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Two function types with different language linkages are distinct types even if they are otherwise identical.
When calling a function, it is undefined behavior if the language linkage of the function type used in the call does not match the language linkage of the function definition. For instance, a mismatch in language linkage specification may corrupt the call stack due to calling convention or other ABI mismatches.
Do not call a function through a type whose language linkage does not match the language linkage of the called function's definition. This restriction applies both to functions called within a C++ program as well as function pointers used to make a function call from outside of the C++ program.
However, many compilers fail to integrate language linkage into the function's type, despite the normative requirement to do so in the C++ Standard. For instance, GCC 6.1.0, Clang 3.9, and Microsoft Visual Studio 2015 all consider the following code snippet to be ill-formed due to a redefinition of f() rather than a well-formed overload of f().
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