Editing Fat binary (section)

===Function multi-versioning===
Even in a program or [[library (computing)|library]] intended for the same [[instruction set architecture]], a programmer may wish to make use of some newer instruction set extensions while keeping compatibility with an older CPU. This can be achieved with ''function multi-versioning'' (FMV): versions of the same function are written into the program, and a piece of code decides which one to use by detecting the CPU's capabilities (such as through [[CPUID]]). [[Intel C++ Compiler]], GCC, and LLVM all have the ability to automatically generate multi-versioned functions.<ref name="Wennborg_2018"/> This is a form of [[dynamic dispatch]] without any semantic effects.

Many math libraries feature hand-written assembly routines that are automatically chosen according to CPU capability. Examples include [[glibc]], [[Intel MKL]], and [[OpenBLAS]]. In addition, the library loader in glibc supports loading from alternative paths for specific CPU features.<ref name="Bahena_2018"/>

A similar, but byte-level granular approach originally devised by Matthias R. Paul and Axel C. Frinke is to let a small self-discarding, [[instruction relaxation|relaxing]] and [[relocating loader]] embedded into the executable file alongside any number of alternative binary code snippets conditionally build a size- or speed-optimized runtime image of a program or driver necessary to perform (or not perform) a particular function in a particular target environment at [[load-time]] through a form of [[dynamic dead code elimination]] (DDCE).<ref name="Paul_1997_FreeKEYB"/><ref name="Paul_2002_DDCE2"/><ref name="Paul_2001_FK"/><ref name="Paul_2001_DDCE"/>