llvm dev - May 2012 - [LLVMdev] Windows question: Dozens of linker warnings and errors

Hi again again,

I'm trying to build my compiler frontend in C++ on Windows 7 x64 using
clang++.exe.  I want to use clang++ for my project so that I get a feel for
how mature and usable the Windows support is as I gradually get up to speed
with LLVM for Windows.  I could develop on Linux, but I need the Windows
support so I figure I might as well do it the hard way.

My code is fairly simple C++ with a few template classes, a rare virtual
function, and nothing very fancy.  I am able to compile my code without
warnings (although clang++ earlier on found a couple of very serious issues
in my code).  But when I get to the link phase, all hell breaks loose:

I get a ton of these warnings:

Memory.o : warning LNK4006: _InterlockedBitTestAndSet already defined
in Stream.o; second definition ignored
Memory.o : warning LNK4006: _InterlockedBitTestAndReset already
defined in Stream.o; second definition ignored
Memory.o : warning LNK4006: _InterlockedBitTestAndComplement already
defined in Stream.o; second definition ignored
Memory.o : warning LNK4006: _MemoryBarrier already defined in
Stream.o; second definition ignored
Memory.o : warning LNK4006: _ReadPMC already defined in Stream.o;
second definition ignored

I don't use InterlockedBitTestAndSet anywhere in my code and the same goes
for the rest of the symbols that are being warned about.

After that, I get a ton of errors form the linker because it complains
about the above symbols already being defined.

I also get a few errors like this:

Bitset_test-423377.o : error LNK2001: unresolved external symbol
__ZTVN10__cxxabiv120__si_class_type_infoE

Any ideas?  Is the Windows support simply not mature enought for real use
or am I doing something wrong?  I invoke the linker through clang++ by
giving the input object files and a library that must be linked against,
made with Microsoft's LIB tool.  I use Microsoft LIB because LINK rejects
libraries created using llvm-ar.

I only use the -c, -o, -v, and -D options to clang++.exe and nothing else.
 Nothing advanced yet.

Is it that clang++/Windows simply don't support the use of libraries yet?
 The hello world example works great, but I do aspire to more than that.

If I have missed an important note in the documentation, then I apologize
greatly in advance.


Sincerely,
Mikael Lyngvig
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On Wed, May 23, 2012 at 4:38 PM, Mikael Lyngvig <mikael at lyngvig.org>
wrote:
> Hi again again,
>
> I'm trying to build my compiler frontend in C++ on Windows 7 x64 using
> clang++.exe.  I want to use clang++ for my project so that I get a feel for
> how mature and usable the Windows support is as I gradually get up to speed
> with LLVM for Windows.  I could develop on Linux, but I need the Windows
> support so I figure I might as well do it the hard way.
>
> My code is fairly simple C++ with a few template classes, a rare virtual
> function, and nothing very fancy.  I am able to compile my code without
> warnings (although clang++ earlier on found a couple of very serious issues
> in my code).  But when I get to the link phase, all hell breaks loose:
>
> I get a ton of these warnings:
>
> Memory.o : warning LNK4006: _InterlockedBitTestAndSet already defined in
> Stream.o; second definition ignored
> Memory.o : warning LNK4006: _InterlockedBitTestAndReset already defined in
> Stream.o; second definition ignored
> Memory.o : warning LNK4006: _InterlockedBitTestAndComplement already
defined
> in Stream.o; second definition ignored
> Memory.o : warning LNK4006: _MemoryBarrier already defined in Stream.o;
> second definition ignored
> Memory.o : warning LNK4006: _ReadPMC already defined in Stream.o; second
> definition ignored
>
> I don't use InterlockedBitTestAndSet anywhere in my code and the same
goes
> for the rest of the symbols that are being warned about.
>
> After that, I get a ton of errors form the linker because it complains
about
> the above symbols already being defined.
This is due to clang not understanding force_inline. These functions
are defined in a header included from Windows.h, so it ends up getting
a definition everywhere it is included.
> I also get a few errors like this:
>
> Bitset_test-423377.o : error LNK2001: unresolved external symbol
> __ZTVN10__cxxabiv120__si_class_type_infoE
>
> Any ideas?  Is the Windows support simply not mature enought for real use
or
> am I doing something wrong?  I invoke the linker through clang++ by giving
> the input object files and a library that must be linked against, made with
> Microsoft's LIB tool.  I use Microsoft LIB because LINK rejects
libraries
> created using llvm-ar.
>
> I only use the -c, -o, -v, and -D options to clang++.exe and nothing else.
>  Nothing advanced yet.
>
> Is it that clang++/Windows simply don't support the use of libraries
yet?
>  The hello world example works great, but I do aspire to more than that.
>
> If I have missed an important note in the documentation, then I apologize
> greatly in advance.
>
>
> Sincerely,
> Mikael Lyngvig
The rest of the issues are due to clang not supporting the Microsoft
C++ ABI yet. To use clang on Windows for C++ code you will need to use
it with MinGW as it provides libraries that use the GNU C++ ABI.

- Michael Spencer

Thanks for the quick reply.  I had a feeling that it was due to missing
Windows support in clang++ and LLVM.

"""
This is due to clang not understanding force_inline. These functions
are defined in a header included from Windows.h, so it ends up getting
a definition everywhere it is included.
"""

How much work would it take to add support for force_inline?  Are there any
plans for when/if it will be supported?  I don't know anything about
force_inline, but I guess supporting it is a relatively simple matter.
 After all, isn't a forced_inline construct similar to an inlined template
method?  In the old MS-OMF days, we'd start talking about COMDATs and stuff
like that, but I don't know how it is done nowadays.

"""
The rest of the issues are due to clang not supporting the Microsoft
C++ ABI yet. To use clang on Windows for C++ code you will need to use
it with MinGW as it provides libraries that use the GNU C++ ABI.

"""
I guess this is quite a mouthful, but when do you roughly expect the
Microsoft C++ ABI to be supported?  v4.0 or later?  Is there anything not
too overwhelming and/or complex that I can do to speed up this process?

I am asking these questions because I see myself as a wannabe client of the
LLVM tools - I don't know much about code generation and I don't really
want to know much about it, all I want to do is to make my own production
language using LLVM as the portable (also to Windows/M$) backend.  My hope
is that LLVM can save me the hassles of meddling around with assembler and
so on, as I'd much rather spend my energy on my language.  But if the
Windows support is broken, partial beyond use, or never to be finished up,
I cannot use LLVM.  Then I'd have spend my energy on writing my own simple
code generator, which would never generate code of a quality anywhere near
LLVM.  Or, I could go ahead and do my own silly backend and then check up
on LLVM in a couple of years, to see if the Windows support was matured.

By the way, I do have a background in linkers and compilers for Windows
platforms, so if I can help with anything, I'll be glad to do so.  Just
don't expect me to work miracles from day one because it has been almost 15
years since I last worked with compilers and linkers.

Perhaps I can contribute in the field of Windows support?   I once wrote a
librarian for OMF (the ancient object file format used under DOS) and COFF.
 I could probably add support for COFF archives to llvm-ar, if need be.
 And stuff like that.


Sincerely,
Mikael
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