* Re: [PATCH] x86-64: Use testl to check __x86_string_control [not found] ` <3cbda329-bc8a-3076-f7c6-89491788fcf8@redhat.com> @ 2021-08-31 15:10 ` H.J. Lu 2022-04-29 22:07 ` Sunil Pandey 0 siblings, 1 reply; 2+ messages in thread From: H.J. Lu @ 2021-08-31 15:10 UTC (permalink / raw) To: Carlos O'Donell; +Cc: GNU C Library, Libc-stable Mailing List 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. ^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: [PATCH] x86-64: Use testl to check __x86_string_control 2021-08-31 15:10 ` [PATCH] x86-64: Use testl to check __x86_string_control H.J. Lu @ 2022-04-29 22:07 ` Sunil Pandey 0 siblings, 0 replies; 2+ messages in thread From: Sunil Pandey @ 2022-04-29 22:07 UTC (permalink / raw) To: H.J. Lu; +Cc: Carlos O'Donell, GNU C Library, Libc-stable Mailing List 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 ^ permalink raw reply [flat|nested] 2+ messages in thread
end of thread, other threads:[~2022-04-29 22:08 UTC | newest]
Thread overview: 2+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
[not found] <20210828131530.539387-1-hjl.tools@gmail.com>
[not found] ` <3cbda329-bc8a-3076-f7c6-89491788fcf8@redhat.com>
2021-08-31 15:10 ` [PATCH] x86-64: Use testl to check __x86_string_control H.J. Lu
2022-04-29 22:07 ` Sunil Pandey
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).