Messages in this thread Patch in this message | | | Date | Fri, 18 Sep 2015 12:19:19 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH 0/3] Add __ioread32_copy() and use it |
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On Wed, 16 Sep 2015 04:55:46 +0200 Andi Kleen <andi@firstfloor.org> 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 _
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