In computing, the Executable and Linkable Format (ELF, formerly called Extensible Linking Format) is a common standard file format for. Introduction. This marks the first of several blog posts that will focus on Executable and Linkable Format (ELF) files. In this series, we’ll introduce. Section Type, executable by the CPU, Desc. code, , no, for storing data. bss, no, for storing program data. debug, no. 4 – Documentation / Reference.

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Executable and Linkable Format 101 – Part 1 Sections and Segments

Segments, which are commonly known as Program Headers, break down the structure of an ELF binary into suitable chunks to prepare the executable to be loaded into memory.

In the normal case of a Unix executable one or more sections are enclosed in one segment. In it was chosen as the standard binary file format for Unix and Unix-like systems on x86 by the 86open project. The overall goal of the series is to help both advanced and beginner Linux users to acquire a sound knowledge of ELF files, along with improving their understanding of the threat landscape in Linux systems. Mainly, this contains general information about the binary.

Otherwise, this field contains zero.

This linkalbe interpretation of multi-byte fields starting with offset 0x The dynamic sections are used to store information used in the dynamic linking process, such as required libraries and relocation entries. Relocations April 23, Executable and Linkable Format This article is in a list format that may be better presented using prose.


Because malware also strikes Linux systems—and it can often happen through this file type—we thought it would be a helpful place to start. In order to display sections using readelf, we can use the following command: The ELF format has replaced older executable formats such as a.

You can help by converting this article to prose, if appropriate. Its interpretation depends on the target ABI.

Executable and Linkable Format – Wikipedia

Sections comprise all information needed for linking a target object file in order to build a working executable. Contains the section index of an associated section. The Complete Reference 2 ed. From Wikipedia, the free encyclopedia. In order to use readelf so that we can display the contents of the ELF header for a given executable, we can use the following command: For instance it supports different endiannesses and amd sizes so it does not exclude any particular central processing unit CPU or instruction set architecture.

The ‘flags’ will tell you what’s actually available in the ELF file. I suggest you do give them different physical pages too if you don’t want to end up with modifiable code.

Executable and Linkable Format (ELF)

As previously mentioned, sections gather all needed information to link foemat given object file and build an executable, while Program Headers split the executable into segments with different attributes, which will eventually be loaded into memory. You can create a library with GCC:.


Dynamic Linking is when the OS gives a program shared libraries if it linmable them. The ELF format has replaced older executable formats in various environments. Any byte in the entire file can be owned by one section at most, and orphan bytes can occur which are unowned by any section.

E32Image file format on Symbian OS 9. Thread Local Storage segment Common in statically linked binaries. With the BSDs having long supported Linux binaries through a compatibility layer and the main x86 Unix vendors having added support for the format, the project decided that Linux ELF was the format chosen by the industry and “declare[d] itself dissolved” on July 25, This is the memory address of the entry point from where the process starts executing.

There are a few simplifying assumptions you can make about the types and location of program headers. Section Header entry size in Section Header Table. Further specifies the ABI version. This page has been accessedtimes. GOT entries dedicated to dynamically linked global variables.

File offset of segment. The ELF header is 52 or 64 bytes long for bit and bit binaries respectively.

It usually follows the file header immediately, making the offset 0x34 or 0x40 for and bit ELF executables, respectively.