objdump to extract contents of text segment to a binary format

Question

How do we use objdump to output to a binary file?

This is definitely not the right way to do so:

objdump -s -j .text /path/firmware.ko > /content.bin

as it is only presenting text format. I only require the bytes of the text segment to be extracted and to be set in binary forms.

why not using objdump to find the offset and size of .text section and then dump it using dd? — tristan, Jan 03 '14 at 07:13
actually, I am also trying to do in C system call, so it has to be preferably in 1 line if possible. — Ursa Major, Jan 03 '14 at 07:16
http://superuser.com/questions/696780/extract-the-contents-of-elf-and-write-to-binary-file || http://stackoverflow.com/questions/3925075/how-do-you-extract-only-the-contents-of-an-elf-section — Ciro Santilli Путлер Капут 六四事, Sep 04 '15 at 13:02

Ursa Major · Accepted Answer · 2014-01-05T12:08:20.380

8

We have to specify the file format explicitly using the -I.

objcopy -I #file type format# -j #ELF segment contents to copy# -O #data type to output, binary, etc# #input file# #output file#

eg.

 
objcopy -I elf32-little -j .text -O binary firmware.ko content.bin

edited Jan 05 '14 at 12:08

answered Jan 05 '14 at 12:03

Ursa Major

score 5 · Answer 2 · answered Jan 03 '14 at 07:27

5

You can use objcopy instead

objcopy -O binary --only-section=.text /path/firmware.ko /content.bin

answered Jan 03 '14 at 07:27

tristan

Hi, It states: objcopy: Unable to recognise the format of the input file '/path/firmware.ko'. – Ursa Major Jan 03 '14 at 08:06
sorry i don't know your architecture but did you run the objcopy that is from the same arch as the .ko file? – tristan Jan 03 '14 at 08:23
The file format is "file format elf32-little". It was stated by objdump. Is there a way to specify this in objcopy? Thank you, @tristan, for your patient guidance. – Ursa Major Jan 03 '14 at 08:29
I see: elf32-little (header little endian, data little endian) i386 l1om k1om plugin – Ursa Major Jan 03 '14 at 17:16

How about something like:

objdump -s -j .text firmware.ko | awk '{print "dd if='firmware.ko' of='content.bin' bs=1 count=$[0x" $3 "] skip=$[0x" $6 "]"}' | bash

? but the syntax is still not correct. – Ursa Major Jan 03 '14 at 18:58

2 Answers2