x/mobile: build doesn't include libc++_shared.so to produced .apk and app immediately crashes upon start

[the-goodies]

What version of Go are you using (go version)?

$ go version
go version go1.16 windows/amd64

Does this issue reproduce with the latest release?

Yes

What operating system and processor architecture are you using (go env)?

go env Output

$ go env
set GO111MODULE=
set GOARCH=amd64
set GOBIN=
set GOCACHE=C:\Users\Gedis\AppData\Local\go-build
set GOENV=C:\Users\Gedis\AppData\Roaming\go\env
set GOEXE=.exe
set GOFLAGS=
set GOHOSTARCH=amd64
set GOHOSTOS=windows
set GOINSECURE=
set GOMODCACHE=C:\Users\Gedis\go\pkg\mod
set GONOPROXY=
set GONOSUMDB=
set GOOS=windows
set GOPATH=C:\Users\Gedis\go
set GOPRIVATE=
set GOPROXY=https://proxy.golang.org,direct
set GOROOT=C:\Program Files\Go
set GOSUMDB=sum.golang.org
set GOTMPDIR=
set GOTOOLDIR=C:\Program Files\Go\pkg\tool\windows_amd64
set GOVCS=
set GOVERSION=go1.16
set GCCGO=gccgo
set AR=ar
set CC=gcc
set CXX=g++
set CGO_ENABLED=1
set GOMOD=C:\Users\Gedis\workspace\gomobile\go.mod
set CGO_CFLAGS=-g -O2
set CGO_CPPFLAGS=
set CGO_CXXFLAGS=-g -O2
set CGO_FFLAGS=-g -O2
set CGO_LDFLAGS=-g -O2
set PKG_CONFIG=pkg-config
set GOGCCFLAGS=-m64 -mthreads -fmessage-length=0 -fdebug-prefix-map=C:\Users\Gedis\AppData\Local\Temp\go-build3903890372=/tmp/go-build -gno-record-gcc-switches

What did you do?

I was trying basic gomobile example (golang.org/x/mobile/example/basic copied to my own module) by running: "gomobile install basic" and it produced basic.apk and it ran fine on a real device.

Then to the same basic example main.go file, I added only a single CGO library import: _ "github.com/inkyblackness/imgui-go/v4" to see if it compiles and works. It compiled without any errors and app installed to the real device, but when running it, it immediately crashed.

To see what error's this crash produced, I ran adb logcat --buffer=crash and heres the output:

03-09 23:58:36.606 16313 16313 E AndroidRuntime: FATAL EXCEPTION: main
03-09 23:58:36.606 16313 16313 E AndroidRuntime: Process: org.golang.todo.network, PID: 16313
03-09 23:58:36.606 16313 16313 E AndroidRuntime: java.lang.UnsatisfiedLinkError: dlopen failed: library "libc++_shared.so" not found
03-09 23:58:36.606 16313 16313 E AndroidRuntime:        at java.lang.Runtime.loadLibrary0(Runtime.java:1016)
03-09 23:58:36.606 16313 16313 E AndroidRuntime:        at java.lang.System.loadLibrary(System.java:1669)
03-09 23:58:36.606 16313 16313 E AndroidRuntime:        at org.golang.app.GoNativeActivity.load(GoNativeActivity.java:56)
03-09 23:58:36.606 16313 16313 E AndroidRuntime:        at org.golang.app.GoNativeActivity.onCreate(GoNativeActivity.java:64)
03-09 23:58:36.606 16313 16313 E AndroidRuntime:        at android.app.Activity.performCreate(Activity.java:7327)
03-09 23:58:36.606 16313 16313 E AndroidRuntime:        at android.app.Activity.performCreate(Activity.java:7318)
03-09 23:58:36.606 16313 16313 E AndroidRuntime:        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1271)
03-09 23:58:36.606 16313 16313 E AndroidRuntime:        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3094)
03-09 23:58:36.606 16313 16313 E AndroidRuntime:        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3257)
03-09 23:58:36.606 16313 16313 E AndroidRuntime:        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
03-09 23:58:36.606 16313 16313 E AndroidRuntime:        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
03-09 23:58:36.606 16313 16313 E AndroidRuntime:        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
03-09 23:58:36.606 16313 16313 E AndroidRuntime:        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1948)
03-09 23:58:36.606 16313 16313 E AndroidRuntime:        at android.os.Handler.dispatchMessage(Handler.java:106)
03-09 23:58:36.606 16313 16313 E AndroidRuntime:        at android.os.Looper.loop(Looper.java:214)
03-09 23:58:36.606 16313 16313 E AndroidRuntime:        at android.app.ActivityThread.main(ActivityThread.java:7050)
03-09 23:58:36.606 16313 16313 E AndroidRuntime:        at java.lang.reflect.Method.invoke(Native Method)
03-09 23:58:36.606 16313 16313 E AndroidRuntime:        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:494)
03-09 23:58:36.606 16313 16313 E AndroidRuntime:        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:965)

It seems like libc++_shared.so library is missing. I tried to search how I can include this with gomobile or some other way, but failed.
Is it possible to add/link this library or I'm doing something wrong and culprit is somewhere else? Thanks.

[toothrot]

/cc @hyangah @eliasnaur

[eliasnaur]

This may be a gomobile bug, but it's probably better to bring it up with the inkyblackness/imgui-go developers to see whether they support Android. And if so, how.

[the-goodies]

inkyblackness/imgui-go doesn't explicitly support Android. It's a pure Dear ImGui bindings library, with no platform or backend layer (there's a separate repository with glfw/sdl and opengl2/3 examples: https://github.com/inkyblackness/imgui-go-examples).
I have a need to create an Android app and at first I tried Flutter, but didn't really like it: dart language, state management is a mess compared to imgui (at least to me it looked way overcomplicated).
Afterwards was thinking maybe I should just use Dear ImGui with C++ (pull request for Android backend was merged like a week ago), since I'm really comfortable with imgui-go and use it a lot for desktop programs. Seems like a decent choice, but it's C++ language, not Go, so I'm hesitant (might still choose this option).
Then we arrive at a current issue where I try imgui-go with gomobile (before hand I didn't even know that gomobile exists) and was kind of hopeful that it could work, because then I could use both Go and ImGui, but it crashes. Was trying various ways to include this libc++_shared.so, but nothing worked.
Anyway, since this issue might not be resolved (at least not soon enough), I still think it could be great to use Go, so next I will try to use your Gio library. It's approach is imgui too and provided sample examples felt good on a touchscreen. So far looks promising and might be good for what I need.

[hajimehoshi]

I run into the same issue when using a C++ file with gomobile-build. Modifying a gradle file might solve this (https://stackoverflow.com/questions/39620739/android-studio-cmake-shared-library-missing-libc-shared-so-can-cmake-bundle) but this is impossible in gomobile anyway so far.

[hajimehoshi]

Adding -static-libstdc++ to LDFLAGS might suppress the exception.

[the-goodies]

Adding -static-libstdc++ to LDFLAGS might suppress the exception.

Where and how? gomobile build -ldflags="-static-libstdc++" didn't work:

gomobile: go build -ldflags -static-libstdc++ -buildmode=c-shared -o C:\Users\Username\AppData\Local\Temp\gomobile-work-425738395\lib\armeabi-v7a\libmobile_app_good.so mobile_app_good failed: exit status 2
# github.com/inkyblackness/imgui-go/v4
warning: unknown warning option '-Wno-subobject-linkage' [-Wunknown-warning-option]
# mobile_app_good
flag provided but not defined: -static-libstdc++
usage: link [options] main.o
  -B note
        add an ELF NT_GNU_BUILD_ID note when using ELF
....

[hajimehoshi]

I added it in a Go file like

// #cgo LDFLAGS: -static-libstdc++
import "C"

[the-goodies]

I added it in a Go file like

// #cgo LDFLAGS: -static-libstdc++
import "C"

Compiles and doesn't crash anymore. Thanks.
Now only need to write platform and backend layers to integrate with ImGui. Hopefully won't run into unsolvable problems.