x/mobile: reduce size of generated artifacts

[ToJen]

The size of Go builds can be shrunk with the ldflags build option like this:
go build -ldflags '-s -w' -o my_app.exe

This can be reduced further with UPX as such:
upx -o my_app_min.exe my_app.exe

More on this here.

I'm able to pass the ldflags into gomobile like this:
gomobile bind -ldflags '-s -w' -target=android github.com/my/app.

I would like to "inject" UPX somewhere in the bind process to reduce the size of my generated .aar and .framework.

A possible flow is this:

1. Build: go build -ldflags '-s -w' -o my_app.exe
2. Shrink: upx -o my_app_min.exe my_app.exe
3. Pass into gomobile:gomobile bind --from-build=my_app_min.exe -target=android github.com/my/app

[toothrot]

/cc @hyangah

[ToJen]

@toothrot @hyangah what's a place to start the investigation. I believe many users will benefit from a smaller aar and framework. Would it make sense at all to achieve it this way?

[ToJen]

i believe it will be somewhere here:
android: https://github.com/golang/mobile/blob/master/cmd/gomobile/bind_androidapp.go#L52
ios: https://github.com/golang/mobile/blob/master/cmd/gomobile/bind_iosapp.go#L38

[BenLubar]

Another way to reduce the size of the APK would be to generate an AAB instead, which would mean an x86 device would only receive x86 code and an ARM device would only get ARM code.

As it currently stands, the APK contains 4 copies of all native code, which totals about 100 megabytes for my app after zip compression.

[ToJen]

@BenLubar I came across this article which doesn't use gomobile. It may be possible to achieve my suggestions with the author's approach.