Messages in this thread | | | Date | Sat, 19 Sep 2015 22:16:29 +0200 | From | Andi Kleen <> | Subject | Re: [PATCH 0/3] Add __ioread32_copy() and use it |
| |
On Fri, Sep 18, 2015 at 12:19:19PM -0700, Andrew Morton wrote: > 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.
Yes,
In a few cases I also used it to work around LTO bugs in older gcc releases. I don't think any of those fixes made it into mainline though, and they are not needed anymore with 5.x
-Andi
| |