From: "peterzhu2118 (Peter Zhu) via ruby-core" <ruby-core@...>
Date: 2023-03-17T14:17:17+00:00
Subject: [ruby-core:112930] [Ruby master Bug#19536] Frozen status loss when moving objects

Issue #19536 has been reported by peterzhu2118 (Peter Zhu).

----------------------------------------
Bug #19536: Frozen status loss when moving objects
https://bugs.ruby-lang.org/issues/19536

* Author: peterzhu2118 (Peter Zhu)
* Status: Open
* Priority: Normal
* Backport: 2.7: DONTNEED, 3.0: DONTNEED, 3.1: DONTNEED, 3.2: REQUIRED
----------------------------------------
GitHub PR: https://github.com/ruby/ruby/pull/7553

When objects are moved between size pools, their frozen status is lost in the shape. This will cause the frozen check to be bypassed when there is an inline cache. For example, the following script should raise a FrozenError, but doesn't on Ruby 3.2 and master.

```ruby
class A
  def add_ivars
    @a = @b = @c = @d = 1
  end

  def set_a
    @a = 10
  end
end

a = A.new
a.add_ivars
a.freeze

b = A.new
b.add_ivars
b.set_a # Set the inline cache in set_a

GC.verify_compaction_references(expand_heap: true, toward: :empty)

a.set_a
```



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