runtime: don't re-initialize itab while looking for missing function

The itab we're initializing again, just to figure out which method
is missing, might be stored in read-only memory.
This can only happen in certain weird generics situations, so it is
pretty rare, but it causes a runtime crash when it does happen.

Fixes #65962

Change-Id: Ia86e216fe33950a794ad8e475e76317f799e9136
Reviewed-on: https://go-review.googlesource.com/c/go/+/567615
Reviewed-by: Cherry Mui <cherryyz@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Keith Randall <khr@google.com>

1 files changed, 48 insertions, 0 deletions

diff --git a/test/fixedbugs/issue65962.go b/test/fixedbugs/issue65962.go
new file mode 100644
index 0000000000..a60cd32fd1
--- /dev/null
+++ b/test/fixedbugs/issue65962.go
@@ -0,0 +1,48 @@
+// run
+
+// Copyright 2024 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
+
+func main() {
+	test1()
+	test2()
+}
+
+type I interface {
+	f()
+	g()
+	h()
+}
+
+//go:noinline
+func ld[T any]() {
+	var x I
+	if _, ok := x.(T); ok {
+	}
+}
+
+func isI(x any) {
+	_ = x.(I)
+}
+
+func test1() {
+	defer func() { recover() }()
+	ld[bool]() // add <bool,I> itab to binary
+	_ = any(false).(I)
+}
+
+type B bool
+
+func (B) f() {
+}
+func (B) g() {
+}
+
+func test2() {
+	defer func() { recover() }()
+	ld[B]() // add <B,I> itab to binary
+	_ = any(B(false)).(I)
+}