[cfe-dev] clang, libc++, libc++ABI & MacOSX 10.6

[Howard Hinnant]

On Dec 20, 2012, at 2:56 PM, James Gregurich <bayoubengal at mac.com> wrote:

> I have a feeling Howard might be the person to discuss this matter, but I'll throw it out here for everyone. I'm sure it is a discussion that would draw interest from other mac developers.
> 
> 
> I'm working on transitioning our codebase to C++11. The problem is that we still have to support 10.6 for another couple of years at least. I got this wild idea that perhaps I could deploy c++11 code to 10.6 by building the latest versions of clang & libc++ on 10.6. I got clang built. I got libc++ to build as a static lib. I got libc++abi to build as a dylib. I was able to build and run a test program with c++11 STL code on 10.6. Test successful.
> 
> HOwever, I have a few questions before I invest any more energy in this:
> 
> 
> 1) If I start using the frameworks and libs in the 10.6 SDK to build full-blown mac applications, am I going to have problems with mixing two std library implementations in a single process?
> 
> 2) I'm using the latest code for all the projects. Is this software stack reliable and production-quality on 10.6? I don't have the expectation that Apple would support using the tools on 10.6, but I'm just asking in terms of what you know about the innards of the technologies involved.
> 
> 3) Am I going to have any limitations on the C++11 functionality on 10.6? For instance, based on previous conversations on this list, I don't expect 'thread_local' to ever work on 10.6. Are there any other such features that have no chance of working on 10.6?
> 
> 4) Since we are a developer of commercial desktop apps, I prefer to use static libs to avoid giving the customers the ability to break the app. On OSX, a dylib wouldn't be a deal-breaker given I could load it in the app's bundle, but I'd still prefer the static libs if possible. I built libc++abi as a static lib, but I'm finding that I get number of duplicate symbol errors when I try to link both libc++.a and libc++abi.a with an executable program. Clearly, I have to merge the two libs. I have not attempted to do any analysis yet on the functions, but I suspect the libc++abi duplicated functions are going to be identical to what is in libc++.  Is this true? Do you foresee any problems with deleting one set of the duplicate functions in one of the libraries?

I feel you pain.  :-\

I know of no reliable way to use libc++ prior to 10.7.

I would be surprised if exception throwing across dylib boundaries (libc++/libstdc++) worked on 10.6.  

If you ship static or dynamic versions of libc++/libc++abi, the likelihood of breakage is strong, especially with exception throwing and dynamic_cast.  libc++abi especially is designed to be the only C++ exception catching mechanism in the process.

About the only thing that I imagine might work is using a template from libc++ headers that you know to be completely instantiated into your code with no dependence whatsoever on libc++.dylib.  You may need to toggle-off the use of "extern template" in libc++ headers to do this.

Howard