[llvmlinux] [PATCH 3/4] x86: Allow building 16-bit code with -m16 with toolchains that support it

David Woodhouse dwmw2 at infradead.org
Tue Jan 14 19:18:35 UTC 2014


Head. With a trivial patch to add -m16 support, that I think I need to update since someone changed that code in clang this week. Will send new patch in a few hours when I get home.

And llvm from git://git.infradead.org/~dwmw2/llvm.git for the 16-bit support.

-- 
dwmw2
(Apologies for HTML and top-posting; Android mailer is broken.)

-------- Original message --------
From: Jan-Simon Möller <dl9pf at gmx.de> 
Date:14/01/2014  19:14  (GMT+00:00) 
To: llvmlinux at lists.linuxfoundation.org 
Cc: x86 at kernel.org,David Woodhouse <David.Woodhouse at intel.com>,	linux-kernel at vger.kernel.org 
Subject: Re: [llvmlinux] [PATCH 3/4] x86: Allow building 16-bit code with
 	-m16 with toolchains that support it 

Hi David,

what version of clang did you use btw ?

-- 

Dipl.-Ing.
Jan-Simon Möller

jansimon.moeller at gmx.de
Am Mittwoch, 8. Januar 2014, 11:21:22 schrieb David Woodhouse:
> I have this working with LLVM/Clang, and a PR is filed for GCC because
> the current hacks we have to do to *try* to ensure that .code16gcc is
> the first thing in the asm output are horrid.
> 
> Signed-off-by: David Woodhouse <David.Woodhouse at intel.com>
> ---
>  arch/x86/Makefile | 15 +++++++++++----
>  1 file changed, 11 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/Makefile b/arch/x86/Makefile
> index ef19271..60fc67d 100644
> --- a/arch/x86/Makefile
> +++ b/arch/x86/Makefile
> @@ -13,14 +13,21 @@ 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 \
> +#
> +# We really want GCC to have a -m16 option like clang, so that we don't
> +# have to play these evil and unreliable tricks to ensure that our
> +# asm(".code16gcc") is first in the asm output. http://gcc.gnu.org/PR59672
> +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

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