lkml.org 
[lkml]   [2015]   [Sep]   [18]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
SubjectRe: [PATCH 0/3] Add __ioread32_copy() and use it
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
_


\
 
 \ /
  Last update: 2015-09-18 21:41    [W:0.071 / U:0.572 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site