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 unconditionally, making the functions a
no-op if the build flag "msan" is not present.

For #64611

Change-Id: If43f29e112ac79a47083c9dbdf2c61a0641e80b1
GitHub-Last-Rev: 0a644bd6f1
GitHub-Pull-Request: golang/go#64637
Reviewed-on: https://go-review.googlesource.com/c/go/+/548676
Reviewed-by: Austin Clements <austin@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

src/go/build/deps_test.go

@@ -75,6 +75,7 @@ var depsRules = `
 	< runtime
 	< sync/atomic
 	< internal/race
+	< internal/msan
 	< internal/asan
 	< sync
 	< internal/bisect

src/internal/msan/doc.go

@@ -0,0 +1,9 @@
+// Copyright 2024 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 +1,28 @@
+// Copyright 2024 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
+
+//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 2024 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) {
+}

src/runtime/msan.go

@@ -29,6 +29,7 @@ const msanenabled = true
 // anyhow for values on the stack. Just ignore msanread when running
 // on the system stack. The other msan functions are fine.
 //
+//go:linkname msanread
 //go:nosplit
 func msanread(addr unsafe.Pointer, sz uintptr) {
 	gp := getg()
@@ -41,15 +42,19 @@ func msanread(addr unsafe.Pointer, sz uintptr) {
 //go:noescape
 func domsanread(addr unsafe.Pointer, sz uintptr)
 
+//go:linkname msanwrite
 //go:noescape
 func msanwrite(addr unsafe.Pointer, sz uintptr)
 
+//go:linkname msanmalloc
 //go:noescape
 func msanmalloc(addr unsafe.Pointer, sz uintptr)
 
+//go:linkname msanfree
 //go:noescape
 func msanfree(addr unsafe.Pointer, sz uintptr)
 
+//go:linkname msanmove
 //go:noescape
 func msanmove(dst, src unsafe.Pointer, sz uintptr)