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From:   Nadav Amit <namit@vmware.com>
To:     "hpa@zytor.com" <hpa@zytor.com>
CC:     Linus Torvalds <torvalds@linux-foundation.org>,
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Subject: Re: [PATCH 2/6] x86: bug: prevent gcc distortions
Thread-Topic: [PATCH 2/6] x86: bug: prevent gcc distortions
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Date:   Fri, 18 May 2018 19:02:50 +0000
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hpa@zytor.com wrote:

> On May 18, 2018 11:50:12 AM PDT, Linus Torvalds <torvalds@linux-foundatio=
n.org> wrote:
>> On Fri, May 18, 2018 at 11:34 AM <hpa@zytor.com> wrote:
>>=20
>>> On May 18, 2018 11:25:32 AM PDT, Linus Torvalds <
>> torvalds@linux-foundation.org> wrote:
>>=20
>>> Unfortunately gcc doesn't guarantee that global assembly inlines will
>> appear at the top of the file.
>>=20
>> Yeah. It really would be better to do the "asm version of -inline".
>>=20
>> We already do something like that for real *.S files on some
>> architectures
>> (because their assembly really wants it, eg
>>=20
>> arch/arm/Makefile:
>> KBUILD_AFLAGS +=3D$(CFLAGS_ABI) $(AFLAGS_ISA) $(arch-y) $(tune-y)
>> -include
>> asm/unified.h -msoft-float
>>=20
>> but I do want to point out that KBUILD_AFLAGS is *not* used for
>> compiler-generated assembly, only for actual *.S files.
>>=20
>> Sadly, I don't actually know any way to make gcc call the 'as' phase
>> with
>> particular options. We can use "-Wa,xyzzy" to pass in xyzzy to the
>> assembler, but there is no "-include" option for GNU as afaik.
>>=20
>> Can you perhaps define a macro symbol for "--defsym"? Probably not.
>>=20
>>                      Linus
>=20
> I looked at this thing a long time ago; it's not there, and the best woul=
d probably be to get global asm() working properly in gcc.

I can add a -Wa,[filename.s] switch. It works, but sort of undocumented.