Enable sentry/fs/host support on arm64.

newfstatat() syscall is not supported on arm64, so we resort
to use the fstatat() syscall.

Signed-off-by: Haibo Xu <haibo.xu@arm.com>
Change-Id: Iea95550ea53bcf85c01f7b3b95da70ad0952177d

pkg/sentry/fs/host/BUILD

@@ -21,6 +21,8 @@ go_library(
         "socket_unsafe.go",
         "tty.go",
         "util.go",
+        "util_amd64_unsafe.go",
+        "util_arm64_unsafe.go",
         "util_unsafe.go",
     ],
     importpath = "gvisor.dev/gvisor/pkg/sentry/fs/host",

pkg/sentry/fs/host/util.go

@@ -155,7 +155,7 @@ func unstableAttr(mo *superOperations, s *syscall.Stat_t) fs.UnstableAttr {
 		AccessTime:       ktime.FromUnix(s.Atim.Sec, s.Atim.Nsec),
 		ModificationTime: ktime.FromUnix(s.Mtim.Sec, s.Mtim.Nsec),
 		StatusChangeTime: ktime.FromUnix(s.Ctim.Sec, s.Ctim.Nsec),
-		Links:            s.Nlink,
+		Links:            uint64(s.Nlink),
 	}
 }
 

pkg/sentry/fs/host/util_amd64_unsafe.go

@@ -0,0 +1,41 @@
+// Copyright 2019 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// +build amd64
+
+package host
+
+import (
+	"syscall"
+	"unsafe"
+)
+
+func fstatat(fd int, name string, flags int) (syscall.Stat_t, error) {
+	var stat syscall.Stat_t
+	namePtr, err := syscall.BytePtrFromString(name)
+	if err != nil {
+		return stat, err
+	}
+	_, _, errno := syscall.Syscall6(
+		syscall.SYS_NEWFSTATAT,
+		uintptr(fd),
+		uintptr(unsafe.Pointer(namePtr)),
+		uintptr(unsafe.Pointer(&stat)),
+		uintptr(flags),
+		0, 0)
+	if errno != 0 {
+		return stat, errno
+	}
+	return stat, nil
+}

pkg/sentry/fs/host/util_arm64_unsafe.go

@@ -0,0 +1,41 @@
+// Copyright 2019 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// +build arm64
+
+package host
+
+import (
+	"syscall"
+	"unsafe"
+)
+
+func fstatat(fd int, name string, flags int) (syscall.Stat_t, error) {
+	var stat syscall.Stat_t
+	namePtr, err := syscall.BytePtrFromString(name)
+	if err != nil {
+		return stat, err
+	}
+	_, _, errno := syscall.Syscall6(
+		syscall.SYS_FSTATAT,
+		uintptr(fd),
+		uintptr(unsafe.Pointer(namePtr)),
+		uintptr(unsafe.Pointer(&stat)),
+		uintptr(flags),
+		0, 0)
+	if errno != 0 {
+		return stat, errno
+	}
+	return stat, nil
+}

pkg/sentry/fs/host/util_unsafe.go

@@ -116,22 +116,3 @@ func setTimestamps(fd int, ts fs.TimeSpec) error {
 	}
 	return nil
 }
-
-func fstatat(fd int, name string, flags int) (syscall.Stat_t, error) {
-	var stat syscall.Stat_t
-	namePtr, err := syscall.BytePtrFromString(name)
-	if err != nil {
-		return stat, err
-	}
-	_, _, errno := syscall.Syscall6(
-		syscall.SYS_NEWFSTATAT,
-		uintptr(fd),
-		uintptr(unsafe.Pointer(namePtr)),
-		uintptr(unsafe.Pointer(&stat)),
-		uintptr(flags),
-		0, 0)
-	if errno != 0 {
-		return stat, errno
-	}
-	return stat, nil
-}