[PATCH 2/4] strcmp: Add a testcase for page boundary

[Carlos O'Donell]

On 6/12/20 4:10 PM, H.J. Lu via Libc-alpha wrote:
> Add a strncmp testcase to cover cases where both strings end on the
> page boundary.
> ---
>  string/test-strcmp.c | 25 +++++++++++++++++++++++++
>  1 file changed, 25 insertions(+)
> 

OK to commit if you:
- Add all the comments.
- s1a iterates over [30,32).

Reviewed-by: Carlos O'Donell <carlos@redhat.com>

> diff --git a/string/test-strcmp.c b/string/test-strcmp.c
> index 8d4784de80..41d95567c7 100644
> --- a/string/test-strcmp.c
> +++ b/string/test-strcmp.c
> @@ -359,6 +359,30 @@ check (void)
>      }
>  }
>  

Add a comment:

/* To trigger bug 25933 we need a size that is equal to the
   vector length times 4. In the case of AVX2 for Intel we
   need 32 * 4. We make this test generic and run it for all
   architectures as additional boundary testing for such
   related algorithms.  */

> +static void
> +check2 (void)
> +{
> +  size_t size = 32 * 4;
> +  CHAR *s1 = (CHAR *) (buf1 + (BUF1PAGES - 1) * page_size);
> +  CHAR *s2 = (CHAR *) (buf2 + (BUF1PAGES - 1) * page_size);
> +  int exp_result;
> +
> +  memset (s1, 'a', page_size);
> +  memset (s2, 'a', page_size);
> +  s1[(page_size / CHARBYTES) - 1] = (CHAR) 0;
> +  s2[(page_size / CHARBYTES) - 1] = (CHAR) 0;
> +

Add comment:

/* Iterate over a size that is just below where we expect
   the bug to trigger up to the size we expect will trigger
   the bug e.g. [99-128].  Likewise iterate the start of
   two strings between 30 and 31 bytes away from the
   boundary to simulate alignment changes.  */

> +  for (size_t s = 99; s <= size; s++)
> +    for (size_t s1a = 31; s1a < 32; s1a++)

Please make s1a iterate over [30,32) like s2a.

> +      for (size_t s2a = 30; s2a < 32; s2a++)
> +	{
> +	  CHAR *s1p = s1 + (page_size / CHARBYTES - s) - s1a;
> +	  CHAR *s2p = s2 + (page_size / CHARBYTES - s) - s2a;
> +	  exp_result = SIMPLE_STRCMP (s1p, s2p);
> +	  FOR_EACH_IMPL (impl, 0)
> +	    check_result (impl, s1p, s2p, exp_result);
> +	}
> +}
>  
>  int
>  test_main (void)
> @@ -367,6 +391,7 @@ test_main (void)
>  
>    test_init ();
>    check();
> +  check2 ();
>  
>    printf ("%23s", "");
>    FOR_EACH_IMPL (impl, 0)
> 


-- 
Cheers,
Carlos.