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author | ian <ian@138bc75d-0d04-0410-961f-82ee72b054a4> | 2011-10-23 19:04:37 +0000 |
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committer | ian <ian@138bc75d-0d04-0410-961f-82ee72b054a4> | 2011-10-23 19:04:37 +0000 |
commit | d477de419fb666727320c0ce7adabe6ce70dfbfc (patch) | |
tree | 664e8146cf480634282350e5f7f68403941ddfea /libgo/go/syscall/exec_unix.go | |
parent | c512f3a475837c5f5cd895a8513e3c3c9ba03648 (diff) | |
download | gcc-d477de419fb666727320c0ce7adabe6ce70dfbfc.tar.gz |
Implement new syscall package.
Calls to library functions now use entersyscall and
exitsyscall as appropriate. This is a first step toward
multiplexing goroutines onto threads.
git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@180345 138bc75d-0d04-0410-961f-82ee72b054a4
Diffstat (limited to 'libgo/go/syscall/exec_unix.go')
-rw-r--r-- | libgo/go/syscall/exec_unix.go | 454 |
1 files changed, 454 insertions, 0 deletions
diff --git a/libgo/go/syscall/exec_unix.go b/libgo/go/syscall/exec_unix.go new file mode 100644 index 00000000000..765f4d12fd5 --- /dev/null +++ b/libgo/go/syscall/exec_unix.go @@ -0,0 +1,454 @@ +// 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. + +// +build darwin freebsd linux openbsd + +// Fork, exec, wait, etc. + +package syscall + +import ( + "sync" + "unsafe" +) + +//sysnb raw_fork() (pid Pid_t, errno int) +//fork() Pid_t + +//sysnb raw_ptrace(request int, pid int, addr *byte, data *byte) (errno int) +//ptrace(request int, pid Pid_t, addr *byte, data *byte) _C_long + +//sysnb raw_setsid() (errno int) +//setsid() Pid_t + +//sysnb raw_chroot(path *byte) (errno int) +//chroot(path *byte) int + +//sysnb raw_chdir(path *byte) (errno int) +//chdir(path *byte) int + +//sysnb raw_fcntl(fd int, cmd int, arg int) (val int, errno int) +//fcntl(fd int, cmd int, arg int) int + +//sysnb raw_close(fd int) (errno int) +//close(fd int) int + +//sysnb raw_ioctl(fd int, cmd int, val int) (rval int, errno int) +//ioctl(fd int, cmd int, val int) int + +//sysnb raw_execve(argv0 *byte, argv **byte, envv **byte) (errno int) +//execve(argv0 *byte, argv **byte, envv **byte) int + +//sysnb raw_read(fd int, p *byte, np int) (n int, errno int) +//read(fd int, buf *byte, count Size_t) Ssize_t + +//sysnb raw_write(fd int, buf *byte, count int) int +//write(fd int, buf *byte, count Size_t) Ssize_t + +//sysnb raw_exit(status int) +//_exit(status int) + +// 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). + +var ForkLock sync.RWMutex + +// Convert array of string to array +// of NUL-terminated byte pointer. +func StringSlicePtr(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 + } + _, err = fcntl(fd, F_SETFL, flag) + return err +} + +// 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. +// 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 int) { + // Declare all variables at top in case any + // declarations require heap allocation (e.g., err1). + var r1 Pid_t + var err1 int + var nextfd int + var i int + + // guard against side effects of shuffling fds below. + fd := append([]int(nil), attr.Files...) + + // About to call fork. + // No more allocation or calls of non-assembly functions. + r1, err1 = raw_fork() + if err1 != 0 { + return 0, int(err1) + } + + if r1 != 0 { + // parent; return PID + return int(r1), 0 + } + + // Fork succeeded, now in child. + + // Enable tracing if requested. + if sys.Ptrace { + err1 = raw_ptrace(_PTRACE_TRACEME, 0, nil, nil) + if err1 != 0 { + goto childerror + } + } + + // Session ID + if sys.Setsid { + err1 = raw_setsid() + if err1 != 0 { + goto childerror + } + } + + // Set process group + if sys.Setpgid { + err1 = Setpgid(0, 0) + if err1 != 0 { + goto childerror + } + } + + // Chroot + if chroot != nil { + err1 = raw_chroot(chroot) + if err1 != 0 { + goto childerror + } + } + + // User and groups + if cred := sys.Credential; cred != nil { + ngroups := len(cred.Groups) + if ngroups == 0 { + err1 = setgroups(0, nil) + } else { + groups := make([]Gid_t, ngroups) + for i, v := range cred.Groups { + groups[i] = Gid_t(v) + } + err1 = setgroups(ngroups, &groups[0]) + } + if err1 != 0 { + goto childerror + } + err1 = Setgid(int(cred.Gid)) + if err1 != 0 { + goto childerror + } + err1 = Setuid(int(cred.Uid)) + if err1 != 0 { + goto childerror + } + } + + // Chdir + if dir != nil { + err1 = raw_chdir(dir) + 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. + nextfd = int(len(fd)) + if pipe < nextfd { + _, err1 = Dup2(pipe, nextfd) + if err1 != 0 { + goto childerror + } + raw_fcntl(nextfd, F_SETFD, FD_CLOEXEC) + pipe = nextfd + nextfd++ + } + for i = 0; i < len(fd); i++ { + if fd[i] >= 0 && fd[i] < int(i) { + _, err1 = Dup2(fd[i], nextfd) + if err1 != 0 { + goto childerror + } + raw_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 { + raw_close(i) + continue + } + if fd[i] == int(i) { + // Dup2(i, i) won't clear close-on-exec flag on Linux, + // probably not elsewhere either. + _, err1 = raw_fcntl(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 = Dup2(fd[i], i) + 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++ { + raw_close(i) + } + + // Detach fd 0 from tty + if sys.Noctty { + _, err1 = raw_ioctl(0, TIOCNOTTY, 0) + if err1 != 0 { + goto childerror + } + } + + // Make fd 0 the tty + if sys.Setctty { + _, err1 = raw_ioctl(0, TIOCSCTTY, 0) + if err1 != 0 { + goto childerror + } + } + + // Time to exec. + err1 = raw_execve(argv0, &argv[0], &envv[0]) + +childerror: + // send error code on pipe + raw_write(pipe, (*byte)(unsafe.Pointer(&err1)), int(unsafe.Sizeof(err1))) + for { + raw_exit(253) + } + + // Calling panic is not actually safe, + // but the for loop above won't break + // and this shuts up the compiler. + panic("unreached") +} + +// Credential holds user and group identities to be assumed +// by a child process started by StartProcess. +type Credential struct { + Uid uint32 // User ID. + Gid uint32 // Group ID. + Groups []uint32 // Supplementary group IDs. +} + +// ProcAttr holds attributes that will be applied to a new process started +// by StartProcess. +type ProcAttr struct { + Dir string // Current working directory. + Env []string // Environment. + Files []int // File descriptors. + Sys *SysProcAttr +} + +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 +} + +var zeroProcAttr ProcAttr +var zeroSysProcAttr SysProcAttr + +func forkExec(argv0 string, argv []string, attr *ProcAttr) (pid int, err int) { + var p [2]int + var n int + var err1 uintptr + var wstatus WaitStatus + + if attr == nil { + attr = &zeroProcAttr + } + sys := attr.Sys + if sys == nil { + sys = &zeroSysProcAttr + } + + p[0] = -1 + p[1] = -1 + + // Convert args to C form. + argv0p := StringBytePtr(argv0) + argvp := StringSlicePtr(argv) + envvp := StringSlicePtr(attr.Env) + + if OS == "freebsd" && len(argv[0]) > len(argv0) { + argvp[0] = argv0p + } + + var chroot *byte + if sys.Chroot != "" { + chroot = StringBytePtr(sys.Chroot) + } + var dir *byte + if attr.Dir != "" { + dir = StringBytePtr(attr.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 + } + if _, err = fcntl(p[0], F_SETFD, FD_CLOEXEC); err != 0 { + goto error + } + if _, err = fcntl(p[1], F_SETFD, FD_CLOEXEC); err != 0 { + goto error + } + + // Kick off child. + pid, err = forkAndExecInChild(argv0p, argvp, envvp, chroot, dir, attr, sys, p[1]) + if err != 0 { + goto error + } + ForkLock.Unlock() + + // Read child error status from pipe. + Close(p[1]) + n, err = raw_read(p[0], (*byte)(unsafe.Pointer(&err1)), int(unsafe.Sizeof(err1))) + Close(p[0]) + if err != 0 || n != 0 { + if n == int(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. + _, err1 := Wait4(pid, &wstatus, 0, nil) + for err1 == EINTR { + _, err1 = Wait4(pid, &wstatus, 0, nil) + } + return 0, err + } + + // Read got EOF, so pipe closed on exec, so exec succeeded. + return pid, 0 + +error: + if p[0] >= 0 { + Close(p[0]) + Close(p[1]) + } + ForkLock.Unlock() + return 0, err +} + +// Combination of fork and exec, careful to be thread safe. +func ForkExec(argv0 string, argv []string, attr *ProcAttr) (pid int, err int) { + return forkExec(argv0, argv, attr) +} + +// StartProcess wraps ForkExec for package os. +func StartProcess(argv0 string, argv []string, attr *ProcAttr) (pid, handle int, err int) { + pid, err = forkExec(argv0, argv, attr) + return pid, 0, err +} + +// Ordinary exec. +func Exec(argv0 string, argv []string, envv []string) (err int) { + err1 := raw_execve(StringBytePtr(argv0), + &StringSlicePtr(argv)[0], + &StringSlicePtr(envv)[0]) + return int(err1) +} |