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

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Message-ID: <60b16c05ca9e4954a7e4fcdd3075e23d@AcuMS.aculab.com>
Date:   Thu, 7 May 2020 07:44:44 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     '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>,
        "H. Peter Anvin" <hpa@...or.com>, 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

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

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