runtime: check that defer/go frames are empty

With GOEXPERIMENT=regabidefer, these frames should always be empty.
Check that.

For #40724.

Change-Id: Id8e418a9e06b4f94543cb16b868a7e10e013c2d9
Reviewed-on: https://go-review.googlesource.com/c/go/+/306009
Trust: Austin Clements <austin@google.com>
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Than McIntosh <thanm@google.com>
Reviewed-by: Cherry Zhang <cherryyz@google.com>

src/runtime/panic.go

@@ -228,6 +228,11 @@ func deferproc(siz int32, fn *funcval) { // arguments of fn follow fn
 		throw("defer on system stack")
 	}
 
+	if experimentRegabiDefer && siz != 0 {
+		// TODO: Make deferproc just take a func().
+		throw("defer with non-empty frame")
+	}
+
 	// the arguments of fn are in a perilous state. The stack map
 	// for deferproc does not describe them. So we can't let garbage
 	// collection or stack copying trigger until we've copied them out
@@ -280,6 +285,9 @@ func deferprocStack(d *_defer) {
 		// go code on the system stack can't defer
 		throw("defer on system stack")
 	}
+	if experimentRegabiDefer && d.siz != 0 {
+		throw("defer with non-empty frame")
+	}
 	// siz and fn are already set.
 	// The other fields are junk on entry to deferprocStack and
 	// are initialized here.
@@ -824,6 +832,9 @@ func runOpenDeferFrame(gp *g, d *_defer) bool {
 		argWidth, fd = readvarintUnsafe(fd)
 		closureOffset, fd = readvarintUnsafe(fd)
 		nArgs, fd = readvarintUnsafe(fd)
+		if experimentRegabiDefer && argWidth != 0 {
+			throw("defer with non-empty frame")
+		}
 		if deferBits&(1<<i) == 0 {
 			for j := uint32(0); j < nArgs; j++ {
 				_, fd = readvarintUnsafe(fd)

src/runtime/proc.go

@@ -4019,6 +4019,12 @@ func malg(stacksize int32) *g {
 //
 //go:nosplit
 func newproc(siz int32, fn *funcval) {
+	if experimentRegabiDefer && siz != 0 {
+		// TODO: When we commit to experimentRegabiDefer,
+		// rewrite newproc's comment, since it will no longer
+		// have a funny stack layout or need to be nosplit.
+		throw("go with non-empty frame")
+	}
 	argp := add(unsafe.Pointer(&fn), sys.PtrSize)
 	gp := getg()
 	pc := getcallerpc()

src/runtime/regabidefer_off.go

@@ -0,0 +1,10 @@
+// Copyright 2021 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 !goexperiment.regabidefer
+// +build !goexperiment.regabidefer
+
+package runtime
+
+const experimentRegabiDefer = false

src/runtime/regabidefer_on.go

@@ -0,0 +1,10 @@
+// Copyright 2021 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 goexperiment.regabidefer
+// +build goexperiment.regabidefer
+
+package runtime
+
+const experimentRegabiDefer = true