1 files changed, 248 insertions, 0 deletions
diff --git a/libgo/syscalls/exec.go b/libgo/syscalls/exec.go
new file mode 100644
index 000000000..d0f56d3b9
--- /dev/null
+++ b/libgo/syscalls/exec.go
@@ -0,0 +1,248 @@
+// exec.go -- fork/exec syscall support.
+
+// Copyright 2009 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.
+
+// Fork, exec, wait, etc.
+
+package syscall
+
+import "unsafe"
+
+func libc_fcntl(fd int, cmd int, arg int) int __asm__ ("fcntl")
+func libc_fork() Pid_t __asm__ ("fork")
+func libc_chdir(name *byte) int __asm__ ("chdir");
+func libc_dup2(int, int) int __asm__ ("dup2")
+func libc_execve(*byte, **byte, **byte) int __asm__ ("execve")
+func libc_sysexit(int) __asm__ ("_exit")
+func libc_wait4(Pid_t, *int, int, *Rusage) Pid_t __asm__ ("wait4")
+
+// Fork, dup fd onto 0..len(fd), and exec(argv0, argvv, envv) in child.
+// If a dup or exec fails, write the errno int to pipe.
+// (Pipe is close-on-exec so if exec succeeds, it will be closed.)
+// In the child, this function must not acquire any locks, because
+// they might have been locked at the time of the fork.  This means
+// no rescheduling, no malloc calls, and no new stack segments.
+func forkAndExecInChild(argv0 *byte, argv []*byte, envv []*byte, traceme bool, dir *byte, fd []int, pipe int) (pid int, err int) {
+	// Declare all variables at top in case any
+	// declarations require heap allocation (e.g., err1).
+	var r1, r2, err1 uintptr;
+	var nextfd int;
+	var i int;
+
+	darwin := OS == "darwin";
+
+	// About to call fork.
+	// No more allocation or calls of non-assembly functions.
+	child := libc_fork();
+	if child == -1 {
+		return 0, GetErrno();
+	}
+
+	if child != 0 {
+		// parent; return PID
+		return int(child), 0
+	}
+
+	// Fork succeeded, now in child.
+
+	// Enable tracing if requested.
+	if traceme {
+		if libc_ptrace(_PTRACE_TRACEME, 0, 0, nil) < 0 {
+			goto childerror;
+		}
+	}
+
+	// Chdir
+	if dir != nil {
+		r := libc_chdir(dir);
+		if r < 0 {
+			goto childerror;
+		}
+	}
+
+	// Pass 1: look for fd[i] < i and move those up above len(fd)
+	// so that pass 2 won't stomp on an fd it needs later.
+	nextfd = int(len(fd));
+	if pipe < nextfd {
+		r := libc_dup2(pipe, nextfd);
+		if r == -1 {
+			goto childerror;
+		}
+		libc_fcntl(nextfd, F_SETFD, FD_CLOEXEC);
+		pipe = nextfd;
+		nextfd++;
+	}
+	for i = 0; i < len(fd); i++ {
+		if fd[i] >= 0 && fd[i] < int(i) {
+			r := libc_dup2(fd[i], nextfd);
+			if r == -1 {
+				goto childerror;
+			}
+			libc_fcntl(nextfd, F_SETFD, FD_CLOEXEC);
+			fd[i] = nextfd;
+			nextfd++;
+			if nextfd == pipe {	// don't stomp on pipe
+				nextfd++;
+			}
+		}
+	}
+
+	// Pass 2: dup fd[i] down onto i.
+	for i = 0; i < len(fd); i++ {
+		if fd[i] == -1 {
+			libc_close(i);
+			continue;
+		}
+		if fd[i] == int(i) {
+			// dup2(i, i) won't clear close-on-exec flag on Linux,
+			// probably not elsewhere either.
+			r := libc_fcntl(fd[i], F_SETFD, 0);
+			if r != 0 {
+				goto childerror;
+			}
+			continue;
+		}
+		// The new fd is created NOT close-on-exec,
+		// which is exactly what we want.
+		r := libc_dup2(fd[i], i);
+		if r == -1 {
+			goto childerror;
+		}
+	}
+
+	// By convention, we don't close-on-exec the fds we are
+	// started with, so if len(fd) < 3, close 0, 1, 2 as needed.
+	// Programs that know they inherit fds >= 3 will need
+	// to set them close-on-exec.
+	for i = len(fd); i < 3; i++ {
+		libc_close(i);
+	}
+
+	// Time to exec.
+	libc_execve(argv0, &argv[0], &envv[0]);
+
+childerror:
+	// send error code on pipe
+	var e uintptr = uintptr(GetErrno());
+	libc_write(pipe, (*byte)(unsafe.Pointer(&e)),
+		   Size_t(unsafe.Sizeof(err1)));
+	for {
+		libc_sysexit(253)
+	}
+
+	// Calling panic is not actually safe,
+	// but the for loop above won't break
+	// and this shuts up the compiler.
+	panic("unreached");
+}
+
+func forkExec(argv0 string, argv []string, envv []string, traceme bool, dir string, fd []int) (pid int, err int) {
+	var p [2]int;
+	var r1 int;
+	var err1 uintptr;
+	var wstatus WaitStatus;
+
+	p[0] = -1;
+	p[1] = -1;
+
+	// Convert args to C form.
+	argv0p := StringBytePtr(argv0);
+	argvp := StringArrayPtr(argv);
+	envvp := StringArrayPtr(envv);
+	var dirp *byte;
+	if len(dir) > 0 {
+		dirp = StringBytePtr(dir);
+	}
+
+	// Acquire the fork lock so that no other threads
+	// create new fds that are not yet close-on-exec
+	// before we fork.
+	ForkLock.Lock();
+
+	// Allocate child status pipe close on exec.
+	if err = Pipe(p[0:]); err != 0 {
+		goto error;
+	}
+	var val int;
+	if val, err = fcntl(p[0], F_SETFD, FD_CLOEXEC); err != 0 {
+		goto error;
+	}
+	if val, err = fcntl(p[1], F_SETFD, FD_CLOEXEC); err != 0 {
+		goto error;
+	}
+
+	// Kick off child.
+	pid, err = forkAndExecInChild(argv0p, argvp, envvp, traceme, dirp, fd, p[1]);
+	if err != 0 {
+	error:
+		if p[0] >= 0 {
+			Close(p[0]);
+			Close(p[1]);
+		}
+		ForkLock.Unlock();
+		return 0, err
+	}
+	ForkLock.Unlock();
+
+	// Read child error status from pipe.
+	Close(p[1]);
+	n := libc_read(p[0], (*byte)(unsafe.Pointer(&err1)),
+		       Size_t(unsafe.Sizeof(err1)));
+	err = 0;
+	if n < 0 {
+		err = GetErrno();
+	}
+	Close(p[0]);
+	if err != 0 || n != 0 {
+		if int(n) == unsafe.Sizeof(err1) {
+			err = int(err1);
+		}
+		if err == 0 {
+			err = EPIPE;
+		}
+
+		// Child failed; wait for it to exit, to make sure
+		// the zombies don't accumulate.
+		pid1, err1 := Wait4(pid, &wstatus, 0, nil);
+		for err1 == EINTR {
+			pid1, err1 = Wait4(pid, &wstatus, 0, nil);
+		}
+		return 0, err
+	}
+
+	// Read got EOF, so pipe closed on exec, so exec succeeded.
+	return pid, 0
+}
+
+// Combination of fork and exec, careful to be thread safe.
+func ForkExec(argv0 string, argv []string, envv []string, dir string, fd []int) (pid int, err int) {
+	return forkExec(argv0, argv, envv, false, dir, fd);
+}
+
+// PtraceForkExec is like ForkExec, but starts the child in a traced state.
+func PtraceForkExec(argv0 string, argv []string, envv []string, dir string, fd []int) (pid int, err int) {
+	return forkExec(argv0, argv, envv, true, dir, fd);
+}
+
+// Ordinary exec.
+func Exec(argv0 string, argv []string, envv []string) (err int) {
+	argv_arg := StringArrayPtr(argv);
+	envv_arg := StringArrayPtr(envv);
+	libc_execve(StringBytePtr(argv0), &argv_arg[0], &envv_arg[0]);
+	return GetErrno();
+}
+
+func Wait4(pid int, wstatus *WaitStatus, options int, rusage *Rusage) (wpid int, errno int) {
+	var status int;
+	r := libc_wait4(Pid_t(pid), &status, options, rusage);
+	wpid = int(r);
+	if r < 0 {
+		errno = GetErrno();
+	}
+	if wstatus != nil {
+		*wstatus = WaitStatus(status);
+	}
+	return;
+}