Finding the load address of a shared library in Linux

Question

At runtime I need to print out an address, and then find which function that address is part of. The functions are in a shared library so are not at a fixed address. My map file obviously just shows the relative offsets for each shared library func. Is it possible at runtime to query where a library has been loaded, so that I can subtract that value from my address to get the correct map file offset?

Currently I'm doing a slightly hacky approch whereby I also print out the address of one function in the library, then find that function in the map file to figure out where the load address must be. I would rather have a generic method that didn't require you to name a reference function.

(GDB is not available in my setup). Thanks.

Answer 1

On a recent linux, you can use dl_iterate_phdr to find out the addresses of the shared libs.

Answer 2

dladdr does this, end of. :-)

More comprehnsively, dladdr will take an address and work out which library and symbol it corresponds to... and then it'll give you the name of the library, the name of the symbol, and the base addresses of each. Personally I think that's nifty, it's also making my current debugging job a lit easier.

Hope this helps!