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/DIE.h

@@ -0,0 +1,94 @@
+/*
+ * 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 "CompilationUnit.h"
+#include "DwarfTypes.h"
+#include <AK/BufferStream.h>
+#include <AK/Function.h>
+#include <AK/NonnullOwnPtr.h>
+#include <AK/Optional.h>
+#include <AK/Types.h>
+
+namespace Dwarf {
+
+class CompilationUnit;
+
+// DIE = Dwarf Information Entry
+class DIE {
+public:
+    DIE(const CompilationUnit&, u32 offset);
+
+    struct AttributeValue {
+        enum class Type {
+            UnsignedNumber,
+            SignedNumber,
+            String,
+            DieReference, // Reference to another DIE in the same compilation unit
+            Boolean,
+            DwarfExpression,
+            SecOffset,
+        } type;
+
+        union {
+            u32 as_u32;
+            i32 as_i32;
+            const char* as_string; // points to bytes in the memory mapped elf image
+            bool as_bool;
+            struct {
+                u32 length;
+                const u8* bytes; // points to bytes in the memory mapped elf image
+            } as_dwarf_expression;
+        } data {};
+    };
+
+    u32 offset() const { return m_offset; }
+    u32 size() const { return m_size; }
+    bool has_children() const { return m_has_children; }
+    EntryTag tag() const { return m_tag; }
+
+    Optional<AttributeValue> get_attribute(const Attribute&) const;
+
+    void for_each_child(Function<void(const DIE& child)> callback) const;
+
+    bool is_null() const { return m_tag == EntryTag::None; }
+
+    DIE get_die_at_offset(u32 offset) const;
+
+private:
+    AttributeValue get_attribute_value(AttributeDataForm form,
+        BufferStream& debug_info_stream) const;
+
+    const CompilationUnit& m_compilation_unit;
+    u32 m_offset { 0 };
+    u32 m_data_offset { 0 };
+    size_t m_abbreviation_code { 0 };
+    EntryTag m_tag { EntryTag::None };
+    bool m_has_children { false };
+    u32 m_size { 0 };
+};
+
+}