LibELF: Actually do the library mapping as early as possible

We previously trusted the `map` part in `map_library` too much, and
assumed that this would already lock in the binary at its final place.

However, the `map()` function of the loader was only called in
`load_main_library`, which ran only right before jumping to the
entrypoint.

Make our binary loading a bit more stable by actually mapping the binary
right after we read its information, and only do the linking right
before jumping to the entrypoint.

Userland/Libraries/LibELF/DynamicLinker.cpp

@@ -98,6 +98,10 @@ static Result<NonnullRefPtr<DynamicLoader>, DlErrorMessage> map_library(String c
  s_current_tls_offset -= loader->tls_size_of_current_object();
  loader->set_tls_offset(s_current_tls_offset);
 
+ // This actually maps the library at the intended and final place.
+ auto main_library_object = loader->map();
+ s_global_objects.set(get_library_name(filename), *main_library_object);
+
  return loader;
 }
 
@@ -316,12 +320,8 @@ static NonnullRefPtrVector<DynamicLoader> collect_loaders_for_library(String con
  return loaders;
 }
 
-static Result<NonnullRefPtr<DynamicLoader>, DlErrorMessage> load_main_library(String const& name, int flags, bool skip_global_objects)
+static Result<void, DlErrorMessage> link_main_library(String const& name, int flags, bool skip_global_objects)
 {
- auto main_library_loader = *s_loaders.get(name);
- auto main_library_object = main_library_loader->map();
- s_global_objects.set(name, *main_library_object);
-
  auto loaders = collect_loaders_for_library(name, skip_global_objects);
 
  for (auto& loader : loaders) {
@@ -360,7 +360,7 @@ static Result<NonnullRefPtr<DynamicLoader>, DlErrorMessage> load_main_library(St
  loader.load_stage_4();
  }
 
- return NonnullRefPtr<DynamicLoader>(*main_library_loader);
+ return {};
 }
 
 static Result<void, DlErrorMessage> __dlclose(void* handle)
@@ -447,7 +447,7 @@ static Result<void*, DlErrorMessage> __dlopen(char const* filename, int flags)
  return result2.error();
  }
 
- auto result = load_main_library(library_name, flags, true);
+ auto result = link_main_library(library_name, flags, true);
  if (result.is_error())
  return result.error();
 
@@ -583,12 +583,12 @@ void ELF::DynamicLinker::linker_main(String&& main_program_name, int main_progra
 
  auto entry_point_function = [&main_program_name] {
  auto library_name = get_library_name(main_program_name);
- auto result = load_main_library(library_name, RTLD_GLOBAL | RTLD_LAZY, false);
+ auto result = link_main_library(library_name, RTLD_GLOBAL | RTLD_LAZY, false);
  if (result.is_error()) {
  warnln("{}", result.error().text);
  _exit(1);
  }
- auto& main_executable_loader = result.value();
+ auto& main_executable_loader = *s_loaders.get(library_name);
  auto entry_point = main_executable_loader->image().entry();
  if (main_executable_loader->is_dynamic())
  entry_point = entry_point.offset(main_executable_loader->base_address().get());