Itanium Name Demangler Library

Introduction

This directory contains the generic itanium name demangler library. The main purpose of the library is to demangle C++ symbols, i.e. convert the string "_Z1fv" into "f()". You can also use the CRTP base ManglingParser to perform some simple analysis on the mangled name, or (in LLVM) use the opaque ItaniumPartialDemangler to query the demangled AST.

Why are there multiple copies of the this library in the source tree?

This directory is mirrored between libcxxabi/demangle and llvm/include/llvm/Demangle. The simple reason for this is that both projects need to demangle symbols, but neither can depend on each other. libcxxabi needs the demangler to implement __cxa_demangle, which is part of the itanium ABI spec. LLVM needs a copy for a bunch of places, but doesn't want to use the system's __cxa_demangle because it a) might not be available (i.e., on Windows), and b) probably isn't that up-to-date on the latest language features.

The copy of the demangler in LLVM has some extra stuff that aren't needed in libcxxabi (ie, the MSVC demangler, ItaniumPartialDemangler), which depend on the shared generic components. Despite these differences, we want to keep the "core" generic demangling library identical between both copies to simplify development and testing.

If you're working on the generic library, then do the work first in libcxxabi, then run the cp-to-llvm.sh script in src/demangle. This script takes as an argument the path to llvm, and re-copies the changes you made to libcxxabi over. Note that this script just blindly overwrites all changes to the generic library in llvm, so be careful.

Because the core demangler needs to work in libcxxabi, everything needs to be declared in an anonymous namespace (see DEMANGLE_NAMESPACE_BEGIN), and you can't introduce any code that depends on the libcxx dylib.

Hopefully, when LLVM becomes a monorepo, we can de-duplicate this code, and have both LLVM and libcxxabi depend on a shared demangler library.

Testing

The tests are split up between libcxxabi/test/{unit,}test_demangle.cpp, and llvm/unittest/Demangle. The llvm directory should only get tests for stuff not included in the core library. In the future though, we should probably move all the tests to LLVM.

It is also a really good idea to run libFuzzer after non-trivial changes, see libcxxabi/fuzz/cxa_demangle_fuzzer.cpp and https://llvm.org/docs/LibFuzzer.html.