Enable clone syscall support on arm64.

sys_clone has many flavors in Linux, and amd64 chose
a different one from x86(different arguments order).
Ref kernel/fork.c for more info.

Signed-off-by: Haibo Xu <haibo.xu@arm.com>
Change-Id: I6c8cbc685f4a6e786b171715ab68292fc95cbf48
COPYBARA_INTEGRATE_REVIEW=https://github.com/google/gvisor/pull/1545 from xiaobo55x:clone 156bd2dfbc63ef5291627b0578ddea77997393b2
PiperOrigin-RevId: 290093953

pkg/sentry/syscalls/linux/BUILD

@@ -13,6 +13,8 @@ go_library(
         "sigset.go",
         "sys_aio.go",
         "sys_capability.go",
+        "sys_clone_amd64.go",
+        "sys_clone_arm64.go",
         "sys_epoll.go",
         "sys_eventfd.go",
         "sys_file.go",

pkg/sentry/syscalls/linux/sys_clone_amd64.go

@@ -0,0 +1,35 @@
+// Copyright 2020 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 linux
+
+import (
+	"gvisor.dev/gvisor/pkg/sentry/arch"
+	"gvisor.dev/gvisor/pkg/sentry/kernel"
+)
+
+// Clone implements linux syscall clone(2).
+// sys_clone has so many flavors. We implement the default one in linux 3.11
+// x86_64:
+//    sys_clone(clone_flags, newsp, parent_tidptr, child_tidptr, tls_val)
+func Clone(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.SyscallControl, error) {
+	flags := int(args[0].Int())
+	stack := args[1].Pointer()
+	parentTID := args[2].Pointer()
+	childTID := args[3].Pointer()
+	tls := args[4].Pointer()
+	return clone(t, flags, stack, parentTID, childTID, tls)
+}

pkg/sentry/syscalls/linux/sys_clone_arm64.go

@@ -0,0 +1,35 @@
+// Copyright 2020 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 linux
+
+import (
+	"gvisor.dev/gvisor/pkg/sentry/arch"
+	"gvisor.dev/gvisor/pkg/sentry/kernel"
+)
+
+// Clone implements linux syscall clone(2).
+// sys_clone has so many flavors, and we implement the default one in linux 3.11
+// arm64(kernel/fork.c with CONFIG_CLONE_BACKWARDS defined in the config file):
+//    sys_clone(clone_flags, newsp, parent_tidptr, tls_val, child_tidptr)
+func Clone(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.SyscallControl, error) {
+	flags := int(args[0].Int())
+	stack := args[1].Pointer()
+	parentTID := args[2].Pointer()
+	tls := args[3].Pointer()
+	childTID := args[4].Pointer()
+	return clone(t, flags, stack, parentTID, childTID, tls)
+}

pkg/sentry/syscalls/linux/sys_thread.go

@@ -220,19 +220,6 @@ func clone(t *kernel.Task, flags int, stack usermem.Addr, parentTID usermem.Addr
 	return uintptr(ntid), ctrl, err
 }
 
-// Clone implements linux syscall clone(2).
-// sys_clone has so many flavors. We implement the default one in linux 3.11
-// x86_64:
-//    sys_clone(clone_flags, newsp, parent_tidptr, child_tidptr, tls_val)
-func Clone(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.SyscallControl, error) {
-	flags := int(args[0].Int())
-	stack := args[1].Pointer()
-	parentTID := args[2].Pointer()
-	childTID := args[3].Pointer()
-	tls := args[4].Pointer()
-	return clone(t, flags, stack, parentTID, childTID, tls)
-}
-
 // Fork implements Linux syscall fork(2).
 func Fork(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.SyscallControl, error) {
 	// "A call to fork() is equivalent to a call to clone(2) specifying flags