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Natives for fork()

• See: dalvik/vm/native/dalvik_system_Zygote.c

/* native public static int fork(); */
static void Dalvik_dalvik_system_Zygote_fork(const u4* args, JValue* pResult)
{
    pid_t pid;
    int err;

    if (!gDvm.zygote) {
        dvmThrowException("Ljava/lang/IllegalStateException;",
            "VM instance not started with -Xzygote");

        RETURN_VOID();
    }

    if (!dvmGcPreZygoteFork()) {
        LOGE("pre-fork heap failed\n");
        dvmAbort();
    }

    setSignalHandler();      

    dvmDumpLoaderStats("zygote");
    pid = fork();

#ifdef HAVE_ANDROID_OS
    if (pid == 0) {
        /* child process */
        extern int gMallocLeakZygoteChild;
        gMallocLeakZygoteChild = 1;
    }
#endif

    RETURN_INT(pid);
}

/* 
 * Utility routine to fork zygote and specialize the child process.
 */
static pid_t forkAndSpecializeCommon(const u4* args)
{
    pid_t pid;

    uid_t uid = (uid_t) args[0];
    gid_t gid = (gid_t) args[1];
    ArrayObject* gids = (ArrayObject *)args[2];
    u4 debugFlags = args[3];
    ArrayObject *rlimits = (ArrayObject *)args[4];

    if (!gDvm.zygote) {
        dvmThrowException("Ljava/lang/IllegalStateException;",
            "VM instance not started with -Xzygote");

        return -1;
    }

    if (!dvmGcPreZygoteFork()) {
        LOGE("pre-fork heap failed\n");
        dvmAbort();
    }

    setSignalHandler();      

    dvmDumpLoaderStats("zygote");
    pid = fork();

    if (pid == 0) {
        int err;
        /* The child process */

#ifdef HAVE_ANDROID_OS
        extern int gMallocLeakZygoteChild;
        gMallocLeakZygoteChild = 1;

        /* keep caps across UID change, unless we're staying root */
        if (uid != 0) {
            err = prctl(PR_SET_KEEPCAPS, 1, 0, 0, 0);

            if (err < 0) {
                LOGW("cannot PR_SET_KEEPCAPS errno: %d", errno);
            }
        }

#endif /* HAVE_ANDROID_OS */

        err = setgroupsIntarray(gids);

        if (err < 0) {
            LOGW("cannot setgroups() errno: %d", errno);
        }

        err = setrlimitsFromArray(rlimits);

        if (err < 0) {
            LOGW("cannot setrlimit() errno: %d", errno);
        }

        err = setgid(gid);
        if (err < 0) {
            LOGW("cannot setgid(%d) errno: %d", gid, errno);
        }

        err = setuid(uid);
        if (err < 0) {
            LOGW("cannot setuid(%d) errno: %d", uid, errno);
        }

        /*
         * Our system thread ID has changed.  Get the new one.
         */
        Thread* thread = dvmThreadSelf();
        thread->systemTid = dvmGetSysThreadId();

        /* configure additional debug options */
        enableDebugFeatures(debugFlags);

        unsetSignalHandler();      
        gDvm.zygote = false;
        if (!dvmInitAfterZygote()) {
            LOGE("error in post-zygote initialization\n");
            dvmAbort();
        }
    } else if (pid > 0) {
        /* the parent process */
    }

    return pid;
}

/* native public static int forkAndSpecialize(int uid, int gid, 
 *     int[] gids, int debugFlags); 
 */
static void Dalvik_dalvik_system_Zygote_forkAndSpecialize(const u4* args,
    JValue* pResult)
{
    pid_t pid;

    pid = forkAndSpecializeCommon(args);

    RETURN_INT(pid);
}

/* native public static int forkSystemServer(int uid, int gid, 
 *     int[] gids, int debugFlags); 
 */
static void Dalvik_dalvik_system_Zygote_forkSystemServer(
        const u4* args, JValue* pResult)
{
    pid_t pid;
    pid = forkAndSpecializeCommon(args);

    /* The zygote process checks whether the child process has died or not. */
    if (pid > 0) {
        int status;

        LOGI("System server process %d has been created", pid);
        gDvm.systemServerPid = pid;
        /* There is a slight window that the system server process has crashed
         * but it went unnoticed because we haven't published its pid yet. So
         * we recheck here just to make sure that all is well.
         */
        if (waitpid(pid, &status, WNOHANG) == pid) {
            LOGE("System server process %d has died. Restarting Zygote!", pid);
            kill(getpid(), SIGKILL);
        }
    }
    RETURN_INT(pid);
}

const DalvikNativeMethod dvm_dalvik_system_Zygote[] = {
    { "fork",            "()I",
        Dalvik_dalvik_system_Zygote_fork },
    { "forkAndSpecialize",            "(II[II[[I)I",
        Dalvik_dalvik_system_Zygote_forkAndSpecialize },
    { "forkSystemServer",            "(II[II[[I)I",
        Dalvik_dalvik_system_Zygote_forkSystemServer },
    { NULL, NULL, NULL },
};