> I mean, linker tricks à la LD_PRELOAD, DYLD_INSERT_LIBRARIES are a lot less work than rewriting code. They don't even require a recompile most of the time.

Thanks. Also, simply providing static symbols during compilation should work (in most cases), as typically a static linker will only pick up the first provided and referenced (yet undefined) symbol.

Probably even a more "stable" (less conflicting) solution would be to use -Wl,--wrap=symbol and then provide __wrap_symbol() sandboxed definition. Agree, this all doable one way or another, and we might take a look at it at some point (we'll be glad to receive any input on that, preferably on the project's mailing list).