Linux user-space ELF loader

Question

I need to do a rather unusual thing: manually execute an elf executable. I.e. load all sections into right places, query main() and call it (and cleanup then). Executable will be statically linked, so there will be no need to link libraries. I also control base address, so no worries about possible conflicts.

So, is there are any libraries for that?

I found OSKit and its liboskit_exec, but project seems to be dead since 2002.

I'm OK with taking parts of projects (respecting licenses, of course) and tailoring them to my need, but as I'm quite a noob in the linux world, I dont even know where to find those parts! :)

PS. I need that for ARM platform.

UPD Well, the matter of loading elfs seems to require some good knowledge about it (sigh), so I'm out to read some specs and manuals. And I think I will stick to bionic/linker and libelfsh. Thanks guys!

Summarized findings:

• libelf: http://directory.fsf.org/project/libelf/
• elfsh and libelfsh (are now part of eresi): http://www.eresi-project.org/
• elfio (another elf library): http://sourceforge.net/projects/elfio/
• OSKit and liboskit_exec (outdated): http://www.cs.utah.edu/flux/oskit/
• bionic/linker: http://android.git.kernel.org/?p=platform/bionic.git

Answer 1

A quick apt-cache search suggests libelf1, libelfg0 and/or libelfsh0. I think the elfsh program (in the namesake package) might be an interesting practical example of how to use libelfsh0.

I haven't tried any myself, but I hope they might be helpful. Good luck :-)

Answer 2

Take a look at libelf for reading the executable format. You are going to have trouble with this I think.

Sounds like, as you don't need libraries for anything, why not just mmap your executable, set data about various memory areas and jmp/b in?

I don't know if ARM has an NX-bit equivalent, but worth checking.

Answer 3

Google's Android, in it's "bionic" libc implementation, has a completely reimplemented ELF loader. It's reasonably clean, and probably a better source than gilbc if you're looking for something simple.

Answer 4

This tool contains an ELF loader: http://bitwagon.com/rtldi/rtldi.html

I reused the code from rtldi for an ELF chainloader in another project. The code is here: http://svn.gna.org/viewcvs/plash/trunk/chroot-jail/elf-chainloader/?rev=877 and there is some background here: http://plash.beasts.org/wiki/Story16. (Apparently I have to break these links because stackoverflow won't let me post >1 link!)

Answer 5

Hi beetoom,

Any Progress u made, I am also trying to do the same. How you are controlling base address?

if we build the elf for a known address and load at same address it wil work fine. when we load ELF to some other location the problem is with Data Section. I am also trying to load a relocatable ELF executable file dynamically to any address. please help me in resolving this.

Thanks,

Ravinder