runtime: add dlog.hexdump

Change-Id: I8149ab9314216bb8f9bf58da55633e2587d75851
Reviewed-on: https://go-review.googlesource.com/c/go/+/681376
Auto-Submit: Austin Clements <austin@google.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

src/runtime/debuglog.go

@@ -196,7 +196,8 @@ const (
 	debugLogPtr
 	debugLogString
 	debugLogConstString
-	debugLogStringOverflow
+	debugLogHexdump
+	debugLogOverflow
 
 	debugLogPC
 	debugLogTraceback
@@ -365,13 +366,39 @@ func (l *dloggerImpl) s(x string) *dloggerImpl {
 		l.w.uvarint(uint64(len(b)))
 		l.w.bytes(b)
 		if len(b) != len(x) {
-			l.w.byte(debugLogStringOverflow)
+			l.w.byte(debugLogOverflow)
 			l.w.uvarint(uint64(len(x) - len(b)))
 		}
 	}
 	return l
 }
 
+//go:nosplit
+func (l dloggerFake) hexdump(p unsafe.Pointer, bytes uintptr) dloggerFake { return l }
+
+//go:nosplit
+func (l *dloggerImpl) hexdump(p unsafe.Pointer, bytes uintptr) *dloggerImpl {
+	var b []byte
+	bb := (*slice)(unsafe.Pointer(&b))
+	bb.array = unsafe.Pointer(p)
+	bb.len, bb.cap = int(bytes), int(bytes)
+	if len(b) > debugLogStringLimit {
+		b = b[:debugLogStringLimit]
+	}
+
+	l.w.byte(debugLogHexdump)
+	l.w.uvarint(uint64(uintptr(p)))
+	l.w.uvarint(uint64(len(b)))
+	l.w.bytes(b)
+
+	if uintptr(len(b)) != bytes {
+		l.w.byte(debugLogOverflow)
+		l.w.uvarint(uint64(bytes) - uint64(len(b)))
+	}
+
+	return l
+}
+
 //go:nosplit
 func (l dloggerFake) pc(x uintptr) dloggerFake { return l }
 
@@ -708,9 +735,30 @@ func (r *debugLogReader) printVal() bool {
 		s := *(*string)(unsafe.Pointer(&str))
 		print(s)
 
-	case debugLogStringOverflow:
+	case debugLogOverflow:
 		print("..(", r.uvarint(), " more bytes)..")
 
+	case debugLogHexdump:
+		p := uintptr(r.uvarint())
+		bl := r.uvarint()
+		if r.begin+bl > r.end {
+			r.begin = r.end
+			print("<hexdump length corrupted>")
+			break
+		}
+		println() // Start on a new line
+		hd := hexdumper{addr: p}
+		for bl > 0 {
+			b := r.data.b[r.begin%uint64(len(r.data.b)):]
+			if uint64(len(b)) > bl {
+				b = b[:bl]
+			}
+			r.begin += uint64(len(b))
+			bl -= uint64(len(b))
+			hd.write(b)
+		}
+		hd.close()
+
 	case debugLogPC:
 		printDebugLogPC(uintptr(r.uvarint()), false)