Fix crash for special constants in too complex generic ivars

peterzhu2118 · peterzhu2118 · commit 0597cbcb1d89 · 2025-02-18T17:09:28.000-05:00
We should skip reference updating for entries in too complex generic ivars that are special constants. This fixes the following crash: MAX_SHAPES = 0x80000 MAX_SHAPES.times do |i| o = [] o.instance_variable_set(:"@foo#{i}", 1) end o = [] o.instance_variable_set(:"@A", 123) GC.compact
diff --git a/gc.c b/gc.c
@@ -3441,6 +3441,8 @@ vm_weak_table_gen_ivar_foreach_too_complex_i(st_data_t _key, st_data_t value, st
 
     GC_ASSERT(!iter_data->weak_only);
 
+    if (SPECIAL_CONST_P((VALUE)value)) return ST_CONTINUE;
+
     return iter_data->callback((VALUE)value, iter_data->data);
 }
 
diff --git a/test/ruby/test_gc_compact.rb b/test/ruby/test_gc_compact.rb
@@ -452,4 +452,21 @@ def set_a
       assert_raise(FrozenError) { a.set_a }
     end;
   end
+
+  def test_moving_too_compex_generic_ivar
+    omit "not compiled with SHAPE_DEBUG" unless defined?(RubyVM::Shape)
+
+    assert_separately([], <<~RUBY)
+      RubyVM::Shape.exhaust_shapes
+
+      obj = []
+      obj.instance_variable_set(:@fixnum, 123)
+      obj.instance_variable_set(:@str, "hello")
+
+      GC.verify_compaction_references(expand_heap: true, toward: :empty)
+
+      assert_equal(123, obj.instance_variable_get(:@fixnum))
+      assert_equal("hello", obj.instance_variable_get(:@str))
+    RUBY
+  end
 end

Original file line number	Diff line number	Diff line change
`@@ -3441,6 +3441,8 @@ vm_weak_table_gen_ivar_foreach_too_complex_i(st_data_t _key, st_data_t value, st`
`3441`	`3441`
`3442`	`3442`	`GC_ASSERT(!iter_data->weak_only);`
`3443`	`3443`
	`3444`	`+ if (SPECIAL_CONST_P((VALUE)value)) return ST_CONTINUE;`
	`3445`	`+`
`3444`	`3446`	`return iter_data->callback((VALUE)value, iter_data->data);`
`3445`	`3447`	`}`
`3446`	`3448`