Add Missing C++ Annotations to Control Symbol Visibility

[david-cattermole]

Hello David,

I have noticed that the flag --cxx-impl-annotations used on the command cxxbridge (from cxxbridge-cmd) does not seem to add annotations to all function and method declarations.

As a result of this problem I was only able to use cxx on Windows by compiling downstream libraries that linked to the Rust library by including the C++ source files. (You can see this in my (CMake based) https://github.com/david-cattermole/cxx-demo-example project. See the main branch with the hack included.)

Since GCC and Clang default to exporting all symbols, but MSVC does not, I suspect this was not caught by other users. Or perhaps it's because I'm using cxxbridge-cmd directly, or maybe it's caused by older Windows compilers (Visual Studio 2015 / MSVC 14).

To fix the missing annotations I have made a commit to my cxx fork; david-cattermole@363c18b. The fix will add annotations to all the function (and method) declarations needed (in my libraries - I could be missing others).

You can see my cxx-demo-example project on the shared-object-symbol-visibility branch which uses my forked cxx repo. This has been tested on both Linux GCC and Windows MSVC and it appears to work (see output for Linux/GCC and Windows/MSVC).

Would you like a PR? Or you can simply use my commit david-cattermole@363c18b to implement a better fix?

Thanks,
David Cattermole

[dtolnay]

FYI @adetaylor — hopefully this matches your understanding of where cxx_impl_annotations should be going.
Mentioning #219, #231.

[dtolnay]

Would you like a PR? Or you can simply use my commit david-cattermole@363c18b to implement a better fix?

It would be great to get a PR adding a CI job which builds our test suite in a way that is sensitive to these annotations.

[david-cattermole]

Hello @dtolnay,

I am still getting missing symbols using cxx v1.0.25 (which includes the changes from #615).

I have fixed the problem for my cxx-demo-example repo using this patch in my fork of cxx:
david-cattermole@d58c650

If you want to test it out, you can use this repo commit:
david-cattermole/cxx-demo-example@7817d31

I don't understand why you were only excluding the annotations from source files.

cxx/gen/src/write.rs

Line 953 in b478fcb

if !out.header {

As I understand it the annotations should only be included in the declarations (header file), but right now in my project if I change begin_function_definition to only run on in headers, like this:

fn begin_function_definition(out: &mut OutFile) {
    if out.header {
        if let Some(annotation) = &out.opt.cxx_impl_annotations {
            write!(out, "{} ", annotation);
        }
    }
}

... I will get missing symbols for ::rust::Box<MyTypeHere>::drop().

I am continuing to debug the underlying problem but the patch (david-cattermole@d58c650) will fix things (for my projects at least) since the auto-generated files are never intended to be edited, so the problem on definition vs declaration doesn't matter - it's just a human readable problem I guess.

Thank you,
David C

P.S. I'm still looking into the GitHub actions to trigger the problem via CI on Windows.
I could checkout https://github.com/david-cattermole/cxx-demo-example and compile it on Windows, however that's using my repo, and I expect everything should be contained in cxx, so I'm going to need to create a minimum reproducible build error (probably using CMake).

[dtolnay]

I pulled that commit into 1.0.26. I don't have a good way to know where those annotations are supposed to go so I am happy to do whatever works for now.

[david-cattermole]

Thanks. I have updated to cxx 1.0.26 and the problem of annotations seem to be fixed.

---

I am however having other symbol problems with the update to 1.0.26 (specifically rust::cxxbridge1::sliceInit);

LINK: command "C:\PROGRA~2\MICROS~2.0\VC\bin\X86_AM~1\link.exe /nologo @CMakeFiles\opencompgraph_tests.dir\objects1.rsp /out:opencompgraph_tests.exe /implib:opencompgraph_tests.lib /pdb:C:\Users\catte\dev\OpenCompGraphMaya\src\OpenCompGraph\build_windows\tests\opencompgraph_tests.pdb /version:0.0 /machine:x64 /INCREMENTAL:NO /subsystem:console ..\src\opencompgraph.lib ..\..\target\release\opencompgraph_rs.lib ws2_32.lib userenv.lib advapi32.lib shell32.lib msvcrt.lib kernel32.lib user32.lib gdi32.lib winspool.lib shell32.lib ole32.lib oleaut32.lib uuid.lib comdlg32.lib advapi32.lib /MANIFEST /MANIFESTFILE:opencompgraph_tests.exe.manifest" failed (exit code 1120) with the following output:
test_i.cpp.obj : error LNK2019: unresolved external symbol "void __cdecl rust::cxxbridge1::sliceInit(void *,void const *,unsigned __int64)" (?sliceInit@cxxbridge1@rust@@YAXPEAXPEBX_K@Z) referenced in function "public: __cdecl rust::cxxbridge1::Slice<unsigned int const >::Slice<unsigned int const >(unsigned int const *,unsigned __int64)" (??0?$Slice@$$CBI@cxxbridge1@rust@@QEAA@PEBI_K@Z)
opencompgraph_tests.exe : fatal error LNK1120: 1 unresolved externals
NMAKE : fatal error U1077: '"C:\Program Files\CMake\bin\cmake.exe"' : return code '0xffffffff'
Stop.
NMAKE : fatal error U1077: '"C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\BIN\nmake.exe"' : return code '0x2'
Stop.
NMAKE : fatal error U1077: '"C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\BIN\nmake.exe"' : return code '0x2'
Stop.

I am currently trying to reproduce the error in cxx-demo-example, but so far everything is working very well in a simpler test environment.
It's probably an error in my code and I am trying to debug it, but I thought I should let you know in case it rings any bells.

[david-cattermole]

Scratch that, please ignore me.

I have discovered the issue and it is unrelated to cxx (I had forgot to update my the cxx version, so I was using the header from 1.0.26 with the cxx.cc file from 1.0.25 - hence causing missing symbol errors.).