From: Sunil Pandey <skpgkp2@gmail.com>
To: "H.J. Lu" <hjl.tools@gmail.com>
Cc: "Carlos O'Donell" <carlos@redhat.com>,
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: Fri, 29 Apr 2022 15:07:44 -0700 [thread overview]
Message-ID: <CAMAf5_eB8pojCgLbMijDHnkD7cDgY9o=HbnNdyE9PigbDjUmnA@mail.gmail.com> (raw)
In-Reply-To: <CAMe9rOqTLqovyCtsrh643N8nz3uQPyfN1+_wGYk+zKPN51ksMg@mail.gmail.com>
On Tue, Aug 31, 2021 at 8:11 AM H.J. Lu via Libc-alpha
<libc-alpha@sourceware.org> wrote:
>
> 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.
I would like to backport this patch to release branches.
Any comments or objections?
--Sunil
prev parent reply other threads:[~2022-04-29 22:08 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
2022-04-29 22:07 ` Sunil Pandey [this message]
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