From 98679fb0927cee2084caddc5277326f18642a58b Mon Sep 17 00:00:00 2001 From: Anton Blanchard Date: Wed, 12 Dec 2012 14:43:12 +0000 Subject: [PATCH] powerpc: Avoid load of static chain register when calling nested functions through a pointer on 64bit The ppc64 ABI has a static chain register (r11) which is only used when calling nested functions through a pointer. Considering that we take a dim view of nested functions in the kernel, we have a lot of unnecessary overhead here. gcc 4.7 has an option to disable loading of r11 so lets use it. If hell freezes over and hipsters manage to litter the kernel with nested functions, gcc will give us an error message and won't simply compile bad code: You cannot take the address of a nested function if you use the -mno-pointers-to-nested-functions option. Furthermore our kernel module trampolines don't setup the static chain register so adding this option and forcing gcc to error out makes even more sense. Signed-off-by: Anton Blanchard Signed-off-by: Benjamin Herrenschmidt --- arch/powerpc/Makefile | 1 + 1 file changed, 1 insertion(+) diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile index 31d8965e0847..967fd23ace78 100644 --- a/arch/powerpc/Makefile +++ b/arch/powerpc/Makefile @@ -85,6 +85,7 @@ endif CFLAGS-$(CONFIG_PPC64) := -mtraceback=no -mcall-aixdesc CFLAGS-$(CONFIG_PPC64) += $(call cc-option,-mcmodel=medium,-mminimal-toc) +CFLAGS-$(CONFIG_PPC64) += $(call cc-option,-mno-pointers-to-nested-functions) CFLAGS-$(CONFIG_PPC32) := -ffixed-r2 -mmultiple CFLAGS-$(CONFIG_GENERIC_CPU) += $(call cc-option,-mtune=power7,-mtune=power4) -- 2.39.2