[dev.typeparams] Revert "[dev.typeparams] runtime: make deferproc take a func() argument"

Temprary revert CL 325918.

Delve relies on the _defer.fn.fn field to get defer frames.
CL 325918 changes the type of _defer.fn to func(), which no
longer has an fn field.

Change-Id: If6c71b15a27bac579593f5273c9a49715e6e35b2
Reviewed-on: https://go-review.googlesource.com/c/go/+/327775
Trust: Cherry Mui <cherryyz@google.com>
Trust: Dan Scales <danscales@google.com>
Run-TryBot: Cherry Mui <cherryyz@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Dan Scales <danscales@google.com>

src/runtime/heapdump.go

@@ -381,13 +381,12 @@ func dumpgoroutine(gp *g) {
 		dumpint(uint64(uintptr(unsafe.Pointer(gp))))
 		dumpint(uint64(d.sp))
 		dumpint(uint64(d.pc))
-		fn := *(**funcval)(unsafe.Pointer(&d.fn))
-		dumpint(uint64(uintptr(unsafe.Pointer(fn))))
-		if fn == nil {
+		dumpint(uint64(uintptr(unsafe.Pointer(d.fn))))
+		if d.fn == nil {
 			// d.fn can be nil for open-coded defers
 			dumpint(uint64(0))
 		} else {
-			dumpint(uint64(uintptr(unsafe.Pointer(fn.fn))))
+			dumpint(uint64(uintptr(unsafe.Pointer(d.fn.fn))))
 		}
 		dumpint(uint64(uintptr(unsafe.Pointer(d.link))))
 	}

src/runtime/panic.go

@@ -226,7 +226,7 @@ func panicmemAddr(addr uintptr) {
 
 // Create a new deferred function fn, which has no arguments and results.
 // The compiler turns a defer statement into a call to this.
-func deferproc(fn func()) {
+func deferproc(fn *funcval) { // TODO: Make deferproc just take a func().
 	gp := getg()
 	if gp.m.curg != gp {
 		// go code on the system stack can't defer
@@ -302,6 +302,16 @@ func deferprocStack(d *_defer) {
 	// been set and must not be clobbered.
 }
 
+// deferFunc returns d's deferred function. This is temporary while we
+// support both modes of GOEXPERIMENT=regabidefer. Once we commit to
+// that experiment, we should change the type of d.fn.
+//go:nosplit
+func deferFunc(d *_defer) func() {
+	var fn func()
+	*(**funcval)(unsafe.Pointer(&fn)) = d.fn
+	return fn
+}
+
 // Each P holds a pool for defers.
 
 // Allocate a Defer, usually using per-P pool.
@@ -461,9 +471,7 @@ func deferreturn() {
 	// called with a callback on an LR architecture and jmpdefer is on the
 	// stack, because the stack trace can be incorrect in that case - see
 	// issue #8153).
-	if fn == nil {
-		fn()
-	}
+	_ = fn.fn
 	jmpdefer(fn, argp)
 }
 
@@ -527,7 +535,7 @@ func Goexit() {
 		} else {
 			// Save the pc/sp in deferCallSave(), so we can "recover" back to this
 			// loop if necessary.
-			deferCallSave(&p, d.fn)
+			deferCallSave(&p, deferFunc(d))
 		}
 		if p.aborted {
 			// We had a recursive panic in the defer d we started, and
@@ -719,12 +727,12 @@ func runOpenDeferFrame(gp *g, d *_defer) bool {
 		if deferBits&(1<<i) == 0 {
 			continue
 		}
-		closure := *(*func())(unsafe.Pointer(d.varp - uintptr(closureOffset)))
+		closure := *(**funcval)(unsafe.Pointer(d.varp - uintptr(closureOffset)))
 		d.fn = closure
 		deferBits = deferBits &^ (1 << i)
 		*(*uint8)(unsafe.Pointer(d.varp - uintptr(deferBitsOffset))) = deferBits
 		p := d._panic
-		deferCallSave(p, d.fn)
+		deferCallSave(p, deferFunc(d))
 		if p != nil && p.aborted {
 			break
 		}
@@ -845,7 +853,8 @@ func gopanic(e interface{}) {
 			}
 		} else {
 			p.argp = unsafe.Pointer(getargp())
-			d.fn()
+			fn := deferFunc(d)
+			fn()
 		}
 		p.argp = nil
 

src/runtime/runtime2.go

@@ -955,7 +955,7 @@ type _defer struct {
 	openDefer bool
 	sp        uintptr  // sp at time of defer
 	pc        uintptr  // pc at time of defer
-	fn        func()  // can be nil for open-coded defers
+	fn        *funcval // can be nil for open-coded defers
 	_panic    *_panic  // panic that is running defer
 	link      *_defer
 

src/runtime/stubs.go

@@ -177,7 +177,7 @@ func cgocallback(fn, frame, ctxt uintptr)
 func gogo(buf *gobuf)
 
 //go:noescape
-func jmpdefer(fv func(), argp uintptr)
+func jmpdefer(fv *funcval, argp uintptr)
 func asminit()
 func setg(gg *g)
 func breakpoint()