linux-kernel - RE: [PATCH] x86: bitops: fix build regression

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Message-ID: <7C32CF96-0519-4C32-B66B-23AD9C1F1F52@zytor.com>
Date:   Thu, 07 May 2020 00:59:03 -0700
From:   hpa@...or.com
To:     David Laight <David.Laight@...LAB.COM>,
        "'Brian Gerst'" <brgerst@...il.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>
CC:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Sedat Dilek <sedat.dilek@...il.com>,
        stable <stable@...r.kernel.org>,
        Jesse Brandeburg <jesse.brandeburg@...el.com>,
        "kernelci . org bot" <bot@...nelci.org>,
        Andy Shevchenko <andriy.shevchenko@...el.com>,
        Ilie Halip <ilie.halip@...il.com>,
        the arch/x86 maintainers <x86@...nel.org>,
        Marco Elver <elver@...gle.com>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Daniel Axtens <dja@...ens.net>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Luc Van Oostenryck <luc.vanoostenryck@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "clang-built-linux@...glegroups.com" 
        <clang-built-linux@...glegroups.com>
Subject: RE: [PATCH] x86: bitops: fix build regression

On May 7, 2020 12:44:44 AM PDT, David Laight <David.Laight@...LAB.COM> wrote:
>From: Brian Gerst
>> Sent: 07 May 2020 07:18
>...
>> > --- a/arch/x86/include/asm/bitops.h
>> > +++ b/arch/x86/include/asm/bitops.h
>> > @@ -54,7 +54,7 @@ arch_set_bit(long nr, volatile unsigned long
>*addr)
>> >         if (__builtin_constant_p(nr)) {
>> >                 asm volatile(LOCK_PREFIX "orb %1,%0"
>> >                         : CONST_MASK_ADDR(nr, addr)
>> > -                       : "iq" (CONST_MASK(nr) & 0xff)
>> > +                       : "iq" ((u8)(CONST_MASK(nr) & 0xff))
>> 
>> I think a better fix would be to make CONST_MASK() return a u8 value
>> rather than have to cast on every use.
>
>Or assign to a local variable - then it doesn't matter how
>the value is actually calculated. So:
>			u8 mask = CONST_MASK(nr);
>			asm volatile(LOCK_PREFIX "orb %1,%0"
>				: CONST_MASK_ADDR(nr, addr)
>				: "iq" mask
>
>	David
>
>-
>Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes,
>MK1 1PT, UK
>Registration No: 1397386 (Wales)

"const u8" please...
-- 
Sent from my Android device with K-9 Mail. Please excuse my brevity.