language

How source code turn to be an executable program

What is an executable program

  • On linux, the format of executable program is ELF (Executable and Linking Format)
  • members of executable program
    • text segment
    • data segment
    • bss segment

How source code be compiled

Relation of source code, object file, library file, bin file

How bin file to load library

  • dynamic library
  • static library

Example

  • Hello world, a.c

    #include <stdio.h>
int main()
{
    printf ("Hello world\n");
}

  • compile

    [dennis@localhost ~]$ gcc a.c
[dennis@localhost ~]$ objdump -f a.out 

a.out:     file format elf64-x86-64
architecture: i386:x86-64, flags 0x00000112:
EXEC_P, HAS_SYMS, D_PAGED
start address 0x0000000000400440
[dennis@localhost ~]$ file a.out
a.out: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux 2.6.32, BuildID[sha1]=7396e4d6e7100d1536548d05ba91a67255bf9592, not stripped
[dennis@localhost ~]$ size a.out
   text       data        bss        dec        hex    filename
   1226        548          4       1778        6f2    a.out
[dennis@localhost ~]$ readelf -h a.out
ELF Header:
  Magic:   7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00 
  Class:                             ELF64
  Data:                              2's complement, little endian
  Version:                           1 (current)
  OS/ABI:                            UNIX - System V
  ABI Version:                       0
  Type:                              EXEC (Executable file)
  Machine:                           Advanced Micro Devices X86-64
  Version:                           0x1
  Entry point address:               0x400440
  Start of program headers:          64 (bytes into file)
  Start of section headers:          4504 (bytes into file)
  Flags:                             0x0
  Size of this header:               64 (bytes)
  Size of program headers:           56 (bytes)
  Number of program headers:         9
  Size of section headers:           64 (bytes)
  Number of section headers:         30
  Section header string table index: 27
[dennis@localhost ~]$ readelf -S a.out

Reference