unix: use posix_spawn instead of fork (#3520)
Remove the conditionals so that posix_spawn will be used whenever possible, and not only on Apple. Tests specifically if posix_spawn works before using it: it is broken on QEMU with glibc, for example, since fork/clone is broken there.
This commit is contained in:
Jameson Nash
GitHub
parent
d19855c702
commit
40d45efebf
@ -33,15 +33,13 @@
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#include <sys/wait.h>
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#include <unistd.h>
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#include <fcntl.h>
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#include <poll.h>
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#include <spawn.h>
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#include <paths.h>
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#include <dlfcn.h>
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#if defined(__APPLE__)
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# include <spawn.h>
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# include <paths.h>
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# include <sys/kauth.h>
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# include <sys/types.h>
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# include <sys/sysctl.h>
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# include <dlfcn.h>
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# include <crt_externs.h>
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# include <xlocale.h>
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# define environ (*_NSGetEnviron())
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@ -53,6 +51,9 @@
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#else
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extern char **environ;
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#ifndef POSIX_SPAWN_SETSID
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# define POSIX_SPAWN_SETSID 0
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#endif
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#endif
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#if defined(__linux__) || \
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@ -70,6 +71,15 @@ extern char **environ;
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#define UV_USE_SIGCHLD
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#endif
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static uv_once_t posix_spawn_init_once = UV_ONCE_INIT;
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static int posix_spawn_can_use_setsid;
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static volatile int posix_spawn_works;
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static struct uv__posix_spawn_fncs_s {
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struct {
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int (*addchdir)(posix_spawn_file_actions_t *, const char *);
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} file_actions;
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} posix_spawn_fncs;
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#ifdef UV_USE_SIGCHLD
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static void uv__chld(uv_signal_t* handle, int signum) {
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@ -423,25 +433,6 @@ static void uv__process_child_init(const uv_process_options_t* options,
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#if defined(__APPLE__)
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typedef struct uv__posix_spawn_fncs_tag {
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struct {
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int (*addchdir_np)(const posix_spawn_file_actions_t *, const char *);
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} file_actions;
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} uv__posix_spawn_fncs_t;
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static uv_once_t posix_spawn_init_once = UV_ONCE_INIT;
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static uv__posix_spawn_fncs_t posix_spawn_fncs;
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static int posix_spawn_can_use_setsid;
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static void uv__spawn_init_posix_spawn_fncs(void) {
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/* Try to locate all non-portable functions at runtime */
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posix_spawn_fncs.file_actions.addchdir_np =
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dlsym(RTLD_DEFAULT, "posix_spawn_file_actions_addchdir_np");
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}
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static void uv__spawn_init_can_use_setsid(void) {
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int which[] = {CTL_KERN, KERN_OSRELEASE};
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unsigned major;
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@ -460,20 +451,52 @@ static void uv__spawn_init_can_use_setsid(void) {
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posix_spawn_can_use_setsid = (major >= 19); /* macOS Catalina */
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}
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#endif
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static void uv__spawn_init_posix_spawn(void) {
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/* Init handles to all potentially non-defined functions */
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uv__spawn_init_posix_spawn_fncs();
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#if !defined(__linux__)
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posix_spawn_works = 1;
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#elif !defined(__ANDROID__)
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pid_t pid;
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int status;
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/* Init feature detection for POSIX_SPAWN_SETSID flag */
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/* Probe whether vfork()/clone(CLONE_VM) correctly shares the address space,
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* i.e. a write by the child before _exit() is visible to the parent once it
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* resumes. On Linux vfork() is equivalent to
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* clone(CLONE_VM|CLONE_VFORK|SIGCHLD). On QEMU and WSL1, CLONE_VM is broken,
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* resulting in glibc errors if we try to use posix_spawn(). */
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posix_spawn_works = 0;
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pid = vfork();
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if (pid == 0) {
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posix_spawn_works = 1;
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_exit(0);
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}
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if (pid > 0)
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waitpid(pid, &status, 0);
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#endif
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/* Try to locate all new functions at runtime.
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* Expected on macOS, glibc, and musl. */
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posix_spawn_fncs.file_actions.addchdir =
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dlsym(RTLD_DEFAULT, "posix_spawn_file_actions_addchdir");
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if (posix_spawn_fncs.file_actions.addchdir == NULL)
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posix_spawn_fncs.file_actions.addchdir =
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dlsym(RTLD_DEFAULT, "posix_spawn_file_actions_addchdir_np");
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#ifdef __APPLE__
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/* Init feature detection for POSIX_SPAWN_SETSID flag. */
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uv__spawn_init_can_use_setsid();
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#elif POSIX_SPAWN_SETSID != 0
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/* Otherwise, if SETSID is defined, we can use it
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* (added in glibc 2.26 circa 2017). */
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posix_spawn_can_use_setsid = 1;
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#endif
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}
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static int uv__spawn_set_posix_spawn_attrs(
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posix_spawnattr_t* attrs,
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const uv__posix_spawn_fncs_t* posix_spawn_fncs,
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const uv_process_options_t* options) {
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int err;
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unsigned int flags;
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@ -495,18 +518,17 @@ static int uv__spawn_set_posix_spawn_attrs(
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}
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/* Set flags for spawn behavior
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* 1) POSIX_SPAWN_CLOEXEC_DEFAULT: (Apple Extension) All descriptors in the
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* 1) POSIX_SPAWN_SETSIGDEF: Signals mentioned in spawn-sigdefault in the
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* spawn attributes will be reset to behave as their default
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* 2) POSIX_SPAWN_SETSIGMASK: Signal mask will be set to the value of
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* spawn-sigmask in attributes
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* 3) POSIX_SPAWN_SETSID: Make the process a new session leader if a detached
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* session was requested.
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* 4) POSIX_SPAWN_CLOEXEC_DEFAULT: (Apple Extension) All descriptors in the
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* parent will be treated as if they had been created with O_CLOEXEC. The
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* only fds that will be passed on to the child are those manipulated by
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* the file actions
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* 2) POSIX_SPAWN_SETSIGDEF: Signals mentioned in spawn-sigdefault in the
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* spawn attributes will be reset to behave as their default
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* 3) POSIX_SPAWN_SETSIGMASK: Signal mask will be set to the value of
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* spawn-sigmask in attributes
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* 4) POSIX_SPAWN_SETSID: Make the process a new session leader if a detached
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* session was requested. */
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flags = POSIX_SPAWN_CLOEXEC_DEFAULT |
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POSIX_SPAWN_SETSIGDEF |
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* the file actions */
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flags = POSIX_SPAWN_SETSIGDEF |
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POSIX_SPAWN_SETSIGMASK;
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if (options->flags & UV_PROCESS_DETACHED) {
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/* If running on a version of macOS where this flag is not supported,
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@ -519,6 +541,9 @@ static int uv__spawn_set_posix_spawn_attrs(
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flags |= POSIX_SPAWN_SETSID;
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}
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#ifdef __APPLE__
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flags |= POSIX_SPAWN_CLOEXEC_DEFAULT;
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#endif
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err = posix_spawnattr_setflags(attrs, flags);
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if (err != 0)
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goto error;
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@ -545,7 +570,6 @@ error:
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static int uv__spawn_set_posix_spawn_file_actions(
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posix_spawn_file_actions_t* actions,
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const uv__posix_spawn_fncs_t* posix_spawn_fncs,
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const uv_process_options_t* options,
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int stdio_count,
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int (*pipes)[2]) {
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@ -562,12 +586,12 @@ static int uv__spawn_set_posix_spawn_file_actions(
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/* Set the current working directory if requested */
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if (options->cwd != NULL) {
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if (posix_spawn_fncs->file_actions.addchdir_np == NULL) {
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if (posix_spawn_fncs.file_actions.addchdir == NULL) {
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err = ENOSYS;
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goto error;
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}
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err = posix_spawn_fncs->file_actions.addchdir_np(actions, options->cwd);
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err = posix_spawn_fncs.file_actions.addchdir(actions, options->cwd);
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if (err != 0)
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goto error;
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}
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@ -580,8 +604,16 @@ static int uv__spawn_set_posix_spawn_file_actions(
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* stdout and stderr go to the same fd, which was not the intention. */
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for (fd = 0; fd < stdio_count; fd++) {
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use_fd = pipes[fd][1];
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#if defined(__APPLE__) || defined(__linux__)
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if (use_fd < 0 || use_fd >= fd)
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continue;
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#else
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/* The behavior of posix_spawn_file_actions_adddup2 may be undefined if
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* use_fd==fd, so we do this extra little dance to copy it up and back, on
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* platforms where we aren't sure if it works. */
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if (use_fd < 0 || use_fd > fd)
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continue;
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#endif
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use_fd = stdio_count;
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for (fd2 = 0; fd2 < stdio_count; fd2++) {
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/* If we were not setting POSIX_SPAWN_CLOEXEC_DEFAULT, we would need to
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@ -623,9 +655,11 @@ static int uv__spawn_set_posix_spawn_file_actions(
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}
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}
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#ifdef __APPLE__
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if (fd == use_fd)
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err = posix_spawn_file_actions_addinherit_np(actions, fd);
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else
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#endif
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err = posix_spawn_file_actions_adddup2(actions, use_fd, fd);
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assert(err != ENOSYS);
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if (err != 0)
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@ -781,22 +815,24 @@ static int uv__spawn_resolve_and_spawn(const uv_process_options_t* options,
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static int uv__spawn_and_init_child_posix_spawn(
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uv_loop_t* loop,
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const uv_process_options_t* options,
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int stdio_count,
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int (*pipes)[2],
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pid_t* pid,
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const uv__posix_spawn_fncs_t* posix_spawn_fncs) {
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pid_t* pid) {
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int err;
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posix_spawnattr_t attrs;
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posix_spawn_file_actions_t actions;
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err = uv__spawn_set_posix_spawn_attrs(&attrs, posix_spawn_fncs, options);
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if (!posix_spawn_works)
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return UV_ENOSYS;
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err = uv__spawn_set_posix_spawn_attrs(&attrs, options);
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if (err != 0)
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goto error;
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/* This may mutate pipes. */
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err = uv__spawn_set_posix_spawn_file_actions(&actions,
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posix_spawn_fncs,
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options,
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stdio_count,
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pipes);
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@ -805,12 +841,23 @@ static int uv__spawn_and_init_child_posix_spawn(
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goto error;
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}
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#ifndef __APPLE__
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/* Acquire write lock to prevent opening new fds in worker threads.
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* Unnecessary on Apple, since we set POSIX_SPAWN_CLOEXEC_DEFAULT. */
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uv_rwlock_wrlock(&loop->cloexec_lock);
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#endif
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/* Try to spawn options->file resolving in the provided environment
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* if any */
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* if any. */
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err = uv__spawn_resolve_and_spawn(options, &attrs, &actions, pid);
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assert(err != ENOSYS);
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/* Destroy the actions/attributes */
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#ifndef __APPLE__
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/* Release lock in parent process. */
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uv_rwlock_wrunlock(&loop->cloexec_lock);
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#endif
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/* Destroy the actions/attributes. */
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(void) posix_spawn_file_actions_destroy(&actions);
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(void) posix_spawnattr_destroy(&attrs);
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@ -819,7 +866,7 @@ error:
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* already destroyed, only the happy path requires cleanup */
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return UV__ERR(err);
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}
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#endif
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static int uv__spawn_and_init_child_fork(const uv_process_options_t* options,
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int stdio_count,
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@ -874,36 +921,21 @@ static int uv__spawn_and_init_child(
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int exec_errorno;
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ssize_t r;
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#if defined(__APPLE__)
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uv_once(&posix_spawn_init_once, uv__spawn_init_posix_spawn);
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/* Special child process spawn case for macOS Big Sur (11.0) onwards
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*
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* Big Sur introduced a significant performance degradation on a call to
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* fork/exec when the process has many pages mmaped in with MAP_JIT, like, say
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* a javascript interpreter. Electron-based applications, for example,
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* are impacted; though the magnitude of the impact depends on how much the
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* app relies on subprocesses.
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*
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* On macOS, though, posix_spawn is implemented in a way that does not
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* exhibit the problem. This block implements the forking and preparation
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* logic with posix_spawn and its related primitives. It also takes advantage of
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* the macOS extension POSIX_SPAWN_CLOEXEC_DEFAULT that makes impossible to
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* leak descriptors to the child process. */
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err = uv__spawn_and_init_child_posix_spawn(options,
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/* Calling posix_spawn is considerably faster, if it supports the given
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* options. The posix_spawn flow will return UV_ENOSYS if any of the
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* posix_spawn_x_np non-standard functions is both _needed_ and _undefined_.
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* In those cases, default back to the fork/execve strategy. For all other
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* errors, just fail. */
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err = uv__spawn_and_init_child_posix_spawn(loop,
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options,
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stdio_count,
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pipes,
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pid,
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&posix_spawn_fncs);
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/* The posix_spawn flow will return UV_ENOSYS if any of the posix_spawn_x_np
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* non-standard functions is both _needed_ and _undefined_. In those cases,
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* default back to the fork/execve strategy. For all other errors, just fail. */
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pid);
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if (err != UV_ENOSYS)
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return err;
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#endif
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/* This pipe is used by the parent to wait until
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* the child has called `execve()`. We need this
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* to avoid the following race condition:
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@ -928,12 +960,12 @@ static int uv__spawn_and_init_child(
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if (err)
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return err;
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/* Acquire write lock to prevent opening new fds in worker threads */
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/* Acquire write lock to prevent opening new fds in worker threads. */
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uv_rwlock_wrlock(&loop->cloexec_lock);
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err = uv__spawn_and_init_child_fork(options, stdio_count, pipes, signal_pipe[1], pid);
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/* Release lock in parent process */
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/* Release lock in parent process. */
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uv_rwlock_wrunlock(&loop->cloexec_lock);
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uv__close(signal_pipe[1]);
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@ -968,6 +1000,7 @@ static int uv__spawn_and_init_child(
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}
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#endif /* ISN'T TARGET_OS_TV || TARGET_OS_WATCH */
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int uv_spawn(uv_loop_t* loop,
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uv_process_t* process,
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const uv_process_options_t* options) {
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Block a user