// About to call fork.
	// No more allocation or calls of non-assembly functions.
	runtime_BeforeFork()
	r1, _, err1 = RawSyscall(SYS_FORK, 0, 0, 0)
	if err1 != 0 {
		runtime_AfterFork()
		return 0, err1
	}

	if r1 != 0 {
		// parent; return PID
		runtime_AfterFork()
		return int(r1), 0
	}

	// Fork succeeded, now in child.

	// Enable tracing if requested.
	if sys.Ptrace {

	// No more allocation or calls of non-assembly functions.
	runtime_BeforeFork()
	r1, _, err1 = RawSyscall(SYS_FORK, 0, 0, 0)
	if err1 != 0 {
		runtime_AfterFork()
		return 0, err1
	}

	if r1 != 0 {
		// parent; return PID
		runtime_AfterFork()
		return int(r1), 0
	}

	// Fork succeeded, now in child.

	// Attach to the given jail, if any. The system call also changes the

	// No more allocation or calls of non-assembly functions.
	runtime_BeforeFork()
	r1, err1 = forkx(0x1) // FORK_NOSIGCHLD
	if err1 != 0 {
		runtime_AfterFork()
		return 0, err1
	}

	if r1 != 0 {
		// parent; return PID
		runtime_AfterFork()
		return int(r1), 0
	}

	// Fork succeeded, now in child.

	// Session ID
	if sys.Setsid {
		_, err1 = setsid()
		if err1 != 0 {

	// No more allocation or calls of non-assembly functions.
	runtime_BeforeFork()
	r1, _, err1 = rawSyscall(abi.FuncPCABI0(libc_fork_trampoline), 0, 0, 0)
	if err1 != 0 {
		runtime_AfterFork()
		return 0, err1
	}

	if r1 != 0 {
		// parent; return PID
		runtime_AfterFork()
		return int(r1), 0
	}

	// Fork succeeded, now in child.

	// Enable tracing if requested.
	if sys.Ptrace {

var (
	none  = [...]byte{'n', 'o', 'n', 'e', 0}
	slash = [...]byte{'/', 0}

	forceClone3 = false // Used by unit tests only.
)

// Implemented in runtime package.
func runtime_BeforeFork()
func runtime_AfterFork()
func runtime_AfterForkInChild()

// Fork, dup fd onto 0..len(fd), and exec(argv0, argvv, envv) in child.
// If a dup or exec fails, write the errno error to pipe.

	// Code between fork and exec must not allocate memory nor even try to grow stack.
	// Here we spoil g.stackguard0 to reliably detect any attempts to grow stack.
	// runtime_AfterFork will undo this in parent process, but not in child.
	gp.stackguard0 = stackFork
}

// Called from syscall package after fork in parent.
//
// syscall_runtime_AfterFork is for package syscall,