From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg1-x52c.google.com (mail-pg1-x52c.google.com [IPv6:2607:f8b0:4864:20::52c]) by sourceware.org (Postfix) with ESMTPS id 96547385843A; Tue, 31 Aug 2021 15:11:08 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 96547385843A Received: by mail-pg1-x52c.google.com with SMTP id w7so15880915pgk.13; Tue, 31 Aug 2021 08:11:08 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=w4vZZvGivCpzVHRTJO3V7rxC36pXOjzzRzakegIFnXk=; b=MbJQjmUyoUmQhaN3sw01AkeiM6HMQNdChxJB8fDJT203PSCIJtoxySSoe14awy1N6e v+WcXV1ZgiDLOK1EQpsVJ1Rl2zAeKl8RsOarP7GOC+clMYXWOyYlix86elpycvoWDsWp QZtIhBy6Rl0jVtbRoRf83ga72ZeMN609opSHsvUooSCchBcgCDG8plO/LvD7oXhEyWGk uWh/Zz2pTI3YJpntakzgwVY0CCAmfWsP1TjbgMd+0mkoMEukWJhlvsV9s9qrHe7BPgtz 2YkExFzsvIG7SYwr4gtEqog5DfIhs7OPMbeeEm0hzeyuXWVa3HmTfrUyEKvXxDj/aFai 6X3A== X-Gm-Message-State: AOAM532KXrIAoR8N/CETkpt66+Tg+lSgEtdfSSUfbde8MxRGQFp3vxzZ FkKarS1ZqacE8GV7KeXEsdqFjnxhQ/GYtTv6ixGzwuX3 X-Google-Smtp-Source: ABdhPJyUzRcJEJIeBvPbSX3oLSpqZvcfQyGBjRqzemiisYOg6ce5pjmzXBHxONbKmh3ONxMDRr6v43wCJYXgpcNCD/k= X-Received: by 2002:a63:164a:: with SMTP id 10mr27710056pgw.161.1630422667592; Tue, 31 Aug 2021 08:11:07 -0700 (PDT) MIME-Version: 1.0 References: <20210828131530.539387-1-hjl.tools@gmail.com> <3cbda329-bc8a-3076-f7c6-89491788fcf8@redhat.com> In-Reply-To: <3cbda329-bc8a-3076-f7c6-89491788fcf8@redhat.com> From: "H.J. Lu" Date: Tue, 31 Aug 2021 08:10:31 -0700 Message-ID: Subject: Re: [PATCH] x86-64: Use testl to check __x86_string_control To: "Carlos O'Donell" Cc: GNU C Library , Libc-stable Mailing List Content-Type: text/plain; charset="UTF-8" X-Spam-Status: No, score=-3030.6 required=5.0 tests=BAYES_00, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, FREEMAIL_FROM, GIT_PATCH_0, RCVD_IN_DNSWL_NONE, SPF_HELO_NONE, SPF_PASS, TXREP autolearn=ham autolearn_force=no version=3.4.4 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on server2.sourceware.org X-BeenThere: libc-stable@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libc-stable mailing list List-Unsubscribe: , List-Archive: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 31 Aug 2021 15:11:10 -0000 On Mon, Aug 30, 2021 at 10:35 AM Carlos O'Donell wrote: > > On 8/28/21 9:15 AM, H.J. Lu via Libc-alpha wrote: > > Use testl, instead of andl, to check __x86_string_control to avoid > > updating __x86_string_control. > > The __x86_string_control is a global variable that is hidden from external > linkage and used internally by various routines. Today the value is RW, > but in the future it could become RO (and probably should after a call > to init_cacheinfo()). We don't want to do an idempotent update (we have > only one bit constant for now), but instead just want to check for the bit. > This code will break when we get another bit, or when it becomes RO. > > LGTM. > > Reviewed-by: Carlos O'Donell I am backporting it to release branches. Thanks. > > --- > > sysdeps/x86_64/multiarch/memmove-vec-unaligned-erms.S | 4 ++-- > > 1 file changed, 2 insertions(+), 2 deletions(-) > > > > diff --git a/sysdeps/x86_64/multiarch/memmove-vec-unaligned-erms.S b/sysdeps/x86_64/multiarch/memmove-vec-unaligned-erms.S > > index 9f02624375..abde8438d4 100644 > > --- a/sysdeps/x86_64/multiarch/memmove-vec-unaligned-erms.S > > +++ b/sysdeps/x86_64/multiarch/memmove-vec-unaligned-erms.S > > @@ -325,7 +325,7 @@ L(movsb): > > /* Avoid slow backward REP MOVSB. */ > > jb L(more_8x_vec_backward) > > # if AVOID_SHORT_DISTANCE_REP_MOVSB > > - andl $X86_STRING_CONTROL_AVOID_SHORT_DISTANCE_REP_MOVSB, __x86_string_control(%rip) > > + testl $X86_STRING_CONTROL_AVOID_SHORT_DISTANCE_REP_MOVSB, __x86_string_control(%rip) > > jz 3f > > movq %rdi, %rcx > > subq %rsi, %rcx > > @@ -333,7 +333,7 @@ L(movsb): > > # endif > > 1: > > # if AVOID_SHORT_DISTANCE_REP_MOVSB > > - andl $X86_STRING_CONTROL_AVOID_SHORT_DISTANCE_REP_MOVSB, __x86_string_control(%rip) > > + testl $X86_STRING_CONTROL_AVOID_SHORT_DISTANCE_REP_MOVSB, __x86_string_control(%rip) > > jz 3f > > movq %rsi, %rcx > > subq %rdi, %rcx > > > > > -- > Cheers, > Carlos. > -- H.J.