public inbox for libc-stable@sourceware.org
 help / color / mirror / Atom feed
From: "H.J. Lu" <hjl.tools@gmail.com>
To: "Carlos O'Donell" <carlos@redhat.com>
Cc: GNU C Library <libc-alpha@sourceware.org>,
	 Libc-stable Mailing List <libc-stable@sourceware.org>
Subject: Re: [PATCH] x86-64: Use testl to check __x86_string_control
Date: Tue, 31 Aug 2021 08:10:31 -0700	[thread overview]
Message-ID: <CAMe9rOqTLqovyCtsrh643N8nz3uQPyfN1+_wGYk+zKPN51ksMg@mail.gmail.com> (raw)
In-Reply-To: <3cbda329-bc8a-3076-f7c6-89491788fcf8@redhat.com>

On Mon, Aug 30, 2021 at 10:35 AM Carlos O'Donell <carlos@redhat.com> 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 <carlos@redhat.com>

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.

       reply	other threads:[~2021-08-31 15:11 UTC|newest]

Thread overview: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20210828131530.539387-1-hjl.tools@gmail.com>
     [not found] ` <3cbda329-bc8a-3076-f7c6-89491788fcf8@redhat.com>
2021-08-31 15:10   ` H.J. Lu [this message]
2022-04-29 22:07     ` Sunil Pandey

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=CAMe9rOqTLqovyCtsrh643N8nz3uQPyfN1+_wGYk+zKPN51ksMg@mail.gmail.com \
    --to=hjl.tools@gmail.com \
    --cc=carlos@redhat.com \
    --cc=libc-alpha@sourceware.org \
    --cc=libc-stable@sourceware.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).