Generating link-time error for deprecated functions

Question

Is there a way with gcc and GNU binutils to mark some functions such that they will generate an error at link-time if used? My situation is that I have some library functions which I am not removing for the sake of compatibility with existing binaries, but I want to ensure that no newly-compiled binary tries to make use of the functions. I can't just use compile-time gcc attributes because the offending code is ignoring my headers and detecting the presence of the functions with a configure script and prototyping them itself. My goal is to generate a link-time error for the bad configure scripts so that they stop detecting the existence of the functions.

Edit: An idea.. would using assembly to specify the wrong .type for the entry points be compatible with the dynamic linker but generate link errors when trying to link new programs?

Answer 1

FreeBSD 9.x does something very close to what you want with the ttyslot() function. This function is meaningless with utmpx. The trick is that there are only non-default versions of this symbol. Therefore, ld will not find it, but rtld will find the versioned definition when an old binary is run. I don't know what happens if an old binary has an unversioned reference, but it is probably sensible if there is only one definition.

For example,

__asm__(".symver hidden_badfunc, badfunc@MYLIB_1.0");

Normally, there would also be a default version, like

__asm__(".symver new_badfunc, badfunc@@MYLIB_1.1");

or via a Solaris-compatible version script, but the trick is not to add one.

Typically, the asm directive is wrapped into a macro.

The trick depends on the GNU extensions to define symbol versions with the .symver assembler directive, so it will probably only work on Linux and FreeBSD. The Solaris-compatible version scripts can only express one definition per symbol.

More information: .symver directive in info gas, Ulrich Drepper's "How to write shared libraries", the commit that deprecated ttyslot() at http://gitorious.org/freebsd/freebsd/commit/3f59ed0d571ac62355fc2bde3edbfe9a4e722845