Merge pull request #876 from xiaobo55x:hostcpu

PiperOrigin-RevId: 270094324

pkg/sentry/hostcpu/BUILD

@@ -7,6 +7,7 @@ go_library(
     name = "hostcpu",
     srcs = [
         "getcpu_amd64.s",
+        "getcpu_arm64.s",
         "hostcpu.go",
     ],
     importpath = "gvisor.dev/gvisor/pkg/sentry/hostcpu",

pkg/sentry/hostcpu/getcpu_arm64.s

@@ -0,0 +1,28 @@
+// 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.
+
+#include "textflag.h"
+
+// GetCPU makes the getcpu(unsigned *cpu, unsigned *node, NULL) syscall for
+// the lack of an optimazed way of getting the current CPU number on arm64.
+
+// func GetCPU() (cpu uint32)
+TEXT ·GetCPU(SB), NOSPLIT, $0-4
+	MOVW ZR, cpu+0(FP)
+	MOVD $cpu+0(FP), R0
+	MOVD $0x0, R1  // unused
+	MOVD $0x0, R2  // unused
+	MOVD $0xA8, R8 // SYS_GETCPU
+	SVC
+	RET