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Date:   Sat, 22 Aug 2020 03:41:33 -0500
From:   Segher Boessenkool <>
To:     Arvind Sankar <>
Cc:     Thomas Gleixner <>,
        Nick Desaulniers <>,
        "Paul E. McKenney" <>,
        Ingo Molnar <>, Arnd Bergmann <>,
        Borislav Petkov <>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <>,
        "H. Peter Anvin" <>,
        "Kirill A. Shutemov" <>,
        Zhenzhong Duan <>,
        Kees Cook <>,
        Peter Zijlstra <>,
        Juergen Gross <>,
        Andy Lutomirski <>,
        Andrew Cooper <>,
        LKML <>,
        clang-built-linux <>,
        Will Deacon <>,
        Linus Torvalds <>
Subject: Re: [PATCH] x86: work around clang IAS bug referencing __force_order

Hi Arvind,

On Fri, Aug 21, 2020 at 11:55:52PM -0400, Arvind Sankar wrote:
> Cc Segher.
> Segher, we were looking at gcc PR82602, where IRA could reorder volatile
> asm's (reported on ARM). The fix was backported to gcc-6.

I know ;-)

> Do you know if
> there is any reason the problem couldn't occur on x86 on older gcc
> without the fix?

No, I see no particular reason, at least GCC 5 seems vulnerable.  (The
GCC 5 release branch was closed at the time this bug report was made,
already).  There is no reason I see why it would work on x86 but fail
elsewhere, either.


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