internal/msan: add new package

The internal/msan package contains helper functions for manually
instrumenting code for the memory sanitizer. It exports the private
msan routines in runtime uncoditionally, making the functions a
no-op if the build flag "msan" is not present.

For #64611

Author: mauri870

src/internal/msan/doc.go

@@ -0,0 +1,12 @@
+// Copyright 2023 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+/*
+Package msan contains helper functions for manually instrumenting code
+for the memory sanitizer.
+
+This package exports the private msan routines in runtime unconditionally
+but without the "msan" build tag they are no-ops.
+*/
+package msan

src/internal/msan/msan.go

@@ -0,0 +1,50 @@
+// Copyright 2023 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build msan
+
+package msan
+
+import (
+	"unsafe"
+)
+
+const Enabled = true
+
+func Read(addr unsafe.Pointer, sz uintptr) {
+	read(addr, sz)
+}
+
+func Write(addr unsafe.Pointer, sz uintptr) {
+	write(addr, sz)
+}
+
+func Malloc(addr unsafe.Pointer, sz uintptr) {
+	malloc(addr, sz)
+}
+
+func Free(addr unsafe.Pointer, sz uintptr) {
+	free(addr, sz)
+}
+
+func Move(dst, src unsafe.Pointer, sz uintptr) {
+	move(dst, src, sz)
+}
+
+// Import private msan functions from runtime.
+//
+//go:linkname read runtime.msanread
+func read(addr unsafe.Pointer, sz uintptr)
+
+//go:linkname write runtime.msanwrite
+func write(addr unsafe.Pointer, sz uintptr)
+
+//go:linkname malloc runtime.msanmalloc
+func malloc(addr unsafe.Pointer, sz uintptr)
+
+//go:linkname free runtime.msanfree
+func free(addr unsafe.Pointer, sz uintptr)
+
+//go:linkname move runtime.msanmove
+func move(dst, src unsafe.Pointer, sz uintptr)

src/internal/msan/nomsan.go

@@ -0,0 +1,28 @@
+// Copyright 2023 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build !msan
+
+package msan
+
+import (
+	"unsafe"
+)
+
+const Enabled = false
+
+func Read(addr unsafe.Pointer, sz uintptr) {
+}
+
+func Write(addr unsafe.Pointer, sz uintptr) {
+}
+
+func Malloc(addr unsafe.Pointer, sz uintptr) {
+}
+
+func Free(addr unsafe.Pointer, sz uintptr) {
+}
+
+func Move(dst, src unsafe.Pointer, sz uintptr) {
+}