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

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Message-Id: <3598C6DD-D62C-4DB5-99D7-5B4420A0EAB2@kernel.crashing.org>
Date:	Wed, 11 Jul 2007 00:06:11 +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

>> 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
>
> OK, how does this look:
>
> 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-toplevel-reorder,\
>                         $(call cc-option, -fno-unit-at-a-time)) \
>                    $(call cc-option, -fno-stack-protector) \
>                    $(call cc-option, -mpreferred-stack-boundary=2)

That looks fine.

> I think dropping -fno-strict-aliasing for this code is probably bad...
> it's pretty low-level stuff which does a lot of bitlevel manipulation.

"Which breaks C aliasing rules all over the place".  Well,
probably not all that often, actually.  But, as I said --
let's not go there now, keep the flag in there, removing
it will take a lot of work.


Segher

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