Initial commit: XOmB exokernel foundation

Core kernel infrastructure:
- Multiboot2 boot with GRUB, long mode setup, higher-half kernel
- Serial port output for debugging
- Unified boot info abstraction for future UEFI support

Memory management:
- Physical frame allocator with bitmap tracking
- Page table manipulation via recursive mapping (PML4[510])
- Support for 4KB, 2MB, and 1GB page mappings
- TLB invalidation and proper NXE support

Build system:
- Cargo-based build with custom x86_64 target
- Makefile for QEMU and Bochs testing
- GRUB ISO generation for multiboot2 boot

linker-multiboot2.ld

@@ -0,0 +1,95 @@
+/* Linker script for XOmB multiboot2 kernel (higher-half) */
+
+ENTRY(_start)
+
+/* Physical load address (standard location for multiboot) */
+KERNEL_PHYS = 0x100000;
+
+/* Virtual address base (top 2GB for kernel code model compatibility) */
+KERNEL_VIRT = 0xFFFFFFFF80000000;
+
+SECTIONS
+{
+    /* ===== Boot sections at physical addresses ===== */
+    /* These run before paging maps the higher-half */
+
+    . = KERNEL_PHYS;
+    _kernel_phys_start = .;
+
+    /* Multiboot2 header must be in the first 32KB of the file */
+    .multiboot2_header : ALIGN(8)
+    {
+        KEEP(*(.multiboot2_header))
+    }
+
+    /* Boot code (32-bit startup and 64-bit trampoline) */
+    /* Must be at physical address for initial execution */
+    .text.boot : ALIGN(4096)
+    {
+        *(.text.boot)
+    }
+
+    /* Record end of low-memory boot sections */
+    . = ALIGN(4096);
+    _boot_end_phys = .;
+
+    /* ===== Kernel sections at higher-half virtual addresses ===== */
+
+    /* Calculate physical address where higher-half sections will be loaded */
+    _higher_half_phys = .;
+
+    /* Switch to higher-half virtual addresses */
+    . = KERNEL_VIRT + _higher_half_phys;
+
+    /* Main kernel code */
+    .text : AT(_higher_half_phys)
+    {
+        _text_start = .;
+        *(.text .text.*)
+        _text_end = .;
+    }
+
+    /* Read-only data - use ALIGN to ensure proper separation */
+    . = ALIGN(4096);
+    .rodata : AT(_higher_half_phys + (. - (KERNEL_VIRT + _higher_half_phys)))
+    {
+        _rodata_start = .;
+        *(.rodata .rodata.*)
+        _rodata_end = .;
+    }
+
+    /* Initialized data */
+    . = ALIGN(4096);
+    .data : AT(_higher_half_phys + (. - (KERNEL_VIRT + _higher_half_phys)))
+    {
+        _data_start = .;
+        *(.data .data.*)
+        _data_end = .;
+    }
+
+    /* BSS (uninitialized data) */
+    . = ALIGN(4096);
+    .bss (NOLOAD) : AT(_higher_half_phys + (. - (KERNEL_VIRT + _higher_half_phys)))
+    {
+        _bss_start = .;
+        __bss_start = .;
+        *(.bss .bss.*)
+        *(.bss.stack)
+        *(COMMON)
+        __bss_end = .;
+        _bss_end = .;
+    }
+
+    /* Kernel end markers */
+    . = ALIGN(4096);
+    _kernel_virt_end = .;
+    _kernel_phys_end = _higher_half_phys + (. - (KERNEL_VIRT + _higher_half_phys));
+
+    /* Discard unnecessary sections */
+    /DISCARD/ :
+    {
+        *(.comment)
+        *(.note.*)
+        *(.eh_frame*)
+    }
+}