# x86_64 Virtual Memory Layout

┌─────────────────────┐ 0xFFFFFFFF_FFFFFFFF
│    Higher Half      │
├─────────────────────┤ 0xFFFFFFFF_FF600000
│     Recursive       │ (Optional: for page table manipulation)
│    Page Mapping     │
├─────────────────────┤ 0xFFFFFFFF_C0000000
│   Kernel Stacks     │ (Multiple 16KB or 32KB stacks, guard pages between)
├─────────────────────┤ 
│   Kernel Heap       │ (Dynamic allocation for kernel)
├─────────────────────┤ 0xFFFFFFFF_80000000
│   Kernel Code       │ (Loaded by bootloader)
├─────────────────────┤ 0x00007FFF_FFFFFFFF
│       Guard         │ (Prevent user->kernel pointer errors)
├─────────────────────┤ 0x00007FFF_00000000
│    User Stacks      │ (Grows down)
├─────────────────────┤
│         ...         │ (Available for mmap, shared libraries, etc.)
├─────────────────────┤
│     User Heap       │ (Grows up)
├─────────────────────┤
│    Program .bss     │ (Uninitialized data)
│    Program .data    │ (Initialized data)
│    Program .rodata  │ (Read-only data)
│    Program .text    │ (Code)
├─────────────────────┤ 0x0000000000400000
│       Guard         │ (Catch null pointer dereference)
└─────────────────────┘ 0x0000000000000000

## Memory Regions Explanation

### Kernel Space (Higher Half)
- **Kernel Code**: Fixed location at -2GB
- **Kernel Heap**: Dynamic memory for kernel operations
- **Kernel Stacks**: Multiple stacks for different CPU modes/tasks
- **Recursive Mapping**: Optional region for page table manipulation

### User Space (Lower Half)
- **Guard Pages**: Protect against null pointer dereference (0-4MB)
- **Program Sections**: Start at 0x400000
  - .text: Program code
  - .rodata: Read-only data
  - .data: Initialized data
  - .bss: Uninitialized data
- **User Heap**: Grows upward from end of program sections
- **Dynamic Region**: Space for mmap allocations, shared libraries
- **User Stacks**: Grows downward from 0x00007FFF_00000000

### Key Features
- Full 48-bit addressing support (256TB virtual address space)
- Clear separation between user and kernel space
- Protected null pointer dereference
- Room for stack/heap growth
- Space for dynamic libraries and mappings