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Date:   Sat, 22 Aug 2020 14:08:27 -0700
From:   Linus Torvalds <>
To:     Miguel Ojeda <>
Cc:     Sedat Dilek <>,
        Segher Boessenkool <>,
        Arvind Sankar <>,
        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 <>
Subject: Re: [PATCH] x86: work around clang IAS bug referencing __force_order

On Sat, Aug 22, 2020 at 11:17 AM Miguel Ojeda
<> wrote:
> However, the important question is whether those users/companies care
> about running the latest kernels. Many of those definitely do not want
> to touch their kernel either. For those that do, there are several
> longterms to pick from that still support 4.9, as well as other
> workarounds.
> Thus I am usually in favor of raising the minimum whenever new hacks
> are required to be added. On the other hand, we already raised the
> version twice this year and it is not clear to me what is the minimum
> version we would need to go for to ensure this does not bite us.

Yeah. The good news is that I haven't seen a lot of pushback on the
gcc version updates so far. I was expecting some complaints. I haven't
seen a single one.

That may be because people did end up finding it very onerous and
complained internally on channels I haven't seen, but it might also be
indicative of us having perhaps been a bit too timid about compiler
version updates.

However, in this case, can we just leave that old "__force_order" hack
alone, and to work around the clang thing, just make a dummy
definition of it anyway.

Alternatively, just use the memory clobber. We use memory clobbers
elsewhere in inline asms to make sure they are serialized, it's not
normally a huge problem. Both clang and gcc should be smart enough to
know that a memory clobber doesn't matter for things like local
variables etc that might be on stack but have never had their address

Or are there other cases than that particular __force_order thing that
people now worry about?


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