[cfe-dev] libc++abi

[Howard Hinnant]

There is a new project at:

http://libcxxabi.llvm.org/

This is libc++abi, and is meant to be the low-level, Itanium ABI (http://www.codesourcery.com/public/cxx-abi/) implementation for libc++.   There isn't much in there right now (additions welcome!).  So far all that is in there is a demangler (__cxa_demangle).

The demangler has been split into three lower-level API's:

__demangle_tree
__demangle(const char* mangled_name, char* buf, size_t bs)

__demangle_tree
__demangle(const char* mangled_name);

char*
__demangle(__demangle_tree dmg_tree, char* buf, size_t* n, int* status);

The first two functions take a mangled name as input and output a __demangle_tree.  This is the "parsing part" of demangling.  The reason for two functions here is so that you can optionally pass in a buffer, which if large enough, will be used instead of allocating memory for the __demangle_tree.

The third function takes the __demangle_tree, and outputs an unmangled name.

Using this low-level API, __cxa_demangle becomes a trivial wrapper above this API:

char*
__cxa_demangle(const char* mangled_name, char* buf, size_t* n, int* status)
{
    if (mangled_name == NULL || (buf != NULL && n == NULL))
    {
        if (status)
            *status = __libcxxabi::invalid_args;
        return NULL;
    }
    const size_t bs = 64 * 1024;
    char static_buf[bs];

    buf = __libcxxabi::__demangle(__libcxxabi::__demangle(mangled_name,
                                                          static_buf, bs),
                                  buf, n, status);
    return buf;
}

It is expected that some tools (compilers, debuggers) will want to make use of an API on __demangle_tree that has yet to be developed.  E.g. how many function arguments and what are they?  How many template arguments and what are they? etc.

Howard