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

[Jonathan Roelofs via cfe-dev]

On 7/28/16 12:33 PM, Himanshu wrote:
> Thanks Jon!
>
> So you suggest the change of function to:
>
> void *wrapAssgnmt(void **,void *, void *ptr){
>    // assgn using first two args
>    ...
>   // return the actual ptr
>   return ptr;
> }

Oh, oops. I put the parens in the wrong spot. I meant to write this:

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

as-in: use the comma operator to perform the assignment of NULL into 'ptr'.


Jon

>
> --
> Himanshu
>
> On Thu, Jul 28, 2016 at 11:29 AM, Jonathan Roelofs
> <jroelofs.lists at gmail.com <mailto:jroelofs.lists at gmail.com>> wrote:
>
>
>
>     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 <mailto:jonathan at codesourcery.com>
>     CodeSourcery / Mentor Embedded
>
>

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