From: Stefan Liebler <stli@linux.vnet.ibm.com>
To: libc-alpha@sourceware.org
Subject: Re: [PATCH] string/stratcliff.c: Replace int with size_t [BZ #21982]
Date: Mon, 21 Aug 2017 15:41:00 -0000 [thread overview]
Message-ID: <b3944bf8-07a2-6460-a564-f973db7ea7fa@linux.vnet.ibm.com> (raw)
In-Reply-To: <CAMe9rOq=oRRMrLg1=mJFcBszKUDGkPOgQ=dGqgQ9p9Vvqm=tkg@mail.gmail.com>
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 âdo_testâ:
>>> 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.
next prev parent reply other threads:[~2017-08-21 15:41 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-08-20 17:17 H.J. Lu
2017-08-21 13:25 ` Joseph Myers
2017-08-21 13:51 ` H.J. Lu
2017-08-21 13:56 ` Joseph Myers
2017-08-21 15:03 ` H.J. Lu
2017-08-21 13:49 ` Stefan Liebler
2017-08-21 14:53 ` H.J. Lu
2017-08-21 15:41 ` Stefan Liebler [this message]
2017-08-21 23:05 ` H.J. Lu
2017-08-22 12:07 ` Stefan Liebler
2017-08-22 12:43 ` H.J. Lu
2017-08-22 14:57 ` Stefan Liebler
2017-08-23 14:49 ` H.J. Lu
2017-09-07 16:20 ` H.J. Lu
2017-09-11 15:46 ` H.J. Lu
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