From: "luke-gru (Luke Gruber) via ruby-core" <ruby-core@...>
Date: 2023-01-14T21:02:53+00:00
Subject: [ruby-core:111811] [Ruby master Bug#19339] Defining ivar on special constants with @ syntax causes segv

Issue #19339 has been reported by luke-gru (Luke Gruber).

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

* Author: luke-gru (Luke Gruber)
* Status: Open
* Priority: Normal
* Backport: 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: UNKNOWN
----------------------------------------
```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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