Trouble linking C++ with Xcode 5 - c++

Question

So I have this legacy project, which I am trying to bring to iOS 7 and Xcode 5. And by legacy, I mean real legacy. Like 2004 legacy.
Anyhow, I am trying to build this thing, and it spits out a few libraries, including some common third party libs. When linking, I get errors like these:
Undefined symbols for architecture ${arch}:
"google::protobuf::internal::WireFormatLite::WriteBytes(int, std::string const&, google::protobuf::io::CodedOutputStream*)"
Upon examination with nm, the old (arm only) binary library still included in the project contains this:
U __ZN6google8protobuf8internal14WireFormatLite10WriteBytesEiRKNSt3__112basic_stringIcNS3_11char_traitsIcEENS3_9allocatorIcEEEEPNS0_2io17CodedOutputStreamE
00000a8c T __ZN6google8protobuf8internal14WireFormatLite10WriteBytesEiRKNSt3__112basic_stringIcNS3_11char_traitsIcEENS3_9allocatorIcEEEEPNS0_2io17CodedOutputStreamE
00002b28 S __ZN6google8protobuf8internal14WireFormatLite10WriteBytesEiRKNSt3__112basic_stringIcNS3_11char_traitsIcEENS3_9allocatorIcEEEEPNS0_2io17CodedOutputStreamE.eh</code>
The new library (universal), created when I run the project through Xcode 5 (and thus, clang/llvm) contains this:
U __ZN6google8protobuf8internal14WireFormatLite10WriteBytesEiRKSsPNS0_2io17CodedOutputStreamE
00000514 T __ZN6google8protobuf8internal14WireFormatLite10WriteBytesEiRKSsPNS0_2io17CodedOutputStreamE
00000b2c S __ZN6google8protobuf8internal14WireFormatLite10WriteBytesEiRKSsPNS0_2io17CodedOutputStreamE.eh
To me, it looks like the parameters are missing in the mangled name.
Is this normal and I need to look somewhere else?
Or if this is the problem: Any idea how to solve it?
EDIT: I mixed up OLD and NEW. I left the original post unchanged

Answer 1

The old, arm only libary seems to indicate:
google::protobuf::internal::WireFormatLite::WriteBytes(int, std::string const&, google::protobuf::io::CodedOutputStream*)
Which has all the hallmarks of being compiled with libstdc++.
The new universal library indicates:
google::protobuf::internal::WireFormatLite::WriteBytes(int, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&, google::protobuf::io::CodedOutputStream*)
This has all the hallmarks of being compiled with libc++
Your link error indicates that there is a problem finding:
google::protobuf::internal::WireFormatLite::WriteBytes(int, std::string const&, google::protobuf::io::CodedOutputStream*)
This would be the case if the code linking to the library was compiled using libstdc++ and, because your new universal library is compiled using libc++ the code will not link.
You have to compile everything with the same libc++/libstdc++ support, you cannot mix and match as they will refuse to link. Make sure that every element in your project is compiled using the same C++ Standard Library and the link error should be resolved.
In general, demangling the symbols (using c++filt) allows you to see the proper signatures, and in the case of this code, once you start seeing std::__1:: in the symbols, it indicates that the library was compiled using libc++, and when you see the link failing with unadorned std:: symbols (i.e. without the inner __1::), then it indicates that the item performing the linking is using libstdc++.

Answer 2

Are you perhaps mixing and matching SDKs or compilers? Name mangling might differ between compilers. The only other thing I know that might affect name mangling is the 'extern "C"' keyword, but that usually turns it off completely, so I don't think that's it.
So, if the old code was still built with GCC 2.x and your new code is clang-built, they probably just mangle differently.
Does the error message really say $(arch) ? Not a particular architecture? If it gave a concrete architecture, I'd expect that you have one project that builds e.g. for arm5 and arm6, linking in a library that only has one of these architectures. Then it usually complains about the symbols in that library not being available, I think.