linux-kernel - Re: [PATCH v2 03/11] selftests/mm: fix "warning: expression which evaluates to zero..." in mlock2-tests.c

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Message-ID: <ZH4CvMFgu7IFFMwk@x1n>
Date:   Mon, 5 Jun 2023 11:43:56 -0400
From:   Peter Xu <peterx@...hat.com>
To:     John Hubbard <jhubbard@...dia.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        David Hildenbrand <david@...hat.com>,
        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 v2 03/11] selftests/mm: fix "warning: expression which
 evaluates to zero..." in mlock2-tests.c

On Fri, Jun 02, 2023 at 07:15:50PM -0700, John Hubbard wrote:
> The stop variable is a char*, and the code was assigning a char value to
> it. This was generating a warning when compiling with clang.
> 
> However, as both David and Peter pointed out, stop is not even used
> after the problematic assignment to a char type. So just delete that
> line entirely.
> 
> Cc: David Hildenbrand <david@...hat.com>
> Cc: Peter Xu <peterx@...hat.com>
> Signed-off-by: John Hubbard <jhubbard@...dia.com>
> ---
>  tools/testing/selftests/mm/mlock2-tests.c | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/tools/testing/selftests/mm/mlock2-tests.c b/tools/testing/selftests/mm/mlock2-tests.c
> index 11b2301f3aa3..80cddc0de206 100644
> --- a/tools/testing/selftests/mm/mlock2-tests.c
> +++ b/tools/testing/selftests/mm/mlock2-tests.c
> @@ -50,7 +50,6 @@ static int get_vm_area(unsigned long addr, struct vm_boundaries *area)
>  			printf("cannot parse /proc/self/maps\n");
>  			goto out;
>  		}
> -		stop = '\0';
>  
>  		sscanf(line, "%lx", &start);
>  		sscanf(end_addr, "%lx", &end);

I'd rather simply make it "*stop = '\0'", or as David suggested dropping
stop completely when we're it (assumes that scanf() will always work with
number ending with space ' ').

No strong opinion here, though.

-- 
Peter Xu