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

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Message-ID: <46942496.2050205@didntduck.org>
Date:	Tue, 10 Jul 2007 20:30:14 -0400
From:	Brian Gerst <bgerst@...ntduck.org>
To:	Adrian Bunk <bunk@...sta.de>
CC:	"H. Peter Anvin" <hpa@...or.com>,
	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

Adrian Bunk wrote:
> 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 ?

To prevent gcc from using instructions (particularly cmovxx) that not
all processors will understand.

--
				Brian Gerst
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