runtime: avoid allocation when printing panic chain

Author: jakebailey

src/runtime/panic.go

@@ -231,36 +231,24 @@ func _recover(useParentFrame bool) interface{} {
 	return nil
 }
 
-// printPanicChain prints the full chain of panics, with annotations for
-// recovered and repanicked entries, matching Go's output format.
 func printPanicChain() {
-	// Collect entries into a slice (they're in reverse order).
-	entry := (*panicEntry)(task.Current().PanicData)
+	printPanicEntry((*panicEntry)(task.Current().PanicData))
+}
+
+func printPanicEntry(entry *panicEntry) {
 	if entry == nil {
 		return
 	}
-	// Count entries.
-	n := 0
-	for e := entry; e != nil; e = e.next {
-		n++
+	if entry.next != nil {
+		printPanicEntry(entry.next)
+		printstring("\t")
 	}
-	// Print from oldest to newest.
-	entries := make([]*panicEntry, n)
-	for i, e := n-1, entry; e != nil; e = e.next {
-		entries[i] = e
-		i--
-	}
-	for i, e := range entries {
-		if i > 0 {
-			printstring("\t")
-		}
-		printstring("panic: ")
-		printitf(e.value)
-		if e.recovered {
-			printstring(" [recovered]")
-		}
-		printnl()
+	printstring("panic: ")
+	printitf(entry.value)
+	if entry.recovered {
+		printstring(" [recovered]")
 	}
+	printnl()
 }
 
 func clearRecoveredPanicEntries() {