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.
next parent 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
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