code review 126960043: go.sys: copy files from syscall package to go.sys/{plan...

unix/exec_bsd.go

Index: unix/exec_bsd.go
===================================================================
new file mode 100644
--- /dev/null
+++ b/unix/exec_bsd.go
@@ -0,0 +1,247 @@
+// Copyright 2011 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.
+
+// +build darwin dragonfly freebsd netbsd openbsd
+
+package syscall
+
+import (
+	"runtime"
+	"unsafe"
+)
+
+type SysProcAttr struct {
+	Chroot     string      // Chroot.
+	Credential *Credential // Credential.
+	Ptrace     bool        // Enable tracing.
+	Setsid     bool        // Create session.
+	Setpgid    bool        // Set process group ID to new pid (SYSV setpgrp)
+	Setctty    bool        // Set controlling terminal to fd 0
+	Noctty     bool        // Detach fd 0 from controlling terminal
+}
+
+// Implemented in runtime package.
+func runtime_BeforeFork()
+func runtime_AfterFork()
+
+// 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.
+// (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.
+// For the same reason compiler does not race instrument it.
+// The calls to RawSyscall are okay because they are assembly
+// functions that do not grow the stack.
+func forkAndExecInChild(argv0 *byte, argv, envv []*byte, chroot, dir *byte, attr *ProcAttr, sys *SysProcAttr, pipe int) (pid int, err Errno) {
+	// Declare all variables at top in case any
+	// declarations require heap allocation (e.g., err1).
+	var (
+		r1, r2 uintptr
+		err1   Errno
+		nextfd int
+		i      int
+	)
+
+	// guard against side effects of shuffling fds below.
+	// Make sure that nextfd is beyond any currently open files so
+	// that we can't run the risk of overwriting any of them.
+	fd := make([]int, len(attr.Files))
+	nextfd = len(attr.Files)
+	for i, ufd := range attr.Files {
+		if nextfd < int(ufd) {
+			nextfd = int(ufd)
+		}
+		fd[i] = int(ufd)
+	}
+	nextfd++
+
+	darwin := runtime.GOOS == "darwin"
+
+	// About to call fork.
+	// No more allocation or calls of non-assembly functions.
+	runtime_BeforeFork()
+	r1, r2, err1 = RawSyscall(SYS_FORK, 0, 0, 0)
+	if err1 != 0 {
+		runtime_AfterFork()
+		return 0, err1
+	}
+
+	// On Darwin:
+	//	r1 = child pid in both parent and child.
+	//	r2 = 0 in parent, 1 in child.
+	// Convert to normal Unix r1 = 0 in child.
+	if darwin && r2 == 1 {
+		r1 = 0
+	}
+
+	if r1 != 0 {
+		// parent; return PID
+		runtime_AfterFork()
+		return int(r1), 0
+	}
+
+	// Fork succeeded, now in child.
+
+	// Enable tracing if requested.
+	if sys.Ptrace {
+		_, _, err1 = RawSyscall(SYS_PTRACE, uintptr(PTRACE_TRACEME), 0, 0)
+		if err1 != 0 {
+			goto childerror
+		}
+	}
+
+	// Session ID
+	if sys.Setsid {
+		_, _, err1 = RawSyscall(SYS_SETSID, 0, 0, 0)
+		if err1 != 0 {
+			goto childerror
+		}
+	}
+
+	// Set process group
+	if sys.Setpgid {
+		_, _, err1 = RawSyscall(SYS_SETPGID, 0, 0, 0)
+		if err1 != 0 {
+			goto childerror
+		}
+	}
+
+	// Chroot
+	if chroot != nil {
+		_, _, err1 = RawSyscall(SYS_CHROOT, uintptr(unsafe.Pointer(chroot)), 0, 0)
+		if err1 != 0 {
+			goto childerror
+		}
+	}
+
+	// User and groups
+	if cred := sys.Credential; cred != nil {
+		ngroups := uintptr(len(cred.Groups))
+		groups := uintptr(0)
+		if ngroups > 0 {
+			groups = uintptr(unsafe.Pointer(&cred.Groups[0]))
+		}
+		_, _, err1 = RawSyscall(SYS_SETGROUPS, ngroups, groups, 0)
+		if err1 != 0 {
+			goto childerror
+		}
+		_, _, err1 = RawSyscall(SYS_SETGID, uintptr(cred.Gid), 0, 0)
+		if err1 != 0 {
+			goto childerror
+		}
+		_, _, err1 = RawSyscall(SYS_SETUID, uintptr(cred.Uid), 0, 0)
+		if err1 != 0 {
+			goto childerror
+		}
+	}
+
+	// Chdir
+	if dir != nil {
+		_, _, err1 = RawSyscall(SYS_CHDIR, uintptr(unsafe.Pointer(dir)), 0, 0)
+		if err1 != 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.
+	if pipe < nextfd {
+		_, _, err1 = RawSyscall(SYS_DUP2, uintptr(pipe), uintptr(nextfd), 0)
+		if err1 != 0 {
+			goto childerror
+		}
+		RawSyscall(SYS_FCNTL, uintptr(nextfd), F_SETFD, FD_CLOEXEC)
+		pipe = nextfd
+		nextfd++
+	}
+	for i = 0; i < len(fd); i++ {
+		if fd[i] >= 0 && fd[i] < int(i) {
+			_, _, err1 = RawSyscall(SYS_DUP2, uintptr(fd[i]), uintptr(nextfd), 0)
+			if err1 != 0 {
+				goto childerror
+			}
+			RawSyscall(SYS_FCNTL, uintptr(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 {
+			RawSyscall(SYS_CLOSE, uintptr(i), 0, 0)
+			continue
+		}
+		if fd[i] == int(i) {
+			// dup2(i, i) won't clear close-on-exec flag on Linux,
+			// probably not elsewhere either.
+			_, _, err1 = RawSyscall(SYS_FCNTL, uintptr(fd[i]), F_SETFD, 0)
+			if err1 != 0 {
+				goto childerror
+			}
+			continue
+		}
+		// The new fd is created NOT close-on-exec,
+		// which is exactly what we want.
+		_, _, err1 = RawSyscall(SYS_DUP2, uintptr(fd[i]), uintptr(i), 0)
+		if err1 != 0 {
+			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++ {
+		RawSyscall(SYS_CLOSE, uintptr(i), 0, 0)
+	}
+
+	// Detach fd 0 from tty
+	if sys.Noctty {
+		_, _, err1 = RawSyscall(SYS_IOCTL, 0, uintptr(TIOCNOTTY), 0)
+		if err1 != 0 {
+			goto childerror
+		}
+	}
+
+	// Make fd 0 the tty
+	if sys.Setctty {
+		_, _, err1 = RawSyscall(SYS_IOCTL, 0, uintptr(TIOCSCTTY), 0)
+		if err1 != 0 {
+			goto childerror
+		}
+	}
+
+	// Time to exec.
+	_, _, err1 = RawSyscall(SYS_EXECVE,
+		uintptr(unsafe.Pointer(argv0)),
+		uintptr(unsafe.Pointer(&argv[0])),
+		uintptr(unsafe.Pointer(&envv[0])))
+
+childerror:
+	// send error code on pipe
+	RawSyscall(SYS_WRITE, uintptr(pipe), uintptr(unsafe.Pointer(&err1)), unsafe.Sizeof(err1))
+	for {
+		RawSyscall(SYS_EXIT, 253, 0, 0)
+	}
+}
+
+// Try to open a pipe with O_CLOEXEC set on both file descriptors.
+func forkExecPipe(p []int) error {
+	err := Pipe(p)
+	if err != nil {
+		return err
+	}
+	_, err = fcntl(p[0], F_SETFD, FD_CLOEXEC)
+	if err != nil {
+		return err
+	}
+	_, err = fcntl(p[1], F_SETFD, FD_CLOEXEC)
+	return err
+}