Commit de3accda authored by David Woodhouse's avatar David Woodhouse Committed by H. Peter Anvin

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