[cfe-commits] [PATCH] Set region size in GRRegionVals transfer function

Ted Kremenek kremenek at apple.com
Wed Nov 5 16:55:40 PST 2008

On Nov 5, 2008, at 3:33 AM, Zhongxing Xu wrote:

> The first step of checking out of bound array references is to get  
> the size of a memory region. In this patch I store the size of  
> MemRegions with the GDM facility of GRState. I put this data into a  
> new transfer function called GRRegionVals. GRRegionVals is intended  
> to be used with the RegionStore when we want to check some  
> properties enabled by RegionStore, for example, out of bound array  
> references and memory leak. For memory leaks we need another piece  
> of GDM to store the state of heap regions.
> I can think of no where to put this piece of data in current  
> components. Store only manages the mapping from region to value.  
> Other components should not manage this region-store specific data.  
> So I made a new transfer function for it.
> Later in this new GRRegionVals we can add an EvalLocation() method  
> to check for out-of-bound array references and other region-store  
> enabled memory checks.

Hi Zhongxing,

I do not think we should introduce a new GRTransferFunc subclass to  
implement this functionality.  Here's why:

(a) This functionality can easily go into StoreManager, and  
conceptually its the right place for it.  StoreManager handles the  
abstraction of memory, and the extent is a natural property of a  
region.  It seem to me that adding the interface would be an easy  
first start:

class StoreManager {
   virtual SVal getExtent(const GRState* state, const MemRegion* R) {
     return UnknownVal();

If the StoreManager cares about tracking region sizes, it should have  
all the information it needs in the GRState* object or in the region  
itself.  If not all of the interfaces are there to do this, this is  
the direction I think we should move to.

(b) The second reason I don't think we should have a GRRegionVals is  
because it partitions functionality into a separate GRTransferFuncs  
object that really can be easily recycled elsewhere through the  
StoreManager interface.

(c) The GRTransferFuncs interface was designed to implement plugin  
transfer function logic for *operations*, e.g. function calls.  This  
is used to implement specific analyses/checkers.  Region sizes seem  
like a fundamental property of regions that all analyses might be  
interested in.

(c) The third reason is that the entire GRTransferFuncs interface  
needs to be overhauled.  What's there now is a mongrel (that I  
created) that serves different masters.  Much of it needs to be  
potentially lifted to GRExprEngine, and in its place have a more  
modular design that allows transfer functions for different checkers/ 
analyses to be composed (e.g., one analysis that tracks reference  
counts, another that tracks the state of a window object, another that  
tracks lock states, etc.).  It's not there yet, but sticking more core  
functionality into the GRTransferFunc is interface doesn't seem ideal  
in the long run.



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