runtime: overwrite existing keys for mapassign_faststr variant

Fixes #45045

Change-Id: Ifcc7bd31591870446ce3e5127489a0b887d413f1
Reviewed-on: https://go-review.googlesource.com/c/go/+/305089
Trust: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

diff --git a/src/runtime/map_faststr.go b/src/runtime/map_faststr.go
index 2d1ac762a81e24d16d6b4826530b072513d0cbba..0673dd39c8ff6a87084668400febbf64520c0fa3 100644 (file)
--- a/src/runtime/map_faststr.go
+++ b/src/runtime/map_faststr.go
@@ -255,6 +255,9 @@ bucketloop:
                        // already have a mapping for key. Update it.
                        inserti = i
                        insertb = b
+                       // Overwrite existing key, so it can be garbage collected.
+                       // The size is already guaranteed to be set correctly.
+                       k.str = key.str
                        goto done
                }
                ovf := b.overflow(t)

diff --git a/test/fixedbugs/issue45045.go b/test/fixedbugs/issue45045.go
new file mode 100644 (file)
index 0000000..6e6db64
--- /dev/null
+++ b/test/fixedbugs/issue45045.go
@@ -0,0 +1,51 @@
+// run
+
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+import (
+       "reflect"
+       "runtime"
+       "unsafe"
+)
+
+func k(c chan string, val string) string {
+       b := make([]byte, 1000)
+       runtime.SetFinalizer(&b[0], func(*byte) {
+               c <- val
+       })
+       var s string
+       h := (*reflect.StringHeader)(unsafe.Pointer(&s))
+       h.Data = uintptr(unsafe.Pointer(&b[0]))
+       h.Len = len(b)
+       return s
+}
+
+func main() {
+       {
+               c := make(chan string, 2)
+               m := make(map[string]int)
+               m[k(c, "first")] = 0
+               m[k(c, "second")] = 0
+               runtime.GC()
+               if s := <-c; s != "first" {
+                       panic("map[string], second key did not retain.")
+               }
+               runtime.KeepAlive(m)
+       }
+
+       {
+               c := make(chan string, 2)
+               m := make(map[[2]string]int)
+               m[[2]string{k(c, "first")}] = 0
+               m[[2]string{k(c, "second")}] = 0
+               runtime.GC()
+               if s := <-c; s != "first" {
+                       panic("map[[2]string], second key did not retain.")
+               }
+               runtime.KeepAlive(m)
+       }
+}