Linux objdump Command Explained for Beginners (7 Examples)
On this page
- Linux objdump command
- Q1. How to make objdump display file header contents?
- Q2. How to make objdump display object format specific file header contents?
- Q3. How to make objdump display contents of section headers?
- Q4. How to make objdump display all headers?
- Q5. How to make objdump display assembler contents of executable sections?
- Q6. How to make objdump display debug information?
- Q7. How to make objdump display contents of the symbol table?
- Conclusion
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 20.04 LTS machine and on Debian 10.
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 0x00000000000067d0
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
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
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
SYMBOL TABLE:
no symbols
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-x86-64
Disassembly of section .init:
0000000000003758 <_init@@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 <_init@@Base+0x12>
3768: ff d0 callq *%rax
376a: 48 83 c4 08 add $0x8,%rsp
376e: c3 retq
Disassembly of section .plt:
0000000000003770 <__ctype_toupper_loc@plt-0x10>:
3770: ff 35 ca c4 21 00 pushq 0x21c4ca(%rip) # 21fc40 <quoting_style_args@@Base+0x260>
3776: ff 25 cc c4 21 00 jmpq *0x21c4cc(%rip) # 21fc48 <quoting_style_args@@Base+0x268>
377c: 0f 1f 40 00 nopl 0x0(%rax)
0000000000003780 <__ctype_toupper_loc@plt>:
3780: ff 25 ca c4 21 00 jmpq *0x21c4ca(%rip) # 21fc50 <__ctype_toupper_loc@GLIBC_2.3>
3786: 68 00 00 00 00 pushq $0x0
378b: e9 e0 ff ff ff jmpq 3770 <_init@@Base+0x18>
0000000000003790 <__uflow@plt>:
3790: ff 25 c2 c4 21 00 jmpq *0x21c4c2(%rip) # 21fc58 <__uflow@GLIBC_2.2.5>
3796: 68 01 00 00 00 pushq $0x1
379b: e9 d0 ff ff ff jmpq 3770 <_init@@Base+0x18>
00000000000037a0 <getenv@plt>:
37a0: ff 25 ba c4 21 00 jmpq *0x21c4ba(%rip) # 21fc60 <getenv@GLIBC_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 the 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.
