linux-kernel - Re: [PATCH 2/6] x86: bug: prevent gcc distortions

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Message-ID: <2F760FAE-C19C-4BC3-A8CC-7D17CEF3B116@zytor.com>
Date:   Fri, 18 May 2018 11:53:25 -0700
From:   hpa@...or.com
To:     Linus Torvalds <torvalds@...ux-foundation.org>
CC:     namit@...are.com, Peter Zijlstra <peterz@...radead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>
Subject: Re: [PATCH 2/6] x86: bug: prevent gcc distortions

On May 18, 2018 11:50:12 AM PDT, Linus Torvalds <torvalds@...ux-foundation.org> wrote:
>On Fri, May 18, 2018 at 11:34 AM <hpa@...or.com> wrote:
>
>> On May 18, 2018 11:25:32 AM PDT, Linus Torvalds <
>torvalds@...ux-foundation.org> wrote:
>
>> Unfortunately gcc doesn't guarantee that global assembly inlines will
>appear at the top of the file.
>
>Yeah. It really would be better to do the "asm version of -inline".
>
>We already do something like that for real *.S files on some
>architectures
>(because their assembly really wants it, eg
>
>  arch/arm/Makefile:
>KBUILD_AFLAGS +=$(CFLAGS_ABI) $(AFLAGS_ISA) $(arch-y) $(tune-y)
>-include
>asm/unified.h -msoft-float
>
>but I do want to point out that KBUILD_AFLAGS is *not* used for
>compiler-generated assembly, only for actual *.S files.
>
>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.
>
>Can you perhaps define a macro symbol for "--defsym"? Probably not.
>
>                       Linus

I looked at this thing a long time ago; it's not there, and the best would probably be to get global asm() working properly in gcc.
-- 
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