1 files changed, 154 insertions, 0 deletions
diff --git a/libgo/syscalls/exec_helpers.go b/libgo/syscalls/exec_helpers.go
new file mode 100644
index 000000000..c8a68a058
--- /dev/null
+++ b/libgo/syscalls/exec_helpers.go
@@ -0,0 +1,154 @@
+// exec_helpers.go -- helper functions used with fork, exec, wait.
+
+// Copyright 2010 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package syscall
+
+import "sync"
+
+// Lock synchronizing creation of new file descriptors with fork.
+//
+// We want the child in a fork/exec sequence to inherit only the
+// file descriptors we intend.  To do that, we mark all file
+// descriptors close-on-exec and then, in the child, explicitly
+// unmark the ones we want the exec'ed program to keep.
+// Unix doesn't make this easy: there is, in general, no way to
+// allocate a new file descriptor close-on-exec.  Instead you
+// have to allocate the descriptor and then mark it close-on-exec.
+// If a fork happens between those two events, the child's exec
+// will inherit an unwanted file descriptor.
+//
+// This lock solves that race: the create new fd/mark close-on-exec
+// operation is done holding ForkLock for reading, and the fork itself
+// is done holding ForkLock for writing.  At least, that's the idea.
+// There are some complications.
+//
+// Some system calls that create new file descriptors can block
+// for arbitrarily long times: open on a hung NFS server or named
+// pipe, accept on a socket, and so on.  We can't reasonably grab
+// the lock across those operations.
+//
+// It is worse to inherit some file descriptors than others.
+// If a non-malicious child accidentally inherits an open ordinary file,
+// that's not a big deal.  On the other hand, if a long-lived child
+// accidentally inherits the write end of a pipe, then the reader
+// of that pipe will not see EOF until that child exits, potentially
+// causing the parent program to hang.  This is a common problem
+// in threaded C programs that use popen.
+//
+// Luckily, the file descriptors that are most important not to
+// inherit are not the ones that can take an arbitrarily long time
+// to create: pipe returns instantly, and the net package uses
+// non-blocking I/O to accept on a listening socket.
+// The rules for which file descriptor-creating operations use the
+// ForkLock are as follows:
+//
+// 1) Pipe.    Does not block.  Use the ForkLock.
+// 2) Socket.  Does not block.  Use the ForkLock.
+// 3) Accept.  If using non-blocking mode, use the ForkLock.
+//             Otherwise, live with the race.
+// 4) Open.    Can block.  Use O_CLOEXEC if available (Linux).
+//             Otherwise, live with the race.
+// 5) Dup.     Does not block.  Use the ForkLock.
+//             On Linux, could use fcntl F_DUPFD_CLOEXEC
+//             instead of the ForkLock, but only for dup(fd, -1).
+
+type WaitStatus int
+
+var ForkLock sync.RWMutex
+
+// Convert array of string to array
+// of NUL-terminated byte pointer.
+func StringArrayPtr(ss []string) []*byte {
+	bb := make([]*byte, len(ss)+1);
+	for i := 0; i < len(ss); i++ {
+		bb[i] = StringBytePtr(ss[i]);
+	}
+	bb[len(ss)] = nil;
+	return bb;
+}
+
+func CloseOnExec(fd int) {
+	fcntl(fd, F_SETFD, FD_CLOEXEC);
+}
+
+func SetNonblock(fd int, nonblocking bool) (errno int) {
+	flag, err := fcntl(fd, F_GETFL, 0);
+	if err != 0 {
+		return err;
+	}
+	if nonblocking {
+		flag |= O_NONBLOCK;
+	} else {
+		flag &= ^O_NONBLOCK;
+	}
+	flag, err = fcntl(fd, F_SETFL, flag);
+	return err;
+}
+
+// Wait status is 7 bits at bottom, either 0 (exited),
+// 0x7F (stopped), or a signal number that caused an exit.
+// The 0x80 bit is whether there was a core dump.
+// An extra number (exit code, signal causing a stop)
+// is in the high bits.  At least that's the idea.
+// There are various irregularities.  For example, the
+// "continued" status is 0xFFFF, distinguishing itself
+// from stopped via the core dump bit.
+
+const (
+	mask = 0x7F;
+	core = 0x80;
+	exited = 0x00;
+	stopped = 0x7F;
+	shift = 8;
+)
+
+func (w WaitStatus) Exited() bool {
+	return w&mask == exited;
+}
+
+func (w WaitStatus) Signaled() bool {
+	return w&mask != stopped && w&mask != exited;
+}
+
+func (w WaitStatus) Stopped() bool {
+	return w&0xFF == stopped;
+}
+
+func (w WaitStatus) Continued() bool {
+	return w == 0xFFFF;
+}
+
+func (w WaitStatus) CoreDump() bool {
+	return w.Signaled() && w&core != 0;
+}
+
+func (w WaitStatus) ExitStatus() int {
+	if !w.Exited() {
+		return -1;
+	}
+	return int(w >> shift) & 0xFF;
+}
+
+func (w WaitStatus) Signal() int {
+	if !w.Signaled() {
+		return -1;
+	}
+	return int(w & mask);
+}
+
+func (w WaitStatus) StopSignal() int {
+	if !w.Stopped() {
+		return -1;
+	}
+	return int(w >> shift) & 0xFF;
+}
+
+func (w WaitStatus) TrapCause() int {
+	if w.StopSignal() != SIGTRAP {
+		return -1;
+	}
+	return int(w >> shift) >> 8;
+}