x/mobile: Feature, add "-target=io/arm,ios/386" and "-nobitcode" to bind command

[Tristian Azuara]

Hi!

First, gomobile has been a real life saver thank you to all of those who have contributed.

The current commit at master (167ebed0ec6dd457a6b24a4f61db913f0af11f70) automatically adds the "-fembed-bitcode" flag to the cflags and 

it also automatically builds for all of iOS architectures.

We currently use `gomobile` to produce a framework for iOS and macOS applications. We also include applications for macOS that do not include 

support for instruction sets such as `386` but iOS does, some of those libraries we have no control over and some are our own.

Our current workaround is for us to manually patch `gomobile`'s source, like follows:

 λ ~/go/src/golang.org/x/mobile (master): git diff -p

diff --git a/cmd/gomobile/env.go b/cmd/gomobile/env.go

index dbf9c8c..8f21b10 100644

--- a/cmd/gomobile/env.go

+++ b/cmd/gomobile/env.go

@@ -23,7 +23,8 @@ var (

        androidArmNM string

        darwinArmNM  string

 

-       allArchs = []string{"arm", "arm64", "386", "amd64"}

+       // allArchs = []string{"arm", "arm64", "386", "amd64"}

+       allArchs = []string{"arm", "arm64", "amd64"}

 )

 

 func buildEnvInit() (cleanup func(), err error) {

@@ -137,7 +138,7 @@ func envInit() (err error) {

                default:

                        panic(fmt.Errorf("unknown GOARCH: %q", arch))

                }

-               cflags += " -fembed-bitcode"

+               // cflags += " -fembed-bitcode"

                if err != nil {

                        return err

                }

I think that the addition of the following options would greatly simplify our CI/CD process, the goal would be to be able to use the command as follows:

$ gomobile bind -target=ios/arm,ios/arm64,ios/amd64 -nobitcode example.com/libs/mobile

By running it that way basically one would be able to exclude iOS simulator arch and the bitcode situation. I understand that probably it may not be something common, but being able to adjust the build process would be a great boon.

Does anyone else find that this would be something useful?, I'd be happy to contribute to this.

Cheers, Tristian.

[ma...@eliasnaur.com]

Hi,

The -target flag does support architectures. Have you tried -target ios/amd64,ios/arm64,ios/arm from your example?

I'm not sure I understand the problem with bitcode and macOS; what is the error you get from  -fembed-bitcode?

  - elias

[Tristian Azuara]

Hi Elias, thank you for the quick reply, I see, you're correct it does support the archs for ios, I had not tried it for ios, because the documentation just mentions that you can specify specific instruction sets when binding for android:

$ gomobile bind --help

By default, -target=android builds shared libraries for all supported

instruction sets (arm, arm64, 386, amd64). A subset of instruction sets

can be selected by specifying target type with the architecture name. E.g.,

-target=android/arm,android/386.

For -target ios, gomobile must be run on an OS X machine with Xcode

installed. The generated Objective-C types can be prefixed with the -prefix

flag.

There's no mention that you can filter out instruction sets for iOS but I just tested using it and it works!, thank you for pointing that out.

Now, regarding the bitcode part basically, because it's added automatically; any libraries that don't have BITCODE enabled don't link properly, here's some sample output:

GO111MODULE=off gomobile bind -v -target=ios/arm,ios/arm64,ios/amd64 -tags=ios example.com/mobile

runtime/cgo

golang.org/x/mobile/internal/mobileinit

os/user

net

example.com/pycore

example.com/jscore

# example.com/pycore

ld: warning: ignoring file pycore/libpython-scriptengine.a, file was built for archive which is not the architecture being linked (armv7): pycore/libpython-scriptengine.a

ld: warning: object file (/Users/tristian/go/src/example.com/pycore/libpython-scriptengine-ios.a(python-scriptengine-ios.o)) was built for newer iOS version (9.3) than being linked (7.0)

ld: '/Users/tristian/go/src/example.com/pycore/libpython-scriptengine-ios.a(python-scriptengine-ios.o)' does not contain bitcode. You must rebuild it with bitcode enabled (Xcode setting ENABLE_BITCODE), obtain an updated library from the vendor, or disable bitcode for this target. for architecture armv7

clang: error: linker command failed with exit code 1 (use -v to see invocation)

# example.com/jscore

ld: warning: ignoring file jscore/libscriptengine-ios-x86_64.a, file was built for archive which is not the architecture being linked (armv7): jscore/libscriptengine-ios-x86_64.a

ld: warning: object file (/Users/tristian/go/src/example.com/jscore/libscriptengine-ios-arm.a(test_lib_for_ios.o)) was built for newer iOS version (10.2) than being linked (7.0)

ld: '/Users/tristian/go/src/example.com/jscore/libscriptengine-ios-arm.a(test_lib_for_ios.o)' does not contain bitcode. You must rebuild it with bitcode enabled (Xcode setting ENABLE_BITCODE), obtain an updated library from the vendor, or disable bitcode for this target. for architecture armv7

clang: error: linker command failed with exit code 1 (use -v to see invocation)

gomobile: darwin-arm: go build -tags ios ios -v -buildmode=c-archive -o /var/folders/g1/v3hz1sm92nv7wbzpg3dx_h_h0000gp/T/gomobile-work-974051835/mobile-arm.a gobind failed: exit status 2

make: *** [Mobile.framework] Error 1

This would force us to recompile libpython-scriptengine-ios.a or any other libraries that don't have bitcode support

When I comment out -fembed-bitcode I no longer see that error.

Best, Tristian

[ma...@eliasnaur.com]

One thing you should be able to do is disable bitcode in the Xcode project settings (suggested as "disable bitcode for this target"). If that doesn't work, please file an issue.

 - elias

[const...@topinvestor.app]

When I compile with:

gomobile bind -target=ios -tags="ios" -v mygomobileios

and importing the generated Mygomobileios.framework

I get an error:

ld: '/mygo/src/mygomobileios/gomobileios_test/Mygomobileios.framework/Mygomobileios(go.o)' does not contain bitcode. You must rebuild it with bitcode enabled (Xcode setting ENABLE_BITCODE), obtain an updated library from the vendor, or disable bitcode for this target. for architecture arm64

clang: error: linker command failed with exit code 1 (use -v to see invocation)

Which indicates the generated framework does not contain bitcode.

Ho to get the bitcode generated?

[Tristian Azuara]

Hi!,

gomobile does not produce BITCODE enabled frameworks,  (AFAIK) you have to set the XCode `ENABLE_BITCODE` build setting to `NO`, `gomobile` (the latest version) automatically adds the `-fembed-bitcode` as C flag, here you can find a better explanation of it:

 * https://stackoverflow.com/a/34965178

[const...@topinvestor.app]

I ran this command:

brew install go --HEAD

Now Xcode compiles without an error and ENABLE_BITCODE=YES