linux-kernel - Re: [x86 setup 13/33] Header file to produce 16-bit code with gcc

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Message-ID: <4693EF48.1080209@zytor.com>
Date:	Tue, 10 Jul 2007 13:42:48 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Segher Boessenkool <segher@...nel.crashing.org>
CC:	Andi Kleen <ak@...e.de>, linux-kernel@...r.kernel.org,
	linux-arch@...r.kernel.org, akpm@...ux-foundation.org
Subject: Re: [x86 setup 13/33] Header file to produce 16-bit code with gcc

Segher Boessenkool wrote:
> 
> Well at least with -fno-toplevel-reorder it is guaranteed
> to work (not the same thing as "is working", heh, but fairly
> close).
> 
> It seems to me GCC should grow an option to insert .code16gcc
> by itself (-m16 perhaps?)  Or GAS could get a flag to include
> a file as a prelude before the main thing.  Neither will help
> Linux right now of course.
> 

-m16 is the right thing, and it also provides a proper hook for
eventually having a real 16-bit backend (there are at least two projects
for doing that.)

For now, I have:

CFLAGS          := $(LINUXINCLUDE) -g -Os -D_SETUP -D__KERNEL__ \
                   $(cflags-$(ARCH)) \
                   -Wall -Wstrict-prototypes \
                   -march=i386 -mregparm=3 \
                   -include $(srctree)/$(src)/code16gcc.h \
                   -fno-strict-aliasing -fomit-frame-pointer \
                   $(call cc-option, -ffreestanding) \
                   $(call cc-option, -fno-unit-at-a-time) \
                   $(call cc-option, -fno-toplevel-reorder) \
                   $(call cc-option, -fno-stack-protector) \
                   $(call cc-option, -mpreferred-stack-boundary=2)

... since that will require less violence to eventually hack in the
proper -m16 option if/when it becomes available.

	-hpa
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