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Date:   Thu, 7 May 2020 13:34:22 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     hpa@zytor.com
Cc:     Nick Desaulniers <ndesaulniers@google.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Sedat Dilek <sedat.dilek@gmail.com>, stable@vger.kernel.org,
        Jesse Brandeburg <jesse.brandeburg@intel.com>,
        "kernelci . org bot" <bot@kernelci.org>,
        Andy Shevchenko <andriy.shevchenko@intel.com>,
        Ilie Halip <ilie.halip@gmail.com>, x86@kernel.org,
        Marco Elver <elver@google.com>,
        "Paul E. McKenney" <paulmck@kernel.org>,
        Daniel Axtens <dja@axtens.net>,
        Masahiro Yamada <yamada.masahiro@socionext.com>,
        Luc Van Oostenryck <luc.vanoostenryck@gmail.com>,
        linux-kernel@vger.kernel.org, clang-built-linux@googlegroups.com
Subject: Re: [PATCH] x86: bitops: fix build regression
Message-ID: <20200507113422.GA3762@hirez.programming.kicks-ass.net>
References: <20200505174423.199985-1-ndesaulniers@google.com>
 <8A776DBC-03AF-485B-9AA6-5920E3C4ACB2@zytor.com>
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On Tue, May 05, 2020 at 11:07:24AM -0700, hpa@zytor.com wrote:
> On May 5, 2020 10:44:22 AM PDT, Nick Desaulniers <ndesaulniers@google.com> wrote:

> >@@ -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))
> > 			: "memory");
> > 	} else {
> > 		asm volatile(LOCK_PREFIX __ASM_SIZE(bts) " %1,%0"
> >@@ -74,7 +74,7 @@ arch_clear_bit(long nr, volatile unsigned long *addr)
> > 	if (__builtin_constant_p(nr)) {
> > 		asm volatile(LOCK_PREFIX "andb %1,%0"
> > 			: CONST_MASK_ADDR(nr, addr)
> >-			: "iq" (CONST_MASK(nr) ^ 0xff));
> >+			: "iq" ((u8)(CONST_MASK(nr) ^ 0xff)));
> > 	} else {
> > 		asm volatile(LOCK_PREFIX __ASM_SIZE(btr) " %1,%0"
> > 			: : RLONG_ADDR(addr), "Ir" (nr) : "memory");
> 
> Drop & 0xff and change ^ 0xff to ~.

But then we're back to sparse being unhappy, no? The thing with ~ is
that it will set high bits which will be truncated, which makes sparse
sad.