LibDebug: Parse DWARF information entries

We can now iterate the tree structure of the DIEs, access attribute
values and parse some very basic DWARF expressions.

Libraries/LibDebug/Dwarf/AbbreviationsMap.h

@@ -0,0 +1,58 @@
+/*
+ * Copyright (c) 2020, Itamar S. <itamar8910@gmail.com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+#include "DwarfTypes.h"
+#include <AK/HashMap.h>
+#include <AK/Optional.h>
+#include <AK/Types.h>
+
+namespace Dwarf {
+class DwarfInfo;
+
+class AbbreviationsMap {
+public:
+    AbbreviationsMap(const DwarfInfo& dwarf_info, u32 offset);
+
+    struct AbbreviationEntry {
+
+        EntryTag tag;
+        bool has_children;
+
+        Vector<AttributeSpecification> attribute_specifications;
+    };
+
+    Optional<AbbreviationEntry> get(u32 code) const;
+
+private:
+    void populate_map();
+
+    const DwarfInfo& m_dwarf_info;
+    u32 m_offset { 0 };
+    HashMap<u32, AbbreviationEntry> m_entries;
+};
+
+}