Re: [PATCH v1] x86: Fix bug in strncmp-evex and strncmp-avx2 [BZ #28895]

[Andreas Schwab <schwab@linux-m68k.org>]

On Feb 15 2022, Noah Goldstein wrote:

> On Tue, Feb 15, 2022 at 10:48 AM Andreas Schwab <schwab@linux-m68k.org> wrote:
>>
>> On Feb 15 2022, Noah Goldstein via Libc-alpha wrote:
>>
>> > diff --git a/string/test-strncmp.c b/string/test-strncmp.c
>> > index 831cb77893..501055de0c 100644
>> > --- a/string/test-strncmp.c
>> > +++ b/string/test-strncmp.c
>> > @@ -423,6 +423,29 @@ check3 (void)
>> >       }
>> >  }
>> >
>> > +
>> > +static void
>> > +check4 (void)
>> > +{
>> > +  /* To trigger bug 28895; We need 1) both s1 and s2 to be within 32 bytes of
>> > +     the end of the page. 2) For there to be no mismatch/null byte before the
>> > +     first page cross. 3) For length (`n`) to be large enough for one string to
>> > +     cross the page. And 4) for there to be either mismatch/null bytes before
>> > +     the start of the strings.  */
>> > +
>> > +  size_t size = 10;
>> > +  CHAR *s1 = (CHAR *)(buf1 + (getpagesize () & 0xffa) / sizeof (CHAR));
>> > +  CHAR *s2 = (CHAR *)(buf2 + (getpagesize () & 0xfed) / sizeof (CHAR));
>>
>> s/&/-/
> ?

(0x1000 & 0xffa) == 0

-- 
Andreas Schwab, schwab@linux-m68k.org
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