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jdk/src/java.base/unix/native/libjava/ProcessImpl_md.c
Thomas Stuefe ca3fe721ba 8357089: Remove VFORK launch mechanism from Process implementation (linux) 
Reviewed-by: rriggs, andrew
2026-03-30 04:54:17 +00:00

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/*
* Copyright (c) 1995, 2026, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Oracle designates this
* particular file as subject to the "Classpath" exception as provided
* by Oracle in the LICENSE file that accompanied this code.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
* or visit www.oracle.com if you need additional information or have any
* questions.
*/
#undef _LARGEFILE64_SOURCE
#define _LARGEFILE64_SOURCE 1
#include "jni.h"
#include "jvm.h"
#include "jvm_md.h"
#include "jni_util.h"
#include "io_util.h"
/*
* Platform-specific support for java.lang.Process
*/
#include <assert.h>
#include <stddef.h>
#include <stdlib.h>
#include <sys/types.h>
#include <ctype.h>
#include <sys/wait.h>
#include <signal.h>
#include <string.h>
#include <fcntl.h>
#include <stdbool.h>
#include <unistd.h>
#include <spawn.h>
#include "childproc.h"
#include "childproc_errorcodes.h"
/*
*
* When starting a child on Unix, we need to do three things:
* - fork off
* - in the child process, do some pre-exec work: duping/closing file
* descriptors to set up stdio-redirection, setting environment variables,
* changing paths...
* - then exec(2) the target binary
*
* On the OS-side are three ways to fork off, but we only use two of them:
*
* A) fork(2). Portable and safe (no side effects) but could fail on very ancient
* Unices that don't employ COW on fork(2). The modern platforms we support
* (Linux, MacOS, AIX) all do. It may have a small performance penalty compared
* to modern posix_spawn(3) implementations - see below.
* fork(2) can be used by specifying -Djdk.lang.Process.launchMechanism=FORK when starting
* the (parent process) JVM.
*
* B) vfork(2): Portable and fast but very unsafe. For details, see JDK-8357090.
* We supported this mode in older releases but removed support for it in JDK 27.
* Modern posix_spawn(3) implementations use techniques similar to vfork(2), but
* in a much safer way
*
* C) posix_spawn(3): Where fork/vfork/clone all fork off the process and leave
* pre-exec work and calling exec(2) to the user, posix_spawn(3) offers the user
* fork+exec-like functionality in one package, similar to CreateProcess() on Windows.
* It is not a system call, but a wrapper implemented in user-space libc in terms
* of one of (fork|vfork|clone)+exec - so whether or not it has advantages over calling
* the naked (fork|vfork|clone) functions depends on how posix_spawn(3) is implemented.
* Modern posix_spawn(3) implementations, on Linux, use clone(2) with CLONE_VM | CLONE_VFORK,
* giving us the best ratio between performance and safety.
* Note however, that posix_spawn(3) can be buggy, depending on the libc implementation.
* E.g., on MacOS, it is still fully not POSIX-compliant. Therefore, we need to retain the
* FORK mode as a backup.
* Posix_spawn mode is used by default, but can be explicitly enabled using
* -Djdk.lang.Process.launchMechanism=POSIX_SPAWN when starting the (parent process) JVM.
*
* Note that when using posix_spawn(3), we exec twice: first a tiny binary called
* the jspawnhelper, then in the jspawnhelper we do the pre-exec work and exec a
* second time, this time the target binary (similar to the "exec-twice-technique"
* described in https://mail.openjdk.org/pipermail/core-libs-dev/2018-September/055333.html).
*
* This is a JDK-specific implementation detail which just happens to be
* implemented for jdk.lang.Process.launchMechanism=POSIX_SPAWN.
*
* --- Linux-specific ---
*
* How does glibc implement posix_spawn?
*
* Before glibc 2.4 (released 2006), posix_spawn(3) used just fork(2)/exec(2). From
* glibc 2.4 up to and including 2.23, it used either fork(2) or vfork(2). None of these
* versions still matter.
*
* Since glibc >= 2.24, glibc uses clone+exec with CLONE_VM | CLONE_VFORK to emulate vfork
* performance but without the inherent dangers (we run inside the parent's memory image
* and stop the parent for as long as it takes the child process to exec).
*
* ---
*
* How does muslc implement posix_spawn?
*
* They always did use the clone (.. CLONE_VM | CLONE_VFORK ...)
* technique. So we are safe to use posix_spawn() here regardless of muslc
* version.
*
* </Linux-specific>
*
* Based on the above analysis, we are currently defaulting to posix_spawn()
* on all Unices including Linux.
*/
static void
setSIGCHLDHandler(JNIEnv *env)
{
/* There is a subtle difference between having the signal handler
* for SIGCHLD be SIG_DFL and SIG_IGN. We cannot obtain process
* termination information for child processes if the signal
* handler is SIG_IGN. It must be SIG_DFL.
*
* We used to set the SIGCHLD handler only on Linux, but it's
* safest to set it unconditionally.
*
* Consider what happens if java's parent process sets the SIGCHLD
* handler to SIG_IGN. Normally signal handlers are inherited by
* children, but SIGCHLD is a controversial case. Solaris appears
* to always reset it to SIG_DFL, but this behavior may be
* non-standard-compliant, and we shouldn't rely on it.
*
* References:
* https://pubs.opengroup.org/onlinepubs/7908799/xsh/exec.html
*/
struct sigaction sa;
sa.sa_handler = SIG_DFL;
sigemptyset(&sa.sa_mask);
sa.sa_flags = SA_NOCLDSTOP | SA_RESTART;
if (sigaction(SIGCHLD, &sa, NULL) < 0)
JNU_ThrowInternalError(env, "Can't set SIGCHLD handler");
}
static void*
xmalloc(JNIEnv *env, size_t size)
{
void *p = malloc(size);
if (p == NULL)
JNU_ThrowOutOfMemoryError(env, NULL);
return p;
}
#define NEW(type, n) ((type *) xmalloc(env, (n) * sizeof(type)))
/**
* If PATH is not defined, the OS provides some default value.
* Unfortunately, there's no portable way to get this value.
* Fortunately, it's only needed if the child has PATH while we do not.
*/
static const char*
defaultPath(void)
{
return ":/bin:/usr/bin";
}
static const char*
effectivePath(void)
{
const char *s = getenv("PATH");
return (s != NULL) ? s : defaultPath();
}
static int
countOccurrences(const char *s, char c)
{
int count;
for (count = 0; *s != '\0'; s++)
count += (*s == c);
return count;
}
static const char * const *
effectivePathv(JNIEnv *env)
{
char *p;
int i;
const char *path = effectivePath();
int count = countOccurrences(path, ':') + 1;
size_t pathvsize = sizeof(const char *) * (count+1);
size_t pathsize = strlen(path) + 1;
const char **pathv = (const char **) xmalloc(env, pathvsize + pathsize);
if (pathv == NULL)
return NULL;
p = (char *) pathv + pathvsize;
memcpy(p, path, pathsize);
/* split PATH by replacing ':' with NULs; empty components => "." */
for (i = 0; i < count; i++) {
char *q = p + strcspn(p, ":");
pathv[i] = (p == q) ? "." : p;
*q = '\0';
p = q + 1;
}
pathv[count] = NULL;
return pathv;
}
JNIEXPORT void JNICALL
Java_java_lang_ProcessImpl_init(JNIEnv *env, jclass clazz)
{
parentPathv = effectivePathv(env);
CHECK_NULL(parentPathv);
setSIGCHLDHandler(env);
}
#ifndef WIFEXITED
#define WIFEXITED(status) (((status)&0xFF) == 0)
#endif
#ifndef WEXITSTATUS
#define WEXITSTATUS(status) (((status)>>8)&0xFF)
#endif
#ifndef WIFSIGNALED
#define WIFSIGNALED(status) (((status)&0xFF) > 0 && ((status)&0xFF00) == 0)
#endif
#ifndef WTERMSIG
#define WTERMSIG(status) ((status)&0x7F)
#endif
#ifndef VERSION_STRING
#error VERSION_STRING must be defined
#endif
static const char *
getBytes(JNIEnv *env, jbyteArray arr)
{
return arr == NULL ? NULL :
(const char*) (*env)->GetByteArrayElements(env, arr, NULL);
}
static void
releaseBytes(JNIEnv *env, jbyteArray arr, const char* parr)
{
if (parr != NULL)
(*env)->ReleaseByteArrayElements(env, arr, (jbyte*) parr, JNI_ABORT);
}
#define IOE_FORMAT "%s, error: %d (%s) %s"
#define SPAWN_HELPER_INTERNAL_ERROR_MSG "\n" \
"Possible reasons:\n" \
" - Spawn helper ran into JDK version mismatch\n" \
" - Spawn helper ran into unexpected internal error\n" \
" - Spawn helper was terminated by another process\n" \
"Possible solutions:\n" \
" - Restart JVM, especially after in-place JDK updates\n" \
" - Check system logs for JDK-related errors\n" \
" - Re-install JDK to fix permission/versioning problems\n" \
" - Switch to legacy launch mechanism with -Djdk.lang.Process.launchMechanism=FORK\n"
static void
throwIOExceptionImpl(JNIEnv *env, int errnum, const char *externalDetail, const char *internalDetail)
{
const char *errorDetail;
char *errmsg;
size_t fmtsize;
char tmpbuf[1024];
jstring s;
if (errnum != 0) {
int ret = getErrorString(errnum, tmpbuf, sizeof(tmpbuf));
if (ret != EINVAL) {
errorDetail = tmpbuf;
} else {
errorDetail = "unknown";
}
} else {
errorDetail = "none";
}
/* ASCII Decimal representation uses 2.4 times as many bits as binary. */
fmtsize = sizeof(IOE_FORMAT) + strlen(externalDetail) + 3 * sizeof(errnum) + strlen(errorDetail) + strlen(internalDetail) + 1;
errmsg = NEW(char, fmtsize);
if (errmsg == NULL)
return;
snprintf(errmsg, fmtsize, IOE_FORMAT, externalDetail, errnum, errorDetail, internalDetail);
s = JNU_NewStringPlatform(env, errmsg);
if (s != NULL) {
jobject x = JNU_NewObjectByName(env, "java/io/IOException",
"(Ljava/lang/String;)V", s);
if (x != NULL)
(*env)->Throw(env, x);
}
free(errmsg);
}
/**
* Throws IOException that signifies an internal error, e.g. spawn helper failure.
*/
static void
throwInternalIOException(JNIEnv *env, int errnum, const char *externalDetail, int mode)
{
switch (mode) {
case MODE_POSIX_SPAWN:
throwIOExceptionImpl(env, errnum, externalDetail, SPAWN_HELPER_INTERNAL_ERROR_MSG);
break;
default:
throwIOExceptionImpl(env, errnum, externalDetail, "");
}
}
/**
* Throws IOException that signifies a normal error.
*/
static void
throwIOException(JNIEnv *env, int errnum, const char *externalDetail)
{
throwIOExceptionImpl(env, errnum, externalDetail, "");
}
/**
* Throws an IOException with a message composed from the result of waitpid status.
*/
static void throwExitCause(JNIEnv *env, int pid, int status, int mode) {
char ebuf[128];
if (WIFEXITED(status)) {
snprintf(ebuf, sizeof ebuf,
"Failed to exec spawn helper: pid: %d, exit code: %d",
pid, WEXITSTATUS(status));
} else if (WIFSIGNALED(status)) {
snprintf(ebuf, sizeof ebuf,
"Failed to exec spawn helper: pid: %d, signal: %d",
pid, WTERMSIG(status));
} else {
snprintf(ebuf, sizeof ebuf,
"Failed to exec spawn helper: pid: %d, status: 0x%08x",
pid, status);
}
throwInternalIOException(env, 0, ebuf, mode);
}
#ifdef DEBUG_PROCESS
/* Debugging process code is difficult; where to write debug output? */
static void
debugPrint(char *format, ...)
{
FILE *tty = fopen("/dev/tty", "w");
va_list ap;
va_start(ap, format);
vfprintf(tty, format, ap);
va_end(ap);
fclose(tty);
}
#endif /* DEBUG_PROCESS */
static void
copyPipe(int from[2], int to[2])
{
to[0] = from[0];
to[1] = from[1];
}
/* arg is an array of pointers to 0 terminated strings. array is terminated
* by a null element.
*
* *nelems and *nbytes receive the number of elements of array (incl 0)
* and total number of bytes (incl. 0)
* Note. An empty array will have one null element
* But if arg is null, then *nelems set to 0, and *nbytes to 0
*/
static void arraysize(const char * const *arg, int *nelems, int *nbytes)
{
int bytes, count;
const char * const *a = arg;
if (arg == 0) {
*nelems = 0;
*nbytes = 0;
return;
}
/* count the array elements and number of bytes */
for (count=0, bytes=0; *a != 0; count++, a++) {
bytes += strlen(*a)+1;
}
*nbytes = bytes;
*nelems = count+1;
}
/* copy the strings from arg[] into buf, starting at given offset
* return new offset to next free byte
*/
static int copystrings(char *buf, int offset, const char * const *arg) {
char *p;
const char * const *a;
int count=0;
if (arg == 0) {
return offset;
}
for (p=buf+offset, a=arg; *a != 0; a++) {
int len = strlen(*a) +1;
memcpy(p, *a, len);
p += len;
count += len;
}
return offset+count;
}
/**
* We are unusually paranoid; use of vfork is
* especially likely to tickle gcc/glibc bugs.
*/
#ifdef __attribute_noinline__ /* See: sys/cdefs.h */
__attribute_noinline__
#endif
static pid_t
forkChild(ChildStuff *c) {
pid_t resultPid;
/*
* From Solaris fork(2): In Solaris 10, a call to fork() is
* identical to a call to fork1(); only the calling thread is
* replicated in the child process. This is the POSIX-specified
* behavior for fork().
*/
resultPid = fork();
if (resultPid == 0) {
childProcess(c);
}
assert(resultPid != 0); /* childProcess never returns */
return resultPid;
}
/* Given two fds, one of which has to be -1, the other one has to be valid,
* return the valid one. */
static int eitherOneOf(int fd1, int fd2) {
if (fd2 == -1) {
assert(fdIsValid(fd1));
return fd1;
}
assert(fd1 == -1);
assert(fdIsValid(fd2));
return fd2;
}
static int call_posix_spawn_file_actions_adddup2(posix_spawn_file_actions_t *file_actions, int filedes, int newfiledes) {
#ifdef __APPLE__
/* MacOS is not POSIX-compliant: dup2 file actions specifying the same fd as source and destination
* should be handled as no-op according to spec, but they cause EBADF. */
if (filedes == newfiledes) {
return 0;
}
#endif
return posix_spawn_file_actions_adddup2(file_actions, filedes, newfiledes);
}
static pid_t
spawnChild(JNIEnv *env, jobject process, ChildStuff *c, const char *helperpath) {
pid_t resultPid;
int offset, rval, bufsize, magic;
char* buf;
char* hlpargs[3];
SpawnInfo sp;
posix_spawn_file_actions_t file_actions;
int child_stdin, child_stdout, child_stderr, child_childenv, child_fail = -1;
/* NULL-terminated argv array.
* argv[0] contains path to jspawnhelper, to follow conventions.
* argv[1] contains the version string as argument to jspawnhelper
*/
hlpargs[0] = (char*)helperpath;
hlpargs[1] = VERSION_STRING;
hlpargs[2] = NULL;
/* Following items are sent down the pipe to the helper
* after it is spawned.
* All strings are null terminated. All arrays of strings
* have an empty string for termination.
* - the ChildStuff struct
* - the SpawnInfo struct
* - the argv strings array
* - the envv strings array
* - the home directory string
* - the parentPath string
* - the parentPathv array
*/
/* First calculate the sizes */
arraysize(c->argv, &sp.nargv, &sp.argvBytes);
bufsize = sp.argvBytes;
arraysize(c->envv, &sp.nenvv, &sp.envvBytes);
bufsize += sp.envvBytes;
sp.dirlen = c->pdir == 0 ? 0 : strlen(c->pdir)+1;
bufsize += sp.dirlen;
arraysize(parentPathv, &sp.nparentPathv, &sp.parentPathvBytes);
bufsize += sp.parentPathvBytes;
/* Prepare file descriptors for jspawnhelper and the target binary. */
/* 0: copy of either "in" pipe read fd or the stdin redirect fd */
child_stdin = eitherOneOf(c->fds[0], c->in[0]);
/* 1: copy of either "out" pipe write fd or the stdout redirect fd */
child_stdout = eitherOneOf(c->fds[1], c->out[1]);
/* 2: redirectErrorStream=1: redirected to child's stdout (Order matters!)
* redirectErrorStream=0: copy of either "err" pipe write fd or stderr redirect fd. */
if (c->redirectErrorStream) {
child_stderr = STDOUT_FILENO; /* Note: this refers to the future stdout in the child process */
} else {
child_stderr = eitherOneOf(c->fds[2], c->err[1]);
}
/* 3: copy of the "fail" pipe write fd */
child_fail = c->fail[1];
/* 4: copy of the "childenv" pipe read end */
child_childenv = c->childenv[0];
assert(fdIsValid(child_stdin));
assert(fdIsValid(child_stdout));
assert(fdIsValid(child_stderr));
assert(fdIsPipe(child_fail));
assert(fdIsPipe(child_childenv));
/* This must always hold true, unless someone deliberately closed 0, 1, or 2 in the parent JVM. */
assert(child_fail > STDERR_FILENO);
assert(child_childenv > STDERR_FILENO);
/* Slot in dup2 file actions. */
posix_spawn_file_actions_init(&file_actions);
#ifdef __APPLE__
/* On MacOS, posix_spawn does not behave in a POSIX-conform way in that the
* kernel closes CLOEXEC file descriptors too early for dup2 file actions to
* copy them after the fork. We have to explicitly prevent that by calling a
* propietary API. */
posix_spawn_file_actions_addinherit_np(&file_actions, child_stdin);
posix_spawn_file_actions_addinherit_np(&file_actions, child_stdout);
posix_spawn_file_actions_addinherit_np(&file_actions, child_stderr);
posix_spawn_file_actions_addinherit_np(&file_actions, child_fail);
posix_spawn_file_actions_addinherit_np(&file_actions, child_childenv);
#endif
/* First dup2 stdin/out/err to 0,1,2. After this, we can safely dup2 over the
* original stdin/out/err. */
if (call_posix_spawn_file_actions_adddup2(&file_actions, child_stdin, STDIN_FILENO) != 0 ||
call_posix_spawn_file_actions_adddup2(&file_actions, child_stdout, STDOUT_FILENO) != 0 ||
/* Order matters: stderr may be redirected to stdout, so this dup2 must happen after the stdout one. */
call_posix_spawn_file_actions_adddup2(&file_actions, child_stderr, STDERR_FILENO) != 0)
{
return -1;
}
/* We dup2 with one intermediary step to prevent accidentally dup2'ing over child_childenv. */
const int tmp_child_childenv = child_fail < 10 ? 10 : child_fail - 1;
if (call_posix_spawn_file_actions_adddup2(&file_actions, child_childenv, tmp_child_childenv) != 0 ||
call_posix_spawn_file_actions_adddup2(&file_actions, child_fail, FAIL_FILENO) != 0 ||
call_posix_spawn_file_actions_adddup2(&file_actions, tmp_child_childenv, CHILDENV_FILENO) != 0)
{
return -1;
}
/* Since we won't use these in jspawnhelper, reset them all */
c->in[0] = c->in[1] = c->out[0] = c->out[1] =
c->err[0] = c->err[1] = c->fail[0] = c->fail[1] =
c->fds[0] = c->fds[1] = c->fds[2] = -1;
c->redirectErrorStream = false;
rval = posix_spawn(&resultPid, helperpath, &file_actions, 0, (char * const *) hlpargs, environ);
if (rval != 0) {
return -1;
}
#ifdef DEBUG
jtregSimulateCrash(resultPid, 1);
#endif
/* now the lengths are known, copy the data */
buf = NEW(char, bufsize);
if (buf == 0) {
return -1;
}
offset = copystrings(buf, 0, &c->argv[0]);
if (c->envv != NULL) {
offset = copystrings(buf, offset, &c->envv[0]);
}
if (c->pdir != NULL) {
if (sp.dirlen > 0) {
memcpy(buf+offset, c->pdir, sp.dirlen);
offset += sp.dirlen;
}
} else {
if (sp.dirlen > 0) {
free(buf);
return -1;
}
}
offset = copystrings(buf, offset, parentPathv);
assert(offset == bufsize);
magic = magicNumber();
/* write the two structs and the data buffer */
if (writeFully(c->childenv[1], (char *)&magic, sizeof(magic)) != sizeof(magic)) { // magic number first
free(buf);
return -1;
}
#ifdef DEBUG
jtregSimulateCrash(resultPid, 2);
#endif
if (writeFully(c->childenv[1], (char *)c, sizeof(*c)) != sizeof(*c) ||
writeFully(c->childenv[1], (char *)&sp, sizeof(sp)) != sizeof(sp) ||
writeFully(c->childenv[1], buf, bufsize) != bufsize) {
free(buf);
return -1;
}
/* We're done. Let jspwanhelper know he can't expect any more data from us. */
close(c->childenv[1]);
c->childenv[1] = -1;
free(buf);
#ifdef DEBUG
jtregSimulateCrash(resultPid, 3);
#endif
/* In this mode an external main() in invoked which calls back into
* childProcess() in this file, rather than directly
* via the statement below */
return resultPid;
}
/*
* Start a child process running function childProcess.
* This function only returns in the parent.
*/
static pid_t
startChild(JNIEnv *env, jobject process, ChildStuff *c, const char *helperpath) {
switch (c->mode) {
case MODE_FORK:
return forkChild(c);
case MODE_POSIX_SPAWN:
return spawnChild(env, process, c, helperpath);
default:
return -1;
}
}
static int pipeSafely(int fd[2]) {
/* Pipe filedescriptors must be CLOEXEC as early as possible - ideally from the point of
* creation on - since at any moment a concurrent (third-party) fork() could inherit copies
* of these descriptors and accidentally keep the pipes open. That could cause the parent
* process to hang (see e.g. JDK-8377907).
* We use pipe2(2), if we have it. If we don't, we use pipe(2) + fcntl(2) immediately.
* The latter is still racy and can therefore still cause hangs as described in JDK-8377907,
* but at least the dangerous time window is as short as we can make it.
*/
int rc = -1;
#ifdef HAVE_PIPE2
rc = pipe2(fd, O_CLOEXEC);
#else
rc = pipe(fd);
if (rc == 0) {
fcntl(fd[0], F_SETFD, FD_CLOEXEC);
fcntl(fd[1], F_SETFD, FD_CLOEXEC);
}
#endif /* HAVE_PIPE2 */
assert(fdIsCloexec(fd[0]));
assert(fdIsCloexec(fd[1]));
return rc;
}
JNIEXPORT jint JNICALL
Java_java_lang_ProcessImpl_forkAndExec(JNIEnv *env,
jobject process,
jint mode,
jbyteArray helperpath,
jbyteArray prog,
jbyteArray argBlock, jint argc,
jbyteArray envBlock, jint envc,
jbyteArray dir,
jintArray std_fds,
jboolean redirectErrorStream)
{
int resultPid = -1;
int in[2], out[2], err[2], fail[2], childenv[2];
jint *fds = NULL;
const char *phelperpath = NULL;
const char *pprog = NULL;
const char *pargBlock = NULL;
const char *penvBlock = NULL;
ChildStuff *c;
in[0] = in[1] = out[0] = out[1] = err[0] = err[1] = fail[0] = fail[1] = -1;
childenv[0] = childenv[1] = -1;
// Reset errno to protect against bogus error messages
errno = 0;
if ((c = NEW(ChildStuff, 1)) == NULL) return -1;
c->argv = NULL;
c->envv = NULL;
c->pdir = NULL;
/* Convert prog + argBlock into a char ** argv.
* Add one word room for expansion of argv for use by
* execve_as_traditional_shell_script.
* This word is also used when using posix_spawn mode
*/
assert(prog != NULL && argBlock != NULL);
if ((phelperpath = getBytes(env, helperpath)) == NULL) goto Catch;
if ((pprog = getBytes(env, prog)) == NULL) goto Catch;
if ((pargBlock = getBytes(env, argBlock)) == NULL) goto Catch;
if ((c->argv = NEW(const char *, argc + 3)) == NULL) goto Catch;
c->argv[0] = pprog;
c->argc = argc + 2;
initVectorFromBlock(c->argv+1, pargBlock, argc);
if (envBlock != NULL) {
/* Convert envBlock into a char ** envv */
if ((penvBlock = getBytes(env, envBlock)) == NULL) goto Catch;
if ((c->envv = NEW(const char *, envc + 1)) == NULL) goto Catch;
initVectorFromBlock(c->envv, penvBlock, envc);
}
if (dir != NULL) {
if ((c->pdir = getBytes(env, dir)) == NULL) goto Catch;
}
assert(std_fds != NULL);
fds = (*env)->GetIntArrayElements(env, std_fds, NULL);
if (fds == NULL) goto Catch;
if ((fds[0] == -1 && pipeSafely(in) < 0) ||
(fds[1] == -1 && pipeSafely(out) < 0) ||
(fds[2] == -1 && !redirectErrorStream && pipeSafely(err) < 0) ||
(pipeSafely(childenv) < 0) ||
(pipeSafely(fail) < 0)) {
throwInternalIOException(env, errno, "Bad file descriptor", mode);
goto Catch;
}
c->fds[0] = fds[0];
c->fds[1] = fds[1];
c->fds[2] = fds[2];
copyPipe(in, c->in);
copyPipe(out, c->out);
copyPipe(err, c->err);
copyPipe(fail, c->fail);
copyPipe(childenv, c->childenv);
c->redirectErrorStream = redirectErrorStream;
c->mode = mode;
/* In posix_spawn mode, require the child process to signal aliveness
* right after it comes up. This is because there are implementations of
* posix_spawn() which do not report failed exec()s back to the caller
* (e.g. glibc, see JDK-8223777). In those cases, the fork() will have
* worked and successfully started the child process, but the exec() will
* have failed. There is no way for us to distinguish this from a target
* binary just exiting right after start.
*
* Note that we could do this additional handshake in all modes but for
* prudence only do it when it is needed (in posix_spawn mode). */
c->sendAlivePing = (mode == MODE_POSIX_SPAWN) ? 1 : 0;
resultPid = startChild(env, process, c, phelperpath);
assert(resultPid != 0);
if (resultPid < 0) {
char * failMessage = "unknown";
switch (c->mode) {
case MODE_FORK:
failMessage = "fork failed";
break;
case MODE_POSIX_SPAWN:
failMessage = "posix_spawn failed";
break;
}
throwInternalIOException(env, errno, failMessage, c->mode);
goto Catch;
}
close(fail[1]); fail[1] = -1; /* See: WhyCantJohnnyExec (childproc.c) */
errcode_t errcode;
/* If we expect the child to ping aliveness, wait for it. */
if (c->sendAlivePing) {
switch(readFully(fail[0], &errcode, sizeof(errcode))) {
case 0: /* First exec failed; */
{
int tmpStatus = 0;
int p = waitpid(resultPid, &tmpStatus, 0);
throwExitCause(env, p, tmpStatus, c->mode);
goto Catch;
}
case sizeof(errcode):
if (errcode.step != ESTEP_CHILD_ALIVE) {
/* This can happen if the child process encounters an error
* before or during initial handshake with the parent. */
char msg[256];
snprintf(msg, sizeof(msg),
"Bad early code from spawn helper " ERRCODE_FORMAT " (Failed to exec spawn helper)",
ERRCODE_FORMAT_ARGS(errcode));
throwInternalIOException(env, 0, msg, c->mode);
goto Catch;
}
break;
default:
throwInternalIOException(env, errno, "Read failed", c->mode);
goto Catch;
}
}
switch (readFully(fail[0], &errcode, sizeof(errcode))) {
case 0: break; /* Exec succeeded */
case sizeof(errcode):
/* Always reap first! */
waitpid(resultPid, NULL, 0);
/* Most of these errors are implementation errors and should result in an internal IOE, but
* a few can be caused by bad user input and need to be communicated to the end user. */
switch(errcode.step) {
case ESTEP_CHDIR_FAIL:
throwIOException(env, errcode.errno_, "Failed to access working directory");
break;
case ESTEP_EXEC_FAIL:
throwIOException(env, errcode.errno_, "Exec failed");
break;
default: {
/* Probably implementation error */
char msg[256];
snprintf(msg, sizeof(msg),
"Bad code from spawn helper " ERRCODE_FORMAT " (Failed to exec spawn helper)",
ERRCODE_FORMAT_ARGS(errcode));
throwInternalIOException(env, 0, msg, c->mode);
}
};
goto Catch;
default:
throwInternalIOException(env, errno, "Read failed", c->mode);
goto Catch;
}
fds[0] = (in [1] != -1) ? in [1] : -1;
fds[1] = (out[0] != -1) ? out[0] : -1;
fds[2] = (err[0] != -1) ? err[0] : -1;
Finally:
/* Always clean up the child's side of the pipes */
closeSafely(in [0]);
closeSafely(out[1]);
closeSafely(err[1]);
/* Always clean up fail and childEnv descriptors */
closeSafely(fail[0]);
closeSafely(fail[1]);
/* We use 'c->childenv' here rather than 'childenv' because 'spawnChild()' might have
* already closed 'c->childenv[1]' and signaled this by setting 'c->childenv[1]' to '-1'.
* Otherwise 'c->childenv' and 'childenv' are the same because we just copied 'childenv'
* to 'c->childenv' (with 'copyPipe()') before calling 'startChild()'. */
closeSafely(c->childenv[0]);
closeSafely(c->childenv[1]);
releaseBytes(env, helperpath, phelperpath);
releaseBytes(env, prog, pprog);
releaseBytes(env, argBlock, pargBlock);
releaseBytes(env, envBlock, penvBlock);
releaseBytes(env, dir, c->pdir);
free(c->argv);
free(c->envv);
free(c);
if (fds != NULL)
(*env)->ReleaseIntArrayElements(env, std_fds, fds, 0);
return resultPid;
Catch:
/* Clean up the parent's side of the pipes in case of failure only */
closeSafely(in [1]); in[1] = -1;
closeSafely(out[0]); out[0] = -1;
closeSafely(err[0]); err[0] = -1;
goto Finally;
}
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