what this function might do to the context. The best way is automatic to make this happen. I see that as the biggest cause of the false alarm on context warnings. Chris -- To unsubscribe from this list: send the line "unsubscribe linux-sparse" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
