[cfe-dev] Distributing libclang-cpp.dll for Windows in the pre-built downloads

[Stephen Crane via cfe-dev]

I was able to successfully build and use both x86 and x64 DLLs on
Windows 10 (MSVC 2019) with the following cmake invocation:
cmake ../llvm -GNinja -DLLVM_ENABLE_PROJECTS=llvm;clang
-DCMAKE_BUILD_TYPE=Release -DLLVM_ENABLE_PDB=ON
-DLLVM_ENABLE_ASSERTIONS=ON -DLLVM_TARGETS_TO_BUILD=X86
-DCMAKE_C_COMPILER=cl -DCMAKE_CXX_COMPILER=cl -DLLVM_ENABLE_RTTI=Off
-DLLVM_BUILD_LLVM_DYLIB=On -DCMAKE_WINDOWS_EXPORT_ALL_SYMBOLS=TRUE

I had to make a few changes to the build system (mostly commenting out
checks preventing building DLLs on Windows). I'd be happy to prep
patches to enable this mode properly in the LLVM cmake scripts, so we
can discuss the merits of that option separately.

- stephen

On Wed, Mar 18, 2020 at 2:39 PM Michael Kruse <llvm at meinersbur.de> wrote:
>
> Cmake also supporte the option WINDOWS_EXPORT_ALL_SYMBOLS for msvc. It
> just creates a .def (list of symbols to export when linking a dll)
> file including all symbols . LLVM's extract_symbols.py does something
> similar.
>
> Michael
>
>
> Am Mi., 18. März 2020 um 16:35 Uhr schrieb Martin Storsjö <martin at martin.st>:
> >
> > On Wed, 18 Mar 2020, Michael Kruse via cfe-dev wrote:
> >
> > > Am Mi., 18. März 2020 um 12:51 Uhr schrieb Stephen Crane <sjc at immunant.com>:
> > >> On Wed, Mar 18, 2020 at 9:23 AM Michael Kruse <llvm at meinersbur.de> wrote:
> > >> > Windows DLLs have a limit of 2^16 exported symbols, that LLVM
> > >> > unfortunately exceeds.
> > >>
> > >> Would the individual libclang* libraries (e.g. libclangAST,
> > >> libclangParse, etc.) exceed this limit? I'll do some experimental
> > >> builds and see what I can determine.
> > >
> > > BUILD_SHARED_LIBS is also not supported on Windows, but I don't know
> > > whether for the same reason.
> >
> > It's not supported when building with MSVC (or with Clang in MSVC mode),
> > as it requires dllexport attributes on all symbols to be visible in the
> > external interface of the DLL (or a def file listing all the exported
> > symbols), and the interfaces of all the internal libraries aren't
> > decorated with such attributes.
> >
> > If building with a MinGW toolchain (either GCC/binutils based, or
> > Clang/lld based), it can export all symbols if none are marked
> > specifically for export with dllexport attributes - and BUILD_SHARED_LIBS
> > should work in this configuration (at least builds with it enabled
> > succeeded last I tested maybe 7 weeks ago).
> >
> > // Martin