vm/native/dalvik_system_Zygote.c

/*
 * Copyright (C) 2008 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

/*
 * dalvik.system.Zygote
 */
#include "Dalvik.h"
#include "native/InternalNativePriv.h"

#include <signal.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <grp.h>
#include <errno.h>

#if defined(HAVE_PRCTL)
# include <sys/prctl.h>
#endif

#define ZYGOTE_LOG_TAG "Zygote"

/* must match values in dalvik.system.Zygote */
enum {
    DEBUG_ENABLE_DEBUGGER           = 1,
    DEBUG_ENABLE_CHECKJNI           = 1 << 1,
    DEBUG_ENABLE_ASSERT             = 1 << 2,
    DEBUG_ENABLE_SAFEMODE           = 1 << 3,
};

/*
 * This signal handler is for zygote mode, since the zygote
 * must reap its children
 */
static void sigchldHandler(int s)
{
    pid_t pid;
    int status;

    while ((pid = waitpid(-1, &status, WNOHANG)) > 0) {
        /* Log process-death status that we care about.  In general it is not
           safe to call LOG(...) from a signal handler because of possible
           reentrancy.  However, we know a priori that the current implementation
           of LOG() is safe to call from a SIGCHLD handler in the zygote process.
           If the LOG() implementation changes its locking strategy or its use
           of syscalls within the lazy-init critical section, its use here may
           become unsafe. */
        if (WIFEXITED(status)) {
            if (WEXITSTATUS(status)) {
                LOG(LOG_DEBUG, ZYGOTE_LOG_TAG, "Process %d exited cleanly (%d)\n",
                    (int) pid, WEXITSTATUS(status));
            } else {
                IF_LOGV(/*should use ZYGOTE_LOG_TAG*/) {
                    LOG(LOG_VERBOSE, ZYGOTE_LOG_TAG,
                        "Process %d exited cleanly (%d)\n",
                        (int) pid, WEXITSTATUS(status));
                }
            }
        } else if (WIFSIGNALED(status)) {
            if (WTERMSIG(status) != SIGKILL) {
                LOG(LOG_DEBUG, ZYGOTE_LOG_TAG,
                    "Process %d terminated by signal (%d)\n",
                    (int) pid, WTERMSIG(status));
            } else {
                IF_LOGV(/*should use ZYGOTE_LOG_TAG*/) {
                    LOG(LOG_VERBOSE, ZYGOTE_LOG_TAG,
                        "Process %d terminated by signal (%d)\n",
                        (int) pid, WTERMSIG(status));
                }
            }
#ifdef WCOREDUMP
            if (WCOREDUMP(status)) {
                LOG(LOG_INFO, ZYGOTE_LOG_TAG, "Process %d dumped core\n",
                    (int) pid);
            }
#endif /* ifdef WCOREDUMP */
        }

        /*
         * If the just-crashed process is the system_server, bring down zygote
         * so that it is restarted by init and system server will be restarted
         * from there.
         */
        if (pid == gDvm.systemServerPid) {
            LOG(LOG_INFO, ZYGOTE_LOG_TAG,
                "Exit zygote because system server (%d) has terminated\n",
                (int) pid);
            kill(getpid(), SIGKILL);
        }
    }

    if (pid < 0) {
        LOG(LOG_WARN, ZYGOTE_LOG_TAG,
            "Zygote SIGCHLD error (%d) in waitpid\n",errno);
    }
}

/*
 * configure sigchld handler for the zygote process
 * This is configured very late, because earlier in the dalvik lifecycle
 * we can fork() and exec() for the verifier/optimizer, and we
 * want to waitpid() for those rather than have them be harvested immediately.
 *
 * This ends up being called repeatedly before each fork(), but there's
 * no real harm in that.
 */
static void setSignalHandler()
{
    int err;
    struct sigaction sa;

    memset(&sa, 0, sizeof(sa));

    sa.sa_handler = sigchldHandler;

    err = sigaction (SIGCHLD, &sa, NULL);

    if (err < 0) {
        LOGW("Error setting SIGCHLD handler errno: %d", errno);
    }
}

/*
 * Set the SIGCHLD handler back to default behavior in zygote children
 */
static void unsetSignalHandler()
{
    int err;
    struct sigaction sa;

    memset(&sa, 0, sizeof(sa));

    sa.sa_handler = SIG_DFL;

    err = sigaction (SIGCHLD, &sa, NULL);

    if (err < 0) {
        LOGW("Error unsetting SIGCHLD handler errno: %d", errno);
    }
}

/*
 * Calls POSIX setgroups() using the int[] object as an argument.
 * A NULL argument is tolerated.
 */

static int setgroupsIntarray(ArrayObject* gidArray)
{
    gid_t *gids;
    u4 i;
    s4 *contents;

    if (gidArray == NULL) {
        return 0;
    }

    /* just in case gid_t and u4 are different... */
    gids = alloca(sizeof(gid_t) * gidArray->length);
    contents = (s4 *)gidArray->contents;

    for (i = 0 ; i < gidArray->length ; i++) {
        gids[i] = (gid_t) contents[i];
    }

    return setgroups((size_t) gidArray->length, gids);
}

/*
 * Sets the resource limits via setrlimit(2) for the values in the
 * two-dimensional array of integers that's passed in. The second dimension
 * contains a tuple of length 3: (resource, rlim_cur, rlim_max). NULL is
 * treated as an empty array.
 *
 * -1 is returned on error.
 */
static int setrlimitsFromArray(ArrayObject* rlimits)
{
    u4 i;
    struct rlimit rlim;

    if (rlimits == NULL) {
        return 0;
    }

    memset (&rlim, 0, sizeof(rlim));

    ArrayObject** tuples = (ArrayObject **)(rlimits->contents);

    for (i = 0; i < rlimits->length; i++) {
        ArrayObject * rlimit_tuple = tuples[i];
        s4* contents = (s4 *)rlimit_tuple->contents;
        int err;

        if (rlimit_tuple->length != 3) {
            LOGE("rlimits array must have a second dimension of size 3");
            return -1;
        }

        rlim.rlim_cur = contents[1];
        rlim.rlim_max = contents[2];

        err = setrlimit(contents[0], &rlim);

        if (err < 0) {
            return -1;
        }
    }

    return 0;
}

/* 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);
}

/*
 * Enable/disable debug features requested by the caller.
 *
 * debugger
 *   If set, enable debugging; if not set, disable debugging.  This is
 *   easy to handle, because the JDWP thread isn't started until we call
 *   dvmInitAfterZygote().
 * checkjni
 *   If set, make sure "check JNI" is eabled.  This is a little weird,
 *   because we already have the JNIEnv for the main thread set up.  However,
 *   since we only have one thread at this point, it's easy to patch up.
 * assert
 *   If set, make sure assertions are enabled.  This gets fairly weird,
 *   because it affects the result of a method called by class initializers,
 *   and hence can't affect pre-loaded/initialized classes.
 * safemode
 *   If set, operates the VM in the safe mode. The definition of "safe mode" is
 *   implementation dependent and currently only the JIT compiler is disabled.
 *   This is easy to handle because the compiler thread and associated resources
 *   are not requested until we call dvmInitAfterZygote().
 */
static void enableDebugFeatures(u4 debugFlags)
{
    LOGV("debugFlags is 0x%02x\n", debugFlags);

    gDvm.jdwpAllowed = ((debugFlags & DEBUG_ENABLE_DEBUGGER) != 0);

    if ((debugFlags & DEBUG_ENABLE_CHECKJNI) != 0) {
        /* turn it on if it's not already enabled */
        dvmLateEnableCheckedJni();
    }

    if ((debugFlags & DEBUG_ENABLE_ASSERT) != 0) {
        /* turn it on if it's not already enabled */
        dvmLateEnableAssertions();
    }

    if ((debugFlags & DEBUG_ENABLE_SAFEMODE) != 0) {
#if defined(WITH_JIT)
        /* turn off the jit if it is explicitly requested by the app */
        if (gDvm.executionMode == kExecutionModeJit)
            gDvm.executionMode = kExecutionModeInterpFast;
#endif
    }

#if HAVE_ANDROID_OS
    if ((debugFlags & DEBUG_ENABLE_DEBUGGER) != 0) {
        /* To let a non-privileged gdbserver attach to this
         * process, we must set its dumpable bit flag. However
         * we are not interested in generating a coredump in
         * case of a crash, so also set the coredump size to 0
         * to disable that
         */
        if (prctl(PR_SET_DUMPABLE, 1, 0, 0, 0) < 0) {
            LOGE("could not set dumpable bit flag for pid %d, errno=%d",
                 getpid(), errno);
        } else {
            struct rlimit rl;
            rl.rlim_cur = 0;
            rl.rlim_max = RLIM_INFINITY;
            if (setrlimit(RLIMIT_CORE, &rl) < 0) {
                LOGE("could not disable core file generation "
                     "for pid %d, errno=%d", getpid(), errno);
            }
        }
    }
#endif
}

/*
 * 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 },
};