ELF format manipulation

Question

I have a requirement where I want to associate an index with a file(in a certain format). I was wondering if I can do any ELF manipulation and still ensure that, consistency is maintained so, the file works fine on linux. The idea here is to create a file format which can be queried by a certain API[self-defined] to get me the index.

a)is it possible to modify the ELF header to store the index(mentioned above).

b)if yes, what is the process?

Answer 1

You can add a new ELF section with whatever data you want to an existing executable. e.g.

$ echo 42 > /tmp/index
$ objcopy --add-section .my_index=/tmp/index /bin/ls myls
$ objdump -s myls | tail
.
.
. 

Contents of section .my_index:
 0000 34320a                               42.    

You can then figure out where to read this data from using libelf.