dynamic-loader | simple Linux dynamic loader capable of loading simple | Build Tool library

Unfortunately there is no way to tweak symbol resolution at per-library level so there is not easy way to achieve this.

If foo is actually implemented in main executable (not just copy-relocated to it) there's nothing you can do because symbols from main executables get the highest priority during resolution (unless you are ok with ultimately hacky runtime-patching of GOT which you aren't).

But if

• foo is implemented in c.so
• and you are desperate enough

you could do the following:

• get return address inside interceptor in a.so (use __builtin_return_address)
• match it against boundaries of b.so (can be obtained from /proc/self/maps)
• depending on result, either do special processing (if caller is in b.so) or forward call to RTLD_NEXT

This of course has obvious limitations e.g. won't work if b.so calls function from yet another d.so which then calls foo but it may be enough in many cases. And yes, I've seen this approach deployed in practice.