[Swig-devel] [ swig-Bugs-1944074 ] SWIG_ConvertPtr interface seems broken.

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Bugs item #1944074, was opened at 2008-04-16 17:00
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Category: None
Group: None
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: Philipp Thomas (pepys)
Assigned to: Nobody/Anonymous (nobody)
Summary: SWIG_ConvertPtr interface seems broken.

Initial Comment:
At least for php, ocaml and perl I get warnings from gcc 4.3 for calls to SWIG_ConvertPtr because it expects a
void ** as second parameter and thus any pointer is
cast to void ** for the call. Now void ** is NOT a generic pointer that may alias any other type (only char * and void * are), so gcc rightfully warns that dereferencing the type-punned pointer will break strict-aliasing rules. The only viable solution I see is making the second parameter of SWIG_ConvertPtr a 'void *' and cast that to void ** inside of SWIG_ConvertPtr.

The plus side is that you just change SWIG_ConvertPtr respectively its language specific versions and then simply remove the explicit cast to void ** wherever SWIG_ConvertPtr is called.

The downside is that you loose type checking.

The alternatives would be either using -fno-strict-aliasing and thus disable some code optimizations or change the call sites to use unions for punning the type, both of which are IMNSHO rather undesireable.


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