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

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Date:	Tue, 10 Jul 2007 23:43:15 +0200
From:	Adrian Bunk <bunk@...sta.de>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Segher Boessenkool <segher@...nel.crashing.org>,
	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

On Tue, Jul 10, 2007 at 01:42:48PM -0700, H. Peter Anvin wrote:
> 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:

Can't you use the global CFLAGS and append your specific ones?

> CFLAGS          := $(LINUXINCLUDE) -g -Os -D_SETUP -D__KERNEL__ \

-g ???

>                    $(cflags-$(ARCH)) \
>                    -Wall -Wstrict-prototypes \
>                    -march=i386 -mregparm=3 \

Why -march=i386 ?

>                    -include $(srctree)/$(src)/code16gcc.h \
>                    -fno-strict-aliasing -fomit-frame-pointer \
>                    $(call cc-option, -ffreestanding) \

No need to test, -ffreestanding is supported by all gcc versions we 
support.

>                    $(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

cu
Adrian

-- 

       "Is there not promise of rain?" Ling Tan asked suddenly out
        of the darkness. There had been need of rain for many days.
       "Only a promise," Lao Er said.
                                       Pearl S. Buck - Dragon Seed

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