solaris elfedit: Is there something similar for linux ? (a shared library editor)?

Question

Linux: It there a way to edit a compiled shared library ?

specifically I am searching on how to add the DT_SYMBOLIC flag on an already compiled binary shared library?

Here is why I am asking this:

our application is composed of

• our own libraries (static libXXX.a)
• some 3rd party libs (binary-only shared libraries libYYY.so)

Everything is fine with the application so far.

Now I have replaced our own static* libXXX.a libraries with shared libraries versions (libXXX.so).

Everything compiles and links fine.

But when I run the application now it starts up and does a lot of expected processing - and then it crashes somewhere on half the way. A gdb backtrace shows that the crash occurs in some of the 3rd party shared libraries.

I searched around on SOF and found an interesting article here.

The tip I am referring to is

... add the DT_SYMBOLIC flag to the dynamic section ...

Although I doubt that it would really help I think it might be worth a try.

Any ideas how I can add the DT_SYMBOLIC flag on an already compiled/linked shared library ?

environment: debian lenny 64bit with g++ v4.2.4 and binutils v20.

EDIT: on solaris there is a program called elfedit. Is there something similar for linux ?

Answer 1

At the very least, you have to re-link the library with -Bsymbolic or -Wl,-Bsymbolic, depending on your compiler as symbol table mapping is a compile-time operation.

Answer 2

If it's just a flag the painful approach is to tweak your elf header with a hex editor.

But if the 3rd party lib is crashing I'd personally look at the other end of things: what has changed about the library loading order because of you moving to shared.

ldd

and

export LD_DEBUG=libs

are your friends here.

dlopen()ing your shared libs after the runtime loader loads your 3rd party libs might be enough.

Answer 3

meanwhile l have found a tool called elfsh. It is an interactive shell for examining and editing ELF objects, binaries and shared libraries.

see here for the project page: http://www.eresi-project.org

Unfortunately it doesn't seem to be very stable. I have experienced a lot of crashes within elfsh itself.