env->NewStringUTF(s) get crash and different ABI version returning different string value

Question

Want to generate random string of fix length from JNI function for that i have used below function

static const char alphanum[] =
        "abcdefghijklmnopqrstuvwxyz";

jstring Utils::getRandomString(JNIEnv *env, const int len) {


    char s[len];
    for (int i = 0; i < len; ++i) {
        int p = rand() % (sizeof(alphanum) - 1);
        s[i] = alphanum[p];
    }
    s[len] = 0;

    __android_log_print(ANDROID_LOG_DEBUG, "LOG_TAG", "getRandomString  %s", s);


  jstring  temp= env->NewStringUTF(s);

    return temp;
}

but application get crash for line jstring temp= env->NewStringUTF(s); only for ABI version armeabi-v7a

for the solution i have tried this solution

jstring Utils::getRandomString(JNIEnv *env, const int len) {


    char s[len];
    for (int i = 0; i < len; ++i) {
        int p = rand() % (sizeof(alphanum) - 1);
        s[i] = alphanum[p];
    }
    s[len] = 0;
    __android_log_print(ANDROID_LOG_DEBUG, "LOG_TAG", "getRandomString 2 %s", s);


    jbyteArray array = env->NewByteArray(len);
    env->SetByteArrayRegion(array, 0, len, (const jbyte *) s);
    jstring strEncode = env->NewStringUTF("UTF-8");
    jclass cls = env->FindClass("java/lang/String");
    jmethodID ctor = env->GetMethodID(cls, "<init>", "([BLjava/lang/String;)V");
    jstring object = (jstring) env->NewObject(cls, ctor, array, strEncode);


    __android_log_print(ANDROID_LOG_DEBUG, "LOG_TAG", "getRandomString 3 %s",
                        env->GetStringUTFChars(object, 0));
//    jstring  temp= env->NewStringUTF(s);

    return object;
}

but it working fine for ABI version armeabi-v7a when we execute same code on ABI x86 it returning unexpected output like PKdhtXMmr18n2L9K�ؾ�����-DL

please provide some solution that return generated string. env->NewStringUTF() working for ABI version x86 it get crash on armeabi-v7a.

thanks in advance