Architecture

🏛 Kernel Core

Sex is a microkernel, meaning it implements only the most fundamental primitives required to build a complete operating system. The goal is to keep the privileged code within a Tiny Trusted Computing Base (TCB) of roughly 5–8 kLOC.

🌟 Design Principles

• Global Single Virtual Address Space (SAS): Every thread, process, and server shares the same 64-bit virtual address space.
• Hardware-Enforced Protection: Isolation is achieved through hardware features like Intel PKU/MPK and CHERI (where available), rather than page table switching.
• Zero-Copy IPC: High-performance messaging through shared memory regions and Protected Procedure Calls (PDX).
• Capability-Based Security: All system resources (memory, IPC ports, interrupts) are managed via unforgeable capabilities.
• Asynchronous I/O (Zero Mediation): Hardware signals are pushed into lockless ring buffers, eliminating context switch jitter.

🔒 Memory & Protection Domains

🌏 Global Single Virtual Address Space (SAS)

In Sex, all data is mapped into a single 64-bit address space. This removes the need for page table switching (and the resulting TLB flushes) when moving between protection domains. Addresses are globally unique across the entire system.

🛡 Protection Domains (PDs)

Isolation is enforced by Protection Domains (PDs). Each domain represents a logical set of permissions (Read, Write, Execute) over specific address ranges.

• Intel PKU / MPK: Sex uses Intel Memory Protection Keys (PKU) to assign a 4-bit "key" to each page. A hardware register (PKRU) defines the current thread's access rights for each of the 16 available keys.
• Atomic PKRU Management: Domain masks are managed via atomic operations to ensure thread-safe switches in multicore environments.

⚡ IPC Primitives: PDX & Ring Buffers

🚀 Protected Procedure Calls (PDX)

The core IPC mechanism is a synchronous Protected Procedure Call (PDX).

1. Safe PDX: Validates a capability before performing a hardware-accelerated domain switch.
2. Fused PDX: Bypasses capability checks for high-frequency hot-paths between "fused" domains.

📦 Asynchronous Ring Buffers

For interrupts and high-volume data transfer, Sex uses lockless, SPSC (Single Producer, Single Consumer) ring buffers. These are cache-line aligned to prevent false sharing on 128-core systems.

🗝 Capability System

Sex uses a Sparse Capability system. A capability is an unforgeable token that proves its holder has the right to access a specific resource.

🛠 Capability Types

• Memory Capabilities: Define access (R/W/X) to a range of virtual memory via "Memory Lending".
• IPC Capabilities: Grant permission to call or listen on a specific PDX port.
• Interrupt Capabilities: Allow a user-space sexdrive to respond to hardware interrupts via ring buffers.
• Domain Capabilities: Allow management and configuration of Protection Domains.

🖥 User-space Servers

All traditional OS services run in isolated user-space Protection Domains.

Server	Responsibility
sext	Manages the global VAS and handles asynchronous page faults via large pages.
Capability Server	Central authority for capability policy, distributed for local core scaling.
sexfiles	Unified file system interface (Phase 3).
sexnet	User-space TCP/IP stack (Phase 3).
sexinput	Isolated hardware management (Mouse, Keyboard, etc.).

🗺 Architecture Roadmap

Phase	Status	Description
0: Bootstrap	Complete ✅	Bootable kernel skeleton, basic HAL, VGA/serial console, UEFI.
1: Core Primitives	Stable 🚀	Physical memory manager, sexting, Protection Domains, PDX, SMP boot.
2: Capabilities & Servers	Stable 🚀	Capability engine, user-space sext, SMP 128-core, interrupt management.
3: Services & sexfiles	Stable 🚀	Standalone sexfiles, real block I/O, ramfs, POSIX syscall bridge.
4: Distribution	Complete ✅	Standalone sexnet, remote PDX routing, zero-copy packet transfer.
5: Hardware & sexdrive	Complete ✅	ARM64 design, DDE-Sex shim, NVIDIA 3070 GPU, sexdrive server.
6: Signal Trampoline	Complete ✅	Background trampoline threads, POSIX sigaction ABI, lock-free signals.
7: Memory Subsystem	Complete ✅	Lock-free buddy allocator, PKU domain management, async #PF forwarding.
8: ELF Loader + PD Spawn	Complete ✅	ELF segment parsing, PD creation, sys_spawn_pd.
9: Driver Enablement	Complete ✅	NVMe/AHCI driver, zero-copy DMA, MSI-X, input stack.
10: Graphical Plumbing	Complete ✅	sexdisplay server, HID routing, zero-copy graphics, Mesa bootstrap.
11: GNU Pipeline	Complete ✅	POSIX pipes, fork/exec, coreutils, signal delivery, Lin-Sex compatibility.
12: Dynamic Translators	Complete ✅	sexnode translator, on-the-fly ELF→Sex binary translation.
13: Self-Hosting	Complete ✅	sex-gemini agent, sexstore packages, full in-Sex build loop.
14: Formal Verification	Complete ✅	Refined allocator, hardened PKU init, CHERI prep, verification hooks.
15: Linux Driver Translation	Complete ✅	DDE-style wrappers, on-the-fly Linux driver translation, hot-plug.
16: Userspace Maturity	Complete ✅	Operational sexnode, GitHub fetch, Linux benchmarks, FLSCHED verification.
19: sexfiles Overhaul	Complete ✅	100% lock-free VFS, zero-copy PKU handover, lock-free LRU cache.
20: Graphical Sex-Store	In Progress 🏗️	One-click sexting, binary caching, app store GUI.