[cxx-abi-dev] Possibly ambiguous mangling of extern "C" functions

[Michael Wong]

Thanks all for the discussion. This case was taken pretty much from the C++
ABI spec.

So it sounds like the spec is OK, in that a valid variant of the case as
Dennis Handly and John Spicer shown below, should be mangled as:
_ZN2CBIL_Z7IsEmptyEE1xE

SO we have:
1. GCC 4.1.2 is in error by missing the _
2. the rest of us are in error by adding the X ...E


Michael Wong
XL C++ Compiler kernel Development
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        Re: [cxx-abi-dev] Possibly ambiguous mangling of extern "C" functions    
                                                                                 
                                                                                 
        John H. Spicer                                                           
                      to:                                                        
                        Mark Mitchell                                            
                                                             08/20/2008 09:11 AM 
                                                                                 
                                                                                 
                                                                                 
                                                                                 
        Cc:                                                                      
           David Vandevoorde, Michael Wong, cxx-abi-dev                          
                                                                                 
                                                                                 
                                                                                 
                                                                                 







On Aug 20, 2008, at 4:19 AM, Mark Mitchell wrote:

      David Vandevoorde wrote:

                  extern "C" bool IsEmpty(char *); // (un)mangled as
                  IsEmpty
                  template<bool (&)(char *)> struct CB { static int x; };
                  // CB<IsEmpty> is mangled as "2CBIL_Z7IsEmptyEE"
                  int *p = &CB<IsEmpty>::x;

            Normally, we issue the following error on that example:
            "t.c", line 4: error: a reference of type "bool (&)(char *)"
            (not
                     const-qualified) cannot be initialized with a value of
            type
                     "bool (char *) C"

      Yes, that's the right error.  G++ has never implemented extern "C"
      function *types*, so doesn't issue this kind of error.  There are
      extern "C" functions, but the linkage isn't part of the type per se.
      This is a known bug.

      So, now we're talking about mangling for an invalid C++ program,
      which is outside the scope of the ABI.

There is a well-formed varient of this case though:

extern "C" {
bool IsEmpty(char *); // (un)mangled as IsEmpty
typedef bool (&ref_func)(char *);
}
template<ref_func> struct CB { static int x; };
int *p = &CB<IsEmpty>::x;

John Spicer
Edison Design Group
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