LibELF: Remove sketchy use of "undefined" ELF::Image::Section

We were using ELF::Image::section(0) to indicate the "undefined"
section, when what we really wanted was just Optional<Section>.

So let's use Optional instead. :^)

Kernel/Syscalls/module.cpp

@@ -65,7 +65,9 @@ KResultOr<int> Process::sys$module_load(Userspace<const char*> user_path, size_t
             return IterationDecision::Continue;
         auto* section_storage = section_storage_by_name.get(section.name()).value_or(nullptr);
         VERIFY(section_storage);
-        section.relocations().for_each_relocation([&](const ELF::Image::Relocation& relocation) {
+        auto relocations = section.relocations();
+        VERIFY(relocations.has_value());
+        relocations->for_each_relocation([&](const ELF::Image::Relocation& relocation) {
             auto& patch_ptr = *reinterpret_cast<ptrdiff_t*>(section_storage + relocation.offset());
             switch (relocation.type()) {
             case R_386_PC32: {

Userland/Libraries/LibDebug/DebugInfo.cpp

@@ -79,10 +79,10 @@ void DebugInfo::parse_scopes_impl(const Dwarf::DIE& die)
 void DebugInfo::prepare_lines()
 {
     auto section = elf().lookup_section(".debug_line");
-    if (section.is_undefined())
+    if (!section.has_value())
         return;
 
-    InputMemoryStream stream { section.bytes() };
+    InputMemoryStream stream { section->bytes() };
 
     Vector<Dwarf::LineProgram::LineInfo> all_lines;
     while (!stream.eof()) {

Userland/Libraries/LibDebug/Dwarf/DwarfInfo.cpp

@@ -24,9 +24,9 @@ DwarfInfo::DwarfInfo(const ELF::Image& elf)
 ReadonlyBytes DwarfInfo::section_data(const String& section_name) const
 {
     auto section = m_elf.lookup_section(section_name);
-    if (section.is_undefined())
+    if (!section.has_value())
         return {};
-    return section.bytes();
+    return section->bytes();
 }
 
 void DwarfInfo::populate_compilation_units()

Userland/Libraries/LibELF/Image.cpp

@@ -257,21 +257,21 @@ Image::Relocation Image::RelocationSection::relocation(unsigned index) const
     return Relocation(m_image, rels[index]);
 }
 
-Image::RelocationSection Image::Section::relocations() const
+Optional<Image::RelocationSection> Image::Section::relocations() const
 {
     StringBuilder builder;
     builder.append(".rel"sv);
     builder.append(name());
 
     auto relocation_section = m_image.lookup_section(builder.to_string());
-    if (relocation_section.type() != SHT_REL)
-        return static_cast<const RelocationSection>(m_image.section(0));
+    if (!relocation_section.has_value())
+        return {};
 
-    dbgln_if(ELF_IMAGE_DEBUG, "Found relocations for {} in {}", name(), relocation_section.name());
-    return static_cast<const RelocationSection>(relocation_section);
+    dbgln_if(ELF_IMAGE_DEBUG, "Found relocations for {} in {}", name(), relocation_section.value().name());
+    return static_cast<RelocationSection>(relocation_section.value());
 }
 
-Image::Section Image::lookup_section(const String& name) const
+Optional<Image::Section> Image::lookup_section(const String& name) const
 {
     VERIFY(m_valid);
     for (unsigned i = 0; i < section_count(); ++i) {
@@ -279,7 +279,7 @@ Image::Section Image::lookup_section(const String& name) const
         if (section.name() == name)
             return section;
     }
-    return section(0);
+    return {};
 }
 
 StringView Image::Symbol::raw_data() const

Userland/Libraries/LibELF/Image.h

@@ -114,8 +114,7 @@ public:
         u32 address() const { return m_section_header.sh_addr; }
         const char* raw_data() const { return m_image.raw_data(m_section_header.sh_offset); }
         ReadonlyBytes bytes() const { return { raw_data(), size() }; }
-        bool is_undefined() const { return m_section_index == SHN_UNDEF; }
-        RelocationSection relocations() const;
+        Optional<RelocationSection> relocations() const;
         u32 flags() const { return m_section_header.sh_flags; }
         bool is_writable() const { return flags() & SHF_WRITE; }
         bool is_executable() const { return flags() & PF_X; }
@@ -177,9 +176,7 @@ public:
     template<typename F>
     void for_each_program_header(F) const;
 
-    // NOTE: Returns section(0) if section with name is not found.
-    // FIXME: I don't love this API.
-    Section lookup_section(const String& name) const;
+    Optional<Section> lookup_section(String const& name) const;
 
     bool is_executable() const { return header().e_type == ET_EXEC; }
     bool is_relocatable() const { return header().e_type == ET_REL; }

Userland/Libraries/LibGUI/FileIconProvider.cpp

@@ -176,10 +176,10 @@ Icon FileIconProvider::icon_for_executable(const String& path)
         auto section = image.lookup_section(icon_section.section_name);
 
         RefPtr<Gfx::Bitmap> bitmap;
-        if (section.is_undefined()) {
+        if (!section.has_value()) {
             bitmap = s_executable_icon.bitmap_for_size(icon_section.image_size);
         } else {
-            bitmap = Gfx::load_png_from_memory(reinterpret_cast<const u8*>(section.raw_data()), section.size());
+            bitmap = Gfx::load_png_from_memory(reinterpret_cast<u8 const*>(section->raw_data()), section->size());
         }
 
         if (!bitmap) {