[PATCH v2] string: Add page tests for test-strncasecmp and test-strncpy

[Paul A. Clarke]

On Wed, Jun 03, 2020 at 05:06:45PM -0300, Raphael Moreira Zinsly wrote:
> Adds tests to check if strings placed at page bondaries are
nit: Add tests
nit: boundaries

> handled correctly by strncasecmp and strncpy similar to tests
> for strncmp and strnlen.  This should catch regressions in the
> optmized functions.
nit: optimized
...but, you can delete this sentence.

> ---
>  string/test-strncasecmp.c | 37 +++++++++++++++++++++++++++++++++++++
>  string/test-strncpy.c     | 35 +++++++++++++++++++++++++++++++++++
>  2 files changed, 72 insertions(+)
> 
> diff --git a/string/test-strncasecmp.c b/string/test-strncasecmp.c
> index 6a9c27beae..bf9838dacb 100644
> --- a/string/test-strncasecmp.c
> +++ b/string/test-strncasecmp.c
> @@ -137,6 +137,42 @@ do_test (size_t align1, size_t align2, size_t n, size_t len, int max_char,
>      do_one_test (impl, s1, s2, n, exp_result);
>  }
> 
> +static void
> +do_page_tests (void)
> +{
> +  size_t i, offset, cacheline_size;
> +  char *s1, *s2;
> +  int exp_result;
> +
> +  offset = page_size - 1;
> +  s1 = (char *) buf1;
> +  memset (s1, '\1', offset);
> +  s1[offset] = '\0';
> +
> +  /* s2 has a fixed offset, almost one page long.
> +     page_size is actually 2 * getpagesize.  */
> +  offset = (page_size / 2) - 10;
> +  s2 = strdup (s1) + offset;

s2 is fixed at 10 bytes short of a page boundary...

> +  /* Start offset for s1.  */
> +  offset = 3 * page_size / 4;
> +  s1 += offset;

s1 starts from midway through the 2nd page...

I misspoke in my earlier review. To start midway through the first
page (of the two pages), it should be page_size / 4.
I was originally thinking 3/4 into the first actual page, which would
actually be 3 * page_size / 8.  That "page_size" is actually two pages
is quite confusing.

> +
> +  /* Try to cross the page boundary at every offset of a cache line.  */
> +  cacheline_size = sysconf (_SC_LEVEL1_DCACHE_LINESIZE);
> +  for (i = 0; i < cacheline_size; ++i)
> +    {
> +      exp_result = *s1;
> +
> +      FOR_EACH_IMPL (impl, 0)
> +	{
> +	  check_result (impl, s1, s2, page_size, -exp_result);
> +	  check_result (impl, s2, s1, page_size, exp_result);
> +	}
> +
> +      s1++;

s1 moves a byte at a time for the length of a cacheline.

It seems that s2 will always cross the boundary at the same offset (10),
and s1 will never cross a page boundary, so you should adjust s1 above
to be somewhere in the middle of the first page.

> +    }
> +}
> +
>  static void
>  do_random_tests (void)
>  {
> @@ -334,6 +370,7 @@ test_locale (const char *locale)
>      }
> 
>    do_random_tests ();
> +  do_page_tests ();
>  }
> 
>  int
> diff --git a/string/test-strncpy.c b/string/test-strncpy.c
> index c978753ad8..fb3332cbac 100644
> --- a/string/test-strncpy.c
> +++ b/string/test-strncpy.c
> @@ -155,6 +155,40 @@ do_test (size_t align1, size_t align2, size_t len, size_t n, int max_char)
>      do_one_test (impl, s2, s1, len, n);
>  }
> 
> +static void
> +do_page_tests (void)
> +{
> +  size_t i, small_len, big_len, short_offset, long_offset;
> +  CHAR *s1, *s2;
> +  /* Calculate the null character offset.  */
> +  size_t last_offset = (page_size / sizeof (CHAR)) - 1;
> +
> +  s2 = (CHAR *) buf1;
> +  s1 = (CHAR *) buf2;
> +  MEMSET (s1, '\1', last_offset);
> +  s1[last_offset] = '\0';
> +
> +  long_offset = (last_offset + 1) / 2;
> +  short_offset = last_offset;
> +  for (i = 0; i < 128; i++)

Consider a comment before this line like what you added for
test-strncasecmp, above:
   /* Try to cross the page boundary at every offset of a cache line.  */
...which then prompts the question as to whether you should
query and use the cache line size as you did there. Probably yes.

> +    {
> +      /* Place long strings ending at page boundary.  */
> +      long_offset++;
> +      big_len = last_offset - long_offset;
> +      /* Place short strings ending at page boundary.  */
> +      short_offset--;
> +      small_len = last_offset - short_offset;
> +
> +      FOR_EACH_IMPL (impl, 0)
> +        {
> +	  do_one_test (impl, s2, (CHAR *) (s1 + short_offset), small_len,
> +	               small_len);
> +	  do_one_test (impl, s2, (CHAR *) (s1 + long_offset), page_size,
> +	               big_len);
> +	}
> +    }
> +}
> +
>  static void
>  do_random_tests (void)
>  {
> @@ -317,6 +351,7 @@ test_main (void)
>      }
> 
>    do_random_tests ();
> +  do_page_tests ();
>    return ret;
>  }

PC