Add build guard to files using go:linkname

Funcion signatures are not validated during compilation. Since
they are not exported, they can change at any time. The guard
ensures that they are verified at least on every version upgrade.

PiperOrigin-RevId: 250733742

pkg/sentry/platform/kvm/bluepill_unsafe.go

@@ -12,6 +12,11 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+// +build go1.12
+// +build !go1.14
+
+// Check go:linkname function signatures when updating Go version.
+
 package kvm
 
 import (

pkg/sentry/platform/kvm/machine_unsafe.go

@@ -12,6 +12,11 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+// +build go1.12
+// +build !go1.14
+
+// Check go:linkname function signatures when updating Go version.
+
 package kvm
 
 import (

pkg/sentry/platform/ptrace/subprocess_unsafe.go

@@ -12,6 +12,11 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+// +build go1.12
+// +build !go1.14
+
+// Check go:linkname function signatures when updating Go version.
+
 package ptrace
 
 import (

pkg/sleep/sleep_unsafe.go

@@ -13,7 +13,9 @@
 // limitations under the License.
 
 // +build go1.11
-// +build !go1.13
+// +build !go1.14
+
+// Check go:linkname function signatures when updating Go version.
 
 // Package sleep allows goroutines to efficiently sleep on multiple sources of
 // notifications (wakers). It offers O(1) complexity, which is different from

pkg/tcpip/link/rawfile/blockingpoll_amd64_unsafe.go

@@ -13,9 +13,10 @@
 // limitations under the License.
 
 // +build linux,amd64
-// +build !go1.13
+// +build go1.12
+// +build !go1.14
 
-// This must be validated with Go 1.13 and future releases.
+// Check go:linkname function signatures when updating Go version.
 
 package rawfile
 

pkg/tcpip/time_unsafe.go

@@ -13,7 +13,9 @@
 // limitations under the License.
 
 // +build go1.9
-// +build !go1.13
+// +build !go1.14
+
+// Check go:linkname function signatures when updating Go version.
 
 package tcpip
 

third_party/gvsync/BUILD

@@ -5,6 +5,8 @@ package(
     licenses = ["notice"],
 )
 
+exports_files(["LICENSE"])
+
 load("//tools/go_generics:defs.bzl", "go_template")
 
 go_template(
@@ -29,6 +31,8 @@ go_template(
 go_library(
     name = "gvsync",
     srcs = [
+        "downgradable_rwmutex_1_12_unsafe.go",
+        "downgradable_rwmutex_1_13_unsafe.go",
         "downgradable_rwmutex_unsafe.go",
         "gvsync.go",
         "memmove_unsafe.go",

third_party/gvsync/downgradable_rwmutex_1_12_unsafe.go

@@ -0,0 +1,21 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Copyright 2019 The gVisor Authors.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build go1.12
+// +build !go1.13
+
+// TODO(b/133868570): Delete once Go 1.12 is no longer supported.
+
+package gvsync
+
+import _ "unsafe"
+
+//go:linkname runtimeSemrelease112 sync.runtime_Semrelease
+func runtimeSemrelease112(s *uint32, handoff bool)
+
+func runtimeSemrelease(s *uint32, handoff bool, skipframes int) {
+	// 'skipframes' is only available starting from 1.13.
+	runtimeSemrelease112(s, handoff)
+}

third_party/gvsync/downgradable_rwmutex_1_13_unsafe.go

@@ -0,0 +1,16 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Copyright 2019 The gVisor Authors.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build go1.13
+// +build !go1.14
+
+// Check go:linkname function signatures when updating Go version.
+
+package gvsync
+
+import _ "unsafe"
+
+//go:linkname runtimeSemrelease sync.runtime_Semrelease
+func runtimeSemrelease(s *uint32, handoff bool, skipframes int)

third_party/gvsync/downgradable_rwmutex_unsafe.go

@@ -3,6 +3,11 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// +build go1.12
+// +build !go1.14
+
+// Check go:linkname function signatures when updating Go version.
+
 // This is mostly copied from the standard library's sync/rwmutex.go.
 //
 // Happens-before relationships indicated to the race detector:
@@ -19,6 +24,9 @@ import (
 	"unsafe"
 )
 
+//go:linkname runtimeSemacquire sync.runtime_Semacquire
+func runtimeSemacquire(s *uint32)
+
 // DowngradableRWMutex is identical to sync.RWMutex, but adds the DowngradeLock
 // method.
 type DowngradableRWMutex struct {
@@ -62,7 +70,7 @@ func (rw *DowngradableRWMutex) RUnlock() {
 		// A writer is pending.
 		if atomic.AddInt32(&rw.readerWait, -1) == 0 {
 			// The last reader unblocks the writer.
-			runtimeSemrelease(&rw.writerSem, false)
+			runtimeSemrelease(&rw.writerSem, false, 0)
 		}
 	}
 	if RaceEnabled {
@@ -103,7 +111,7 @@ func (rw *DowngradableRWMutex) Unlock() {
 	}
 	// Unblock blocked readers, if any.
 	for i := 0; i < int(r); i++ {
-		runtimeSemrelease(&rw.readerSem, false)
+		runtimeSemrelease(&rw.readerSem, false, 0)
 	}
 	// Allow other writers to proceed.
 	rw.w.Unlock()
@@ -126,7 +134,7 @@ func (rw *DowngradableRWMutex) DowngradeLock() {
 	// Unblock blocked readers, if any. Note that this loop starts as 1 since r
 	// includes this goroutine.
 	for i := 1; i < int(r); i++ {
-		runtimeSemrelease(&rw.readerSem, false)
+		runtimeSemrelease(&rw.readerSem, false, 0)
 	}
 	// Allow other writers to proceed to rw.w.Lock(). Note that they will still
 	// block on rw.writerSem since at least this reader exists, such that
@@ -136,9 +144,3 @@ func (rw *DowngradableRWMutex) DowngradeLock() {
 		RaceEnable()
 	}
 }
-
-//go:linkname runtimeSemacquire sync.runtime_Semacquire
-func runtimeSemacquire(s *uint32)
-
-//go:linkname runtimeSemrelease sync.runtime_Semrelease
-func runtimeSemrelease(s *uint32, handoff bool)

third_party/gvsync/memmove_unsafe.go

@@ -3,12 +3,21 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// +build go1.12
+// +build !go1.14
+
+// Check go:linkname function signatures when updating Go version.
+
 package gvsync
 
 import (
 	"unsafe"
 )
 
+//go:linkname memmove runtime.memmove
+//go:noescape
+func memmove(to, from unsafe.Pointer, n uintptr)
+
 // Memmove is exported for SeqAtomicLoad/SeqAtomicTryLoad<T>, which can't
 // define it because go_generics can't update the go:linkname annotation.
 // Furthermore, go:linkname silently doesn't work if the local name is exported
@@ -17,7 +26,3 @@ import (
 func Memmove(to, from unsafe.Pointer, n uintptr) {
 	memmove(to, from, n)
 }
-
-//go:linkname memmove runtime.memmove
-//go:noescape
-func memmove(to, from unsafe.Pointer, n uintptr)