Commit-ID: 372cb9eef903d1e18961d2c1a34c75f027f0bd8f Gitweb: http://git.kernel.org/tip/372cb9eef903d1e18961d2c1a34c75f027f0bd8f Author: David Woodhouse <dw...@infradead.org> AuthorDate: Wed, 29 Jan 2014 12:16:47 +0000 Committer: H. Peter Anvin <h...@linux.intel.com> CommitDate: Wed, 29 Jan 2014 09:47:49 -0800
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.) Signed-off-by: David Woodhouse <david.woodho...@intel.com> Link: http://lkml.kernel.org/r/1390997807.20153.133.ca...@i7.infradead.org Signed-off-by: H. Peter Anvin <h...@linux.intel.com> --- arch/x86/Makefile | 16 ++++++++++++---- 1 file changed, 12 insertions(+), 4 deletions(-) diff --git a/arch/x86/Makefile b/arch/x86/Makefile index 9ecbc1c..dbc9b2b 100644 --- a/arch/x86/Makefile +++ b/arch/x86/Makefile @@ -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 := -m16 + +REALMODE_CFLAGS := -g -Os -D__KERNEL__ -DDISABLE_BRANCH_PROFILING \ + $(call cc-option, $(M16_CFLAGS), $(CODE16GCC_CFLAGS)) \ -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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
