bpf.c

#include "build/dev_bithole_bpf_BPF.h"
#include <sys/syscall.h>
#include <unistd.h>
#include <stdio.h>

JNIEXPORT jint JNICALL Java_dev_bithole_bpf_BPF_syscall(JNIEnv *env, jobject this, jint command, jbyteArray attrIn) {
    jbyte *attr = (*env)->GetByteArrayElements(env, attrIn, NULL);
    int retval = syscall(SYS_bpf, command, (union bpf_attr *)attr, (*env)->GetArrayLength(env, attrIn));
    (*env)->ReleaseByteArrayElements(env, attrIn, attr, 0);
    return retval;
}

BPF.java

package dev.bithole.bpf;
import java.lang.UnsatisfiedLinkError;
import java.io.File;
import java.io.IOException;
import java.lang.ExceptionInInitializerError;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.FileOutputStream;

public class BPF {

    static {
        try {
            System.loadLibrary("bpf");
        } catch(UnsatisfiedLinkError err) {
            try {
                File tempFile = File.createTempFile("bpf", "");
                tempFile.deleteOnExit();
                InputStream input = BPF.class.getResourceAsStream("/libbpf.so");
                try(OutputStream output = new FileOutputStream(tempFile)) {
                    input.transferTo(output);
                } catch(IOException e) {
                    throw e;
                }
                System.load(tempFile.getPath());
            } catch(IOException e) {
                throw new ExceptionInInitializerError(e);
            }
        }
    }

    public native int syscall(int command, byte[] attr);

}

build.sh

javac -h build -d bin BPF.java
gcc -c bpf.c -o build/bpf.o -I"$JAVA_HOME/include" -I"$JAVA_HOME/include/linux" -Wall -Wextra -Wpedantic
gcc -shared -o bin/libbpf.so build/bpf.o
jar cf bpf.jar -C bin .