runtime: add go:yeswritebarrierrec to panic functions

Panic avoids any write barriers in the runtime by checking first
and throwing if called inappropriately, so it is "okay".  Adding
this annotation repairs recursive write barrier checking, which
becomes more thorough when the local package naming convention
is changed from "" to the actual package name.

This CL is a prerequisite for a pending code cleanup,
https://go-review.googlesource.com/c/go/+/393715

Updates #51734.

Change-Id: If831a3598c6c8cd37a8e9ba269f822cd81464a13
Reviewed-on: https://go-review.googlesource.com/c/go/+/405900
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Run-TryBot: David Chase <drchase@google.com>

src/runtime/panic.go

@@ -106,38 +106,54 @@ func panicCheck2(err string) {
 // a space-minimal register calling convention.
 
 // failures in the comparisons for s[x], 0 <= x < y (y == len(s))
+//
+//go:yeswritebarrierrec
 func goPanicIndex(x int, y int) {
 	panicCheck1(getcallerpc(), "index out of range")
 	panic(boundsError{x: int64(x), signed: true, y: y, code: boundsIndex})
 }
+
+//go:yeswritebarrierrec
 func goPanicIndexU(x uint, y int) {
 	panicCheck1(getcallerpc(), "index out of range")
 	panic(boundsError{x: int64(x), signed: false, y: y, code: boundsIndex})
 }
 
 // failures in the comparisons for s[:x], 0 <= x <= y (y == len(s) or cap(s))
+//
+//go:yeswritebarrierrec
 func goPanicSliceAlen(x int, y int) {
 	panicCheck1(getcallerpc(), "slice bounds out of range")
 	panic(boundsError{x: int64(x), signed: true, y: y, code: boundsSliceAlen})
 }
+
+//go:yeswritebarrierrec
 func goPanicSliceAlenU(x uint, y int) {
 	panicCheck1(getcallerpc(), "slice bounds out of range")
 	panic(boundsError{x: int64(x), signed: false, y: y, code: boundsSliceAlen})
 }
+
+//go:yeswritebarrierrec
 func goPanicSliceAcap(x int, y int) {
 	panicCheck1(getcallerpc(), "slice bounds out of range")
 	panic(boundsError{x: int64(x), signed: true, y: y, code: boundsSliceAcap})
 }
+
+//go:yeswritebarrierrec
 func goPanicSliceAcapU(x uint, y int) {
 	panicCheck1(getcallerpc(), "slice bounds out of range")
 	panic(boundsError{x: int64(x), signed: false, y: y, code: boundsSliceAcap})
 }
 
 // failures in the comparisons for s[x:y], 0 <= x <= y
+//
+//go:yeswritebarrierrec
 func goPanicSliceB(x int, y int) {
 	panicCheck1(getcallerpc(), "slice bounds out of range")
 	panic(boundsError{x: int64(x), signed: true, y: y, code: boundsSliceB})
 }
+
+//go:yeswritebarrierrec
 func goPanicSliceBU(x uint, y int) {
 	panicCheck1(getcallerpc(), "slice bounds out of range")
 	panic(boundsError{x: int64(x), signed: false, y: y, code: boundsSliceB})
@@ -1017,6 +1033,7 @@ func sync_fatal(s string) {
 //
 // throw should be used for runtime-internal fatal errors where Go itself,
 // rather than user code, may be at fault for the failure.
+//
 //go:nosplit
 func throw(s string) {
 	// Everything throw does should be recursively nosplit so it
@@ -1035,6 +1052,7 @@ func throw(s string) {
 //
 // fatal does not include runtime frames, system goroutines, or frame metadata
 // (fp, sp, pc) in the stack trace unless GOTRACEBACK=system or higher.
+//
 //go:nosplit
 func fatal(s string) {
 	// Everything fatal does should be recursively nosplit so it