How do I find where a symbol is defined among static libraries
Suppose you work with a codebase comprising several tools and libraries and you want to port (or resurrect) some component within such codebase but any clue about where symbols lie within the various libs is either lost or will take ages to find out by looking at the code itself (yes improved documentation can avoid such issues but is quite demanding). What is the fastest way to discover in which library you can find symbols used in the code?
Answer
Assuming a linux box, the nm tool, listing names in library files, comes to the rescue.
It can be used to do an extensive search as follows: one can first find all the libraries available (assuming the project have been successfully compiled without the component you are adding) with a find, then such find can be enclosed in a loop where you call nm on all discovered libraries; the output you then grep for discarding "U" references (undefined symbols, aka where else the symbol is being used). On a single bash line that gives:
for lib in $(find base_path -name \*.a) ; do echo $lib ; nm $lib | grep my_symbol | grep -v " U " ; done
where:
- base_path is the root of your codebase
- my_symbol is the symbol you are looking for
The echo generates a list of all libraries found, which is not so clean since it outputs names of libs not holding the symbol, but it was the fastest way I found to have a direct reference to the library so when you see a:
base_path/component/libA.a
0000000000000080 D my_symbol
You have found your usual suspect.