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 <anton@samba.org> Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
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@ -85,6 +85,7 @@ endif
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CFLAGS-$(CONFIG_PPC64) := -mtraceback=no -mcall-aixdesc
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CFLAGS-$(CONFIG_PPC64) += $(call cc-option,-mcmodel=medium,-mminimal-toc)
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CFLAGS-$(CONFIG_PPC64) += $(call cc-option,-mno-pointers-to-nested-functions)
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CFLAGS-$(CONFIG_PPC32) := -ffixed-r2 -mmultiple
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CFLAGS-$(CONFIG_GENERIC_CPU) += $(call cc-option,-mtune=power7,-mtune=power4)
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