How to catch unintentional function interpositioning?

Question

Reading through my book Expert C Programming, I came across the chapter on function interpositioning and how it can lead to some serious hard to find bugs if done unintentionally.

The example given in the book is the following:

my_source.c

mktemp() { ... }

main() {
  mktemp();
  getwd();
}

libc

mktemp(){ ... }
getwd(){ ...; mktemp(); ... }

According to the book, what happens in main() is that mktemp() (a standard C library function) is interposed by the implementation in my_source.c. Although having main() call my implementation of mktemp() is intended behavior, having getwd() (another C library function) also call my implementation of mktemp() is not.

Apparently, this example was a real life bug that existed in SunOS 4.0.3's version of lpr. The book goes on to explain the fix was to add the keyword static to the definition of mktemp() in my_source.c; although changing the name altogether should have fixed this problem as well.

This chapter leaves me with some unresolved questions that I hope you guys could answer:

1. Does GCC have a way to warn about function interposition? We certainly don't ever intend on this happening and I'd like to know about it if it does.
2. Should our software group adopt the practice of putting the keyword static in front of all functions that we don't want to be exposed?
3. Can interposition happen with functions introduced by static libraries?

Thanks for the help.

EDIT

I should note that my question is not just aimed at interposing over standard C library functions, but also functions contained in other libraries, perhaps 3rd party, perhaps ones created in-house. Essentially, I want to catch any instance of interpositioning regardless of where the interposed function resides.

Answer 1

It sounds like what you want is for the tools to detect that there are name conflicts in functions - ie., you don't want your externally accessible function names form accidentally having the same name and therefore 'override' or hide functions with the same name in a library.

There was a recent SO question related to this problem: Linking Libraries with Duplicate Class Names using GCC

Using the --whole-archive option on all the libraries you link against may help (but as I mentioned in the answer over there, I really don't know how well this works or how easy it is to convince builds to apply the option to all libraries)