深入理解Intel 80386：汇编指南与保护模式详解

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"《英特尔80386程序员参考手册》（1986年版）是针对Intel 80386处理器的专业文档，由英特尔公司编写，旨在为程序员提供全面的技术指导。该手册涵盖了重要的汇编指令集、80386微处理器的架构细节以及保护模式等核心内容。 80386作为一代经典处理器，其指令集包含了基础的算术逻辑运算、数据移动、条件转移、控制流操作等，这些指令对于理解并编写高效的机器级代码至关重要。手册详尽地解释了如何通过指令集进行内存访问、处理中断、执行多任务处理以及利用80386的硬件保护机制，如段寄存器、段描述符表和分段式存储管理，以实现程序的隔离和安全性。保护模式是80386的一个重要特性，它允许用户空间程序对硬件直接访问，同时也提供了内核模式以执行系统级任务。手册阐述了两种模式之间的权限划分，以及如何在模式切换时确保数据的一致性和系统稳定性。此外，手册还提醒读者注意版权和使用限制，强调Intel保留随时更新规格的权利，并建议在购买前联系销售办公室获取最新版本。手册中还列出了Intel公司的多个商标，这些商标可用于标识真正的Intel产品，以避免混淆或侵权。《英特尔80386程序员参考手册》是80386时代软件开发人员的必备参考资料，对于深入理解微处理器工作原理、优化代码性能以及开发兼容80386架构的系统具有不可替代的价值。"

INTEL 80386 PROGRAMMER'S REFERENCE MANUAL 1986

Page 16 of 421

1. Protected Mode.

2. Real-Address Mode.

3. Virtual 8086 Mode.

Protected mode is the natural 32-bit environment of the 80386 processor. In

this mode all instructions and features are available.

Real-address mode (often called just "real mode") is the mode of the

processor immediately after RESET. In real mode the 80386 appears to

programmers as a fast 8086 with some new instructions. Most applications of

the 80386 will use real mode for initialization only.

Virtual 8086 mode (also called V86 mode) is a dynamic mode in the sense

that the processor can switch repeatedly and rapidly between V86 mode and

protected mode. The CPU enters V86 mode from protected mode to execute an

8086 program, then leaves V86 mode and enters protected mode to continue

executing a native 80386 program.

The features that are available to applications programs in protected mode

and to all programs in V86 mode are the same. These features form the

content of Part I. The additional features that are available to systems

software in protected mode form Part II. Part III explains real-address

mode and V86 mode, as well as how to execute a mix of 32-bit and 16-bit

programs.

Available in All Modes Part I ── Applications Programming

Available in Protected Part II ── Systems Programming

Mode Only

Compatibility Modes Part III ── Compatibility

1.1.1 Part I ── Applications Programming

This part presents those aspects of the architecture that are customarily

used by applications programmers.

Chapter 2 ── Basic Programming Model: Introduces the models of memory

organization. Defines the data types. Presents the register set used by

applications. Introduces the stack. Explains string operations. Defines the

parts of an instruction. Explains addressing calculations. Introduces

interrupts and exceptions as they may apply to applications programming.

Chapter 3 ── Application Instruction Set: Surveys the instructions commonly

used for applications programming. Considers instructions in functionally

related groups; for example, string instructions are considered in one

section, while control-transfer instructions are considered in another.

Explains the concepts behind the instructions. Details of individual

instructions are deferred until Part IV, the instruction-set reference.

INTEL 80386 PROGRAMMER'S REFERENCE MANUAL 1986

Page 17 of 421

1.1.2 Part II ── Systems Programming

This part presents those aspects of the architecture that are customarily

used by programmers who write operating systems, device drivers, debuggers,

and other software that supports applications programs in the protected mode

of the 80386.

Chapter 4 ── Systems Architecture: Surveys the features of the 80386 that

are used by systems programmers. Introduces the remaining registers and data

structures of the 80386 that were not discussed in Part I. Introduces the

systems-oriented instructions in the context of the registers and data

structures they support. Points to the chapter where each register, data

structure, and instruction is considered in more detail.

Chapter 5 ── Memory Management: Presents details of the data structures,

registers, and instructions that support virtual memory and the concepts of

segmentation and paging. Explains how systems designers can choose a model

of memory organization ranging from completely linear ("flat") to fully

paged and segmented.

Chapter 6 ── Protection: Expands on the memory management features of the

80386 to include protection as it applies to both segments and pages.

Explains the implementation of privilege rules, stack switching, pointer

validation, user and supervisor modes. Protection aspects of multitasking

are deferred until the following chapter.

Chapter 7 ── Multitasking: Explains how the hardware of the 80386 supports

multitasking with context-switching operations and intertask protection.

Chapter 8 ── Input/Output: Reveals the I/O features of the 80386, including

I/O instructions, protection as it relates to I/O, and the I/O permission

map.

Chapter 9 ── Exceptions and Interrupts: Explains the basic interrupt

mechanisms of the 80386. Shows how interrupts and exceptions relate to

protection. Discusses all possible exceptions, listing causes and including

information needed to handle and recover from the exception.

Chapter 10 ── Initialization: Defines the condition of the processor after

RESET or power-up. Explains how to set up registers, flags, and data

structures for either real-address mode or protected mode. Contains an

example of an initialization program.

Chapter 11 ── Coprocessing and Multiprocessing: Explains the instructions

and flags that support a numerics coprocessor and multiple CPUs with shared

memory.

Chapter 12 ── Debugging: Tells how to use the debugging registers of the

80386.

INTEL 80386 PROGRAMMER'S REFERENCE MANUAL 1986

Page 18 of 421

1.1.3 Part III ── Compatibility

Other parts of the book treat the processor primarily as a 32-bit machine,

omitting for simplicity its facilities for 16-bit operations. Indeed, the

80386 is a 32-bit machine, but its design fully supports 16-bit operands and

addressing, too. This part completes the picture of the 80386 by explaining

the features of the architecture that support 16-bit programs and 16-bit

operations in 32-bit programs. All three processor modes are used to

execute 16-bit programs: protected mode can directly execute 16-bit 80286

protected mode programs, real mode executes 8086 programs and real-mode

80286 programs, and virtual 8086 mode executes 8086 programs in a

multitasking environment with other 80386 protected-mode programs. In

addition, 32-bit and 16-bit modules and individual 32-bit and 16-bit

operations can be mixed in protected mode.

Chapter 13 ── Executing 80286 Protected-Mode Code: In its protected mode,

the 80386 can execute complete 80286 protected-mode systems, because 80286

capabilities are a subset of 80386 capabilities.

Chapter 14 ── 80386 Real-Address Mode: Explains the real mode of the 80386

CPU. In this mode the 80386 appears as a fast real-mode 80286 or fast 8086

enhanced with additional instructions.

Chapter 15 ── Virtual 8086 Mode: The 80386 can switch rapidly between its

protected mode and V86 mode, giving it the ability to multiprogram 8086

programs along with "native mode" 32-bit programs.

Chapter 16 ── Mixing 16-Bit and 32-Bit Code: Even within a program or task,

the 80386 can mix 16-bit and 32-bit modules. Furthermore, any given module

can utilize both 16-bit and 32-bit operands and addresses.

1.1.4 Part IV ── Instruction Set

Parts I, II, and III present overviews of the instructions as they relate

to specific aspects of the architecture, but this part presents the

instructions in alphabetical order, providing the detail needed by

assembly-language programmers and programmers of debuggers, compilers,

operating systems, etc. Instruction descriptions include algorithmic

description of operation, effect of flag settings, effect on flag settings,

effect of operand- or address-size attributes, effect of processor modes,

and possible exceptions.

1.1.5 Appendices

The appendices present tables of encodings and other details in a format

designed for quick reference by assembly-language and systems programmers.

INTEL 80386 PROGRAMMER'S REFERENCE MANUAL 1986

Page 20 of 421

● When loading a register, always load the undefined bits as zeros or

reload them with values previously stored from the same register.

────────────────────────────────────────────────────────────────────────────

NOTE

Depending upon the values of undefined register bits will make software

dependent upon the unspecified manner in which the 80386 handles these

bits. Depending upon undefined values risks making software incompatible

with future processors that define usages for these bits. AVOID ANY

SOFTWARE DEPENDENCE UPON THE STATE OF UNDEFINED 80386 REGISTER BITS.

Figure 1-1. Example Data Structure

GREATEST DATA STRUCTURE

ADDRESS

31 23 15 7 0 ◄──BIT

╔═══════════════╪═══════════════╪═══════════════╪═══════════════╗ OFFSET

║ ║28

╠═══════════════╪═══════════════╪═══════════════╪═══════════════╣

║ ║24

╠═══════════════╪═══════════════╪═══════════════╪═══════════════╣

║ ║20

╠═══════════════╪═══════════════╪═══════════════╪═══════════════╣

║ ║16

╠═══════════════╪═══════════════╪═══════════════╪═══════════════╣

║ ║12

╠═══════════════╪═══════════════╪═══════════════╪═══════════════╣

║ ║8

╠═══════════════╪═══════════════╪═══════════════╪═══════════════╣

║ UNDEFINED ║4

╠═══════════════╪═══════════════╪═══════════════╪═══════════════╣ SMALLEST

║ BYTE 3 BYTE 2 BYTE 1 BYTE 0 ║0 ADDRESS

╚═══════════════╪═══════════════╪═══════════════╪═══════════════╝▲

BYTE OFFSET───┘

1.3.3 Instruction Operands

When instructions are represented symbolically, a subset of the 80386

Assembly Language is used. In this subset, an instruction has the following

format:

label: prefix mnemonic argument1, argument2, argument3

where:

● A label is an identifier that is followed by a colon.

● A prefix is an optional reserved name for one of the instruction

prefixes.

● A mnemonic is a reserved name for a class of instruction opcodes that

have the same function.

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