internal/gocore: handle unsafe.pointer case for hchan.buf in chan

In the hchan struct, buf field is an unsefa.Pointer, and its actual type is
an array of length hchan.dataqsiz and type hchan.elemtype.
Correct its type so that the object it points to can continue to be analyzed.

For golang/go#57447.

Change-Id: I47969a9a8e2870bb9573587bac5416fbea9db9ac
Reviewed-on: https://go-review.googlesource.com/c/debug/+/547536
Reviewed-by: Keith Randall <khr@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Keith Randall <khr@golang.org>
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>

internal/gocore/type.go

@@ -137,6 +137,7 @@ func readNameLen(p *Process, a core.Address) (int64, int64) {
 
 // Convert the address of a runtime._type to a *Type.
 // The "d" is the address of the second field of an interface, used to help disambiguate types.
+// If "d" is 0, just return *Type and not to do the interface disambiguation.
 // Guaranteed to return a non-nil *Type.
 func (p *Process) runtimeType2Type(a core.Address, d core.Address) *Type {
 	if t := p.runtimeMap[a]; t != nil {
@@ -202,7 +203,7 @@ func (p *Process) runtimeType2Type(a core.Address, d core.Address) *Type {
 	// in the same package name, but in the different package paths. eg. path-1/pkg.Foo and path-2/pkg.Foo.
 	// Match the object size may be a proper choice, just for try best, since we have no other choices.
 	// If the interface is of type T, for direct interfaces, that pointer points to a T.Elem.
-	if len(candidates) > 1 && !ifaceIndir(a, p) {
+	if d != 0 && len(candidates) > 1 && !ifaceIndir(a, p) {
 		ptr := p.proc.ReadPtr(d)
 		obj, off := p.FindObject(ptr)
 		// only usefull while it point to the head of an object,
@@ -724,7 +725,6 @@ func (p *Process) typeObject(a core.Address, t *Type, r reader, add func(core.Ad
 			add(bPtr, bTyp, n)
 			// TODO: also oldbuckets
 		}
-		// TODO: also special case for channels?
 		for _, f := range t.Fields {
 			// sync.entry.p(in sync.map) is an unsafe.pointer to an empty interface.
 			if t.Name == "sync.entry" && f.Name == "p" && f.Type.Kind == KindPtr && f.Type.Elem == nil {
@@ -737,6 +737,14 @@ func (p *Process) typeObject(a core.Address, t *Type, r reader, add func(core.Ad
 					add(ptr, typ, 1)
 				}
 			}
+			// hchan.buf(in chan) is an unsafe.pointer to an [dataqsiz]elemtype.
+			if strings.HasPrefix(t.Name, "hchan<") && f.Name == "buf" && f.Type.Kind == KindPtr {
+				elemType := p.proc.ReadPtr(a.Add(t.field("elemtype").Off))
+				bufPtr := r.ReadPtr(a.Add(t.field("buf").Off))
+				rTyp := p.runtimeType2Type(elemType, 0)
+				dataqsiz := p.proc.ReadUintptr(a.Add(t.field("dataqsiz").Off))
+				add(bufPtr, rTyp, int64(dataqsiz))
+			}
 			p.typeObject(a.Add(f.Off), f.Type, r, add)
 		}
 	default: