sys: Work around nil references in Select.

This fixes #612.

sys/fdset_freebsd.go

@@ -8,15 +8,16 @@ package sys
 
 import (
 	"reflect"
-	"syscall"
+
+	"golang.org/x/sys/unix"
 )
 
-var nFdBits = (uint)(reflect.TypeOf(syscall.FdSet{}.X__fds_bits[0]).Size() * 8)
+var nFdBits = (uint)(reflect.TypeOf(unix.FdSet{}.X__fds_bits[0]).Size() * 8)
 
-type FdSet syscall.FdSet
+type FdSet unix.FdSet
 
-func (fs *FdSet) s() *syscall.FdSet {
-	return (*syscall.FdSet)(fs)
+func (fs *FdSet) s() *unix.FdSet {
+	return (*unix.FdSet)(fs)
 }
 
 func NewFdSet(fds ...int) *FdSet {

sys/fdset_notfreebsd.go

@@ -3,16 +3,17 @@
 package sys
 
 import (
-	"syscall"
 	"unsafe"
+
+	"golang.org/x/sys/unix"
 )
 
-var nFdBits = uint(8 * unsafe.Sizeof(syscall.FdSet{}.Bits[0]))
+var nFdBits = uint(8 * unsafe.Sizeof(unix.FdSet{}.Bits[0]))
 
-type FdSet syscall.FdSet
+type FdSet unix.FdSet
 
-func (fs *FdSet) s() *syscall.FdSet {
-	return (*syscall.FdSet)(fs)
+func (fs *FdSet) s() *unix.FdSet {
+	return (*unix.FdSet)(fs)
 }
 
 func NewFdSet(fds ...int) *FdSet {

sys/select_bsd.go

@@ -2,8 +2,8 @@
 
 package sys
 
-import "syscall"
+import "golang.org/x/sys/unix"
 
-func Select(nfd int, r *FdSet, w *FdSet, e *FdSet, timeout *syscall.Timeval) (err error) {
-	return syscall.Select(nfd, r.s(), w.s(), e.s(), timeout)
+func Select(nfd int, r *FdSet, w *FdSet, e *FdSet) error {
+	return unix.Select(nfd, r.s(), w.s(), e.s(), nil)
 }

sys/select_linux.go

@@ -2,13 +2,12 @@
 
 package sys
 
-import "syscall"
+import "golang.org/x/sys/unix"
 
-func Select(nfd int, r *FdSet, w *FdSet, e *FdSet, timeout *syscall.Timeval) error {
-	// On ARM64, MIPS64 and MIPS64LE, syscall.Select is emulated in userland and
-	// will dereference timeout. In that case, if the timeout argument is nil,
-	// the call will panic. This is not POSIX-conformant behavior, but we work
-	// around this by supplying a default value for timeout.
-	_, err := syscall.Select(nfd, r.s(), w.s(), e.s(), timeout)
+func Select(nfd int, r *FdSet, w *FdSet, e *FdSet) error {
+	// On ARM64, MIPS64 and MIPS64LE, unix.Select is emulated in userland and
+	// will dereference timeout. In that case, we use Pselect to work around the
+	// problem. Bug: https://github.com/golang/go/issues/24189
+	_, err := unix.Pselect(nfd, r.s(), w.s(), e.s(), nil, nil)
 	return err
 }

sys/select_test.go

@@ -3,8 +3,9 @@
 package sys
 
 import (
-	"syscall"
 	"testing"
+
+	"golang.org/x/sys/unix"
 )
 
 func TestFdSet(t *testing.T) {
@@ -30,8 +31,8 @@ func TestFdSet(t *testing.T) {
 
 func TestSelect(t *testing.T) {
 	var p1, p2 [2]int
-	mustNil(syscall.Pipe(p1[:]))
-	mustNil(syscall.Pipe(p2[:]))
+	mustNil(unix.Pipe(p1[:]))
+	mustNil(unix.Pipe(p2[:]))
 	fs := NewFdSet(p1[0], p2[0])
 	var maxfd int
 	if p1[0] > p2[0] {
@@ -40,16 +41,16 @@ func TestSelect(t *testing.T) {
 		maxfd = p2[0] + 1
 	}
 	go func() {
-		syscall.Write(p1[1], []byte("to p1"))
-		syscall.Write(p2[1], []byte("to p2"))
-		syscall.Close(p1[1])
-		syscall.Close(p2[1])
+		unix.Write(p1[1], []byte("to p1"))
+		unix.Write(p2[1], []byte("to p2"))
+		unix.Close(p1[1])
+		unix.Close(p2[1])
 	}()
-	e := Select(maxfd+1, fs, nil, nil, nil)
+	e := Select(maxfd+1, fs, nil, nil)
 	if e != nil {
-		t.Errorf("Select(%v, %v, nil, nil, nil) => %v, want <nil>",
+		t.Errorf("Select(%v, %v, nil, nil) => %v, want <nil>",
 			maxfd+1, fs, e)
 	}
-	syscall.Close(p1[0])
-	syscall.Close(p2[0])
+	unix.Close(p1[0])
+	unix.Close(p2[0])
 }

sys/waitforread_unix.go

@@ -20,7 +20,7 @@ func WaitForRead(files ...*os.File) (ready []bool, err error) {
 		}
 		fdset.Set(fd)
 	}
-	err = Select(maxfd+1, fdset, nil, nil, nil)
+	err = Select(maxfd+1, fdset, nil, nil)
 	ready = make([]bool, len(files))
 	for i, file := range files {
 		ready[i] = fdset.IsSet(int(file.Fd()))