LibC+LibELF: Correctly call destructors on exit()

We currently don't call any DT_FINI_ARRAY functions, so change that.

The call to `_fini` in `exit` is unnecessary, as we now call the
function referenced by DT_FINI in `__call_fini_functions`.

Userland/Libraries/LibC/stdlib.cpp

@@ -345,6 +345,8 @@ static T c_str_to_floating_point(char const* str, char** endptr)
 
 extern "C" {
 
+void (*__call_fini_functions)();
+
 void exit(int status)
 {
     __cxa_finalize(nullptr);
@@ -352,8 +354,7 @@ void exit(int status)
     if (secure_getenv("LIBC_DUMP_MALLOC_STATS"))
         serenity_dump_malloc_stats();
 
-    extern void _fini();
-    _fini();
+    __call_fini_functions();
     fflush(nullptr);
 
 #ifndef _DYNAMIC_LOADER

Userland/Libraries/LibELF/DynamicLinker.cpp

@@ -38,12 +38,16 @@ namespace ELF {
 
 static HashMap<DeprecatedString, NonnullRefPtr<ELF::DynamicLoader>> s_loaders;
 static DeprecatedString s_main_program_path;
+
+// Dependencies have to always be added after the object that depends on them in `s_global_objects`.
+// This is needed for calling the destructors in the correct order.
 static OrderedHashMap<DeprecatedString, NonnullRefPtr<ELF::DynamicObject>> s_global_objects;
 
 using EntryPointFunction = int (*)(int, char**, char**);
 using LibCExitFunction = void (*)(int);
 using DlIteratePhdrCallbackFunction = int (*)(struct dl_phdr_info*, size_t, void*);
 using DlIteratePhdrFunction = int (*)(DlIteratePhdrCallbackFunction, void*);
+using CallFiniFunctionsFunction = void (*)();
 
 extern "C" [[noreturn]] void _invoke_entry(int argc, char** argv, char** envp, EntryPointFunction entry);
 
@@ -65,6 +69,7 @@ static Result<void, DlErrorMessage> __dlclose(void* handle);
 static Result<void*, DlErrorMessage> __dlopen(char const* filename, int flags);
 static Result<void*, DlErrorMessage> __dlsym(void* handle, char const* symbol_name);
 static Result<void, DlErrorMessage> __dladdr(void const* addr, Dl_info* info);
+static void __call_fini_functions();
 
 Optional<DynamicObject::SymbolLookupResult> DynamicLinker::lookup_global_symbol(StringView name)
 {
@@ -305,6 +310,10 @@ static void initialize_libc(DynamicObject& libc)
     VERIFY(res.has_value());
     *((DlAddrFunction*)res.value().address.as_ptr()) = __dladdr;
 
+    res = libc.lookup_symbol("__call_fini_functions"sv);
+    VERIFY(res.has_value());
+    *((CallFiniFunctionsFunction*)res.value().address.as_ptr()) = __call_fini_functions;
+
     res = libc.lookup_symbol("__libc_init"sv);
     VERIFY(res.has_value());
     typedef void libc_init_func();
@@ -384,11 +393,9 @@ static Result<void, DlErrorMessage> link_main_library(DeprecatedString const& pa
 
     auto loaders = collect_loaders_for_library(path);
 
-    for (auto& loader : loaders) {
-        auto dynamic_object = loader->map();
-        if (dynamic_object)
-            s_global_objects.set(dynamic_object->filepath(), *dynamic_object);
-    }
+    // Verify that all objects are already mapped
+    for (auto& loader : loaders)
+        VERIFY(!loader->map());
 
     for (auto& loader : loaders) {
         bool success = loader->link(flags);
@@ -594,6 +601,36 @@ static Result<void, DlErrorMessage> __dladdr(void const* addr, Dl_info* info)
     return {};
 }
 
+static void __call_fini_functions()
+{
+    typedef void (*FiniFunc)();
+
+    for (auto& it : s_global_objects) {
+        auto object = it.value;
+
+        if (object->has_fini_array_section()) {
+            auto fini_array_section = object->fini_array_section();
+
+            FiniFunc* fini_begin = (FiniFunc*)(fini_array_section.address().as_ptr());
+            FiniFunc* fini_end = fini_begin + fini_array_section.entry_count();
+            while (fini_begin != fini_end) {
+                --fini_end;
+
+                // Android sources claim that these can be -1, to be ignored.
+                // 0 deffiniely shows up. Apparently 0/-1 are valid? Confusing.
+                if (!*fini_end || ((FlatPtr)*fini_end == (FlatPtr)-1))
+                    continue;
+                (*fini_end)();
+            }
+        }
+
+        if (object->has_fini_section()) {
+            auto fini_function = object->fini_section_function();
+            (fini_function)();
+        }
+    }
+}
+
 static void read_environment_variables()
 {
     for (char** env = s_envp; *env; ++env) {

Userland/Libraries/LibELF/DynamicLoader.cpp

@@ -803,7 +803,7 @@ void DynamicLoader::call_object_init_functions()
     typedef void (*InitFunc)();
 
     if (m_dynamic_object->has_init_section()) {
-        auto init_function = (InitFunc)(m_dynamic_object->init_section().address().as_ptr());
+        auto init_function = m_dynamic_object->init_section_function();
         (init_function)();
     }
 

Userland/Libraries/LibELF/DynamicObject.cpp

@@ -377,6 +377,12 @@ DynamicObject::InitializationFunction DynamicObject::init_section_function() con
     return (InitializationFunction)init_section().address().as_ptr();
 }
 
+DynamicObject::FinalizationFunction DynamicObject::fini_section_function() const
+{
+    VERIFY(has_fini_section());
+    return (FinalizationFunction)fini_section().address().as_ptr();
+}
+
 char const* DynamicObject::name_for_dtag(ElfW(Sword) d_tag)
 {
     switch (d_tag) {

Userland/Libraries/LibELF/DynamicObject.h

@@ -245,14 +245,19 @@ public:
     Symbol symbol(unsigned) const;
 
     typedef void (*InitializationFunction)();
+    typedef void (*FinalizationFunction)();
     typedef ElfW(Addr) (*IfuncResolver)();
 
     bool has_init_section() const { return m_init_offset != 0; }
     bool has_init_array_section() const { return m_init_array_offset != 0; }
     Section init_section() const;
     InitializationFunction init_section_function() const;
-    Section fini_section() const;
     Section init_array_section() const;
+
+    bool has_fini_section() const { return m_fini_offset != 0; }
+    bool has_fini_array_section() const { return m_fini_array_offset != 0; }
+    Section fini_section() const;
+    FinalizationFunction fini_section_function() const;
     Section fini_array_section() const;
 
     HashSection hash_section() const