x86_64 Architecture

Relevant source files

src/x86_64/mod.rs

Purpose and Scope

This document provides an overview of the x86_64 architecture support in axcpu, which represents the most comprehensive and mature architecture implementation in the codebase. The x86_64 module provides CPU context management, trap handling, system call support, and hardware initialization for Intel/AMD 64-bit processors.

This page covers the overall module organization and key data structures. For detailed information about specific aspects, see:

Context switching and CPU state management: Context Management
Exception and interrupt handling: Trap and Exception Handling
System call implementation: System Calls
Hardware initialization procedures: System Initialization

For user space support across all architectures, see User Space Support.

Module Organization

The x86_64 architecture support is organized into several specialized modules, each handling different aspects of CPU management:

x86_64 Module Structure

Sources: src/x86_64/mod.rs(L1 - L21)

Core Data Structures

The x86_64 implementation exports several key data structures that represent different aspects of CPU state:

Exported Types and Their Purposes

flowchart TD
subgraph subGraph2["External Dependencies"]
    X86_64_CRATE["x86_64::structures::tss"]
end
subgraph subGraph1["Hardware Tables"]
    TASK_CONTEXT["TaskContextMinimal context for task switching"]
    EXTENDED_STATE["ExtendedStateFPU and SIMD state"]
    TRAP_FRAME["TrapFrameComplete CPU state during exceptions"]
    FXSAVE_AREA["FxsaveAreax86 FXSAVE format"]
    GDT_STRUCT["GdtStructGlobal descriptor table"]
    IDT_STRUCT["IdtStructInterrupt descriptor table"]
    TSS["TaskStateSegmentTask state segment"]
end
subgraph subGraph0["Context Management"]
    TASK_CONTEXT["TaskContextMinimal context for task switching"]
    EXTENDED_STATE["ExtendedStateFPU and SIMD state"]
    TRAP_FRAME["TrapFrameComplete CPU state during exceptions"]
    FXSAVE_AREA["FxsaveAreax86 FXSAVE format"]
    GDT_STRUCT["GdtStructGlobal descriptor table"]
end

GDT_STRUCT --> TSS
TASK_CONTEXT --> EXTENDED_STATE
TRAP_FRAME --> FXSAVE_AREA
TSS --> X86_64_CRATE

Sources: src/x86_64/mod.rs(L17 - L20)

Data Structure	Purpose	Module Source
TaskContext	Stores callee-saved registers and stack pointer for task switching	context
TrapFrame	Captures complete CPU state during exceptions and interrupts	context
ExtendedState	Manages FPU and SIMD register state	context
FxsaveArea	x86-specific FXSAVE/FXRSTOR data format	context
GdtStruct	Global descriptor table management	gdt
IdtStruct	Interrupt descriptor table management	idt
TaskStateSegment	Hardware task state segment (from x86_64 crate)	External

Feature-Based Compilation

The x86_64 module uses conditional compilation to enable different capabilities based on build configuration:

Conditional Module Loading

flowchart TD
subgraph subGraph2["Compilation Conditions"]
    TARGET_NONE["target_os = \none\"]
    USPACE_FEAT["feature = \uspace\"]
end
subgraph subGraph1["Conditional Modules"]
    TRAP_MOD["trap.rs"]
    SYSCALL_MOD["syscall.rs"]
    USPACE_MOD["uspace.rs"]
end
subgraph subGraph0["Base Modules"]
    BASE_MODS["context, gdt, idt, asm, init"]
end

BASE_MODS --> SYSCALL_MOD
BASE_MODS --> TRAP_MOD
BASE_MODS --> USPACE_MOD
TARGET_NONE --> TRAP_MOD
USPACE_FEAT --> SYSCALL_MOD
USPACE_FEAT --> USPACE_MOD

Sources: src/x86_64/mod.rs(L8 - L15)

The conditional compilation enables:

Trap handling (target_os = "none"): Exception and interrupt processing for bare-metal environments
User space support (feature = "uspace"): System call handling and user-kernel transitions
System call interface (feature = "uspace"): Dedicated syscall entry points and parameter handling

Key Components Overview

The x86_64 architecture support provides several essential capabilities:

Hardware Abstraction Layer

Context Management: Efficient task switching using minimal register sets in TaskContext
Exception Handling: Complete trap frame capture and restoration for all exception types
Memory Management: Integration with x86_64 paging hardware and TLB management
FPU/SIMD Support: Extended state preservation for floating-point and vector operations

System Integration

Descriptor Tables: GDT and IDT management for privilege level transitions
Task State Segment: Hardware task switching support (though typically unused in modern kernels)
System Calls: Fast system call entry points using SYSCALL/SYSRET instructions
User Space: Complete user-kernel isolation with separate address spaces

Assembly Interface

The asm module provides low-level operations that cannot be expressed in safe Rust, including:

Context switching routines
Trap entry/exit sequences
CPU state manipulation
Hardware feature detection and configuration

This architecture implementation serves as the foundation for kernel development on x86_64 platforms, providing all necessary abstractions for task management, memory protection, and hardware interaction.

Sources: src/x86_64/mod.rs(L1 - L21)

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