[cfe-dev] Wrapping assignments in function call for simulation

[Jonathan Roelofs via cfe-dev]

On 7/28/16 12:09 PM, Himanshu via cfe-dev wrote:
> Hi All,
>
> I would like to perform for simulation experiments on a C codebase where
> based on the type of the variable, an assignment to a pointer of this
> type is followed by some additional instruction (lets say an external
> counter increment --- just to create a simple scenario). I have
> implemented a RecuriveASTVisitor that visits BinaryOps (after checking
> they are assignments) and rewrites the source by replacement.
>
> However, there are issues with multiple assignments within the same
> source line (such as ptr1 = ptr2 = NULL), as well as some macro
> expansions. I would like a robust way of doing so without breaking the code.
>
> Could someone kindly answer the following:
> 1. Is there some existing libTool to do so?
>
> if not, then:
> 2. My wrapper function is of the form: (listing a simplified version)
>       void * wrapAssgnmt (void **ptrToLhsPtr, void *rhsPtr){
>               *ptrToLhsPtr = rhsPtr;
>               // do other things for simulation
>               return *ptrToLhsPtr; // so that NULL based checks work.
>       }
>     compilation gives me: "warning: comparison between pointer and
> integer" for cases of pattern:
>     type *ptr;  // original code is  if( (ptr = malloc ( ... )) = NULL) ...
>     if((wrapAssgnmt( &ptr , malloc( ... ) ) = NULL)
>
>     I understand the warning, but I am not sure about the cause/reason.
> Could someone please suggest the correction?

This happens because your translation is not precise enough. It needs to 
be something like:

   if ((wrapAssgnmt(&ptr, malloc( ... ), ptr) = NULL)


Jon

>
> Thanks!
>
>
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-- 
Jon Roelofs
jonathan at codesourcery.com
CodeSourcery / Mentor Embedded