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.

6 files changed, 36 insertions, 57 deletions

diff --git a/arch/x86_64/CMakeLists.txt b/arch/x86_64/CMakeLists.txt
index 6bb9e53..58daa3b 100644
--- a/arch/x86_64/CMakeLists.txt
+++ b/arch/x86_64/CMakeLists.txt
@@ -35,9 +35,8 @@ target_sources("arch-x86_64" PRIVATE
 
 target_sources("arch-x86_64" PRIVATE
     "src/boot/boot32.S"
-    "src/boot/crti.s"
-    "src/boot/crtn.s"
     "src/boot/entry64.s"
+    "src/boot/initialize_runtime.cpp"
     "src/boot/multiboot.s"
 )
 
diff --git a/arch/x86_64/scripts/kernel.ld b/arch/x86_64/scripts/kernel.ld
index 6ba8b80..064b8d7 100644
--- a/arch/x86_64/scripts/kernel.ld
+++ b/arch/x86_64/scripts/kernel.ld
@@ -68,33 +68,11 @@ SECTIONS
   . = ALIGN(4K);
   . += TEACHOS_VMA;
 
-  .init ALIGN(4K) : AT(ADDR(.init) - TEACHOS_VMA)
-  {
-    /* 
-     * Make sure that the crt code is wrapped around the compiler generated
-     * initialization code.
-     */
-    KEEP(*crti.s.o*(.init))
-    KEEP(*(EXCLUDE_FILE (*crti.s.o* *crtn.s.o*) .init))
-    KEEP(*crtn.s.o*(.init))
-  } :text
-
-  .fini ALIGN(4K) : AT(ADDR (.fini) - TEACHOS_VMA)
-  {
-    /* 
-     * Make sure that the crt code is wrapped around the compiler generated
-     * finalizer code.
-     */
-    KEEP(*crti.s.o*(.fini))
-    KEEP(*(EXCLUDE_FILE (*crti.s.o* *crtn.s.o*) .fini))
-    KEEP(*crtn.s.o*(.fini))
-  }
-
   .stl_text ALIGN(4K) : AT(ADDR (.stl_text) - TEACHOS_VMA)
   {
     *(.stl_text .stl_text*)
     KEEP(*libstdc++.a:*(.text .text.*))
-  }
+  } :text
 
   .text ALIGN(4K) : AT(ADDR (.text) - TEACHOS_VMA)
   {
@@ -114,18 +92,18 @@ SECTIONS
 
   .ctors ALIGN(4K) : AT (ADDR (.ctors) - TEACHOS_VMA)
   {
-    KEEP(*crtbegin.o(.ctors))
-    KEEP(*(EXCLUDE_FILE (*crtend.o) .ctors))
+    __ctors_start = .;
     KEEP(*(SORT(.ctors.*)))
-    KEEP(*crtend.o(.ctors))
+    KEEP(*(.ctors))
+    __ctors_end = .;
   } :data
 
-  .dtors ALIGN(4K) : AT (ADDR (.dtors) - TEACHOS_VMA)
+  .init_array ALIGN(4K) : AT (ADDR (.init_array) - TEACHOS_VMA)
   {
-    KEEP(*crtbegin.o(.dtors))
-    KEEP(*(EXCLUDE_FILE (*crtend.o) .dtors))
-    KEEP(*(SORT(.dtors.*)))
-    KEEP(*crtend.o(.dtors))
+    __init_array_start = .;
+    KEEP(*(SORT_BY_INIT_PRIORITY(.init_array.*)))
+    KEEP(*(.init_array))
+    __init_array_end = .;
   }
 
   .bss ALIGN(4K) : AT (ADDR (.bss) - TEACHOS_VMA)
diff --git a/arch/x86_64/src/boot/crti.s b/arch/x86_64/src/boot/crti.s
deleted file mode 100644
index 26878fe..0000000
--- a/arch/x86_64/src/boot/crti.s
+++ /dev/null
@@ -1,13 +0,0 @@
-.code64
-
-.section .init
-.global _init
-_init:
-    push %rbp
-    movq %rsp, %rbp
-
-.section .fini
-.global _fini
-_fini:
-    push %rbp
-    movq %rsp, %rbp
diff --git a/arch/x86_64/src/boot/crtn.s b/arch/x86_64/src/boot/crtn.s
deleted file mode 100644
index 06fb7ce..0000000
--- a/arch/x86_64/src/boot/crtn.s
+++ /dev/null
@@ -1,9 +0,0 @@
-.code64
-
-.section .init
-    popq %rbp
-    ret
-
-.section .fini
-    popq %rbp
-    ret
diff --git a/arch/x86_64/src/boot/entry64.s b/arch/x86_64/src/boot/entry64.s
index f575c50..110ced8 100644
--- a/arch/x86_64/src/boot/entry64.s
+++ b/arch/x86_64/src/boot/entry64.s
@@ -12,8 +12,8 @@ _entry64:
 
     xor %rax, %rax
 
-    call _init
-
+    call invoke_global_constructors
+    
     call main
 
 1:
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);
+  }
+}