From: "naruse (Yui NARUSE) via ruby-core" <ruby-core@...>
Date: 2023-01-24T02:05:47+00:00
Subject: [ruby-core:111999] [Ruby master Bug#19339] Defining ivar on special constants with @ syntax causes segv

Issue #19339 has been updated by naruse (Yui NARUSE).

Backport changed from 2.7: DONTNEED, 3.0: DONTNEED, 3.1: DONTNEED, 3.2: REQUIRED to 2.7: DONTNEED, 3.0: DONTNEED, 3.1: DONTNEED, 3.2: DONE

ruby_3_2 c0df0a85dec77a09308caddb1e1efd4d38fbf7b8 merged revision(s) ed6fbb79e19bf401db0e85447fee955fd10a25c7.

----------------------------------------
Bug #19339: Defining ivar on special constants with @ syntax causes segv
https://bugs.ruby-lang.org/issues/19339#change-101433

* Author: luke-gru (Luke Gruber)
* Status: Closed
* Priority: Normal
* Backport: 2.7: DONTNEED, 3.0: DONTNEED, 3.1: DONTNEED, 3.2: DONE
----------------------------------------
```ruby
1.instance_eval do
  @a = 1
end
```

There's a missing check at the top of vm_setivar_fastpath, should be:

```c
    if (UNLIKELY(RB_SPECIAL_CONST_P(obj))) { // example code: 1.instance_eval { @a = 1 }
        rb_check_frozen(obj); // raise FrozenError, because it's always frozen
        return Qundef;
    }
```



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