From: hpa@zytor.com
To: David Laight <David.Laight@ACULAB.COM>,
"'Brian Gerst'" <brgerst@gmail.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 <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>,
"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 Mailing List <linux-kernel@vger.kernel.org>,
"clang-built-linux@googlegroups.com"
<clang-built-linux@googlegroups.com>
Subject: RE: [PATCH] x86: bitops: fix build regression
Date: Thu, 07 May 2020 12:31:19 -0700 [thread overview]
Message-ID: <A6FD91D2-8D3A-4767-B6AD-D35B056C58C4@zytor.com> (raw)
In-Reply-To: <9c701ca55bc442c1899a70896f3ea73e@AcuMS.aculab.com>
On May 7, 2020 8:09:35 AM PDT, David Laight <David.Laight@ACULAB.COM> wrote:
>From: Brian Gerst
>> Sent: 07 May 2020 14:32
>...
>> I think the bug this worked around was that the compiler didn't
>detect
>> that CONST_MASK(nr) was also constant and doesn't need to be put into
>> a register. The question is does that bug still exist on compiler
>> versions we care about?
>
>Hmmm...
>That ought to have been fixed instead of worrying about the fact
>that an invalid register was used.
>
>Alternatively is there any reason not to use the bts/btc instructions?
>Yes, I know they'll do wider accesses, but variable bit numbers do.
>It is also possible that the assembler will support constant bit
>numbers >= 32 by adding to the address offset.
>
> David
>
>-
>Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes,
>MK1 1PT, UK
>Registration No: 1397386 (Wales)
They're slower, and for unaligned locked fields can be severely so.
--
Sent from my Android device with K-9 Mail. Please excuse my brevity.
next prev parent reply other threads:[~2020-05-07 19:31 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-05 17:44 [PATCH] x86: bitops: fix build regression Nick Desaulniers
2020-05-05 18:07 ` hpa
2020-05-05 18:22 ` Nick Desaulniers
2020-05-07 11:34 ` Peter Zijlstra
2020-05-07 14:00 ` Brian Gerst
2020-05-07 19:19 ` Nick Desaulniers
2020-05-07 22:29 ` Nick Desaulniers
2020-05-08 1:57 ` Brian Gerst
2020-05-08 17:21 ` Nick Desaulniers
2020-05-08 17:31 ` H. Peter Anvin
2020-05-10 11:59 ` David Laight
2020-05-10 12:33 ` hpa
2020-05-07 19:29 ` hpa
2020-05-06 4:30 ` Nathan Chancellor
2020-05-06 9:22 ` Sedat Dilek
2020-05-06 15:41 ` Nathan Chancellor
2020-05-06 16:37 ` Nick Desaulniers
2020-05-06 16:55 ` Ilie Halip
2020-05-07 6:18 ` Brian Gerst
2020-05-07 7:02 ` hpa
2020-05-07 13:32 ` Brian Gerst
2020-05-07 15:09 ` David Laight
2020-05-07 19:31 ` hpa [this message]
2020-05-07 19:29 ` hpa
2020-05-07 7:44 ` David Laight
2020-05-07 7:59 ` hpa
2020-05-07 8:35 ` David Laight
2020-05-07 8:38 ` hpa
2020-05-07 9:17 ` Andy Shevchenko
2020-05-07 19:22 ` Nick Desaulniers
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