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Commit de3accda authored by David Woodhouse's avatar David Woodhouse Committed by H. Peter Anvin
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x86, build: Build 16-bit code with -m16 where possible 



Both clang 3.5 and GCC 4.9 will support this (as of r199754 and r207196
respectively). Both have been tested to produce booting kernels when the
16-bit code is built with -m16. (Modulo LLVM PR3997, at least.)

[ hpa: folded test for -m16 into M16_CFLAGS ]

Signed-off-by: default avatarDavid Woodhouse <David.Woodhouse@intel.com>
Link: http://lkml.kernel.org/r/1390997807.20153.133.camel@i7.infradead.org


Signed-off-by: default avatarH. Peter Anvin <hpa@linux.intel.com>
parent 5fbbc25a

arch/x86/Makefile

+12 −4
Original line number Diff line number Diff line
@@ -13,14 +13,22 @@ endif 


# How to compile the 16-bit code.  Note we always compile for -march=i386;

# that way we can complain to the user if the CPU is insufficient.

REALMODE_CFLAGS	:= -m32 -g -Os -D__KERNEL__ -DDISABLE_BRANCH_PROFILING \

#

# The -m16 option is supported by GCC >= 4.9 and clang >= 3.5. For

# older versions of GCC, we need to play evil and unreliable tricks to

# attempt to ensure that our asm(".code16gcc") is first in the asm

# output.

CODE16GCC_CFLAGS := -m32 -include $(srctree)/arch/x86/boot/code16gcc.h \

		    $(call cc-option, -fno-toplevel-reorder,\

		      $(call cc-option, -fno-unit-at-a-time))

M16_CFLAGS	 := $(call cc-option, -m16, $(CODE16GCC_CFLAGS))



REALMODE_CFLAGS	:= $(M16_CFLAGS) -g -Os -D__KERNEL__ \

		   -DDISABLE_BRANCH_PROFILING \

		   -Wall -Wstrict-prototypes -march=i386 -mregparm=3 \

		   -include $(srctree)/arch/x86/boot/code16gcc.h \

		   -fno-strict-aliasing -fomit-frame-pointer -fno-pic \

		   -mno-mmx -mno-sse \

		   $(call cc-option, -ffreestanding) \

		   $(call cc-option, -fno-toplevel-reorder,\

		   $(call cc-option, -fno-unit-at-a-time)) \

		   $(call cc-option, -fno-stack-protector) \

		   $(call cc-option, -mpreferred-stack-boundary=2)

export REALMODE_CFLAGS