x/mobile/cmd/gomobile: c++ with SWIG

[vrabeux]

• go version 1.7
• OSX

Hi,

I am trying to use gomobile to compile a small SDK (android + ios). This SDK contains both Go sources and C++ sources. C++ Go wrappers are generated with SWIG.

Sample project can be found here : https://github.com/vrabeux/testinggomobile

The command line :go build works but the gomobile bind -target=android fails with the folowing error :

gomobile: loadExportData failed go install -pkgdir=/Users/zoolonly/workspace/goworkspace/pkg/gomobile/pkg_android_arm -tags="" -gcflags=-shared -ldflags=-shared bitbucket.org/avcl/testinggomobile failed: exit status 2
# bitbucket.org/avcl/testinggomobile/testgomobcpp
testgomobcpp/simple.cpp:2:10: fatal error: 'string' file not found

For info, I have installed Android SDK. There is 2 version of NDK installed there plsu the one from gomobile.

echo $ANDROID_HOME
/Users/zoolonly/Library/Android/sdk/

The gomobile bind -target=ios also fails :

gomobile: go install -pkgdir=/Users/zoolonly/workspace/goworkspace/pkg/gomobile/pkg_darwin_arm -tags="" github.com/vrabeux/testinggomobile failed: exit status 2
# github.com/vrabeux/testinggomobile/testgomobcpp
ld: warning: ignoring file $WORK/github.com/vrabeux/testinggomobile/testgomobcpp/_obj/simple.cpp.o, file was built for x86_64 which is not the architecture being linked (armv7): $WORK/github.com/vrabeux/testinggomobile/testgomobcpp/_obj/simple.cpp.o
[....]

Thanks for your help !

[jlouazel]

Did someone succeed to do so?

[jlouazel]

@vrabeux By any chance, did you succeed to get over this issue?

[EtienneL]

@jlouazel No sorry, I did not find a solution for this. However, you can easily "inject" C++ into your golang mobile SDK via a C++ <-> ObjC++ <-> ObjC <-> Go. Not perfect of course, but it does work.

Hope it helps

[eliasnaur]

Please provide me with a (small) complete example that demonstrates the issue. Also, make sure you use Go 1.10 and run go get -u golang.org/x/mobile/cmd/... first to ensure that gomobile is updated.

[tadovas]

The problem is with env variables (how gomobile passes them to go build when crosscompiling to ios):
Here is the link to the patch, which fixed the problem: golang/mobile@c6ae098

A short summary:

1. Clang++ needs to be called to handle .cpp files (therefore CXX needs to be setup correctly) - clang can compile .cpp too, but a lot of issues will be generated on link phase as go build correctly detects that cpp was used, and links with clang++ with auto included standart c++ libraries
2. CGO_CXXFLAGS should receive arch we are building for ( ignores arm7 therefore warning about ignoring file build for x86_64 (default arch for clang) when linking for arm7

[eliasnaur]

Thank you. Can you submit a pull request so I can review and merge your fix?

[tadovas]

Absolutely. golang/mobile#20

[dmitshur]

This issue was resolved by CL 134975, but didn't get closed automatically because the commit message wasn't using the pattern described at https://golang.org/wiki/CommitMessage#other-repos.