mirror of
https://github.com/golang/go.git
synced 2025-12-08 06:10:04 +00:00
syscall: add ForkExec, Syscall12 on Windows
R=brainman, rsc CC=golang-dev https://golang.org/cl/1578041
This commit is contained in:
Daniel Theophanes
Alex Brainman
parent
e57657683f
commit
7f9e247489
10 changed files with 356 additions and 5 deletions
312
src/pkg/syscall/exec_unix.go
Normal file
312
src/pkg/syscall/exec_unix.go
Normal file
|
|
@ -0,0 +1,312 @@
|
|||
// 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 (
|
||||
"sync"
|
||||
"unsafe"
|
||||
)
|
||||
|
||||
// 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 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
|
||||
}
|
||||
_, 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 []*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.
|
||||
r1, r2, err1 = RawSyscall(SYS_FORK, 0, 0, 0)
|
||||
if err1 != 0 {
|
||||
return 0, int(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
|
||||
return int(r1), 0
|
||||
}
|
||||
|
||||
// Fork succeeded, now in child.
|
||||
|
||||
// Enable tracing if requested.
|
||||
if traceme {
|
||||
_, _, err1 = RawSyscall(SYS_PTRACE, uintptr(PTRACE_TRACEME), 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.
|
||||
nextfd = int(len(fd))
|
||||
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)
|
||||
}
|
||||
|
||||
// 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)), uintptr(unsafe.Sizeof(err1)))
|
||||
for {
|
||||
RawSyscall(SYS_EXIT, 253, 0, 0)
|
||||
}
|
||||
|
||||
// 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 n 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
|
||||
}
|
||||
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, 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, err = read(p[0], (*byte)(unsafe.Pointer(&err1)), unsafe.Sizeof(err1))
|
||||
Close(p[0])
|
||||
if err != 0 || n != 0 {
|
||||
if 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.
|
||||
_, 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
|
||||
}
|
||||
|
||||
// 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) {
|
||||
_, _, err1 := RawSyscall(SYS_EXECVE,
|
||||
uintptr(unsafe.Pointer(StringBytePtr(argv0))),
|
||||
uintptr(unsafe.Pointer(&StringArrayPtr(argv)[0])),
|
||||
uintptr(unsafe.Pointer(&StringArrayPtr(envv)[0])))
|
||||
return int(err1)
|
||||
}
|
||||
Loading…
Add table
Add a link
Reference in a new issue