Executable and Linkable Format (ELF)elf文件格式说明文档，英文

文件名称: Executable and Linkable Format (ELF)

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详细说明：elf文件格式说明文档，英文 1 OBJECT FILES Introduction 1-1 ELF Header 1-3 Sections 1-8 String Table 1-16 Symbol Table 1-17 Relocation 1-21 2 PROGRAM LOADING AND DYNAMIC LINKING Introduction 2-1 Program Header 2-2 Program Loading 2-7 Dynamic Linking 2-10 3 C LIBRARY C Library 3-1 I Index Index I-1Portable Formats Specification, Version 1.1 Tool Interface Stand ards(TIs) Tool Interface Standards(TIS) Portable Formats Sipation, Version 1.1 The Executable and Linking Format was originally developed and published by UNIX System Labora- tories (USL) as part of the Application Binary Interface(ABI). The Tool Interface Standards committee (TIs has selected the evolving elF standard as a portable object file format that works on 32-bit Intel Architecture environments for a variety of operating systems The elf standard is intended to streamline software development by providing developers with a set of binary interface definitions that extend across multiple operating environments. This should reduce the number of different interface implementations, thereby reducing the need for recoding and recompiling d This document is intended for developers who are creating object or executable files on various 32-bit environment operating systems. It is divided into the following thrce parts Part 1,Object Files'"describes the elF object file format for the three main types of object files Part 2," Program Loading and Dynamic Linking describes the object file information and system actions that create running programs Part 3, C Library lists the symbols contained in the standard ANSi C and routines, and the global data symbo ls required by the routines Tool Interface Standards(TIS Portable Formats Specification, Version 1.1 Tool Interface Standards(TIS) Portable Formats Specification, Version 1.1 Part 1 describes the iABl object file format, called ELF (Executable and Linking Format). There are three main types of object files A relocatable file holds code and data suitable for linking with other object files to create an execut- able or a shared object file An executable file holds a program suitable for exccution; the file specifics how (BA OS)creates a program s process image A shared object file holds code and data suitable for linking in two contexts. First, the link editor [see (SD CMD)] may process it with other relocatable and shared object files to create another object file. Second, the dynamic linker combines it with an executable file and other shared objects to create a process image. Created by the assembler and link editor, object files are binary representations of programs intended to execute directly on a processor. Programs that require other abstract machines, such as shell scripts, are excluded After the introductory material, Part 1 focuses on the file format and how it pertains to building pro- grams. Part 2 also describes parts of the object file, concentrating on the information necessary to execute a program Object files participate in program linking(building a program)and program execution (running a pro gram). For convenience and efficiency, the object file format provides parallel views of a files contents, reflecting the differing needs of these activities. Figure 1-1 shows an object files organization Linking view ExecutionⅤiew elF header EL上 header Program header table Program header table tional Section 1 egmont 1 ection n Segment 2 Section header table Section header table optional An elf header resides at the beginning and holds a"road map"describing the file's organization. Sec tions hold the bulk of object file information for the linking view: instructions, data, symbol table, reloca- tion information, and so on. Descriptions of special sections appear laterin Part 1. Part 2 discusses seg- ments and the program execution view of the file Tool Interface Standards(TIS) Portable Formats Specification, Version 1.1 A program header table, if present, tells the system how to create a process image. Files used to build a pro cess image(execute a program)must have a program header table; relocatable files do not need one. 4 section header table contains information describing the files sections. Every section has an entry in the table; each entry gives information such as the section name, the section size, ctc. Files used during link ing must have a section header table; other object files may or may not have one As described here, the object file format supports various processors with 8-bit by tes and 32-bit architec tures. Nevertheless, it is intended to be extensible to larger(or smaller)architectures. Object files there fore 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 encod ing of the target processor, regardless of the machine on which the file was created N ame Size Alignment Purpose 51 ddre 424441 2 Unsigned medium integer Unsigned file offset ign ge integer Unsigned large integer Unsigned small integer 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, etc. Data also have suitable alignment from the beginning of the file. Thus, for example, a structure containing an member will be aligne on a 4-byte boundary within the file 上 or portability reasons上L上 uses no bit- fields. Portable Formats Specification, Version 1.1 Tool Interface Stand ards(TIs) Some object file control structures can grow because the elf header contains their actual sizes If the object file format changes, a program may encounter control structures that are larger or smaller than expected. Programs might therefore ignore"extra"information. The treatment of missing"informa tion depends on context and will be specified when and if extensions are defined The initial bytes mark the file as an object file and provide machine-independent data below,in"ELF Identification. pret the file s contents. Complete descriptions appear with which to decode and inte This member identifies the object file type Meaning Relocatab le fil Executable file Shared object file Core file rocessor-specific rocessor-specific Although the core file contents are unspecified, type is reserved to mark the file. Values from hou (inclusive) are reserved for processor-specific semantics. Other values are reserved and will be assigned to new object file types as necessary Tool Interface Standards(TIS) Portable Formats Specification, Version 1.1 This member's value specifies the required architecture for an individual file ame Value ning at&T We 32100 SPARC Intel 80386 Motorola 68000 Motorola 88000 Intel 80860 MIPS RS3000 Other values are reserved and will be assigned to new machines as necessary Proc ific ELF names use the machine to distinguish them For exampl the flags mentioned below use the prefix a flag named for the chine would be called This member identifies the object file version ame Valt Meaning version Current version The value signifies the original file format; extensions will create new versions with higher numbers. The value of though given as above, will change as necessary to reflect the current version number This member gives the virtual address to which the system first transfers control, thus starting the process. If the file has no associated entry point this member holds zero This member holds the program header table's file offset in bytes. If the file has no program header table, this member holds zero This member holds the section header table's file offset in bytes. If the file has no sec tion header table. this member holds zero This member holds processor-specific flags associated with the file. Flag names take the form machine flag. See" Machine Information for flag definitions This member holds the elF header's size in bytes This member holds the size in bytes of one entry in the files program header table, all entries are the same size This member holds the number of entries in the program header table. Thus the pro duct of d gives the tables size in bytes. If a file has no pro gram header table holds the value zero This member holds a section headers size in bytes. A section header is one entry in the section header table all entries are the same size This member holds the number of entries in the section header table. Thus the product and gives the section header tables size in bytes. If a file has no section header table holds the value zero Portable Formats Specification, Version 1.1 Tool Interface Stand ards(TIs)

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