| Message ID | 1489512487-24860-1-git-send-email-adhemerval.zanella@linaro.org |
|---|---|
| State | Accepted |
| Commit | 3abeeec5f46ff036bd9df60bb096e20314ccd078 |
| Headers | show |
On 03/14/2017 02:28 PM, Adhemerval Zanella wrote: > This patch fixes the regression added by 23d2770 for final address > overflow calculation. The subtraction of the considered size (16) > at line 120 is at wrong place, for sizes less than 16 subsequent > overflow check will not take in consideration an invalid size (since > the subtraction will be negative). Also, the lea instruction also > does not raise the carry flag (CF) that is used in subsequent jbe > to check for overflow. > > The fix is to follow x86_64 logic from 3daef2c where the overflow > is first check and a sub instruction is issued. In case of resulting > negative size, CF will be set by the sub instruction and a NULL > result will be returned. The patch also add similar tests reported > in bug report. > > Checked on i686-linux-gnu and x86_64-linux-gnu. > > [BZ# 21182] > * string/test-memchr.c (do_test): Add BZ#21182 checks for address > near end of a page. > * sysdeps/i386/i686/multiarch/memchr-sse2.S (__memchr): Fix > overflow calculation. > --- > ChangeLog | 7 +++++++ > string/test-memchr.c | 6 ++++++ > sysdeps/i386/i686/multiarch/memchr-sse2.S | 2 +- > 3 files changed, 14 insertions(+), 1 deletion(-) > > diff --git a/string/test-memchr.c b/string/test-memchr.c > index d64d10c..87a077b 100644 > --- a/string/test-memchr.c > +++ b/string/test-memchr.c > @@ -210,6 +210,12 @@ test_main (void) > do_test (0, i, i + 1, i + 1, 0); > } > > + /* BZ#21182 - wrong overflow calculation for i686 implementation > + with address near end of the page. */ > + for (i = 2; i < 16; ++i) > + /* page_size is in fact getpagesize() * 2. */ > + do_test (page_size/2 - i, i, i, 1, 0x9B); page_size / 2 > + > do_random_tests (); > return ret; > } > diff --git a/sysdeps/i386/i686/multiarch/memchr-sse2.S b/sysdeps/i386/i686/multiarch/memchr-sse2.S > index 910679c..e41f324 100644 > --- a/sysdeps/i386/i686/multiarch/memchr-sse2.S > +++ b/sysdeps/i386/i686/multiarch/memchr-sse2.S > @@ -117,7 +117,6 @@ L(crosscache): > > # ifndef USE_AS_RAWMEMCHR > jnz L(match_case2_prolog1) > - lea -16(%edx), %edx > /* Calculate the last acceptable address and check for possible > addition overflow by using satured math: > edx = ecx + edx > @@ -125,6 +124,7 @@ L(crosscache): > add %ecx, %edx > sbb %eax, %eax > or %eax, %edx > + sub $16, %edx > jbe L(return_null) > lea 16(%edi), %edi > # else
Ping (with the page_size/2 fix included). On 14/03/2017 14:28, Adhemerval Zanella wrote: > This patch fixes the regression added by 23d2770 for final address > overflow calculation. The subtraction of the considered size (16) > at line 120 is at wrong place, for sizes less than 16 subsequent > overflow check will not take in consideration an invalid size (since > the subtraction will be negative). Also, the lea instruction also > does not raise the carry flag (CF) that is used in subsequent jbe > to check for overflow. > > The fix is to follow x86_64 logic from 3daef2c where the overflow > is first check and a sub instruction is issued. In case of resulting > negative size, CF will be set by the sub instruction and a NULL > result will be returned. The patch also add similar tests reported > in bug report. > > Checked on i686-linux-gnu and x86_64-linux-gnu. > > [BZ# 21182] > * string/test-memchr.c (do_test): Add BZ#21182 checks for address > near end of a page. > * sysdeps/i386/i686/multiarch/memchr-sse2.S (__memchr): Fix > overflow calculation. > --- > ChangeLog | 7 +++++++ > string/test-memchr.c | 6 ++++++ > sysdeps/i386/i686/multiarch/memchr-sse2.S | 2 +- > 3 files changed, 14 insertions(+), 1 deletion(-) > > diff --git a/string/test-memchr.c b/string/test-memchr.c > index d64d10c..87a077b 100644 > --- a/string/test-memchr.c > +++ b/string/test-memchr.c > @@ -210,6 +210,12 @@ test_main (void) > do_test (0, i, i + 1, i + 1, 0); > } > > + /* BZ#21182 - wrong overflow calculation for i686 implementation > + with address near end of the page. */ > + for (i = 2; i < 16; ++i) > + /* page_size is in fact getpagesize() * 2. */ > + do_test (page_size/2 - i, i, i, 1, 0x9B); > + > do_random_tests (); > return ret; > } > diff --git a/sysdeps/i386/i686/multiarch/memchr-sse2.S b/sysdeps/i386/i686/multiarch/memchr-sse2.S > index 910679c..e41f324 100644 > --- a/sysdeps/i386/i686/multiarch/memchr-sse2.S > +++ b/sysdeps/i386/i686/multiarch/memchr-sse2.S > @@ -117,7 +117,6 @@ L(crosscache): > > # ifndef USE_AS_RAWMEMCHR > jnz L(match_case2_prolog1) > - lea -16(%edx), %edx > /* Calculate the last acceptable address and check for possible > addition overflow by using satured math: > edx = ecx + edx > @@ -125,6 +124,7 @@ L(crosscache): > add %ecx, %edx > sbb %eax, %eax > or %eax, %edx > + sub $16, %edx > jbe L(return_null) > lea 16(%edi), %edi > # else >
On Tue, Mar 28, 2017 at 12:22 PM, Adhemerval Zanella <adhemerval.zanella@linaro.org> wrote: > Ping (with the page_size/2 fix included). > > On 14/03/2017 14:28, Adhemerval Zanella wrote: >> This patch fixes the regression added by 23d2770 for final address >> overflow calculation. The subtraction of the considered size (16) >> at line 120 is at wrong place, for sizes less than 16 subsequent >> overflow check will not take in consideration an invalid size (since >> the subtraction will be negative). Also, the lea instruction also >> does not raise the carry flag (CF) that is used in subsequent jbe >> to check for overflow. >> >> The fix is to follow x86_64 logic from 3daef2c where the overflow >> is first check and a sub instruction is issued. In case of resulting >> negative size, CF will be set by the sub instruction and a NULL >> result will be returned. The patch also add similar tests reported >> in bug report. >> >> Checked on i686-linux-gnu and x86_64-linux-gnu. >> >> [BZ# 21182] >> * string/test-memchr.c (do_test): Add BZ#21182 checks for address >> near end of a page. >> * sysdeps/i386/i686/multiarch/memchr-sse2.S (__memchr): Fix >> overflow calculation. >> --- >> ChangeLog | 7 +++++++ >> string/test-memchr.c | 6 ++++++ >> sysdeps/i386/i686/multiarch/memchr-sse2.S | 2 +- >> 3 files changed, 14 insertions(+), 1 deletion(-) >> >> diff --git a/string/test-memchr.c b/string/test-memchr.c >> index d64d10c..87a077b 100644 >> --- a/string/test-memchr.c >> +++ b/string/test-memchr.c >> @@ -210,6 +210,12 @@ test_main (void) >> do_test (0, i, i + 1, i + 1, 0); >> } >> >> + /* BZ#21182 - wrong overflow calculation for i686 implementation >> + with address near end of the page. */ >> + for (i = 2; i < 16; ++i) >> + /* page_size is in fact getpagesize() * 2. */ >> + do_test (page_size/2 - i, i, i, 1, 0x9B); >> + >> do_random_tests (); >> return ret; >> } >> diff --git a/sysdeps/i386/i686/multiarch/memchr-sse2.S b/sysdeps/i386/i686/multiarch/memchr-sse2.S >> index 910679c..e41f324 100644 >> --- a/sysdeps/i386/i686/multiarch/memchr-sse2.S >> +++ b/sysdeps/i386/i686/multiarch/memchr-sse2.S >> @@ -117,7 +117,6 @@ L(crosscache): >> >> # ifndef USE_AS_RAWMEMCHR >> jnz L(match_case2_prolog1) >> - lea -16(%edx), %edx >> /* Calculate the last acceptable address and check for possible >> addition overflow by using satured math: >> edx = ecx + edx >> @@ -125,6 +124,7 @@ L(crosscache): >> add %ecx, %edx >> sbb %eax, %eax >> or %eax, %edx >> + sub $16, %edx >> jbe L(return_null) >> lea 16(%edi), %edi >> # else >> Looks good. Thanks. -- H.J.
On Tue, Mar 28, 2017 at 2:47 PM, H.J. Lu <hjl.tools@gmail.com> wrote: > On Tue, Mar 28, 2017 at 12:22 PM, Adhemerval Zanella > <adhemerval.zanella@linaro.org> wrote: >> Ping (with the page_size/2 fix included). >> >> On 14/03/2017 14:28, Adhemerval Zanella wrote: >>> This patch fixes the regression added by 23d2770 for final address >>> overflow calculation. The subtraction of the considered size (16) >>> at line 120 is at wrong place, for sizes less than 16 subsequent >>> overflow check will not take in consideration an invalid size (since >>> the subtraction will be negative). Also, the lea instruction also >>> does not raise the carry flag (CF) that is used in subsequent jbe >>> to check for overflow. >>> >>> The fix is to follow x86_64 logic from 3daef2c where the overflow >>> is first check and a sub instruction is issued. In case of resulting >>> negative size, CF will be set by the sub instruction and a NULL >>> result will be returned. The patch also add similar tests reported >>> in bug report. >>> >>> Checked on i686-linux-gnu and x86_64-linux-gnu. >>> >>> [BZ# 21182] >>> * string/test-memchr.c (do_test): Add BZ#21182 checks for address >>> near end of a page. >>> * sysdeps/i386/i686/multiarch/memchr-sse2.S (__memchr): Fix >>> overflow calculation. >>> --- >>> ChangeLog | 7 +++++++ >>> string/test-memchr.c | 6 ++++++ >>> sysdeps/i386/i686/multiarch/memchr-sse2.S | 2 +- >>> 3 files changed, 14 insertions(+), 1 deletion(-) >>> >>> diff --git a/string/test-memchr.c b/string/test-memchr.c >>> index d64d10c..87a077b 100644 >>> --- a/string/test-memchr.c >>> +++ b/string/test-memchr.c >>> @@ -210,6 +210,12 @@ test_main (void) >>> do_test (0, i, i + 1, i + 1, 0); >>> } >>> >>> + /* BZ#21182 - wrong overflow calculation for i686 implementation >>> + with address near end of the page. */ >>> + for (i = 2; i < 16; ++i) >>> + /* page_size is in fact getpagesize() * 2. */ >>> + do_test (page_size/2 - i, i, i, 1, 0x9B); >>> + >>> do_random_tests (); >>> return ret; >>> } >>> diff --git a/sysdeps/i386/i686/multiarch/memchr-sse2.S b/sysdeps/i386/i686/multiarch/memchr-sse2.S >>> index 910679c..e41f324 100644 >>> --- a/sysdeps/i386/i686/multiarch/memchr-sse2.S >>> +++ b/sysdeps/i386/i686/multiarch/memchr-sse2.S >>> @@ -117,7 +117,6 @@ L(crosscache): >>> >>> # ifndef USE_AS_RAWMEMCHR >>> jnz L(match_case2_prolog1) >>> - lea -16(%edx), %edx >>> /* Calculate the last acceptable address and check for possible >>> addition overflow by using satured math: >>> edx = ecx + edx >>> @@ -125,6 +124,7 @@ L(crosscache): >>> add %ecx, %edx >>> sbb %eax, %eax >>> or %eax, %edx >>> + sub $16, %edx >>> jbe L(return_null) >>> lea 16(%edi), %edi >>> # else >>> > > Looks good. > > Just a thought. Is this approach /* Calculate "edx + ecx - 16" by using "edx - (16 - ecx)" instead of "(edx + ecx) - 16" to void possible addition overflow. */ neg %ecx add $16, %ecx sub %ecx, %edx jbe L(return_null) a little bit better? -- H.J.
On 19/05/2017 10:44, H.J. Lu wrote: > On Tue, Mar 28, 2017 at 2:47 PM, H.J. Lu <hjl.tools@gmail.com> wrote: >> On Tue, Mar 28, 2017 at 12:22 PM, Adhemerval Zanella >> <adhemerval.zanella@linaro.org> wrote: >>> Ping (with the page_size/2 fix included). >>> >>> On 14/03/2017 14:28, Adhemerval Zanella wrote: >>>> This patch fixes the regression added by 23d2770 for final address >>>> overflow calculation. The subtraction of the considered size (16) >>>> at line 120 is at wrong place, for sizes less than 16 subsequent >>>> overflow check will not take in consideration an invalid size (since >>>> the subtraction will be negative). Also, the lea instruction also >>>> does not raise the carry flag (CF) that is used in subsequent jbe >>>> to check for overflow. >>>> >>>> The fix is to follow x86_64 logic from 3daef2c where the overflow >>>> is first check and a sub instruction is issued. In case of resulting >>>> negative size, CF will be set by the sub instruction and a NULL >>>> result will be returned. The patch also add similar tests reported >>>> in bug report. >>>> >>>> Checked on i686-linux-gnu and x86_64-linux-gnu. >>>> >>>> [BZ# 21182] >>>> * string/test-memchr.c (do_test): Add BZ#21182 checks for address >>>> near end of a page. >>>> * sysdeps/i386/i686/multiarch/memchr-sse2.S (__memchr): Fix >>>> overflow calculation. >>>> --- >>>> ChangeLog | 7 +++++++ >>>> string/test-memchr.c | 6 ++++++ >>>> sysdeps/i386/i686/multiarch/memchr-sse2.S | 2 +- >>>> 3 files changed, 14 insertions(+), 1 deletion(-) >>>> >>>> diff --git a/string/test-memchr.c b/string/test-memchr.c >>>> index d64d10c..87a077b 100644 >>>> --- a/string/test-memchr.c >>>> +++ b/string/test-memchr.c >>>> @@ -210,6 +210,12 @@ test_main (void) >>>> do_test (0, i, i + 1, i + 1, 0); >>>> } >>>> >>>> + /* BZ#21182 - wrong overflow calculation for i686 implementation >>>> + with address near end of the page. */ >>>> + for (i = 2; i < 16; ++i) >>>> + /* page_size is in fact getpagesize() * 2. */ >>>> + do_test (page_size/2 - i, i, i, 1, 0x9B); >>>> + >>>> do_random_tests (); >>>> return ret; >>>> } >>>> diff --git a/sysdeps/i386/i686/multiarch/memchr-sse2.S b/sysdeps/i386/i686/multiarch/memchr-sse2.S >>>> index 910679c..e41f324 100644 >>>> --- a/sysdeps/i386/i686/multiarch/memchr-sse2.S >>>> +++ b/sysdeps/i386/i686/multiarch/memchr-sse2.S >>>> @@ -117,7 +117,6 @@ L(crosscache): >>>> >>>> # ifndef USE_AS_RAWMEMCHR >>>> jnz L(match_case2_prolog1) >>>> - lea -16(%edx), %edx >>>> /* Calculate the last acceptable address and check for possible >>>> addition overflow by using satured math: >>>> edx = ecx + edx >>>> @@ -125,6 +124,7 @@ L(crosscache): >>>> add %ecx, %edx >>>> sbb %eax, %eax >>>> or %eax, %edx >>>> + sub $16, %edx >>>> jbe L(return_null) >>>> lea 16(%edi), %edi >>>> # else >>>> >> >> Looks good. >> >> > > Just a thought. Is this approach > > /* Calculate "edx + ecx - 16" by using "edx - (16 - ecx)" > instead of "(edx + ecx) - 16" to void possible addition > overflow. */ > neg %ecx > add $16, %ecx > sub %ecx, %edx > jbe L(return_null) > > a little bit better? I do not have a strong preference here, although imho it is simpler to understand why the saturated math would work here and it is the same strategy used on other arch implementations. May you might outline in comment that ecx is always in the range of [0,64) so '-ecx + 16' can possible underflow. Is is this change just for micro-optimization?
On 19/05/2017 11:45, Adhemerval Zanella wrote: > > > On 19/05/2017 10:44, H.J. Lu wrote: >> On Tue, Mar 28, 2017 at 2:47 PM, H.J. Lu <hjl.tools@gmail.com> wrote: >>> On Tue, Mar 28, 2017 at 12:22 PM, Adhemerval Zanella >>> <adhemerval.zanella@linaro.org> wrote: >>>> Ping (with the page_size/2 fix included). >>>> >>>> On 14/03/2017 14:28, Adhemerval Zanella wrote: >>>>> This patch fixes the regression added by 23d2770 for final address >>>>> overflow calculation. The subtraction of the considered size (16) >>>>> at line 120 is at wrong place, for sizes less than 16 subsequent >>>>> overflow check will not take in consideration an invalid size (since >>>>> the subtraction will be negative). Also, the lea instruction also >>>>> does not raise the carry flag (CF) that is used in subsequent jbe >>>>> to check for overflow. >>>>> >>>>> The fix is to follow x86_64 logic from 3daef2c where the overflow >>>>> is first check and a sub instruction is issued. In case of resulting >>>>> negative size, CF will be set by the sub instruction and a NULL >>>>> result will be returned. The patch also add similar tests reported >>>>> in bug report. >>>>> >>>>> Checked on i686-linux-gnu and x86_64-linux-gnu. >>>>> >>>>> [BZ# 21182] >>>>> * string/test-memchr.c (do_test): Add BZ#21182 checks for address >>>>> near end of a page. >>>>> * sysdeps/i386/i686/multiarch/memchr-sse2.S (__memchr): Fix >>>>> overflow calculation. >>>>> --- >>>>> ChangeLog | 7 +++++++ >>>>> string/test-memchr.c | 6 ++++++ >>>>> sysdeps/i386/i686/multiarch/memchr-sse2.S | 2 +- >>>>> 3 files changed, 14 insertions(+), 1 deletion(-) >>>>> >>>>> diff --git a/string/test-memchr.c b/string/test-memchr.c >>>>> index d64d10c..87a077b 100644 >>>>> --- a/string/test-memchr.c >>>>> +++ b/string/test-memchr.c >>>>> @@ -210,6 +210,12 @@ test_main (void) >>>>> do_test (0, i, i + 1, i + 1, 0); >>>>> } >>>>> >>>>> + /* BZ#21182 - wrong overflow calculation for i686 implementation >>>>> + with address near end of the page. */ >>>>> + for (i = 2; i < 16; ++i) >>>>> + /* page_size is in fact getpagesize() * 2. */ >>>>> + do_test (page_size/2 - i, i, i, 1, 0x9B); >>>>> + >>>>> do_random_tests (); >>>>> return ret; >>>>> } >>>>> diff --git a/sysdeps/i386/i686/multiarch/memchr-sse2.S b/sysdeps/i386/i686/multiarch/memchr-sse2.S >>>>> index 910679c..e41f324 100644 >>>>> --- a/sysdeps/i386/i686/multiarch/memchr-sse2.S >>>>> +++ b/sysdeps/i386/i686/multiarch/memchr-sse2.S >>>>> @@ -117,7 +117,6 @@ L(crosscache): >>>>> >>>>> # ifndef USE_AS_RAWMEMCHR >>>>> jnz L(match_case2_prolog1) >>>>> - lea -16(%edx), %edx >>>>> /* Calculate the last acceptable address and check for possible >>>>> addition overflow by using satured math: >>>>> edx = ecx + edx >>>>> @@ -125,6 +124,7 @@ L(crosscache): >>>>> add %ecx, %edx >>>>> sbb %eax, %eax >>>>> or %eax, %edx >>>>> + sub $16, %edx >>>>> jbe L(return_null) >>>>> lea 16(%edi), %edi >>>>> # else >>>>> >>> >>> Looks good. >>> >>> >> >> Just a thought. Is this approach >> >> /* Calculate "edx + ecx - 16" by using "edx - (16 - ecx)" >> instead of "(edx + ecx) - 16" to void possible addition >> overflow. */ >> neg %ecx >> add $16, %ecx >> sub %ecx, %edx >> jbe L(return_null) >> >> a little bit better? > > I do not have a strong preference here, although imho it is simpler to > understand why the saturated math would work here and it is the same > strategy used on other arch implementations. May you might outline in > comment that ecx is always in the range of [0,64) so '-ecx + 16' can > possible underflow. Is is this change just for micro-optimization? > Sorry, my bad here. I made some confusion, in fact what I meant was ecx was indeed in range [0,16) (is the and instruction for alignment that uses 64) and your suggestion *can't* overflow. I would recommend you to just outline the possible value of 'edx' in comments.
On Fri, May 19, 2017 at 8:10 AM, Adhemerval Zanella <adhemerval.zanella@linaro.org> wrote: > > > On 19/05/2017 11:45, Adhemerval Zanella wrote: >> >> >> On 19/05/2017 10:44, H.J. Lu wrote: >>> On Tue, Mar 28, 2017 at 2:47 PM, H.J. Lu <hjl.tools@gmail.com> wrote: >>>> On Tue, Mar 28, 2017 at 12:22 PM, Adhemerval Zanella >>>> <adhemerval.zanella@linaro.org> wrote: >>>>> Ping (with the page_size/2 fix included). >>>>> >>>>> On 14/03/2017 14:28, Adhemerval Zanella wrote: >>>>>> This patch fixes the regression added by 23d2770 for final address >>>>>> overflow calculation. The subtraction of the considered size (16) >>>>>> at line 120 is at wrong place, for sizes less than 16 subsequent >>>>>> overflow check will not take in consideration an invalid size (since >>>>>> the subtraction will be negative). Also, the lea instruction also >>>>>> does not raise the carry flag (CF) that is used in subsequent jbe >>>>>> to check for overflow. >>>>>> >>>>>> The fix is to follow x86_64 logic from 3daef2c where the overflow >>>>>> is first check and a sub instruction is issued. In case of resulting >>>>>> negative size, CF will be set by the sub instruction and a NULL >>>>>> result will be returned. The patch also add similar tests reported >>>>>> in bug report. >>>>>> >>>>>> Checked on i686-linux-gnu and x86_64-linux-gnu. >>>>>> >>>>>> [BZ# 21182] >>>>>> * string/test-memchr.c (do_test): Add BZ#21182 checks for address >>>>>> near end of a page. >>>>>> * sysdeps/i386/i686/multiarch/memchr-sse2.S (__memchr): Fix >>>>>> overflow calculation. >>>>>> --- >>>>>> ChangeLog | 7 +++++++ >>>>>> string/test-memchr.c | 6 ++++++ >>>>>> sysdeps/i386/i686/multiarch/memchr-sse2.S | 2 +- >>>>>> 3 files changed, 14 insertions(+), 1 deletion(-) >>>>>> >>>>>> diff --git a/string/test-memchr.c b/string/test-memchr.c >>>>>> index d64d10c..87a077b 100644 >>>>>> --- a/string/test-memchr.c >>>>>> +++ b/string/test-memchr.c >>>>>> @@ -210,6 +210,12 @@ test_main (void) >>>>>> do_test (0, i, i + 1, i + 1, 0); >>>>>> } >>>>>> >>>>>> + /* BZ#21182 - wrong overflow calculation for i686 implementation >>>>>> + with address near end of the page. */ >>>>>> + for (i = 2; i < 16; ++i) >>>>>> + /* page_size is in fact getpagesize() * 2. */ >>>>>> + do_test (page_size/2 - i, i, i, 1, 0x9B); >>>>>> + >>>>>> do_random_tests (); >>>>>> return ret; >>>>>> } >>>>>> diff --git a/sysdeps/i386/i686/multiarch/memchr-sse2.S b/sysdeps/i386/i686/multiarch/memchr-sse2.S >>>>>> index 910679c..e41f324 100644 >>>>>> --- a/sysdeps/i386/i686/multiarch/memchr-sse2.S >>>>>> +++ b/sysdeps/i386/i686/multiarch/memchr-sse2.S >>>>>> @@ -117,7 +117,6 @@ L(crosscache): >>>>>> >>>>>> # ifndef USE_AS_RAWMEMCHR >>>>>> jnz L(match_case2_prolog1) >>>>>> - lea -16(%edx), %edx >>>>>> /* Calculate the last acceptable address and check for possible >>>>>> addition overflow by using satured math: >>>>>> edx = ecx + edx >>>>>> @@ -125,6 +124,7 @@ L(crosscache): >>>>>> add %ecx, %edx >>>>>> sbb %eax, %eax >>>>>> or %eax, %edx >>>>>> + sub $16, %edx >>>>>> jbe L(return_null) >>>>>> lea 16(%edi), %edi >>>>>> # else >>>>>> >>>> >>>> Looks good. >>>> >>>> >>> >>> Just a thought. Is this approach >>> >>> /* Calculate "edx + ecx - 16" by using "edx - (16 - ecx)" >>> instead of "(edx + ecx) - 16" to void possible addition >>> overflow. */ >>> neg %ecx >>> add $16, %ecx >>> sub %ecx, %edx >>> jbe L(return_null) >>> >>> a little bit better? >> >> I do not have a strong preference here, although imho it is simpler to >> understand why the saturated math would work here and it is the same >> strategy used on other arch implementations. May you might outline in >> comment that ecx is always in the range of [0,64) so '-ecx + 16' can >> possible underflow. Is is this change just for micro-optimization? >> > > Sorry, my bad here. I made some confusion, in fact what I meant was ecx > was indeed in range [0,16) (is the and instruction for alignment that > uses 64) and your suggestion *can't* overflow. I would recommend > you to just outline the possible value of 'edx' in comments. Here is a patch for SSE2 memchr. OK for master? -- H.J.From 70c5d56431e54c7ef8dc8b8eb300a343a97ab72d Mon Sep 17 00:00:00 2001 From: "H.J. Lu" <hjl.tools@gmail.com> Date: Fri, 19 May 2017 09:04:23 -0700 Subject: [PATCH] x86: Optimize SSE2 memchr overflow calculation SSE2 memchr computes "edx + ecx - 16" where ecx is less than 16. Use "edx - (16 - ecx)", instead of satured math, to avoid possible addition overflow. This replaces add %ecx, %edx sbb %eax, %eax or %eax, %edx sub $16, %edx with neg %ecx add $16, %ecx sub %ecx, %edx It is the same for x86_64, except for rcx/rdx, instead of ecx/edx. * sysdeps/i386/i686/multiarch/memchr-sse2.S (MEMCHR): Use "edx + ecx - 16" to avoid possible addition overflow. * sysdeps/x86_64/memchr.S (memchr): Likewise. --- sysdeps/i386/i686/multiarch/memchr-sse2.S | 14 ++++++-------- sysdeps/x86_64/memchr.S | 14 ++++++-------- 2 files changed, 12 insertions(+), 16 deletions(-) diff --git a/sysdeps/i386/i686/multiarch/memchr-sse2.S b/sysdeps/i386/i686/multiarch/memchr-sse2.S index e41f324..172d70d 100644 --- a/sysdeps/i386/i686/multiarch/memchr-sse2.S +++ b/sysdeps/i386/i686/multiarch/memchr-sse2.S @@ -117,14 +117,12 @@ L(crosscache): # ifndef USE_AS_RAWMEMCHR jnz L(match_case2_prolog1) - /* Calculate the last acceptable address and check for possible - addition overflow by using satured math: - edx = ecx + edx - edx |= -(edx < ecx) */ - add %ecx, %edx - sbb %eax, %eax - or %eax, %edx - sub $16, %edx + /* "ecx" is less than 16. Calculate "edx + ecx - 16" by using + "edx - (16 - ecx)" instead of "(edx + ecx) - 16" to void + possible addition overflow. */ + neg %ecx + add $16, %ecx + sub %ecx, %edx jbe L(return_null) lea 16(%edi), %edi # else diff --git a/sysdeps/x86_64/memchr.S b/sysdeps/x86_64/memchr.S index a205a25..f82e1c5 100644 --- a/sysdeps/x86_64/memchr.S +++ b/sysdeps/x86_64/memchr.S @@ -76,14 +76,12 @@ L(crosscache): .p2align 4 L(unaligned_no_match): - /* Calculate the last acceptable address and check for possible - addition overflow by using satured math: - rdx = rcx + rdx - rdx |= -(rdx < rcx) */ - add %rcx, %rdx - sbb %rax, %rax - or %rax, %rdx - sub $16, %rdx + /* "rcx" is less than 16. Calculate "rdx + rcx - 16" by using + "rdx - (16 - rcx)" instead of "(rdx + rcx) - 16" to void + possible addition overflow. */ + neg %rcx + add $16, %rcx + sub %rcx, %rdx jbe L(return_null) add $16, %rdi sub $64, %rdx -- 2.9.4
On 19/05/2017 13:14, H.J. Lu wrote: > On Fri, May 19, 2017 at 8:10 AM, Adhemerval Zanella > <adhemerval.zanella@linaro.org> wrote: >> >> >> On 19/05/2017 11:45, Adhemerval Zanella wrote: >>> >>> >>> On 19/05/2017 10:44, H.J. Lu wrote: >>>> On Tue, Mar 28, 2017 at 2:47 PM, H.J. Lu <hjl.tools@gmail.com> wrote: >>>>> On Tue, Mar 28, 2017 at 12:22 PM, Adhemerval Zanella >>>>> <adhemerval.zanella@linaro.org> wrote: >>>>>> Ping (with the page_size/2 fix included). >>>>>> >>>>>> On 14/03/2017 14:28, Adhemerval Zanella wrote: >>>>>>> This patch fixes the regression added by 23d2770 for final address >>>>>>> overflow calculation. The subtraction of the considered size (16) >>>>>>> at line 120 is at wrong place, for sizes less than 16 subsequent >>>>>>> overflow check will not take in consideration an invalid size (since >>>>>>> the subtraction will be negative). Also, the lea instruction also >>>>>>> does not raise the carry flag (CF) that is used in subsequent jbe >>>>>>> to check for overflow. >>>>>>> >>>>>>> The fix is to follow x86_64 logic from 3daef2c where the overflow >>>>>>> is first check and a sub instruction is issued. In case of resulting >>>>>>> negative size, CF will be set by the sub instruction and a NULL >>>>>>> result will be returned. The patch also add similar tests reported >>>>>>> in bug report. >>>>>>> >>>>>>> Checked on i686-linux-gnu and x86_64-linux-gnu. >>>>>>> >>>>>>> [BZ# 21182] >>>>>>> * string/test-memchr.c (do_test): Add BZ#21182 checks for address >>>>>>> near end of a page. >>>>>>> * sysdeps/i386/i686/multiarch/memchr-sse2.S (__memchr): Fix >>>>>>> overflow calculation. >>>>>>> --- >>>>>>> ChangeLog | 7 +++++++ >>>>>>> string/test-memchr.c | 6 ++++++ >>>>>>> sysdeps/i386/i686/multiarch/memchr-sse2.S | 2 +- >>>>>>> 3 files changed, 14 insertions(+), 1 deletion(-) >>>>>>> >>>>>>> diff --git a/string/test-memchr.c b/string/test-memchr.c >>>>>>> index d64d10c..87a077b 100644 >>>>>>> --- a/string/test-memchr.c >>>>>>> +++ b/string/test-memchr.c >>>>>>> @@ -210,6 +210,12 @@ test_main (void) >>>>>>> do_test (0, i, i + 1, i + 1, 0); >>>>>>> } >>>>>>> >>>>>>> + /* BZ#21182 - wrong overflow calculation for i686 implementation >>>>>>> + with address near end of the page. */ >>>>>>> + for (i = 2; i < 16; ++i) >>>>>>> + /* page_size is in fact getpagesize() * 2. */ >>>>>>> + do_test (page_size/2 - i, i, i, 1, 0x9B); >>>>>>> + >>>>>>> do_random_tests (); >>>>>>> return ret; >>>>>>> } >>>>>>> diff --git a/sysdeps/i386/i686/multiarch/memchr-sse2.S b/sysdeps/i386/i686/multiarch/memchr-sse2.S >>>>>>> index 910679c..e41f324 100644 >>>>>>> --- a/sysdeps/i386/i686/multiarch/memchr-sse2.S >>>>>>> +++ b/sysdeps/i386/i686/multiarch/memchr-sse2.S >>>>>>> @@ -117,7 +117,6 @@ L(crosscache): >>>>>>> >>>>>>> # ifndef USE_AS_RAWMEMCHR >>>>>>> jnz L(match_case2_prolog1) >>>>>>> - lea -16(%edx), %edx >>>>>>> /* Calculate the last acceptable address and check for possible >>>>>>> addition overflow by using satured math: >>>>>>> edx = ecx + edx >>>>>>> @@ -125,6 +124,7 @@ L(crosscache): >>>>>>> add %ecx, %edx >>>>>>> sbb %eax, %eax >>>>>>> or %eax, %edx >>>>>>> + sub $16, %edx >>>>>>> jbe L(return_null) >>>>>>> lea 16(%edi), %edi >>>>>>> # else >>>>>>> >>>>> >>>>> Looks good. >>>>> >>>>> >>>> >>>> Just a thought. Is this approach >>>> >>>> /* Calculate "edx + ecx - 16" by using "edx - (16 - ecx)" >>>> instead of "(edx + ecx) - 16" to void possible addition >>>> overflow. */ >>>> neg %ecx >>>> add $16, %ecx >>>> sub %ecx, %edx >>>> jbe L(return_null) >>>> >>>> a little bit better? >>> >>> I do not have a strong preference here, although imho it is simpler to >>> understand why the saturated math would work here and it is the same >>> strategy used on other arch implementations. May you might outline in >>> comment that ecx is always in the range of [0,64) so '-ecx + 16' can >>> possible underflow. Is is this change just for micro-optimization? >>> >> >> Sorry, my bad here. I made some confusion, in fact what I meant was ecx >> was indeed in range [0,16) (is the and instruction for alignment that >> uses 64) and your suggestion *can't* overflow. I would recommend >> you to just outline the possible value of 'edx' in comments. > > Here is a patch for SSE2 memchr. OK for master? > LGTM, thanks.
diff --git a/string/test-memchr.c b/string/test-memchr.c index d64d10c..87a077b 100644 --- a/string/test-memchr.c +++ b/string/test-memchr.c @@ -210,6 +210,12 @@ test_main (void) do_test (0, i, i + 1, i + 1, 0); } + /* BZ#21182 - wrong overflow calculation for i686 implementation + with address near end of the page. */ + for (i = 2; i < 16; ++i) + /* page_size is in fact getpagesize() * 2. */ + do_test (page_size/2 - i, i, i, 1, 0x9B); + do_random_tests (); return ret; } diff --git a/sysdeps/i386/i686/multiarch/memchr-sse2.S b/sysdeps/i386/i686/multiarch/memchr-sse2.S index 910679c..e41f324 100644 --- a/sysdeps/i386/i686/multiarch/memchr-sse2.S +++ b/sysdeps/i386/i686/multiarch/memchr-sse2.S @@ -117,7 +117,6 @@ L(crosscache): # ifndef USE_AS_RAWMEMCHR jnz L(match_case2_prolog1) - lea -16(%edx), %edx /* Calculate the last acceptable address and check for possible addition overflow by using satured math: edx = ecx + edx @@ -125,6 +124,7 @@ L(crosscache): add %ecx, %edx sbb %eax, %eax or %eax, %edx + sub $16, %edx jbe L(return_null) lea 16(%edi), %edi # else