This is the PDF of the Tool Interface Standard (TIS)
Executable and Linking Format (ELF) Specification, Version 1.2.
From the document about ELF and what this standard is:
About ELF: Executable and Linking Format The Executable and Linking Format was originally developed and published by UNIX System Laboratories (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 code. About This Document This document is intended for developers who are creating object or executable files on various 32-bit environment operating systems. In order to extend ELf into different operating systems, the current ELF version 1.2 document has been reorganized based on operating system-specific information. It is divided into the following three books: • Book I: Executable and Linking Format, describes the object file format called ELF. This book also contains an appendix that describes historical references and lists processor and operating system reserved names and words. • Book II: Processor Specific (Intel Achitecture), conveys hardware-specific ELF information, such as Intel Architecture information. • Book III: Operating System Specific, describes ELF information that is operating system dependent, such as System V Release 4 information. This book also contains an appendix that describes ELF information that is both operating system and processor dependent.