On Wed, 16 Sep 2015 04:55:46 +0200 Andi Kleen <andi@xxxxxxxxxxxxxx> wrote: > > Under what circumstances will the compiler (or linker?) do this? > > Compiler. > > > LTO enabled? > > Yes it's for LTO. The optimization allows the compiler to drop unused > functions, which is very popular with users (a lot use it to get smaller > kernel images) > Does this look truthful and complete? --- a/include/linux/compiler-gcc.h~a +++ a/include/linux/compiler-gcc.h @@ -205,7 +205,10 @@ #if GCC_VERSION >= 40600 /* - * Tell the optimizer that something else uses this function or variable. + * When used with Link Time Optimization, gcc can optimize away C functions or + * variables which are referenced only from assembly code. __visible tells the + * optimizer that something else uses this function or variable, thus preventing + * this. */ #define __visible __attribute__((externally_visible)) #endif _
