[native-image] Graal cannot generate native images for applications that use JNR

[Glavo]

Graal reported an error when I tried to generate a native image for this simple example:

public class Main {
    public interface LibC {
        int printf(String fmt, Object... args);
    }

    public static void main(String[] args) {
        LibC libc = LibraryLoader.create(LibC.class).load("c");

        libc.printf("Hello, World!\n");
    }
}

glavo@glavo:~/IdeaProjects/JNRTest/build/libs$ /opt/graalvm/graalvm-ce-1.0.0-rc4/bin/native-image -jar JNRTest-1.0-SNAPSHOT.jar 
Build on Server(pid: 5476, port: 45611)*
   classlist:   1,155.06 ms
       (cap):   1,708.10 ms
       setup:   3,036.95 ms
    analysis:   8,199.65 ms
error: com.oracle.graal.pointsto.constraints.UnsupportedFeatureException: Unsupported method java.lang.ClassLoader.defineClass(String, byte[], int, int) is reachable: The declaring class of this element has been substituted, but this element is not present in the substitution class
To diagnose the issue, you can add the option -H:+ReportUnsupportedElementsAtRuntime. The unsupported element is then reported at run time when it is accessed the first time.
Detailed message:
Error: com.oracle.graal.pointsto.constraints.UnsupportedFeatureException: Unsupported method java.lang.ClassLoader.defineClass(String, byte[], int, int) is reachable: The declaring class of this element has been substituted, but this element is not present in the substitution class
To diagnose the issue, you can add the option -H:+ReportUnsupportedElementsAtRuntime. The unsupported element is then reported at run time when it is accessed the first time.
Trace: 
        at parsing jnr.ffi.provider.jffi.AsmClassLoader.defineClass(AsmClassLoader.java:39)
Call path from entry point to jnr.ffi.provider.jffi.AsmClassLoader.defineClass(String, byte[]): 
        at jnr.ffi.provider.jffi.AsmClassLoader.defineClass(AsmClassLoader.java:39)
        at jnr.ffi.provider.jffi.AsmLibraryLoader.generateInterfaceImpl(AsmLibraryLoader.java:235)
        at jnr.ffi.provider.jffi.AsmLibraryLoader.loadLibrary(AsmLibraryLoader.java:89)
        at jnr.ffi.provider.jffi.NativeLibraryLoader.loadLibrary(NativeLibraryLoader.java:44)
        at jnr.ffi.LibraryLoader.load(LibraryLoader.java:325)
        at jnr.ffi.LibraryLoader.load(LibraryLoader.java:304)
        at org.glavo.Main.main(Main.java:11)
        at com.oracle.svm.reflect.proxies.Proxy_1_Main_main.invoke(Unknown Source)
        at java.lang.reflect.Method.invoke(Method.java:498)
        at com.oracle.svm.core.JavaMainWrapper.run(JavaMainWrapper.java:173)
        at com.oracle.svm.core.code.CEntryPointCallStubs.com_002eoracle_002esvm_002ecore_002eJavaMainWrapper_002erun_0028int_002corg_002egraalvm_002enativeimage_002ec_002etype_002eCCharPointerPointer_0029(generated:0)

Error: Processing image build request failed

[peter-hofer]

JNR generates and loads proxy classes at runtime, but native-image does not support dynamic class loading, which is why you see an error about ClassLoader.defineClass being an unsupported method. You can try triggering the creation of the proxy classes already during the image build by calling LibraryLoader.create(...) from a static initializer (static {...}). You might also need to call load(...) already during the image build, in which case you will need to trigger loading the library again at runtime (possibly also libffi, the backend of JNR). However, getting JNR to work might be more complex than that.

[peter-hofer]

Closing this issue because supporting JNR at runtime is an unlikely prospect with the ahead-of-time nature of image generation. However, #2442 could make it possible to incorporate JNR classes into the image build via native-image-agent.