linux-kernel - Re: [PATCH 04/12] selftests/mm: fix a char* assignment in mlock2-tests.c

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Date:   Fri, 2 Jun 2023 11:52:42 -0700
From:   John Hubbard <jhubbard@...dia.com>
To:     Peter Xu <peterx@...hat.com>, David Hildenbrand <david@...hat.com>
CC:     Andrew Morton <akpm@...ux-foundation.org>,
        Shuah Khan <shuah@...nel.org>,
        Nathan Chancellor <nathan@...nel.org>, <linux-mm@...ck.org>,
        <linux-kselftest@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 04/12] selftests/mm: fix a char* assignment in
 mlock2-tests.c

On 6/2/23 08:24, Peter Xu wrote:
> On Fri, Jun 02, 2023 at 12:04:57PM +0200, David Hildenbrand wrote:
>> On 02.06.23 03:33, John Hubbard wrote:
>>> The stop variable is a char*, so use "\0" when assigning to it, rather
>>> than attempting to assign a character type. This was generating a
>>> warning when compiling with clang.
>>>
>>> Signed-off-by: John Hubbard <jhubbard@...dia.com>
>>> ---
>>>    tools/testing/selftests/mm/mlock2-tests.c | 2 +-
>>>    1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/tools/testing/selftests/mm/mlock2-tests.c b/tools/testing/selftests/mm/mlock2-tests.c
>>> index 11b2301f3aa3..8ee95077dc25 100644
>>> --- a/tools/testing/selftests/mm/mlock2-tests.c
>>> +++ b/tools/testing/selftests/mm/mlock2-tests.c
>>> @@ -50,7 +50,7 @@ static int get_vm_area(unsigned long addr, struct vm_boundaries *area)
>>>    			printf("cannot parse /proc/self/maps\n");
>>>    			goto out;
>>>    		}
>>> -		stop = '\0';
>>> +		stop = "\0";
>>>    		sscanf(line, "%lx", &start);
>>>    		sscanf(end_addr, "%lx", &end);
>>
>>
>> I'm probably missing something, but what is the stop variable supposed to do
>> here? It's completely unused, no?
>>
>> if (!strchr(end_addr, ' ')) {
>> 	printf("cannot parse /proc/self/maps\n");
>> 	goto out;
>> }

Yes it is! I certainly had tunnel vision on that one. I've changed the
patch to simply delete that line, for v2, thanks.

> 
> I guess it wanted to do "*stop = '\0'" but it just didn't matter a lot
> since the sscanf() just worked..
> 

Maybe, yes. Hard to tell the original intent at this point...it might
have been used in an early draft version of the loop that didn't get
posted, perhaps.
thanks,
-- 
John Hubbard
NVIDIA