Memory Map

Detailed memory layout of the NØNOS kernel.

---

Physical Memory Layout

The kernel is loaded at the standard x86 kernel location:

┌────────────────────────────────────────────────────────────────┐
│                    PHYSICAL MEMORY MAP                         │
├────────────────────────────────────────────────────────────────┤
│                                                                │
│  0x00000000 ─┬─ Real Mode IVT / BIOS Data                      │
│              │                                                 │
│  0x00100000 ─┼─ KERNEL LOAD ADDRESS (1 MB)                     │
│              │                                                 │
│              ├─ .multiboot    Bootloader handoff structure     │
│              │                                                 │
│  0x00101000 ─├─ .text         Executable code (R-X)            │
│              │                                                 │
│  0x00102000 ─├─ .rodata       Read-only data (R--)             │
│              │                                                 │
│  0x00103000 ─├─ .data         Initialized data (RW-)           │
│              │                                                 │
│  0x00104000 ─├─ .bss          Zero-initialized data (RW-)      │
│              │  __bss_start                                    │
│              │  __bss_end                                      │
│              │                                                 │
│  0x00105000 ─├─ .nonos.manifest   Kernel manifest (R--)        │
│              │  __nonos_manifest_start                         │
│              │  __nonos_manifest_end                           │
│              │                                                 │
│              ├─ .nonos.sig    Ed25519 signature (R--)          │
│              │  __nonos_signature_start                        │
│              │  __nonos_signature_end                          │
│              │  (aligned to 8 bytes)                           │
│              │                                                 │
│  0x001FF000 ─├─ __stack_bottom                                 │
│              │                                                 │
│              │  ┌────────────────────────┐                     │
│              │  │     KERNEL STACK       │                     │
│              │  │        64 KB           │                     │
│              │  │    (grows downward)    │                     │
│              │  └────────────────────────┘                     │
│              │                                                 │
│  0x0020F000 ─├─ __stack_top                                    │
│              │                                                 │
│              │  ... Heap / Dynamic Memory ...                  │
│              │                                                 │
└────────────────────────────────────────────────────────────────┘

---

Linker Script Symbols

The linker exports these symbols for runtime use:

Symbol	Description
__bss_start	Start of BSS section
__bss_end	End of BSS section
__nonos_manifest_start	Start of manifest section
__nonos_manifest_end	End of manifest section
__nonos_signature_start	Start of signature (64 bytes)
__nonos_signature_end	End of signature
__stack_bottom	Bottom of kernel stack
__stack_top	Top of kernel stack

---

Virtual Address Space

NØNOS uses higher-half kernel mapping:

┌────────────────────────────────────────────────────────────────┐
│                   VIRTUAL ADDRESS SPACE                         │
├────────────────────────────────────────────────────────────────┤
│                                                                │
│  0xFFFFFFFF_FFFFFFFF ─┐                                        │
│                       │  KERNEL SPACE                          │
│  0xFFFFFFFF_80000000 ─┤  (Higher Half)                         │
│                       │                                        │
│                       ├─ .text      (R-X) Executable code      │
│                       │                                        │
│                       ├─ .rodata    (R--) Constants, strings   │
│                       │                                        │
│                       ├─ .data      (RW-) Global variables     │
│                       │                                        │
│                       ├─ .bss       (RW-) Zero-initialized     │
│                       │                                        │
│                       ├─ Heap       (RW-) kmalloc / Box        │
│                       │                                        │
│                       ├─ Per-CPU    (RW-) Thread-local storage │
│                       │                                        │
│                       └─ Stacks     (RW-) Per-task stacks      │
│                          (with guard pages)                    │
│                                                                │
│  0x00007FFF_FFFFFFFF ─┐                                        │
│                       │  USER SPACE                            │
│                       │  (Reserved for future use)             │
│  0x00000000_00000000 ─┘                                        │
│                                                                │
└────────────────────────────────────────────────────────────────┘

Page Table Structure

NØNOS uses 4-level x86_64 paging:

CR3 Register
     │
     ▼
┌─────────┐     ┌─────────┐     ┌─────────┐     ┌─────────┐
│  PML4   │────►│  PDPT   │────►│   PD    │────►│   PT    │
│ 512 ent │     │ 512 ent │     │ 512 ent │     │ 512 ent │
└─────────┘     └─────────┘     └─────────┘     └─────────┘
                                                     │
                                                     ▼
                                              Physical Frame
                                                 (4 KB)

Page Sizes

Size	Levels Used	Address Bits
4 KB	PML4 → PDPT → PD → PT	12
2 MB	PML4 → PDPT → PD (huge)	21
1 GB	PML4 → PDPT (huge)	30

---

Page Flags

Flag	Bit	Description
Present	0	Page is mapped
Writable	1	Write access allowed
User	2	User-mode accessible
Write-Through	3	Write-through caching
Cache Disable	4	Disable caching
Accessed	5	Page was accessed
Dirty	6	Page was written
Huge	7	2MB or 1GB page
Global	8	Don't flush from TLB
No-Execute	63	Disable code execution

W^X Enforcement

NØNOS enforces Write XOR Execute (W^X):

Section	Writable	Executable
.text	No	Yes
.rodata	No	No
.data	Yes	No
.bss	Yes	No
Heap	Yes	No
Stack	Yes	No

No page is ever both writable AND executable.

---

Stack Layout

Each task has its own stack with guard pages:

┌────────────────────────┐ High Address
│      GUARD PAGE        │ (Unmapped - triggers page fault)
│      (4 KB)            │
├────────────────────────┤
│                        │
│                        │
│     STACK SPACE        │
│       (64 KB)          │
│                        │
│    (grows downward)    │
│          │             │
│          ▼             │
│                        │
├────────────────────────┤
│      GUARD PAGE        │ (Unmapped - triggers page fault)
│      (4 KB)            │
└────────────────────────┘ Low Address

---

Heap Allocator

NØNOS uses a linked-list allocator:

Parameter	Value
Allocator Type	Linked-list
Thread Safety	Spinlock
Minimum Allocation	8 bytes
Page Allocation	≥4 KB direct
Growth	On demand

---

KASLR

Kernel Address Space Layout Randomization:

• Kernel base randomized at boot

• Stack locations randomized

• Entropy source: RDRAND/RDSEED

---

Memory Regions from UEFI

The bootloader passes memory map from UEFI:

Type	Description	Usage
Conventional	Available RAM	Allocation
Reserved	Hardware reserved	Avoid
ACPI Reclaim	ACPI tables (reclaimable)	Parse then free
ACPI NVS	ACPI non-volatile	Preserve
Unusable	Defective memory	Avoid
Framebuffer	GPU memory	Display only