Re: [PATCH] x86: bitops: fix build regression

From: Brian Gerst <brgerst@gmail.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>,
	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 <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>,
	"the arch/x86 maintainers" <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 Mailing List <linux-kernel@vger.kernel.org>,
	clang-built-linux@googlegroups.com
Subject: Re: [PATCH] x86: bitops: fix build regression
Date: Thu, 7 May 2020 10:00:16 -0400	[thread overview]
Message-ID: <CAMzpN2hXUYvLuTA63N56ef4DEzyWXt_uVVq6PV0r8YQT-YN42g@mail.gmail.com> (raw)
In-Reply-To: <20200507113422.GA3762@hirez.programming.kicks-ass.net>

On Thu, May 7, 2020 at 7:38 AM Peter Zijlstra <peterz@infradead.org> wrote:
>
> 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.

This change will make sparse happy and allow these cleanups:
#define CONST_MASK(nr)                 ((u8)1 << ((nr) & 7))

Tested with GCC 9.3.1.

--
Brian Gerst