Kotlin Multiplatform - Objective-C interoperability architecture issue Undefined symbols for architecture x86_64

Question

I just tried using native interop feature since I need native code written in Objective-C to be used in my library. So first I'm trying to test using simple hello to interop an Objective-C code

gradle :

kotlin {
     ...
 
     val iosX64 = iosX64("ios") {
          compilations.getByName("main) {
              val myInterop by cinterops.creating {
                 defFile(project.file("src/nativeInterop/cinterop/objective-c-file.def"))
              }
          }
     }

     val iosArm32 = iosArm32 ("iosArm32 ") {
          compilations.getByName("main) {
              val myInterop by cinterops.creating {
                 defFile(project.file("src/nativeInterop/cinterop/objective-c-file.def"))
              }
          }
     }

     val iosArm64 = iosArm64("iosArm64") {
          compilations.getByName("main) {
              val myInterop by cinterops.creating {
                 defFile(project.file("src/nativeInterop/cinterop/objective-c-file.def"))
              }
          }
     }

     ...
}

my .def configuration :

language = Objective-C
headers = Hello.h Foundation/Foundation.h
package = org.native

compilerOpts = -Isrc/nativeInterop/include

linkerOpts = -framework Foundation "-F/Applications/Xcode 11.3.1.app/Contents/Developer/Platforms/"

this is the project structure look like

my Hello.h

#import <Foundation/Foundation.h>

@interface Hello: NSObject

+ (id) init;
- (void) helloObjectiveC;

@end

Hello.m

#import "Hello.h"

@implementation Hello

+ (id) init {}
- (void) helloObjectiveC {
    printf("hello Objective c interop")
}

@end

after run cinterop task from gradle, the klib generated from that hello class and of course now I can import it to my kotlin project. for example in my iOS module:

package bca.lib

import org.native.Hello

actual object Platform {

    actual fun getPlatform() = "iOSMain"
    
    fun helloNativeInterop() {
        val hello = Hello()
        hello.helloObjectiveC()
    }

}

Then I'm trying to call it in my unit test to check if I can get the result or I aslo try to build it to framework but I got an error :

> Task :cleanIosTest UP-TO-DATE
> Task :cinteropMyInteropIos UP-TO-DATE
> Task :generateBuildKonfig UP-TO-DATE
> Task :generateIosMainAppDatabaseInterface UP-TO-DATE
> Task :compileKotlinIos UP-TO-DATE
> Task :iosProcessResources UP-TO-DATE
> Task :iosMainKlibrary UP-TO-DATE
> Task :compileTestKotlinIos UP-TO-DATE
> Task :linkDebugTestIos FAILED
e: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/ld invocation reported errors
Please try to disable compiler caches and rerun the build. To disable compiler caches, add the following line to the gradle.properties file in the project's root directory:
    
    kotlin.native.cacheKind=none
    
Also, consider filing an issue with full Gradle log here: https://kotl.in/issue
The /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/ld command returned non-zero exit code: 1.
output:
Undefined symbols for architecture x86_64:
  "_OBJC_CLASS_$_Hello", referenced from:
      objc-class-ref in result.o
ld: symbol(s) not found for architecture x86_64
FAILURE: Build failed with an exception.
* What went wrong:
Execution failed for task ':linkDebugTestIos'.
> Compilation finished with errors
* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.
* Get more help at https://help.gradle.org
Deprecated Gradle features were used in this build, making it incompatible with Gradle 7.0.
Use '--warning-mode all' to show the individual deprecation warnings.
See https://docs.gradle.org/6.6.1/userguide/command_line_interface.html#sec:command_line_warnings
BUILD FAILED in 8s

Anyone know how to resolve this issue or maybe is it impossible to interop in that way? I just needed so it can be used in my iOS app later after I successfully build it to .framework

Technically speaking, the issue is simple. The interop processor generates Kotlin from the Objc headers. However, you also need to build the Objc and link the binary. `linkDebugTestIos` is trying to build a test kexe, but can't find `_OBJC_CLASS_$_Hello`. I don't know of a great way to do that off hand, or I'd make this an answer rather than a comment :) I'm sure somebody has a very easy and obvious way to do this. — Kevin Galligan, Mar 01 '21 at 14:41
@KevinGalligan So that means I need to do something with the binary linking.., when the build happen..? — Davin Reinaldo Gozali, Mar 03 '21 at 06:20

score 1 · Accepted Answer · answered Mar 10 '21 at 09:16

1

This is a known limitation, described in the Kotlin issue tracker some time ago: KT-39562. Long story short, the cinterop tool does not provide an option to work with source files out-of-the-box. The easiest way here will be to create a framework from your Objective-C code. After that, you'll be able to work with it in a simple way, described in the documentation.

answered Mar 10 '21 at 09:16

Artyom Degtyarev

2,704
8
23

I see, yes I can do it easily with compile it to static library then include it in the def file. Well noted then if this way is not supported. Thank you so much! – Davin Reinaldo Gozali Mar 10 '21 at 10:54

Kotlin Multiplatform - Objective-C interoperability architecture issue Undefined symbols for architecture x86_64

1 Answers1