Linux objdump Command Explained for Beginners (7 Examples)

If you are into programming on Linux and your work revolves around compilers, there are a handful of command line utilities that you should be aware of. One such tool is objdump. In this tutorial, we will discuss the basics of this command using some easy to understand examples.

But before we do that, it’s worth mentioning that all examples here have been tested on an Ubuntu 18.04 LTS machine.

Linux objdump command

The objdump command in Linux, as the name suggests, displays information from object files. Following is the tool’s syntax:

objdump OPTIONS objfile …

And here’s what the man page says about it:

objdump displays information about one or more object files. The options control what particular
information to display. This information is mostly useful to programmers who are working on the
compilation tools, as opposed to programmers who just want their program to compile and work.

objfile... are the object files to be examined. When you specify archives, objdump shows
information on each of the member object files.

Following are some Q&A-styled examples that should give you an even better idea on how objdump works.

Q1. How to make objdump display file header contents?

This can be done using the -f command line option.

For example:

objdump -f /bin/ls

And here’s the output of the above command:

/bin/ls:     file format elf64-x86-64
architecture: i386:x86-64, flags 0x00000150:
HAS_SYMS, DYNAMIC, D_PAGED
start address 0x0000000000005850

So you can see the header contents of ‘ls’ were displayed in the output.

Q2. How to make objdump display object format specific file header contents?

This can be done using the -p command line option. For example, the following command:

objdump -p /bin/ls

Produced the following output:

/bin/ls: file format elf64-x86-64

Program Header:
    PHDR off    0x0000000000000040 vaddr 0x0000000000000040 paddr 0x0000000000000040 align 2**3
         filesz 0x00000000000001f8 memsz 0x00000000000001f8 flags r-x
INTERP off    0x0000000000000238 vaddr 0x0000000000000238 paddr 0x0000000000000238 align 2**0
         filesz 0x000000000000001c memsz 0x000000000000001c flags r--
    LOAD off    0x0000000000000000 vaddr 0x0000000000000000 paddr 0x0000000000000000 align 2**21
         filesz 0x000000000001e6e8 memsz 0x000000000001e6e8 flags r-x
    LOAD off    0x000000000001eff0 vaddr 0x000000000021eff0 paddr 0x000000000021eff0 align 2**21
         filesz 0x0000000000001278 memsz 0x0000000000002570 flags rw-
DYNAMIC off    0x000000000001fa38 vaddr 0x000000000021fa38 paddr 0x000000000021fa38 align 2**3
         filesz 0x0000000000000200 memsz 0x0000000000000200 flags rw-
    NOTE off    0x0000000000000254 vaddr 0x0000000000000254 paddr 0x0000000000000254 align 2**2
         filesz 0x0000000000000044 memsz 0x0000000000000044 flags r--
EH_FRAME off    0x000000000001b1a0 vaddr 0x000000000001b1a0 paddr 0x000000000001b1a0 align 2**2
         filesz 0x0000000000000884 memsz 0x0000000000000884 flags r--
   STACK off    0x0000000000000000 vaddr 0x0000000000000000 paddr 0x0000000000000000 align 2**4
         filesz 0x0000000000000000 memsz 0x0000000000000000 flags rw-
   RELRO off    0x000000000001eff0 vaddr 0x000000000021eff0 paddr 0x000000000021eff0 align 2**0
         filesz 0x0000000000001010 memsz 0x0000000000001010 flags r--

Dynamic Section:
NEEDED               libselinux.so.1
NEEDED               libc.so.6
INIT                 0x0000000000003758
FINI                 0x000000000001636c
INIT_ARRAY           0x000000000021eff0
INIT_ARRAYSZ         0x0000000000000008
FINI_ARRAY           0x000000000021eff8
FINI_ARRAYSZ         0x0000000000000008
GNU_HASH             0x0000000000000298
STRTAB               0x0000000000001180
SYMTAB               0x0000000000000388
STRSZ                0x0000000000000682
SYMENT               0x0000000000000018
DEBUG                0x0000000000000000
PLTGOT               0x000000000021fc38
PLTRELSZ             0x0000000000000a68
PLTREL               0x0000000000000007
JMPREL               0x0000000000002cf0
RELA                 0x00000000000019a0
RELASZ               0x0000000000001350
RELAENT              0x0000000000000018
FLAGS                0x0000000000000008
FLAGS_1              0x0000000008000001
VERNEED              0x0000000000001930
VERNEEDNUM           0x0000000000000001
VERSYM               0x0000000000001802
RELACOUNT            0x00000000000000c1

Version References:
required from libc.so.6:
    0x06969194 0x00 07 GLIBC_2.14
    0x0d696914 0x00 06 GLIBC_2.4
    0x06969197 0x00 05 GLIBC_2.17
    0x09691974 0x00 04 GLIBC_2.3.4
    0x09691a75 0x00 03 GLIBC_2.2.5
    0x0d696913 0x00 02 GLIBC_2.3

Q3. How to make objdump display contents of section headers?

This can be done using the -h command line option. For example, the following command:

objdump -h /bin/ls

produced the following output on my system:

/bin/ls: file format elf64-x86-64

Sections:
Idx Name          Size      VMA               LMA               File off Algn
0 .interp       0000001c 0000000000000238 0000000000000238 00000238 2**0
                  CONTENTS, ALLOC, LOAD, READONLY, DATA
1 .note.ABI-tag 00000020 0000000000000254 0000000000000254 00000254 2**2
                  CONTENTS, ALLOC, LOAD, READONLY, DATA
2 .note.gnu.build-id 00000024 0000000000000274 0000000000000274 00000274 2**2
                  CONTENTS, ALLOC, LOAD, READONLY, DATA
3 .gnu.hash     000000ec 0000000000000298 0000000000000298 00000298 2**3
                  CONTENTS, ALLOC, LOAD, READONLY, DATA
4 .dynsym       00000df8 0000000000000388 0000000000000388 00000388 2**3
                  CONTENTS, ALLOC, LOAD, READONLY, DATA
5 .dynstr       00000682 0000000000001180 0000000000001180 00001180 2**0
                  CONTENTS, ALLOC, LOAD, READONLY, DATA
6 .gnu.version 0000012a 0000000000001802 0000000000001802 00001802 2**1
                  CONTENTS, ALLOC, LOAD, READONLY, DATA
7 .gnu.version_r 00000070 0000000000001930 0000000000001930 00001930 2**3
                  CONTENTS, ALLOC, LOAD, READONLY, DATA
8 .rela.dyn     00001350 00000000000019a0 00000000000019a0 000019a0 2**3
                  CONTENTS, ALLOC, LOAD, READONLY, DATA
9 .rela.plt     00000a68 0000000000002cf0 0000000000002cf0 00002cf0 2**3
                  CONTENTS, ALLOC, LOAD, READONLY, DATA
10 .init         00000017 0000000000003758 0000000000003758 00003758 2**2
                  CONTENTS, ALLOC, LOAD, READONLY, CODE
11 .plt          00000700 0000000000003770 0000000000003770 00003770 2**4
                  CONTENTS, ALLOC, LOAD, READONLY, CODE
12 .plt.got      00000018 0000000000003e70 0000000000003e70 00003e70 2**3
                  CONTENTS, ALLOC, LOAD, READONLY, CODE
13 .text         000124d9 0000000000003e90 0000000000003e90 00003e90 2**4
                  CONTENTS, ALLOC, LOAD, READONLY, CODE
14 .fini         00000009 000000000001636c 000000000001636c 0001636c 2**2
                  CONTENTS, ALLOC, LOAD, READONLY, CODE
15 .rodata       00004e1d 0000000000016380 0000000000016380 00016380 2**5
                  CONTENTS, ALLOC, LOAD, READONLY, DATA
16 .eh_frame_hdr 00000884 000000000001b1a0 000000000001b1a0 0001b1a0 2**2
                  CONTENTS, ALLOC, LOAD, READONLY, DATA
17 .eh_frame     00002cc0 000000000001ba28 000000000001ba28 0001ba28 2**3
                  CONTENTS, ALLOC, LOAD, READONLY, DATA
18 .init_array   00000008 000000000021eff0 000000000021eff0 0001eff0 2**3
                  CONTENTS, ALLOC, LOAD, DATA
19 .fini_array   00000008 000000000021eff8 000000000021eff8 0001eff8 2**3
                  CONTENTS, ALLOC, LOAD, DATA
20 .data.rel.ro 00000a38 000000000021f000 000000000021f000 0001f000 2**5
                  CONTENTS, ALLOC, LOAD, DATA
21 .dynamic      00000200 000000000021fa38 000000000021fa38 0001fa38 2**3
                  CONTENTS, ALLOC, LOAD, DATA
22 .got          000003c8 000000000021fc38 000000000021fc38 0001fc38 2**3
                  CONTENTS, ALLOC, LOAD, DATA
23 .data         00000268 0000000000220000 0000000000220000 00020000 2**5
                  CONTENTS, ALLOC, LOAD, DATA
24 .bss          000012e0 0000000000220280 0000000000220280 00020268 2**5
                  ALLOC
25 .gnu_debuglink 00000034 0000000000000000 0000000000000000 00020268 2**2
                  CONTENTS, READONLY

Q4. How to make objdump display all headers?

To make objdump display all headers, use the -x command line option.

objdump -x /bin/ls

Following is the output this command produced on my system:

/bin/ls: file format elf64-x86-64
/bin/ls
architecture: i386:x86-64, flags 0x00000150:
HAS_SYMS, DYNAMIC, D_PAGED
start address 0x0000000000005850

Q5. How to make objdump display assembler contents of executable sections?

For this, use the -d command line option. Here’s an example showing this option in action:

objdump -d /bin/ls

And here’s an excerpt from the output:

/bin/ls:     file format elf64-x86-64Disassembly of section .init:
0000000000003758 <[email protected]@Base>:
    3758:    48 83 ec 08              sub    $0x8,%rsp
    375c:    48 8b 05 7d c8 21 00     mov    0x21c87d(%rip),%rax        # 21ffe0 <__gmon_start__>
    3763:    48 85 c0                 test   %rax,%rax
    3766:    74 02                    je     376a <[email protected]@Base+0x12>
    3768:    ff d0                    callq  *%rax
    376a:    48 83 c4 08              add    $0x8,%rsp
    376e:    c3                       retq   
Disassembly of section .plt:
0000000000003770 <[email protected]>:
    3770:    ff 35 ca c4 21 00        pushq  0x21c4ca(%rip)        # 21fc40 <[email protected]@Base+0x260>
    3776:    ff 25 cc c4 21 00        jmpq   *0x21c4cc(%rip)        # 21fc48 <[email protected]@Base+0x268>
    377c:    0f 1f 40 00              nopl   0x0(%rax)
0000000000003780 <[email protected]>:
    3780:    ff 25 ca c4 21 00        jmpq   *0x21c4ca(%rip)        # 21fc50 <[email protected]_2.3>
    3786:    68 00 00 00 00           pushq  $0x0
    378b:    e9 e0 ff ff ff           jmpq   3770 <[email protected]@Base+0x18>
0000000000003790 <[email protected]>:
    3790:    ff 25 c2 c4 21 00        jmpq   *0x21c4c2(%rip)        # 21fc58 <[email protected]_2.2.5>
    3796:    68 01 00 00 00           pushq  $0x1
    379b:    e9 d0 ff ff ff           jmpq   3770 <[email protected]@Base+0x18>
00000000000037a0 <[email protected]>:
    37a0:    ff 25 ba c4 21 00        jmpq   *0x21c4ba(%rip)        # 21fc60 <[email protected]_2.2.5>
    37a6:    68 02 00 00 00           pushq  $0x2

Similarly, you can use the -D command line option to make objdump display assembler contents of all sections, and -S option to make sure the tool intermixes source code with disassembly.

Q6. How to make objdump display debug information?

This can be made possible by using the -S command line option.

objdump -g /bin/ls

Following is an excerpt from the output produced by this command:

Contents of the .eh_frame section (loaded from /bin/ls):

00000000 0000000000000014 00000000 CIE
Version:               1
Augmentation:          "zR"
Code alignment factor: 1
Data alignment factor: -8
Return address column: 16
Augmentation data:     1b
DW_CFA_def_cfa: r7 (rsp) ofs 8
DW_CFA_offset: r16 (rip) at cfa-8
DW_CFA_undefined: r16 (rip)

00000018 0000000000000014 0000001c FDE cie=00000000 pc=0000000000005850..000000000000587b
DW_CFA_nop
DW_CFA_nop
DW_CFA_nop
DW_CFA_nop
DW_CFA_nop
DW_CFA_nop
DW_CFA_nop

00000030 0000000000000014 00000000 CIE
Version:               1
Augmentation:          "zR"
Code alignment factor: 1
Data alignment factor: -8
Return address column: 16
Augmentation data:     1b
DW_CFA_def_cfa: r7 (rsp) ofs 8
DW_CFA_offset: r16 (rip) at cfa-8

Q7. How to make objdump display contents of symbol table?

This can be done using the -t command line option.

objdump -t /bin/ls

Conclusion

We’ve just scratched the surface here, as the objdump command offers a lot of command line options. Once you’re done practicing these, you can learn more about the tool by heading to its man page.

About Himanshu Arora

Himanshu Arora has been working on Linux since 2007. He carries professional experience in system level programming, networking protocols, and command line. In addition to HowtoForge, Himanshu’s work has also been featured in some of world’s other leading publications including Computerworld, IBM DeveloperWorks, and Linux Journal.

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Linux objdump Command Explained for Beginners (7 Examples)