Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Tue, 05 May 2020 11:07:24 -0700
User-Agent: K-9 Mail for Android
In-Reply-To: <20200505174423.199985-1-ndesaulniers@google.com>
References: <20200505174423.199985-1-ndesaulniers@google.com>
MIME-Version: 1.0
Content-Type: text/plain;
 charset=utf-8
Content-Transfer-Encoding: quoted-printable
Subject: Re: [PATCH] x86: bitops: fix build regression
To:     Nick Desaulniers <ndesaulniers@google.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>
CC:     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>,
        "Peter Zijlstra (Intel)" <peterz@infradead.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
From:   hpa@zytor.com
Message-ID: <8A776DBC-03AF-485B-9AA6-5920E3C4ACB2@zytor.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On May 5, 2020 10:44:22 AM PDT, Nick Desaulniers <ndesaulniers@google=2Ecom=
> wrote:
>From: Sedat Dilek <sedat=2Edilek@gmail=2Ecom>
>
>It turns out that if your config tickles __builtin_constant_p via
>differences in choices to inline or not, this now produces invalid
>assembly:
>
>$ cat foo=2Ec
>long a(long b, long c) {
>  asm("orb\t%1, %0" : "+q"(c): "r"(b));
>  return c;
>}
>$ gcc foo=2Ec
>foo=2Ec: Assembler messages:
>foo=2Ec:2: Error: `%rax' not allowed with `orb'
>
>The "q" constraint only has meanting on -m32 otherwise is treated as
>"r"=2E
>
>This is easily reproducible via Clang+CONFIG_STAGING=3Dy+CONFIG_VT6656=3D=
m,
>or Clang+allyesconfig=2E
>
>Keep the masking operation to appease sparse (`make C=3D1`), add back the
>cast in order to properly select the proper 8b register alias=2E
>
> [Nick: reworded]
>
>Cc: stable@vger=2Ekernel=2Eorg
>Cc: Jesse Brandeburg <jesse=2Ebrandeburg@intel=2Ecom>
>Link: https://github=2Ecom/ClangBuiltLinux/linux/issues/961
>Link: https://lore=2Ekernel=2Eorg/lkml/20200504193524=2EGA221287@google=
=2Ecom/
>Fixes: 1651e700664b4 ("x86: Fix bitops=2Eh warning with a moved cast")
>Reported-by: Sedat Dilek <sedat=2Edilek@gmail=2Ecom>
>Reported-by: kernelci=2Eorg bot <bot@kernelci=2Eorg>
>Suggested-by: Andy Shevchenko <andriy=2Eshevchenko@intel=2Ecom>
>Suggested-by: Ilie Halip <ilie=2Ehalip@gmail=2Ecom>
>Tested-by: Sedat Dilek <sedat=2Edilek@gmail=2Ecom>
>Signed-off-by: Sedat Dilek <sedat=2Edilek@gmail=2Ecom>
>Signed-off-by: Nick Desaulniers <ndesaulniers@google=2Ecom>
>---
> arch/x86/include/asm/bitops=2Eh | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
>diff --git a/arch/x86/include/asm/bitops=2Eh
>b/arch/x86/include/asm/bitops=2Eh
>index b392571c1f1d=2E=2E139122e5b25b 100644
>--- a/arch/x86/include/asm/bitops=2Eh
>+++ b/arch/x86/include/asm/bitops=2Eh
>@@ -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 ~=2E

The redundancy is confusing=2E
--=20
Sent from my Android device with K-9 Mail=2E Please excuse my brevity=2E