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

unix/exec_linux.go

+// 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 linux
+
+package syscall
+
+import (
+        "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 Ctty (only meaningful if Setsid is set)
+        Noctty     bool        // Detach fd 0 from controlling terminal
+        Ctty       int         // Controlling TTY fd (Linux only)
+        Pdeathsig  Signal      // Signal that the process will get when its parent dies (Linux only)
+        Cloneflags uintptr     // Flags for clone calls (Linux only)
+}
+
+// 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     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++
+
+        // About to call fork.
+        // No more allocation or calls of non-assembly functions.
+        runtime_BeforeFork()
+        r1, _, err1 = RawSyscall6(SYS_CLONE, uintptr(SIGCHLD)|sys.Cloneflags, 0, 0, 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.
+
+        // Parent death signal
+        if sys.Pdeathsig != 0 {
+                _, _, err1 = RawSyscall6(SYS_PRCTL, PR_SET_PDEATHSIG, uintptr(sys.Pdeathsig), 0, 0, 0, 0)
+                if err1 != 0 {
+                        goto childerror
+                }
+
+                // Signal self if parent is already dead. This might cause a
+                // duplicate signal in rare cases, but it won't matter when
+                // using SIGKILL.
+                r1, _, _ = RawSyscall(SYS_GETPPID, 0, 0, 0)
+                if r1 == 1 {
+                        pid, _, _ := RawSyscall(SYS_GETPID, 0, 0, 0)
+                        _, _, err1 := RawSyscall(SYS_KILL, pid, uintptr(sys.Pdeathsig), 0)
+                        if err1 != 0 {
+                                goto childerror
+                        }
+                }
+        }
+
+        // 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))
+                var groups unsafe.Pointer
+                if ngroups > 0 {
+                        groups = unsafe.Pointer(&cred.Groups[0])
+                }
+                _, _, err1 = RawSyscall(SYS_SETGROUPS, ngroups, uintptr(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
+                }
+        }
+
+        // Set the controlling TTY to Ctty
+        if sys.Setctty && sys.Ctty >= 0 {
+                _, _, err1 = RawSyscall(SYS_IOCTL, uintptr(sys.Ctty), 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) (err error) {
+        err = Pipe2(p, O_CLOEXEC)
+        // pipe2 was added in 2.6.27 and our minimum requirement is 2.6.23, so it
+        // might not be implemented.
+        if err == ENOSYS {
+                if err = Pipe(p); err != nil {
+                        return
+                }
+                if _, err = fcntl(p[0], F_SETFD, FD_CLOEXEC); err != nil {
+                        return
+                }
+                _, err = fcntl(p[1], F_SETFD, FD_CLOEXEC)
+        }
+        return
+}