[cfe-dev] libc++ in Windows

[Nikola Smiljanic]

But Win32 doesn't use the standard library and it's no different than
using STLPort or other STL implementation, and people have been doing
that for ages. Provided that all third party libraries are also built
with the same standard library implementation. I'm very curious where
exactly you ran into problems?

On Sun, Jun 30, 2013 at 5:57 AM, James Gregurich <bayoubengal at mac.com> wrote:
> I'm curious.  How are you going to set this up so that you can use libc++ on Windows for standard Win32 apps without clashing with Microsoft's c++ standard library at link time? I once made an effort to use libc++ on OSX 10.6 which is based on libstdc++. I could get a program to work, but once I tried to link with system APIs to actually build a real mac application, it would clash with libstdc++.
>
>
>
> -James
>
>
>
> On Jun 26, 2013, at 7:35 AM, Nico Rieck <nico.rieck at gmail.com> wrote:
>
>> On 26.06.2013 02:57, Daniel Dilts wrote:
>>> When I was looking at libc++ it didn’t appear to support Windows except maybe under MinGW.  What would be a good place to start to get libc++ to work on Windows?
>>
>> I've been working on this on and off. Here's a braindump of what's needed:
>>
>> 1. Port OS-specific things.
>>
>>   This is rather small and I've done most of this already.
>>
>> 2. C Standard Library.
>>
>>   Microsoft's CRT is a royal PITA. It doesn't support a lot of things
>>   required or expected, and other things have subtle differences.
>>   Which is why I wrote a new standard library to make point 1 easier.
>>   At first it was only a set of standard-compliant headers and
>>   implementation stubs to get it to compile, but I've since
>>   implemented certain parts. The hardest part for this route is, for
>>   me at least, libm, and I don't know any modern BSD-licensed libm
>>   that could be used.
>>   The other way would be to further try and shoehorn MSVCRT and give
>>   up C99- and full C++11-compatibility.
>>
>> 3. Implement full dllimport/dllexport semantics so that libc++ can be
>>   used as a DLL.
>>
>>   Clang only support rudimentary dllimport/dllexport for functions.
>>   Making it work with classes is a rather large non-trivial change.
>>   I've been working on this and apart from vtable-handling and
>>   cleanups it's mostly finished. Depending on that last point I may
>>   put up some patches for review soon.
>>
>>   This also requires changes to how libc++ applies those attributes.
>>   Using them like ELF visibility doesn't work correctly for templates.
>>
>> 4. Weak externals for PE to enable replacing operator new/delete.
>>
>>   This was impossible with how dllimport was represented in LLVM
>>   before. If my patches are excepted, it should be doable, but I
>>   haven't looked into it again.
>>
>> 5. Port an ABI library like libc++abi.
>>
>>   I've ported some parts of libc++abi, but it's incomplete and
>>   untested. It also needs an unwind library, which quickly leads
>>   to the next point:
>>
>> 6. Exception handling
>>
>>   This is probably the biggest hurdle. There is some low-level support
>>   for 64-bit SEH directives in LLVM already. 32-bit has the additional
>>   Borland patent issue for SEH exception handling. The data structures
>>   used by MSVC are also undocumented.
>>   Implementing this for 64-bit by using the DWARF exception tables and
>>   providing an appropriate personality routine is the easiest case,
>>   and would also allow catching SEH exceptions from the OS.
>>   Maybe it's also possible to implement such DWARF-based table-based
>>   exception handling for 32-bit, without any way to catch SEH
>>   exceptions.
>>
>> 7. Some minor bugfixes I encountered along the way, like proper COMDAT
>>   linkage for EH sections, proper varargs handling. I'll try to get
>>   those committed soon.
>>
>>
>> -Nico
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