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

[John H. Spicer]

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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