I upgrade a program that needs to run on both old and new platform. In the new platform, I have new config so certain functions will not get called in the old platform. However, when I run the program on old platform, it complains missing shared library. What I need is something like "lazyload" or "delayload" mechanism such that when a function is not called the system won't bother to load its dependent library. But so far I haven't found a way to achieve it on Linux. I use gcc/c with normal link options.

I try simple approach of "-Wl,-z,nodefs" but with error.

/usr/bin/ld: warning: -z nodefs ignored.

So how to enforce it?

CodePudding user response：

You have two options:

1. Instead of calling functions in the optional shared library as normal, call them via dlopen() and dlsym(). This will let you explicitly load your shared library at runtime, when needed.
2. On the platform where the shared library is not available, make a dummy shared library and link that (or load it using LD_PRELOAD). It will need to contain dummy versions of whatever functions your program calls, they don't need to do anything useful if you don't actually invoke them.

CodePudding user response：

It looks like your particular linker (you didn't specify which one, but we can guess it might be the default ld.bfd linker) does not support -z nodefs. Try --allow-shlib-undefined to achieve the same result.