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

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Message-Id: <763AC431-73A6-4A5F-9453-A66A86D7DEEB@kernel.crashing.org>
Date:	Tue, 10 Jul 2007 23:10:05 +0200
From:	Segher Boessenkool <segher@...nel.crashing.org>
To:	"H. Peter Anvin" <hpa@...or.com>
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

>> It seems to me GCC should grow an option to insert .code16gcc
>> by itself (-m16 perhaps?)

> -m16 is the right thing,

Probably not actually, -m16 might have 16-bit "int" etc.
-mabi=16 is closer to what other architectures do here.

> and it also provides a proper hook for
> eventually having a real 16-bit backend (there are at least two  
> projects
> for doing that.)

Those would use -m16, yes.

> 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.

Looks good, except you don't want -fno-unit-at-a-time if
-fno-toplevel-reorder works.  And of course it would be
good to get rid of -fno-strict-aliasing, but let's not
go there today ;-P


Segher

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