Linux Kernel Architecture

Mauerer runapp05.tex V1 - 09/04/2008 6:13pm Page 1242

Appendix E: The ELF Binary Format.........................................

❑ The program header table provides the system with information on how the data of an

executable file is to be arranged in the virtual address space of a process. It also indicates

how many sections the file may contain, where they are located, and what purpose

they serve.

❑ The individual sections hold the various forms of data associated with a file; for example, the

symbol table, the actual binary code or fixed values such as strings, or numeric constants used

by the program.

❑ The section header table contains additional information on the individual sections.

Link View

Program

Header Table

Section 1

Section 2

...
Section n
Section
Header Table

ELF Header

Execution View

Program

Header Table

Segment 1

Segment 2

Section

Header Table

ELF Header Mandatory

Optional

...

Figure E-1: Basic layout of ELF files.

readelfis a useful tool for analyzing the structure of ELF files, as demonstrated in the following simple

program.

#include<stdio.h>

int add (int a, int b) {

printf("Numbers are added together\n");

return a+b;

}

int main() {

int a,b;

a=3;

b=4;

int ret = add(a,b);

printf("Result: %u\n");

exit(0);

}

Of course, this program is not necessarily the most useful of its kind, but it serves as a good example to

illustrate how an executable file and an object file are generated:

wolfgang@meitner>gcc test.c -o test

wolfgang@meitner>gcc test.c -c -o test.o