"libc++abi" C++ Standard Library Support
libc++abi is a new implementation of low level support for a standard C++ library.
All of the code in libc++abi is dual licensed under the MIT license and the UIUC License (a BSD-like license).
Features and Goals
- Correctness as defined by the C++11 standard.
- Provide a portable sublayer to ease the porting of libc++
- On Mac OS X, be ABI compatible with the existing low-level support.
libc++abi is known to work on the following platforms, using clang.
libc++abi is complete. Here is a list of functionality.
Get it and get involved!
To check out the code (including llvm and others), use:
git clone https://github.com/llvm/llvm-project.git
mkdir build && cd build
cmake -DLLVM_ENABLE_PROJECTS=libcxxabi ../llvm # on linux you may need to specify -DCMAKE_C_COMPILER=clang -DCMAKE_CXX_COMPILER=clang++
To do a standalone build:
- Check out the source tree. This includes the other subprojects, but you'll only use the libcxxabi part.
mkdir build-libcxxabi && cd build-libcxxabi
cmake -DLIBCXXABI_LIBCXX_PATH=path/to/libcxx ../libcxxabi # on linux you may need -DCMAKE_C_COMPILER=clang -DCMAKE_CXX_COMPILER=clang++
By default CMake uses
llvm-config to locate the required
LLVM sources. If CMake cannot find
llvm-config then you must
configure CMake using either of the following options.
To run the tests:
Note: in a standalone build, the system's libc++ will be used for tests. If the system's libc++ was statically linked against libc++abi (or linked against a different ABI library), this may interfere with test results.
Send discussions to the (libcxx-dev mailing list).
Frequently asked questions
Q: Why are the destructors for the standard exception classes defined in libc++abi? They're just empty, can't they be defined inline?
A: The destructors for them live in libc++abi because they are "key" functions.
The Itanium ABI describes a "key" function as the first virtual declared.
And wherever the key function is defined, that is where the
type_info gets defined.
And in libc++ types are the same type if and only if they have the same
(as in there must be only one type info per type in the entire application).
And on OS X, libstdc++ and libc++ share these exception types.
So to be able to throw in one dylib and catch in another (a
std::exception for example),
there must be only one
std::exception type_info in the entire app.
That typeinfo gets laid down beside
~exception() in libc++abi (for both libstdc++ and libc++).