CPU dependent code: how to avoid function pointers?

Question

I have performance critical code written for multiple CPUs. I detect CPU at run-time and based on that I use appropriate function for the detected CPU. So, now I have to use fun

Answer 1

You may want to lookup the GNU dynamic linker extension STT_GNU_IFUNC. From Drepper's blog when it was added:

Therefore I’ve designed an ELF extension which allows to make the decision about which implementation to use once per process run. It is implemented using a new ELF symbol type (STT_GNU_IFUNC). Whenever the a symbol lookup resolves to a symbol with this type the dynamic linker does not immediately return the found value. Instead it is interpreting the value as a function pointer to a function that takes no argument and returns the real function pointer to use. The code called can be under control of the implementer and can choose, based on whatever information the implementer wants to use, which of the two or more implementations to use.

Source: http://udrepper.livejournal.com/20948.html

Nonetheless, as others have said, I think you're mistaken about the performance impact of indirect calls. All code in shared libraries will be called via a (hidden) function pointer in the GOT and a PLT entry that loads/calls that function pointer.