AK+Kernel+LibELF: Remove the need for IteratorDecision::Continue

By constraining two implementations, the compiler will select the best
fitting one. All this will require is duplicating the implementation and
simplifying for the `void` case.

This constraining also informs both the caller and compiler by passing
the callback parameter types as part of the constraint
(e.g.: `IterationFunction<int>`).

Some `for_each` functions in LibELF only take functions which return
`void`. This is a minimal correctness check, as it removes one way for a
function to incompletely do something.

There seems to be a possible idiom where inside a lambda, a `return;` is
the same as `continue;` in a for-loop.

Userland/Libraries/LibELF/DynamicLinker.cpp

@@ -125,9 +125,8 @@ static Vector<String> get_dependencies(const String& name)
 
     lib->for_each_needed_library([&dependencies, &name](auto needed_name) {
         if (name == needed_name)
-            return IterationDecision::Continue;
+            return;
         dependencies.append(needed_name);
-        return IterationDecision::Continue;
     });
     return dependencies;
 }

Userland/Libraries/LibELF/DynamicLoader.cpp

@@ -93,7 +93,6 @@ const DynamicObject& DynamicLoader::dynamic_object() const
             if (program_header.type() == PT_DYNAMIC) {
                 dynamic_section_address = VirtualAddress(program_header.raw_data());
             }
-            return IterationDecision::Continue;
         });
         VERIFY(!dynamic_section_address.is_null());
 
@@ -109,7 +108,6 @@ size_t DynamicLoader::calculate_tls_size() const
         if (program_header.type() == PT_TLS) {
             tls_size = program_header.size_in_memory();
         }
-        return IterationDecision::Continue;
     });
     return tls_size;
 }
@@ -194,7 +192,6 @@ void DynamicLoader::do_main_relocations()
         case RelocationResult::Success:
             break;
         }
-        return IterationDecision::Continue;
     };
     m_dynamic_object->relocation_section().for_each_relocation(do_single_relocation);
     m_dynamic_object->plt_relocation_section().for_each_relocation(do_single_relocation);
@@ -273,7 +270,6 @@ void DynamicLoader::load_program_headers()
             VERIFY(!relro_region.has_value());
             relro_region = region;
         }
-        return IterationDecision::Continue;
     });
 
     VERIFY(!text_regions.is_empty() || !data_regions.is_empty());

Userland/Libraries/LibELF/DynamicObject.cpp

@@ -49,7 +49,6 @@ void DynamicObject::dump() const
         String name_field = String::formatted("({})", name_for_dtag(entry.tag()));
         builder.appendff("{:#08x} {:17} {:#08x}\n", entry.tag(), name_field, entry.val());
         num_dynamic_sections++;
-        return IterationDecision::Continue;
     });
 
     if (m_has_soname)
@@ -171,7 +170,6 @@ void DynamicObject::parse()
             VERIFY_NOT_REACHED(); // FIXME: Maybe just break out here and return false?
             break;
         }
-        return IterationDecision::Continue;
     });
 
     if (!m_size_of_relocation_entry) {

Userland/Libraries/LibELF/DynamicObject.h

@@ -8,6 +8,7 @@
 #pragma once
 
 #include <AK/Assertions.h>
+#include <AK/Concepts.h>
 #include <AK/RefCounted.h>
 #include <AK/String.h>
 #include <Kernel/VirtualAddress.h>
@@ -125,8 +126,11 @@ public:
         unsigned relocation_count() const { return entry_count(); }
         Relocation relocation(unsigned index) const;
         Relocation relocation_at_offset(unsigned offset) const;
-        template<typename F>
+
+        template<IteratorFunction<DynamicObject::Relocation&> F>
         void for_each_relocation(F) const;
+        template<VoidFunction<DynamicObject::Relocation&> F>
+        void for_each_relocation(F func) const;
     };
 
     class Relocation {
@@ -251,16 +255,18 @@ public:
     ElfW(Half) program_header_count() const;
     const ElfW(Phdr) * program_headers() const;
 
-    template<typename F>
+    template<VoidFunction<StringView> F>
     void for_each_needed_library(F) const;
 
-    template<typename F>
+    template<VoidFunction<InitializationFunction&> F>
     void for_each_initialization_array_function(F f) const;
 
-    template<typename F>
+    template<IteratorFunction<DynamicEntry&> F>
     void for_each_dynamic_entry(F) const;
+    template<VoidFunction<DynamicEntry&> F>
+    void for_each_dynamic_entry(F func) const;
 
-    template<typename F>
+    template<VoidFunction<Symbol&> F>
     void for_each_symbol(F) const;
 
     struct SymbolLookupResult {
@@ -341,7 +347,7 @@ private:
     // End Section information from DT_* entries
 };
 
-template<typename F>
+template<IteratorFunction<DynamicObject::Relocation&> F>
 inline void DynamicObject::RelocationSection::for_each_relocation(F func) const
 {
     for (unsigned i = 0; i < relocation_count(); ++i) {
@@ -353,16 +359,24 @@ inline void DynamicObject::RelocationSection::for_each_relocation(F func) const
     }
 }
 
-template<typename F>
+template<VoidFunction<DynamicObject::Relocation&> F>
+inline void DynamicObject::RelocationSection::for_each_relocation(F func) const
+{
+    for_each_relocation([&](auto& reloc) {
+        func(reloc);
+        return IterationDecision::Continue;
+    });
+}
+
+template<VoidFunction<DynamicObject::Symbol&> F>
 inline void DynamicObject::for_each_symbol(F func) const
 {
     for (unsigned i = 0; i < symbol_count(); ++i) {
-        if (func(symbol(i)) == IterationDecision::Break)
-            break;
+        func(symbol(i));
     }
 }
 
-template<typename F>
+template<IteratorFunction<DynamicObject::DynamicEntry&> F>
 inline void DynamicObject::for_each_dynamic_entry(F func) const
 {
     auto* dyns = reinterpret_cast<const ElfW(Dyn)*>(m_dynamic_address.as_ptr());
@@ -374,21 +388,29 @@ inline void DynamicObject::for_each_dynamic_entry(F func) const
             break;
     }
 }
-template<typename F>
-inline void DynamicObject::for_each_needed_library(F func) const
+
+template<VoidFunction<DynamicObject::DynamicEntry&> F>
+inline void DynamicObject::for_each_dynamic_entry(F func) const
 {
-    for_each_dynamic_entry([func, this](auto entry) {
-        if (entry.tag() != DT_NEEDED)
-            return IterationDecision::Continue;
-        ElfW(Word) offset = entry.val();
-        StringView name { (const char*)(m_base_address.offset(m_string_table_offset).offset(offset)).as_ptr() };
-        if (func(StringView(name)) == IterationDecision::Break)
-            return IterationDecision::Break;
+    for_each_dynamic_entry([&](auto& dyn) {
+        func(dyn);
         return IterationDecision::Continue;
     });
 }
 
-template<typename F>
+template<VoidFunction<StringView> F>
+inline void DynamicObject::for_each_needed_library(F func) const
+{
+    for_each_dynamic_entry([func, this](auto entry) {
+        if (entry.tag() != DT_NEEDED)
+            return;
+        ElfW(Word) offset = entry.val();
+        StringView name { (const char*)(m_base_address.offset(m_string_table_offset).offset(offset)).as_ptr() };
+        func(name);
+    });
+}
+
+template<VoidFunction<DynamicObject::InitializationFunction&> F>
 void DynamicObject::for_each_initialization_array_function(F f) const
 {
     if (!has_init_array_section())

Userland/Libraries/LibELF/Image.cpp

@@ -97,7 +97,6 @@ void Image::dump() const
         dbgln("      offset: {:x}", program_header.offset());
         dbgln("       flags: {:x}", program_header.flags());
         dbgln("    }}");
-        return IterationDecision::Continue;
     });
 
     for (unsigned i = 0; i < header().e_shnum; ++i) {
@@ -344,7 +343,6 @@ NEVER_INLINE void Image::sort_symbols() const
     m_sorted_symbols.ensure_capacity(symbol_count());
     for_each_symbol([this](const auto& symbol) {
         m_sorted_symbols.append({ symbol.value(), symbol.name(), {}, symbol });
-        return IterationDecision::Continue;
     });
     quick_sort(m_sorted_symbols, [](auto& a, auto& b) {
         return a.address < b.address;

Userland/Libraries/LibELF/Image.h

@@ -6,6 +6,7 @@
 
 #pragma once
 
+#include <AK/Concepts.h>
 #include <AK/String.h>
 #include <AK/Vector.h>
 #include <Kernel/VirtualAddress.h>
@@ -134,7 +135,8 @@ public:
         }
         unsigned relocation_count() const { return entry_count(); }
         Relocation relocation(unsigned index) const;
-        template<typename F>
+
+        template<VoidFunction<Image::Relocation&> F>
         void for_each_relocation(F) const;
     };
 
@@ -167,13 +169,24 @@ public:
     ProgramHeader program_header(unsigned) const;
     FlatPtr program_header_table_offset() const;
 
-    template<typename F>
+    template<IteratorFunction<Image::Section> F>
     void for_each_section(F) const;
-    template<typename F>
+    template<VoidFunction<Section> F>
+    void for_each_section(F) const;
+
+    template<IteratorFunction<Section&> F>
     void for_each_section_of_type(unsigned, F) const;
-    template<typename F>
+    template<VoidFunction<Section&> F>
+    void for_each_section_of_type(unsigned, F) const;
+
+    template<IteratorFunction<Symbol> F>
     void for_each_symbol(F) const;
-    template<typename F>
+    template<VoidFunction<Symbol> F>
+    void for_each_symbol(F) const;
+
+    template<IteratorFunction<ProgramHeader> F>
+    void for_each_program_header(F func) const;
+    template<VoidFunction<ProgramHeader> F>
     void for_each_program_header(F) const;
 
     Optional<Section> lookup_section(String const& name) const;
@@ -222,15 +235,26 @@ private:
     mutable Vector<SortedSymbol> m_sorted_symbols;
 };
 
-template<typename F>
+template<IteratorFunction<Image::Section> F>
 inline void Image::for_each_section(F func) const
 {
     auto section_count = this->section_count();
-    for (unsigned i = 0; i < section_count; ++i)
-        func(section(i));
+    for (unsigned i = 0; i < section_count; ++i) {
+        if (func(section(i)) == IterationDecision::Break)
+            break;
+    }
 }
 
-template<typename F>
+template<VoidFunction<Image::Section> F>
+inline void Image::for_each_section(F func) const
+{
+    for_each_section([&](auto section) {
+        func(move(section));
+        return IterationDecision::Continue;
+    });
+}
+
+template<IteratorFunction<Image::Section&> F>
 inline void Image::for_each_section_of_type(unsigned type, F func) const
 {
     auto section_count = this->section_count();
@@ -243,17 +267,25 @@ inline void Image::for_each_section_of_type(unsigned type, F func) const
     }
 }
 
-template<typename F>
+template<VoidFunction<Image::Section&> F>
+inline void Image::for_each_section_of_type(unsigned type, F func) const
+{
+    for_each_section_of_type(type, [&](auto& section) {
+        func(section);
+        return IterationDecision::Continue;
+    });
+}
+
+template<VoidFunction<Image::Relocation&> F>
 inline void Image::RelocationSection::for_each_relocation(F func) const
 {
     auto relocation_count = this->relocation_count();
     for (unsigned i = 0; i < relocation_count; ++i) {
-        if (func(relocation(i)) == IterationDecision::Break)
-            break;
+        func(relocation(i));
     }
 }
 
-template<typename F>
+template<IteratorFunction<Image::Symbol> F>
 inline void Image::for_each_symbol(F func) const
 {
     auto symbol_count = this->symbol_count();
@@ -263,14 +295,32 @@ inline void Image::for_each_symbol(F func) const
     }
 }
 
-template<typename F>
+template<VoidFunction<Image::Symbol> F>
+inline void Image::for_each_symbol(F func) const
+{
+    for_each_symbol([&](auto symbol) {
+        func(move(symbol));
+        return IterationDecision::Continue;
+    });
+}
+
+template<IteratorFunction<Image::ProgramHeader> F>
 inline void Image::for_each_program_header(F func) const
 {
     auto program_header_count = this->program_header_count();
     for (unsigned i = 0; i < program_header_count; ++i) {
         if (func(program_header(i)) == IterationDecision::Break)
-            return;
+            break;
     }
 }
 
+template<VoidFunction<Image::ProgramHeader> F>
+inline void Image::for_each_program_header(F func) const
+{
+    for_each_program_header([&](auto header) {
+        func(move(header));
+        return IterationDecision::Continue;
+    });
+}
+
 } // end namespace ELF