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Re: [PATCH] string/stratcliff.c: Replace int with size_t [BZ #21982]


On 08/22/2017 02:43 PM, H.J. Lu wrote:
On Tue, Aug 22, 2017 at 5:07 AM, Stefan Liebler <stli@linux.vnet.ibm.com> wrote:
On 08/22/2017 01:05 AM, H.J. Lu wrote:

On Mon, Aug 21, 2017 at 8:41 AM, Stefan Liebler <stli@linux.vnet.ibm.com>
wrote:

On 08/21/2017 04:53 PM, H.J. Lu wrote:


On Mon, Aug 21, 2017 at 6:48 AM, Stefan Liebler
<stli@linux.vnet.ibm.com>
wrote:


On 08/20/2017 07:17 PM, H.J. Lu wrote:



Fix GCC 7 errors when string/stratcliff.c is compiled with -O3:

stratcliff.c: In function ‘do_test’:
cc1: error: assuming signed overflow does not occur when assuming that
(X
- c) <= X is always true [-Werror=strict-overflow]

OK for master?

H.J.
---
           [BZ #21982]
           * string/stratcliff.c (do_test): Declare size, nchars,
inner,
           middle and outer with size_t instead of int.  Repleace %d
with
           %Zd in printf.
---
     string/stratcliff.c | 72
++++++++++++++++++++++++++---------------------------
     1 file changed, 36 insertions(+), 36 deletions(-)

diff --git a/string/stratcliff.c b/string/stratcliff.c
index e28b0c5058..ae780379cb 100644
--- a/string/stratcliff.c
+++ b/string/stratcliff.c
@@ -58,8 +58,8 @@
     int
     do_test (void)
     {
-  int size = sysconf (_SC_PAGESIZE);
-  int nchars = size / sizeof (CHAR);
+  size_t size = sysconf (_SC_PAGESIZE);
+  size_t nchars = size / sizeof (CHAR);
       CHAR *adr;
       CHAR *dest;
       int result = 0;
@@ -80,7 +80,7 @@ do_test (void)
         }
       else
         {
-      int inner, middle, outer;
+      size_t inner, middle, outer;

           mprotect (adr, size, PROT_NONE);
           mprotect (adr + 2 * nchars, size, PROT_NONE);
@@ -101,7 +101,7 @@ do_test (void)

                 if (STRLEN (&adr[outer]) != (size_t) (inner - outer))
                   {
-                 printf ("%s flunked for outer = %d, inner = %d\n",
+                 printf ("%s flunked for outer = %Zd, inner = %Zd\n",
                             STRINGIFY (STRLEN), outer, inner);
                     result = 1;
                   }
                   {
-                 printf ("%s flunked for outer = %d, middle = %d\n",
+                 printf ("%s flunked for outer = %Zd, middle =
%Zd\n",
                             STRINGIFY (rawmemchr), outer, middle);
                     result = 1;
                   }
Hi H.J. Lu,




I've applied your patch and the warnings does not occur anymore on
s390.



Great.

The outer loops of the string tests are all using the following:
size_t nchars, outer;
for (outer = nchars - 1; outer >= MAX (0, nchars - 128); --outer)

I think we can assume, that nchars is always > 128 as it is derived by
the
pagesize.
But if nchars would be equal to 128, this would result in an infinite
loop
(outer >= 0)?
If nchars would be less than 128, the tests would be skipped.

Should we add a check that nchars > 128 at the beginning and replace
the
"MAX (0, nchars - 128)" with only "nchars - 128"?



This is a separate issue beyond BZ #21982.


Your patch is introducing this behaviour.
Before your patch, nchars and outer was an int and the for-loop-condition
"outer >= MAX (0, nchars - 128)" does not lead to an infinite loop or to
skipping the test if nchars <= 128.


How about this patch?

This solves the cases if nchars < 128.
But if nchars == 128, then the condition of the for-loop is "size_t outer >=
0", which is always true.

Could we check once if nchars > 128 and exit the test with an error if
nchars is <= 128?
Are there architectures where the page size is < 4096?
Or where wchar_t > 4byte?


Here is the updated patch.  I added

  if (outer == 0)
    break;

at the end of loop.


Okay. This fixes the case nchars == 128.
I've retested this patch on s390x with gcc 7 -O3 and the warnings does not occur anymore.

Thanks.
Stefan


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