Merge remote-tracking branch 'kbuild/for-next'

1 files changed, 73 insertions, 0 deletions

diff --git a/init/Kconfig b/init/Kconfig
index 9d3585bb2a7..0f0f351029e 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1255,6 +1255,77 @@ config CC_OPTIMIZE_FOR_SIZE
 
 	  If unsure, say N.
 
+config LTO_MENU
+	bool "Enable gcc link time optimization (LTO)"
+	# Only tested on X86 for now. For other architectures you likely
+	# have to fix some things first, like adding asmlinkages etc.
+	depends on X86
+	# lto does not support excluding flags for specific files
+	# right now. Can be removed if that is fixed.
+	depends on !FUNCTION_TRACER
+	help
+	  With this option gcc will do whole program optimizations for
+	  the whole kernel and module. This increases compile time, but can
+	  lead to better code. It allows gcc to inline functions between
+	  different files and do other optimization.  It might also trigger
+	  bugs due to more aggressive optimization. It allows gcc to drop unused
+	  code. On smaller monolithic kernel configurations
+	  it usually leads to smaller kernels, especially when modules
+	  are disabled.
+
+	  With this option gcc will also do some global checking over
+	  different source files. It also disables a number of kernel
+	  features.
+
+	  This option is recommended for release builds. With LTO
+	  the kernel always has to be re-optimized (but not re-parsed)
+	  on each build.
+
+	  This requires a gcc 4.8 or later compiler and
+	  Linux binutils 2.21.51.0.3 or later.  gcc 4.9 builds significantly
+	  faster than 4.8 It does not currently work with a FSF release of
+	  binutils or with the gold linker.
+
+	  On larger configurations this may need more than 4GB of RAM.
+	  It will likely not work on those with a 32bit compiler.
+
+	  When the toolchain support is not available this will (hopefully)
+	  be automatically disabled.
+
+	  For more information see Documentation/lto-build
+
+config LTO_DISABLE
+         bool "Disable LTO again"
+         depends on LTO_MENU
+         default n
+         help
+           This option is merely here so that allyesconfig or allmodconfig do
+           not enable LTO. If you want to actually use LTO do not enable.
+
+config LTO
+	bool
+	default y
+	depends on LTO_MENU && !LTO_DISABLE
+
+config LTO_DEBUG
+	bool "Enable LTO compile time debugging"
+	depends on LTO
+	help
+	  Enable LTO debugging in the compiler. The compiler dumps
+	  some log files that make it easier to figure out LTO
+	  behavior. The log files also allow to reconstruct
+	  the global inlining and a global callgraph.
+	  They however add some (single threaded) cost to the
+	  compilation.  When in doubt do not enable.
+
+config LTO_CP_CLONE
+	bool "Allow aggressive cloning for function specialization"
+	depends on LTO
+	help
+	  Allow the compiler to clone and specialize functions for specific
+	  arguments when it determines these arguments are very commonly
+	  called.  Experimential. Will increase text size.
+
 config SYSCTL
 	bool
 
@@ -1744,6 +1815,8 @@ config MODULE_FORCE_UNLOAD
 
 config MODVERSIONS
 	bool "Module versioning support"
+	# LTO should work with gcc 4.9
+	depends on !LTO
 	help
 	  Usually, you have to use modules compiled with your kernel.
 	  Saying Y here makes it sometimes possible to use modules