TIS 1.2：可执行链接格式ELF标准，打造兼容软件的全面指南

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本文档是关于Tool Interface Standard (TIS) 可执行和链接格式(ELF) Specification的版本1.2。TIS，即工具接口标准委员会，于1995年5月发布了这份规范，旨在提供一种通用的软件标准，使得软件能够符合TIS的要求，实现跨平台的兼容性和互操作性。TIS允许开发者在不支付任何版权费用的情况下，利用这份规格书来确保其软件产品与TIS兼容，但需明确指出，这并不构成任何形式的独家许可，且使用者需自行承担可能存在的风险。 ELF（Executable and Linking Format）是一种用于操作系统和编译器之间交换可执行程序和共享库的文件格式，它最初由Digital Equipment Corporation (DEC) 开发，后来被业界广泛采用，包括在Unix、Linux、FreeBSD等系统中。ELF格式包含了丰富的元数据，如符号表、段信息和重定位表，使得链接器能够准确地定位代码、数据和符号引用，从而实现程序的动态链接和加载。本规格书详细描述了ELF的各种版本特性和结构，包括头部（ELF Header）、节（Sections）、符号表（Symbol Table）以及重定位表（Relocation Tables）。它还涵盖了如何创建、解析和处理不同类型的ELF文件，例如可执行文件（ELF Executable, .exe或.dyn）和共享库（ELF Shared Object, .so）。此外，文档强调了对知识产权的尊重，规定了使用规范，如不得侵犯他人的专利权，并明确指出TIS委员会不对规范中的错误或信息更新负责。值得注意的是，文中提到了IBM作为注册商标，OS/2是IBM的产品，以及Intel的商标，这些品牌在ELF相关技术中可能扮演着重要角色，如处理器架构或特定平台的优化。这份TIS ELF规范版本1.2是软件开发人员和工具厂商的重要参考资料，它定义了如何在广泛的平台上构建、链接和运行可执行程序，同时提供了法律依据和责任划分，确保了技术的标准化和互操作性。对于深入理解并实施ELF标准的开发者来说，它是不可或缺的技术文档。

Introduction

1-2 Book I: ELF (Executable and Linking Format)

An ELF header resides at the beginning and holds a "road map'' describing the file's

organization. Sections hold the bulk of object file information for the linking view: instructions,

data, symbol table, relocation information, and so on. Descriptions of special sections appear

later in this section. Chapter 2 also describes segments and the program execution view of the

file.

A program header table, if present, tells the system how to create a process image. Files used

to build a process image (execute a program) must have a program header table; relocatable

files do not need one. A section header table contains information describing the file's sections.

Every section has an entry in the table; each entry gives information such as the section name,

the section size, and so on. Files used during linking must have a section header table; other

object files may or may not have one.

NOTE. Although the figure shows the program header table immediately after the

ELF header, and the section header table following the sections, actual

files may differ. Moreover, sections and segments have no specified

order. Only the ELF header has a fixed position in the file.

Data Representation

As described here, the object file format supports various processors with 8-bit bytes and 32-bit

architectures. Nevertheless, it is intended to be extensible to larger (or smaller) architectures.

Object files therefore represent some control data with a machine-independent format, making

it possible to identify object files and interpret their contents in a common way. Remaining

data in an object file use the encoding of the target processor, regardless of the machine on

which the file was created.

All data structures that the object file format defines follow the "natural'' size and alignment

guidelines for the relevant class. If necessary, data structures contain explicit padding to ensure

4-byte alignment for 4-byte objects, to force structure sizes to a multiple of 4, and so on. Data

also have suitable alignment from the beginning of the file. Thus, for example, a structure

containing an

Elf32_Addr member will be aligned on a 4-byte boundary within the file.

For portability reasons, ELF uses no bit fields.

Figure 1-2. 32-Bit Data Types

Name Size Alignment Purpose

Elf32_Addr 4 4 Unsigned program address

Elf32_Half 2 2 Unsigned medium integer

Elf32_Off 4 4 Unsigned file offset

Elf32_Sword 4 4 Signed large integer

Elf32_Word 4 4 Unsigned large integer

unsigned char 1 1 Unsigned small integer

Introduction

OBJECT FILES 1-3

Character Representations

This section describes the default ELF character representation and defines the standard

character set used for external files that should be portable among systems. Several external

file formats represent control information with characters. These single-byte characters use the

7-bit ASCII character set. In other words, when the ELF interface document mentions character

constants, such as, ‘/’ or ‘\n’ their numerical values should follow the 7-bit ASCII guidelines.

For the previous character constants, the single-byte values would be 47 and 10, respectively.

Character values outside the range of 0 to 127 may occupy one or more bytes, according to the

character encoding. Applications can control their own character sets, using different character

set extensions for different languages as appropriate. Although TIS-conformance does not

restrict the character sets, they generally should follow some simple guidelines.

• Character values between 0 and 127 should correspond to the 7-bit ASCII code. That is,

character sets with encodings above 127 should include the 7-bit ASCII code as a subset.

• Multibyte character encodings with values above 127 should contain only bytes with values

outside the range of 0 to 127. That is, a character set that uses more than one byte per character

should not "embed'' a byte resembling a 7-bit ASCII character within a multibyte, non-ASCII

character.

• Multibyte characters should be self-identifying. That allows, for example, any multibyte

character to be inserted between any pair of multibyte characters, without changing the

characters' interpretations.

These cautions are particularly relevant for multilingual applications.

NOTE. There are naming conventions for ELF constants that have processor

ranges specified. Names such as DT_, PT_, for processor specific

extensions, incorporate the name of the processor: DT_M32_SPECIAL,

for example. However, pre-existing processor extensions not using this

convention will be supported.

Pre-existing Extensions

DT_JMP_REL

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TIS 1.2：可执行链接格式ELF标准，打造兼容软件的全面指南

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