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      1 /*
      2  * Copyright (c) 1995, 2008, Oracle and/or its affiliates. All rights reserved.
      3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
      4  *
      5  * This code is free software; you can redistribute it and/or modify it
      6  * under the terms of the GNU General Public License version 2 only, as
      7  * published by the Free Software Foundation.  Oracle designates this
      8  * particular file as subject to the "Classpath" exception as provided
      9  * by Oracle in the LICENSE file that accompanied this code.
     10  *
     11  * This code is distributed in the hope that it will be useful, but WITHOUT
     12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
     13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
     14  * version 2 for more details (a copy is included in the LICENSE file that
     15  * accompanied this code).
     16  *
     17  * You should have received a copy of the GNU General Public License version
     18  * 2 along with this work; if not, write to the Free Software Foundation,
     19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
     20  *
     21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
     22  * or visit www.oracle.com if you need additional information or have any
     23  * questions.
     24  */
     25 
     26 #undef  _LARGEFILE64_SOURCE
     27 #define _LARGEFILE64_SOURCE 1
     28 
     29 #include "jni.h"
     30 #include "jvm.h"
     31 #include "jvm_md.h"
     32 #include "jni_util.h"
     33 #include "io_util.h"
     34 #include "JNIHelp.h"
     35 
     36 #define NATIVE_METHOD(className, functionName, signature) \
     37 { #functionName, signature, (void*)(className ## _ ## functionName) }
     38 
     39 /*
     40  * Platform-specific support for java.lang.Process
     41  */
     42 #include <assert.h>
     43 #include <stddef.h>
     44 #include <stdlib.h>
     45 #include <sys/types.h>
     46 #include <ctype.h>
     47 #ifdef _ALLBSD_SOURCE
     48 #include <wait.h>
     49 #else
     50 #include <sys/wait.h>
     51 #endif
     52 #include <signal.h>
     53 #include <string.h>
     54 #include <errno.h>
     55 #include <dirent.h>
     56 #include <unistd.h>
     57 #include <fcntl.h>
     58 #include <limits.h>
     59 
     60 #ifdef __APPLE__
     61 #include <crt_externs.h>
     62 #define environ (*_NSGetEnviron())
     63 #endif
     64 
     65 /*
     66  * There are 3 possible strategies we might use to "fork":
     67  *
     68  * - fork(2).  Very portable and reliable but subject to
     69  *   failure due to overcommit (see the documentation on
     70  *   /proc/sys/vm/overcommit_memory in Linux proc(5)).
     71  *   This is the ancient problem of spurious failure whenever a large
     72  *   process starts a small subprocess.
     73  *
     74  * - vfork().  Using this is scary because all relevant man pages
     75  *   contain dire warnings, e.g. Linux vfork(2).  But at least it's
     76  *   documented in the glibc docs and is standardized by XPG4.
     77  *   http://www.opengroup.org/onlinepubs/000095399/functions/vfork.html
     78  *   On Linux, one might think that vfork() would be implemented using
     79  *   the clone system call with flag CLONE_VFORK, but in fact vfork is
     80  *   a separate system call (which is a good sign, suggesting that
     81  *   vfork will continue to be supported at least on Linux).
     82  *   Another good sign is that glibc implements posix_spawn using
     83  *   vfork whenever possible.  Note that we cannot use posix_spawn
     84  *   ourselves because there's no reliable way to close all inherited
     85  *   file descriptors.
     86  *
     87  * - clone() with flags CLONE_VM but not CLONE_THREAD.  clone() is
     88  *   Linux-specific, but this ought to work - at least the glibc
     89  *   sources contain code to handle different combinations of CLONE_VM
     90  *   and CLONE_THREAD.  However, when this was implemented, it
     91  *   appeared to fail on 32-bit i386 (but not 64-bit x86_64) Linux with
     92  *   the simple program
     93  *     Runtime.getRuntime().exec("/bin/true").waitFor();
     94  *   with:
     95  *     #  Internal Error (os_linux_x86.cpp:683), pid=19940, tid=2934639536
     96  *     #  Error: pthread_getattr_np failed with errno = 3 (ESRCH)
     97  *   We believe this is a glibc bug, reported here:
     98  *     http://sources.redhat.com/bugzilla/show_bug.cgi?id=10311
     99  *   but the glibc maintainers closed it as WONTFIX.
    100  *
    101  * Based on the above analysis, we are currently using vfork() on
    102  * Linux and fork() on other Unix systems, but the code to use clone()
    103  * remains.
    104  */
    105 
    106 #define START_CHILD_USE_CLONE 0  /* clone() currently disabled; see above. */
    107 
    108 #ifndef START_CHILD_USE_CLONE
    109   #ifdef __linux__
    110     #define START_CHILD_USE_CLONE 1
    111   #else
    112     #define START_CHILD_USE_CLONE 0
    113   #endif
    114 #endif
    115 
    116 /* By default, use vfork() on Linux. */
    117 #ifndef START_CHILD_USE_VFORK
    118   #ifdef __linux__
    119     #define START_CHILD_USE_VFORK 1
    120   #else
    121     #define START_CHILD_USE_VFORK 0
    122   #endif
    123 #endif
    124 
    125 #if START_CHILD_USE_CLONE
    126 #include <sched.h>
    127 #define START_CHILD_SYSTEM_CALL "clone"
    128 #elif START_CHILD_USE_VFORK
    129 #define START_CHILD_SYSTEM_CALL "vfork"
    130 #else
    131 #define START_CHILD_SYSTEM_CALL "fork"
    132 #endif
    133 
    134 #ifndef STDIN_FILENO
    135 #define STDIN_FILENO 0
    136 #endif
    137 
    138 #ifndef STDOUT_FILENO
    139 #define STDOUT_FILENO 1
    140 #endif
    141 
    142 #ifndef STDERR_FILENO
    143 #define STDERR_FILENO 2
    144 #endif
    145 
    146 #ifndef SA_NOCLDSTOP
    147 #define SA_NOCLDSTOP 0
    148 #endif
    149 
    150 #ifndef SA_RESTART
    151 #define SA_RESTART 0
    152 #endif
    153 
    154 #define FAIL_FILENO (STDERR_FILENO + 1)
    155 
    156 /* TODO: Refactor. */
    157 #define RESTARTABLE(_cmd, _result) do { \
    158   do { \
    159     _result = _cmd; \
    160   } while((_result == -1) && (errno == EINTR)); \
    161 } while(0)
    162 
    163 /* This is one of the rare times it's more portable to declare an
    164  * external symbol explicitly, rather than via a system header.
    165  * The declaration is standardized as part of UNIX98, but there is
    166  * no standard (not even de-facto) header file where the
    167  * declaration is to be found.  See:
    168  * http://www.opengroup.org/onlinepubs/009695399/functions/environ.html
    169  * http://www.opengroup.org/onlinepubs/009695399/functions/xsh_chap02_02.html
    170  *
    171  * "All identifiers in this volume of IEEE Std 1003.1-2001, except
    172  * environ, are defined in at least one of the headers" (!)
    173  */
    174 extern char **environ;
    175 
    176 
    177 static void
    178 setSIGCHLDHandler(JNIEnv *env)
    179 {
    180     /* There is a subtle difference between having the signal handler
    181      * for SIGCHLD be SIG_DFL and SIG_IGN.  We cannot obtain process
    182      * termination information for child processes if the signal
    183      * handler is SIG_IGN.  It must be SIG_DFL.
    184      *
    185      * We used to set the SIGCHLD handler only on Linux, but it's
    186      * safest to set it unconditionally.
    187      *
    188      * Consider what happens if java's parent process sets the SIGCHLD
    189      * handler to SIG_IGN.  Normally signal handlers are inherited by
    190      * children, but SIGCHLD is a controversial case.  Solaris appears
    191      * to always reset it to SIG_DFL, but this behavior may be
    192      * non-standard-compliant, and we shouldn't rely on it.
    193      *
    194      * References:
    195      * http://www.opengroup.org/onlinepubs/7908799/xsh/exec.html
    196      * http://www.pasc.org/interps/unofficial/db/p1003.1/pasc-1003.1-132.html
    197      */
    198     struct sigaction sa;
    199     sa.sa_handler = SIG_DFL;
    200     sigemptyset(&sa.sa_mask);
    201     sa.sa_flags = SA_NOCLDSTOP | SA_RESTART;
    202     if (sigaction(SIGCHLD, &sa, NULL) < 0)
    203         JNU_ThrowInternalError(env, "Can't set SIGCHLD handler");
    204 }
    205 
    206 static void*
    207 xmalloc(JNIEnv *env, size_t size)
    208 {
    209     void *p = malloc(size);
    210     if (p == NULL)
    211         JNU_ThrowOutOfMemoryError(env, NULL);
    212     return p;
    213 }
    214 
    215 #define NEW(type, n) ((type *) xmalloc(env, (n) * sizeof(type)))
    216 
    217 /**
    218  * If PATH is not defined, the OS provides some default value.
    219  * Unfortunately, there's no portable way to get this value.
    220  * Fortunately, it's only needed if the child has PATH while we do not.
    221  */
    222 static const char*
    223 defaultPath(void)
    224 {
    225 #ifdef __solaris__
    226     /* These really are the Solaris defaults! */
    227     return (geteuid() == 0 || getuid() == 0) ?
    228         "/usr/xpg4/bin:/usr/ccs/bin:/usr/bin:/opt/SUNWspro/bin:/usr/sbin" :
    229         "/usr/xpg4/bin:/usr/ccs/bin:/usr/bin:/opt/SUNWspro/bin:";
    230 #else
    231     return ":/bin:/usr/bin";    /* glibc */
    232 #endif
    233 }
    234 
    235 static const char*
    236 effectivePath(void)
    237 {
    238     const char *s = getenv("PATH");
    239     return (s != NULL) ? s : defaultPath();
    240 }
    241 
    242 static int
    243 countOccurrences(const char *s, char c)
    244 {
    245     int count;
    246     for (count = 0; *s != '\0'; s++)
    247         count += (*s == c);
    248     return count;
    249 }
    250 
    251 static const char * const *
    252 splitPath(JNIEnv *env, const char *path)
    253 {
    254     const char *p, *q;
    255     char **pathv;
    256     int i;
    257     int count = countOccurrences(path, ':') + 1;
    258 
    259     pathv = NEW(char*, count+1);
    260     pathv[count] = NULL;
    261     for (p = path, i = 0; i < count; i++, p = q + 1) {
    262         for (q = p; (*q != ':') && (*q != '\0'); q++)
    263             ;
    264         if (q == p)             /* empty PATH component => "." */
    265             pathv[i] = "./";
    266         else {
    267             int addSlash = ((*(q - 1)) != '/');
    268             pathv[i] = NEW(char, q - p + addSlash + 1);
    269             memcpy(pathv[i], p, q - p);
    270             if (addSlash)
    271                 pathv[i][q - p] = '/';
    272             pathv[i][q - p + addSlash] = '\0';
    273         }
    274     }
    275     return (const char * const *) pathv;
    276 }
    277 
    278 /**
    279  * Cached value of JVM's effective PATH.
    280  * (We don't support putenv("PATH=...") in native code)
    281  */
    282 static const char *parentPath;
    283 
    284 /**
    285  * Split, canonicalized version of parentPath
    286  */
    287 static const char * const *parentPathv;
    288 
    289 static jfieldID field_exitcode;
    290 
    291 JNIEXPORT void JNICALL
    292 UNIXProcess_initIDs(JNIEnv *env, jclass clazz)
    293 {
    294     field_exitcode = (*env)->GetFieldID(env, clazz, "exitcode", "I");
    295 
    296     parentPath  = effectivePath();
    297     parentPathv = splitPath(env, parentPath);
    298 
    299     setSIGCHLDHandler(env);
    300 }
    301 
    302 
    303 #ifndef WIFEXITED
    304 #define WIFEXITED(status) (((status)&0xFF) == 0)
    305 #endif
    306 
    307 #ifndef WEXITSTATUS
    308 #define WEXITSTATUS(status) (((status)>>8)&0xFF)
    309 #endif
    310 
    311 #ifndef WIFSIGNALED
    312 #define WIFSIGNALED(status) (((status)&0xFF) > 0 && ((status)&0xFF00) == 0)
    313 #endif
    314 
    315 #ifndef WTERMSIG
    316 #define WTERMSIG(status) ((status)&0x7F)
    317 #endif
    318 
    319 /* Block until a child process exits and return its exit code.
    320    Note, can only be called once for any given pid. */
    321 JNIEXPORT jint JNICALL
    322 UNIXProcess_waitForProcessExit(JNIEnv* env,
    323                                               jobject junk,
    324                                               jint pid)
    325 {
    326     /* We used to use waitid() on Solaris, waitpid() on Linux, but
    327      * waitpid() is more standard, so use it on all POSIX platforms. */
    328     int status;
    329     /* Wait for the child process to exit.  This returns immediately if
    330        the child has already exited. */
    331     while (waitpid(pid, &status, 0) < 0) {
    332         switch (errno) {
    333         case ECHILD: return 0;
    334         case EINTR: break;
    335         default: return -1;
    336         }
    337     }
    338 
    339     if (WIFEXITED(status)) {
    340         /*
    341          * The child exited normally; get its exit code.
    342          */
    343         return WEXITSTATUS(status);
    344     } else if (WIFSIGNALED(status)) {
    345         /* The child exited because of a signal.
    346          * The best value to return is 0x80 + signal number,
    347          * because that is what all Unix shells do, and because
    348          * it allows callers to distinguish between process exit and
    349          * process death by signal.
    350          * Unfortunately, the historical behavior on Solaris is to return
    351          * the signal number, and we preserve this for compatibility. */
    352 #ifdef __solaris__
    353         return WTERMSIG(status);
    354 #else
    355         return 0x80 + WTERMSIG(status);
    356 #endif
    357     } else {
    358         /*
    359          * Unknown exit code; pass it through.
    360          */
    361         return status;
    362     }
    363 }
    364 
    365 static ssize_t
    366 restartableWrite(int fd, const void *buf, size_t count)
    367 {
    368     ssize_t result;
    369     RESTARTABLE(write(fd, buf, count), result);
    370     return result;
    371 }
    372 
    373 static int
    374 restartableDup2(int fd_from, int fd_to)
    375 {
    376     int err;
    377     RESTARTABLE(dup2(fd_from, fd_to), err);
    378     return err;
    379 }
    380 
    381 static int
    382 restartableClose(int fd)
    383 {
    384     int err;
    385     RESTARTABLE(close(fd), err);
    386     return err;
    387 }
    388 
    389 static int
    390 closeSafely(int fd)
    391 {
    392     return (fd == -1) ? 0 : restartableClose(fd);
    393 }
    394 
    395 static int
    396 isAsciiDigit(char c)
    397 {
    398   return c >= '0' && c <= '9';
    399 }
    400 
    401 #ifdef _ALLBSD_SOURCE
    402 #define FD_DIR "/dev/fd"
    403 #define dirent64 dirent
    404 #define readdir64 readdir
    405 #else
    406 #define FD_DIR "/proc/self/fd"
    407 #endif
    408 
    409 static int
    410 closeDescriptors(void)
    411 {
    412     DIR *dp;
    413     struct dirent64 *dirp;
    414     int from_fd = FAIL_FILENO + 1;
    415 
    416     /* We're trying to close all file descriptors, but opendir() might
    417      * itself be implemented using a file descriptor, and we certainly
    418      * don't want to close that while it's in use.  We assume that if
    419      * opendir() is implemented using a file descriptor, then it uses
    420      * the lowest numbered file descriptor, just like open().  So we
    421      * close a couple explicitly.  */
    422 
    423     restartableClose(from_fd);          /* for possible use by opendir() */
    424     restartableClose(from_fd + 1);      /* another one for good luck */
    425 
    426     if ((dp = opendir(FD_DIR)) == NULL)
    427         return 0;
    428 
    429     /* We use readdir64 instead of readdir to work around Solaris bug
    430      * 6395699: /proc/self/fd fails to report file descriptors >= 1024 on Solaris 9
    431      */
    432     while ((dirp = readdir64(dp)) != NULL) {
    433         int fd;
    434         if (isAsciiDigit(dirp->d_name[0]) &&
    435             (fd = strtol(dirp->d_name, NULL, 10)) >= from_fd + 2)
    436             restartableClose(fd);
    437     }
    438 
    439     closedir(dp);
    440 
    441     return 1;
    442 }
    443 
    444 static int
    445 moveDescriptor(int fd_from, int fd_to)
    446 {
    447     if (fd_from != fd_to) {
    448         if ((restartableDup2(fd_from, fd_to) == -1) ||
    449             (restartableClose(fd_from) == -1))
    450             return -1;
    451     }
    452     return 0;
    453 }
    454 
    455 static const char *
    456 getBytes(JNIEnv *env, jbyteArray arr)
    457 {
    458     return arr == NULL ? NULL :
    459         (const char*) (*env)->GetByteArrayElements(env, arr, NULL);
    460 }
    461 
    462 static void
    463 releaseBytes(JNIEnv *env, jbyteArray arr, const char* parr)
    464 {
    465     if (parr != NULL)
    466         (*env)->ReleaseByteArrayElements(env, arr, (jbyte*) parr, JNI_ABORT);
    467 }
    468 
    469 static void
    470 initVectorFromBlock(const char**vector, const char* block, int count)
    471 {
    472     int i;
    473     const char *p;
    474     for (i = 0, p = block; i < count; i++) {
    475         /* Invariant: p always points to the start of a C string. */
    476         vector[i] = p;
    477         while (*(p++));
    478     }
    479     vector[count] = NULL;
    480 }
    481 
    482 static void
    483 throwIOException(JNIEnv *env, int errnum, const char *defaultDetail)
    484 {
    485     static const char * const format = "error=%d, %s";
    486     const char *detail = defaultDetail;
    487     char *errmsg;
    488     jstring s;
    489 
    490     if (errnum != 0) {
    491         const char *s = strerror(errnum);
    492         if (strcmp(s, "Unknown error") != 0)
    493             detail = s;
    494     }
    495     /* ASCII Decimal representation uses 2.4 times as many bits as binary. */
    496     size_t newsize = strlen(format) + strlen(detail) + 3 * sizeof(errnum);
    497     errmsg = NEW(char, newsize);
    498     snprintf(errmsg, newsize, format, errnum, detail);
    499     s = JNU_NewStringPlatform(env, errmsg);
    500     if (s != NULL) {
    501         jobject x = JNU_NewObjectByName(env, "java/io/IOException",
    502                                         "(Ljava/lang/String;)V", s);
    503         if (x != NULL)
    504             (*env)->Throw(env, x);
    505     }
    506     free(errmsg);
    507 }
    508 
    509 #ifdef DEBUG_PROCESS
    510 /* Debugging process code is difficult; where to write debug output? */
    511 static void
    512 debugPrint(char *format, ...)
    513 {
    514     FILE *tty = fopen("/dev/tty", "w");
    515     va_list ap;
    516     va_start(ap, format);
    517     vfprintf(tty, format, ap);
    518     va_end(ap);
    519     fclose(tty);
    520 }
    521 #endif /* DEBUG_PROCESS */
    522 
    523 /**
    524  * Exec FILE as a traditional Bourne shell script (i.e. one without #!).
    525  * If we could do it over again, we would probably not support such an ancient
    526  * misfeature, but compatibility wins over sanity.  The original support for
    527  * this was imported accidentally from execvp().
    528  */
    529 static void
    530 execve_as_traditional_shell_script(const char *file,
    531                                    const char *argv[],
    532                                    const char *const envp[])
    533 {
    534     /* Use the extra word of space provided for us in argv by caller. */
    535     const char *argv0 = argv[0];
    536     const char *const *end = argv;
    537     while (*end != NULL)
    538         ++end;
    539     memmove(argv+2, argv+1, (end-argv) * sizeof (*end));
    540     argv[0] = "/bin/sh";
    541     argv[1] = file;
    542     execve(argv[0], (char **) argv, (char **) envp);
    543     /* Can't even exec /bin/sh?  Big trouble, but let's soldier on... */
    544     memmove(argv+1, argv+2, (end-argv) * sizeof (*end));
    545     argv[0] = argv0;
    546 }
    547 
    548 /**
    549  * Like execve(2), except that in case of ENOEXEC, FILE is assumed to
    550  * be a shell script and the system default shell is invoked to run it.
    551  */
    552 static void
    553 execve_with_shell_fallback(const char *file,
    554                            const char *argv[],
    555                            const char *const envp[])
    556 {
    557 #if START_CHILD_USE_CLONE || START_CHILD_USE_VFORK
    558     /* shared address space; be very careful. */
    559     execve(file, (char **) argv, (char **) envp);
    560     if (errno == ENOEXEC)
    561         execve_as_traditional_shell_script(file, argv, envp);
    562 #else
    563     /* unshared address space; we can mutate environ. */
    564     environ = (char **) envp;
    565     execvp(file, (char **) argv);
    566 #endif
    567 }
    568 
    569 /**
    570  * 'execvpe' should have been included in the Unix standards,
    571  * and is a GNU extension in glibc 2.10.
    572  *
    573  * JDK_execvpe is identical to execvp, except that the child environment is
    574  * specified via the 3rd argument instead of being inherited from environ.
    575  */
    576 static void
    577 JDK_execvpe(const char *file,
    578             const char *argv[],
    579             const char *const envp[])
    580 {
    581     if (envp == NULL || (char **) envp == environ) {
    582         execvp(file, (char **) argv);
    583         return;
    584     }
    585 
    586     if (*file == '\0') {
    587         errno = ENOENT;
    588         return;
    589     }
    590 
    591     if (strchr(file, '/') != NULL) {
    592         execve_with_shell_fallback(file, argv, envp);
    593     } else {
    594         /* We must search PATH (parent's, not child's) */
    595         char expanded_file[PATH_MAX];
    596         int filelen = strlen(file);
    597         int sticky_errno = 0;
    598         const char * const * dirs;
    599         for (dirs = parentPathv; *dirs; dirs++) {
    600             const char * dir = *dirs;
    601             int dirlen = strlen(dir);
    602             if (filelen + dirlen + 1 >= PATH_MAX) {
    603                 errno = ENAMETOOLONG;
    604                 continue;
    605             }
    606             memcpy(expanded_file, dir, dirlen);
    607             memcpy(expanded_file + dirlen, file, filelen);
    608             expanded_file[dirlen + filelen] = '\0';
    609             execve_with_shell_fallback(expanded_file, argv, envp);
    610             /* There are 3 responses to various classes of errno:
    611              * return immediately, continue (especially for ENOENT),
    612              * or continue with "sticky" errno.
    613              *
    614              * From exec(3):
    615              *
    616              * If permission is denied for a file (the attempted
    617              * execve returned EACCES), these functions will continue
    618              * searching the rest of the search path.  If no other
    619              * file is found, however, they will return with the
    620              * global variable errno set to EACCES.
    621              */
    622             switch (errno) {
    623             case EACCES:
    624                 sticky_errno = errno;
    625                 /* FALLTHRU */
    626             case ENOENT:
    627             case ENOTDIR:
    628 #ifdef ELOOP
    629             case ELOOP:
    630 #endif
    631 #ifdef ESTALE
    632             case ESTALE:
    633 #endif
    634 #ifdef ENODEV
    635             case ENODEV:
    636 #endif
    637 #ifdef ETIMEDOUT
    638             case ETIMEDOUT:
    639 #endif
    640                 break; /* Try other directories in PATH */
    641             default:
    642                 return;
    643             }
    644         }
    645         if (sticky_errno != 0)
    646             errno = sticky_errno;
    647     }
    648 }
    649 
    650 /*
    651  * Reads nbyte bytes from file descriptor fd into buf,
    652  * The read operation is retried in case of EINTR or partial reads.
    653  *
    654  * Returns number of bytes read (normally nbyte, but may be less in
    655  * case of EOF).  In case of read errors, returns -1 and sets errno.
    656  */
    657 static ssize_t
    658 readFully(int fd, void *buf, size_t nbyte)
    659 {
    660     ssize_t remaining = nbyte;
    661     for (;;) {
    662         ssize_t n = read(fd, buf, remaining);
    663         if (n == 0) {
    664             return nbyte - remaining;
    665         } else if (n > 0) {
    666             remaining -= n;
    667             if (remaining <= 0)
    668                 return nbyte;
    669             /* We were interrupted in the middle of reading the bytes.
    670              * Unlikely, but possible. */
    671             buf = (void *) (((char *)buf) + n);
    672         } else if (errno == EINTR) {
    673             /* Strange signals like SIGJVM1 are possible at any time.
    674              * See http://www.dreamsongs.com/WorseIsBetter.html */
    675         } else {
    676             return -1;
    677         }
    678     }
    679 }
    680 
    681 typedef struct _ChildStuff
    682 {
    683     int in[2];
    684     int out[2];
    685     int err[2];
    686     int fail[2];
    687     int fds[3];
    688     const char **argv;
    689     const char **envv;
    690     const char *pdir;
    691     jboolean redirectErrorStream;
    692 #if START_CHILD_USE_CLONE
    693     void *clone_stack;
    694 #endif
    695 } ChildStuff;
    696 
    697 static void
    698 copyPipe(int from[2], int to[2])
    699 {
    700     to[0] = from[0];
    701     to[1] = from[1];
    702 }
    703 
    704 /**
    705  * Child process after a successful fork() or clone().
    706  * This function must not return, and must be prepared for either all
    707  * of its address space to be shared with its parent, or to be a copy.
    708  * It must not modify global variables such as "environ".
    709  */
    710 static int
    711 childProcess(void *arg)
    712 {
    713     const ChildStuff* p = (const ChildStuff*) arg;
    714 
    715     /* Close the parent sides of the pipes.
    716        Closing pipe fds here is redundant, since closeDescriptors()
    717        would do it anyways, but a little paranoia is a good thing. */
    718     if ((closeSafely(p->in[1])   == -1) ||
    719         (closeSafely(p->out[0])  == -1) ||
    720         (closeSafely(p->err[0])  == -1) ||
    721         (closeSafely(p->fail[0]) == -1))
    722         goto WhyCantJohnnyExec;
    723 
    724     /* Give the child sides of the pipes the right fileno's. */
    725     /* Note: it is possible for in[0] == 0 */
    726     if ((moveDescriptor(p->in[0] != -1 ?  p->in[0] : p->fds[0],
    727                         STDIN_FILENO) == -1) ||
    728         (moveDescriptor(p->out[1]!= -1 ? p->out[1] : p->fds[1],
    729                         STDOUT_FILENO) == -1))
    730         goto WhyCantJohnnyExec;
    731 
    732     if (p->redirectErrorStream) {
    733         if ((closeSafely(p->err[1]) == -1) ||
    734             (restartableDup2(STDOUT_FILENO, STDERR_FILENO) == -1))
    735             goto WhyCantJohnnyExec;
    736     } else {
    737         if (moveDescriptor(p->err[1] != -1 ? p->err[1] : p->fds[2],
    738                            STDERR_FILENO) == -1)
    739             goto WhyCantJohnnyExec;
    740     }
    741 
    742     if (moveDescriptor(p->fail[1], FAIL_FILENO) == -1)
    743         goto WhyCantJohnnyExec;
    744 
    745     /* close everything */
    746     if (closeDescriptors() == 0) { /* failed,  close the old way */
    747         int max_fd = (int)sysconf(_SC_OPEN_MAX);
    748         int fd;
    749         for (fd = FAIL_FILENO + 1; fd < max_fd; fd++)
    750             if (restartableClose(fd) == -1 && errno != EBADF)
    751                 goto WhyCantJohnnyExec;
    752     }
    753 
    754     /* change to the new working directory */
    755     if (p->pdir != NULL && chdir(p->pdir) < 0)
    756         goto WhyCantJohnnyExec;
    757 
    758     if (fcntl(FAIL_FILENO, F_SETFD, FD_CLOEXEC) == -1)
    759         goto WhyCantJohnnyExec;
    760 
    761     JDK_execvpe(p->argv[0], p->argv, p->envv);
    762 
    763  WhyCantJohnnyExec:
    764     /* We used to go to an awful lot of trouble to predict whether the
    765      * child would fail, but there is no reliable way to predict the
    766      * success of an operation without *trying* it, and there's no way
    767      * to try a chdir or exec in the parent.  Instead, all we need is a
    768      * way to communicate any failure back to the parent.  Easy; we just
    769      * send the errno back to the parent over a pipe in case of failure.
    770      * The tricky thing is, how do we communicate the *success* of exec?
    771      * We use FD_CLOEXEC together with the fact that a read() on a pipe
    772      * yields EOF when the write ends (we have two of them!) are closed.
    773      */
    774     {
    775         int errnum = errno;
    776         restartableWrite(FAIL_FILENO, &errnum, sizeof(errnum));
    777     }
    778     restartableClose(FAIL_FILENO);
    779     _exit(-1);
    780     return 0;  /* Suppress warning "no return value from function" */
    781 }
    782 
    783 /**
    784  * Start a child process running function childProcess.
    785  * This function only returns in the parent.
    786  * We are unusually paranoid; use of clone/vfork is
    787  * especially likely to tickle gcc/glibc bugs.
    788  */
    789 #ifdef __attribute_noinline__  /* See: sys/cdefs.h */
    790 __attribute_noinline__
    791 #endif
    792 static pid_t
    793 startChild(ChildStuff *c) {
    794 #if START_CHILD_USE_CLONE
    795 #define START_CHILD_CLONE_STACK_SIZE (64 * 1024)
    796     /*
    797      * See clone(2).
    798      * Instead of worrying about which direction the stack grows, just
    799      * allocate twice as much and start the stack in the middle.
    800      */
    801     if ((c->clone_stack = malloc(2 * START_CHILD_CLONE_STACK_SIZE)) == NULL)
    802         /* errno will be set to ENOMEM */
    803         return -1;
    804     return clone(childProcess,
    805                  c->clone_stack + START_CHILD_CLONE_STACK_SIZE,
    806                  CLONE_VFORK | CLONE_VM | SIGCHLD, c);
    807 #else
    808   #if START_CHILD_USE_VFORK
    809     /*
    810      * We separate the call to vfork into a separate function to make
    811      * very sure to keep stack of child from corrupting stack of parent,
    812      * as suggested by the scary gcc warning:
    813      *  warning: variable 'foo' might be clobbered by 'longjmp' or 'vfork'
    814      */
    815     volatile pid_t resultPid = vfork();
    816   #else
    817     /*
    818      * From Solaris fork(2): In Solaris 10, a call to fork() is
    819      * identical to a call to fork1(); only the calling thread is
    820      * replicated in the child process. This is the POSIX-specified
    821      * behavior for fork().
    822      */
    823     pid_t resultPid = fork();
    824   #endif
    825     if (resultPid == 0)
    826         childProcess(c);
    827     assert(resultPid != 0);  /* childProcess never returns */
    828     return resultPid;
    829 #endif /* ! START_CHILD_USE_CLONE */
    830 }
    831 
    832 JNIEXPORT jint JNICALL
    833 UNIXProcess_forkAndExec(JNIEnv *env,
    834                                        jobject process,
    835                                        jbyteArray prog,
    836                                        jbyteArray argBlock, jint argc,
    837                                        jbyteArray envBlock, jint envc,
    838                                        jbyteArray dir,
    839                                        jintArray std_fds,
    840                                        jboolean redirectErrorStream)
    841 {
    842     int errnum;
    843     int resultPid = -1;
    844     int in[2], out[2], err[2], fail[2];
    845     jint *fds = NULL;
    846     const char *pprog = NULL;
    847     const char *pargBlock = NULL;
    848     const char *penvBlock = NULL;
    849     ChildStuff *c;
    850 
    851     in[0] = in[1] = out[0] = out[1] = err[0] = err[1] = fail[0] = fail[1] = -1;
    852 
    853     if ((c = NEW(ChildStuff, 1)) == NULL) return -1;
    854     c->argv = NULL;
    855     c->envv = NULL;
    856     c->pdir = NULL;
    857 #if START_CHILD_USE_CLONE
    858     c->clone_stack = NULL;
    859 #endif
    860 
    861     /* Convert prog + argBlock into a char ** argv.
    862      * Add one word room for expansion of argv for use by
    863      * execve_as_traditional_shell_script.
    864      */
    865     assert(prog != NULL && argBlock != NULL);
    866     if ((pprog     = getBytes(env, prog))       == NULL) goto Catch;
    867     if ((pargBlock = getBytes(env, argBlock))   == NULL) goto Catch;
    868     if ((c->argv = NEW(const char *, argc + 3)) == NULL) goto Catch;
    869     c->argv[0] = pprog;
    870     initVectorFromBlock(c->argv+1, pargBlock, argc);
    871 
    872     if (envBlock != NULL) {
    873         /* Convert envBlock into a char ** envv */
    874         if ((penvBlock = getBytes(env, envBlock))   == NULL) goto Catch;
    875         if ((c->envv = NEW(const char *, envc + 1)) == NULL) goto Catch;
    876         initVectorFromBlock(c->envv, penvBlock, envc);
    877     }
    878 
    879     if (dir != NULL) {
    880         if ((c->pdir = getBytes(env, dir)) == NULL) goto Catch;
    881     }
    882 
    883     assert(std_fds != NULL);
    884     fds = (*env)->GetIntArrayElements(env, std_fds, NULL);
    885     if (fds == NULL) goto Catch;
    886 
    887     if ((fds[0] == -1 && pipe(in)  < 0) ||
    888         (fds[1] == -1 && pipe(out) < 0) ||
    889         (fds[2] == -1 && pipe(err) < 0) ||
    890         (pipe(fail) < 0)) {
    891         throwIOException(env, errno, "Bad file descriptor");
    892         goto Catch;
    893     }
    894     c->fds[0] = fds[0];
    895     c->fds[1] = fds[1];
    896     c->fds[2] = fds[2];
    897 
    898     copyPipe(in,   c->in);
    899     copyPipe(out,  c->out);
    900     copyPipe(err,  c->err);
    901     copyPipe(fail, c->fail);
    902 
    903     c->redirectErrorStream = redirectErrorStream;
    904 
    905     resultPid = startChild(c);
    906     assert(resultPid != 0);
    907 
    908     if (resultPid < 0) {
    909         throwIOException(env, errno, START_CHILD_SYSTEM_CALL " failed");
    910         goto Catch;
    911     }
    912 
    913     restartableClose(fail[1]); fail[1] = -1; /* See: WhyCantJohnnyExec */
    914 
    915     switch (readFully(fail[0], &errnum, sizeof(errnum))) {
    916     case 0: break; /* Exec succeeded */
    917     case sizeof(errnum):
    918         waitpid(resultPid, NULL, 0);
    919         throwIOException(env, errnum, "Exec failed");
    920         goto Catch;
    921     default:
    922         throwIOException(env, errno, "Read failed");
    923         goto Catch;
    924     }
    925 
    926     fds[0] = (in [1] != -1) ? in [1] : -1;
    927     fds[1] = (out[0] != -1) ? out[0] : -1;
    928     fds[2] = (err[0] != -1) ? err[0] : -1;
    929 
    930  Finally:
    931 #if START_CHILD_USE_CLONE
    932     free(c->clone_stack);
    933 #endif
    934 
    935     /* Always clean up the child's side of the pipes */
    936     closeSafely(in [0]);
    937     closeSafely(out[1]);
    938     closeSafely(err[1]);
    939 
    940     /* Always clean up fail descriptors */
    941     closeSafely(fail[0]);
    942     closeSafely(fail[1]);
    943 
    944     releaseBytes(env, prog,     pprog);
    945     releaseBytes(env, argBlock, pargBlock);
    946     releaseBytes(env, envBlock, penvBlock);
    947     releaseBytes(env, dir,      c->pdir);
    948 
    949     free(c->argv);
    950     free(c->envv);
    951     free(c);
    952 
    953     if (fds != NULL)
    954         (*env)->ReleaseIntArrayElements(env, std_fds, fds, 0);
    955 
    956     return resultPid;
    957 
    958  Catch:
    959     /* Clean up the parent's side of the pipes in case of failure only */
    960     closeSafely(in [1]);
    961     closeSafely(out[0]);
    962     closeSafely(err[0]);
    963     goto Finally;
    964 }
    965 
    966 JNIEXPORT void JNICALL
    967 UNIXProcess_destroyProcess(JNIEnv *env, jobject junk, jint pid)
    968 {
    969     kill(pid, SIGTERM);
    970 }
    971 
    972 static JNINativeMethod gMethods[] = {
    973   NATIVE_METHOD(UNIXProcess, destroyProcess, "(I)V"),
    974   NATIVE_METHOD(UNIXProcess, forkAndExec, "([B[BI[BI[B[IZ)I"),
    975   NATIVE_METHOD(UNIXProcess, waitForProcessExit, "(I)I"),
    976   NATIVE_METHOD(UNIXProcess, initIDs, "()V"),
    977 };
    978 
    979 void register_java_lang_UNIXProcess(JNIEnv* env) {
    980   jniRegisterNativeMethods(env, "java/lang/UNIXProcess", gMethods, NELEM(gMethods));
    981 }
    982