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From:   Nick Desaulniers <ndesaulniers@google.com>
Date:   Thu, 7 May 2020 12:22:30 -0700
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Subject: Re: [PATCH] x86: bitops: fix build regression
To:     Brian Gerst <brgerst@gmail.com>
Cc:     Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
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        Andy Shevchenko <andriy.shevchenko@intel.com>,
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On Wed, May 6, 2020 at 11:18 PM Brian Gerst <brgerst@gmail.com> wrote:
>
> I think a better fix would be to make CONST_MASK() return a u8 value
> rather than have to cast on every use.
>
> Also I question the need for the "q" constraint.  It was added in
> commit 437a0a54 as a workaround for GCC 3.4.4.  Now that the minimum
> GCC version is 4.6, is this still necessary?

TL;DR yes

ah, thanks for the git archeology, it's useful.  I don't think this is
a compiler bug however, just the compiler being more strict that the
`b` suffix on `orb` requires a 8b register operand.  For 32b x86, `q`
asm constraint is required, because not all GPR's had lower 8b
register aliases, as Arnd found and HPA noted as well.

I like your suggested change to CONST_MASK, and will send that in a bit.
-- 
Thanks,
~Nick Desaulniers