ELF Format

ELF represents Executable and Linkable Format, which is a common standard file format for executable files, object code, shared libraries, and core dumps. It is a standard binary file format for *nix-like systems on x86 processors.

let us make a simple program

// hello.c
#include <stdlib.h>
char str[] = "Hello World\n";
int main (int argc, char** argv) {
    printf("%s", str);
    return 0;
}

Then compile it

gcc hello.c

Layout

A ELF file at least contains one ELF header and followed by file data:

Program header table, describing zero or more memory segments
Section header table, describing zero or more sections
Data referred to by entries in the program header table or section header table

For example:

objdump -h a.out

elf layout

As can been seen above, a.out contains may section headers.

Section headers

Section headers table¹

Header Names	Meaning
.text	for codes
.data	for global tables, variables, etc
.bss	for uninitialized arrays and variable
.rodata	for strings
.comment & .note	just comments put there by the compiler/linker toolchain
.stab & .stabstr	debugging symbols & similar information.

Reference

OSdev 2017, ELF, http://wiki.osdev.org/ELF ↩