llvm dev - Nov 2018 - Trying to cross-compile LLVM runtimes to Windows

I have been using this project with great success to achieve this : 
https://github.com/mstorsjo/llvm-mingw

It generates a linux-based windows cross-compiler with clang, libc++, etc.

I was able to build a large part of Qt with it afterwards for instance.


Best,

Jean-Michaël

On 06/11/2018 04:21, Petr Hosek via llvm-dev wrote:
> I've tried building libc++ for Windows on Linux by setting clang-cl as
> the compiler and lld-link as the linker, but I immediately hit
> roadblocks. The first issue seems to be the fact that CMake appears to
> ignore the value of CMAKE_RC_COMPILER variable and hardcodes "rc"
as
> the resource compiler. This got resolved in upstream 12 days ago
>
(https://github.com/Kitware/CMake/commit/bd9bfc644954a48b1bf7ea18fc260a1231840671)
>
> I managed to workaround this issue by symlinking llvm-rc as rc.
> However, that's not sufficient because CMake uses following invocation
> (https://github.com/Kitware/CMake/blob/master/Source/cmcmd.cxx#L1815):
>
> rc /foCMakeFiles/cmTC_2c376.dir/manifest.res
> CMakeFiles/cmTC_2c376.dir/manifest.rc
>
> llvm-rc option parses requires /fo option argument to be separate.
> I've modified the flag to support both joined and separate value which
> helped getting past that error, but I immediately hit another error:
> https://reviews.llvm.org/P8113
>
> The problem seems to be that the .rc file generated by CMake contains
> an absolute path to the resource, but llvm-rc expects the path to be
> always relative. However, I couldn't fine any documentation that would
> explain whether that's a requirement and it's CMake's fault or
whether
> llvm-rc should be handling absolute paths as well. Is anyone familiar
> with Windows resource file semantics?
>
> All of these errors seem to suggest that this cross-compiling for
> Windows with Clang using CMake isn't a well explored area. Has anyone
> had more success with cross-compiling LLVM runtimes (libc++,
> compiler-rt) to Windows?
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev

On Tue, 6 Nov 2018, Jean-Michaël Celerier via llvm-dev wrote:
> I have been using this project with great success to achieve this : 
> https://github.com/mstorsjo/llvm-mingw
>
> It generates a linux-based windows cross-compiler with clang, libc++, etc.
FWIW, lately I've added prebuilt packages of it that you can run on actual 
windows as well, even though cross compilation was my first/main focus.
> I was able to build a large part of Qt with it afterwards for instance.
Any particular part of Qt which you weren't able to build with it? I 
regularly build Qt (qtbase) for i686/x86_64/armv7/aarch64, and as part of 
VLC, I also build a few more Qt modules (qtdeclarative, qtquickcontrols2) 
for i686 and x86_64.

// Martin

I suspect mingw is going to be incompatible with Petr’s needs. Adding Nico
as he probably does the most cross compiling.  I did it a little several
weeks ago, just not with libc++, and I don’t remember running into any
problems.

One thing that’s not clear to me is why the resource compiler is even being
invoked at all

On Tue, Nov 6, 2018 at 5:46 AM Martin Storsjö via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> On Tue, 6 Nov 2018, Jean-Michaël Celerier via llvm-dev wrote:
>
> > I have been using this project with great success to achieve this :
> > https://github.com/mstorsjo/llvm-mingw
> >
> > It generates a linux-based windows cross-compiler with clang, libc++,
> etc.
>
> FWIW, lately I've added prebuilt packages of it that you can run on
actual
> windows as well, even though cross compilation was my first/main focus.
>
> > I was able to build a large part of Qt with it afterwards for
instance.
>
> Any particular part of Qt which you weren't able to build with it? I
> regularly build Qt (qtbase) for i686/x86_64/armv7/aarch64, and as part of
> VLC, I also build a few more Qt modules (qtdeclarative, qtquickcontrols2)
> for i686 and x86_64.
>
> // Martin
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
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No, it's just that I didn't try to build qtwebkit / qtwebengine / qt3d 
since I don't use them. Everything else seemed to build fine (including 
the qml stuff as you mentioned).

On 06/11/2018 14:46, Martin Storsjö wrote:
>
> Any particular part of Qt which you weren't able to build with it?