Possibly ambiguous mangling of extern "C" functions

[Michael Wong]

The example in question is at the end of "5.1.5 Type encodings".  of 
http://www.codesourcery.com/public/cxx-abi/abi.html.

In this example, it is using an extern "C" function as a parameter to a 
class template. There are two problems:
1. Should there be full mangling, partial mangling, or no mangling of the 
extern 'C" function as a template parameter?
2. Should there be an X...E (after the I and before the L) since there is 
a <expr-primary> production under <template-arg> that makes that the case.

Here is the example I actually used:

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;


The example is shown without any supporting rules in the spec which makes 
it hard to justify other then an intuition, and it is shown with just the 
_Z7 prefix mangling on the function. It does not mangle the function 
parameter, which may be OK if the group decides it is so since extern "C" 
function can't be overloaded anyway and you can't have it with different 
parameters. But then why bother to mangle it at all?

Checking various versions of GNU also shows different mangling with the 
latest that I have (4.1.2) deviating the most from the example. I show the 
example with and without the extern "C".

gcc (GCC) 4.1.2 20071124 (Red Hat 4.1.2-42)
with extern "C":
_ZN2CBILZ7IsEmptyEE1xE <== GCC missing X and has the Z (but no underscore)

without extern "C":
_ZN2CBILZ7IsEmptyPcEE1xE <=== This is close but it is still missing the X 
and has no _Z

gcc (GCC) 3.3.4
with extern "C":
_ZN2CBIXL7IsEmptyEEE1xE <== Older GCC has the X, but leaves out the _Z or 
Z (same as us with extern "C"), indicating no mangling, but it has the 7

without extern "C":
_ZN2CBIXL_Z7IsEmptyPcEEE1xE <== This one looks OK, same as us without 
extern "C"

Anybody can report what EDG/Intel generates? Thanks.

Michael Wong
XL C++ Compiler kernel Development
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