Is it possible to demangle C++ symbols by hand?

Question

I'm getting some errors like this:

dyld: lazy symbol binding failed: Symbol not found: __ZN2nm8RationalIxEC1ERKNS_10RubyObjectE
  Referenced from: /Users/jwoods/Projects/nmatrix/lib/nmatrix.bundle
  Expected in: flat namespace

dyld: Symbol not found: __ZN2nm8RationalIxEC1ERKNS_10RubyObjectE
  Referenced from: /Users/jwoods/Projects/nmatrix/lib/nmatrix.bundle
  Expected in: flat namespace

and then the same for __ZN2nm7ComplexIfEC1ERKNS_10RubyObjectE.

Unfortunately, c++filt doesn't seem to want to demangle these. When I try inputting them in the c++filtjs online interface, I get "Not a mangled C++ symbol."

I'm a bit puzzled by the error message, since the example c++filtjs gives is _ZN9wikipedia7article8wikilinkC1ERKSs, which represents wikipedia::article::wikilink::wikilink(std::string const&). I see several patterns, among them ZN#, 7 and 8 for ::, and C1ERK for what I'm guessing is some kind of pass-by-reference to a constructor.

I'd guess it's complaining that it's missing one of my constructors for class Rational, such as Rational::Rational(RubyObject const&). Rational is a template, however, so it would be helpful for me to understand which version is missing.

But the question here is really how I can demangle by hand. =)

Answer 1

The symbol looks like one produced by clang or gcc. Both of these compilers use an ABI based on the Itanium ABI. This document includes a section on demangling describing how external symbols are constructed. If you internalize the corresponding rules, you should be able to demangle the names.

I couldn't locate the document on the original site and off-hand I don't know where the official document lives.