AK: Add Eternal<T> and use it in various places.

This is useful for static locals that never need to be destroyed:

Thing& Thing::the()
{
    static Eternal<Thing> the;
    return the;
}

The object will be allocated in data segment memory and will never have
its destructor invoked.

2 files changed, 31 insertions, 0 deletions

diff --git a/AK/Eternal.h b/AK/Eternal.h
new file mode 100644
index 0000000000..6db63a300f
--- /dev/null
+++ b/AK/Eternal.h
@@ -0,0 +1,30 @@
+#pragma once
+
+#include <AK/StdLibExtras.h>
+
+namespace AK {
+
+template<typename T>
+class Eternal {
+public:
+    template<typename... Args>
+    Eternal(Args&&... args)
+    {
+        new (m_slot) T(forward<Args>(args)...);
+    }
+
+    T& get() { return *reinterpret_cast<T*>(&m_slot); }
+    const T& get() const { return *reinterpret_cast<T*>(&m_slot); }
+    T* operator->() { return &get(); }
+    const T* operator->() const { return &get(); }
+    operator T&() { return get(); }
+    operator const T&() const { return get(); }
+
+
+private:
+    [[gnu::aligned(alignof(T))]] char m_slot[sizeof(T)];
+};
+
+}
+
+using AK::Eternal;
diff --git a/AK/kmalloc.h b/AK/kmalloc.h
index 3b28b0a4f4..d6a5966e3d 100644
--- a/AK/kmalloc.h
+++ b/AK/kmalloc.h
@@ -8,6 +8,7 @@
 #define AK_MAKE_ETERNAL \
 public: \
     void* operator new(size_t size) { return kmalloc_eternal(size); } \
+    void* operator new(size_t, void* ptr) { return ptr; } \
 private:
 #else
 #define AK_MAKE_ETERNAL