x86_64: implement robust C++ global initialization

Implement a comprehensive mechanism to ensure correct C++ runtime
initialization before the kernel main function is called. This replaces
the previous, incomplete reliance on an `_init` function.

The new design robustly handles both legacy `.ctors` and modern
`.init_array` initialization schemes used by the GNU toolchain. A single
C++ function, `invoke_global_constructors`, now iterates through both
arrays of function pointers to ensure all types of global initializers
are executed.

1 files changed, 24 insertions, 0 deletions

diff --git a/arch/x86_64/src/boot/initialize_runtime.cpp b/arch/x86_64/src/boot/initialize_runtime.cpp
new file mode 100644
index 0000000..9a3df0e
--- /dev/null
+++ b/arch/x86_64/src/boot/initialize_runtime.cpp
@@ -0,0 +1,24 @@
+#include <algorithm>
+#include <functional>
+#include <span>
+
+extern "C"
+{
+  using global_initializer = auto (*)() -> void;
+
+  extern global_initializer __ctors_start;
+  extern global_initializer __ctors_end;
+  extern global_initializer __init_array_start;
+  extern global_initializer __init_array_end;
+
+  auto invoke_global_constructors() -> void
+  {
+    auto constructors = std::span{&__ctors_start, &__ctors_end};
+    auto initializers = std::span{&__init_array_start, &__init_array_end};
+
+    auto apply_invoke = [](auto invokable) { return std::invoke(invokable); };
+
+    std::ranges::for_each(constructors, apply_invoke);
+    std::ranges::for_each(initializers, apply_invoke);
+  }
+}