linux-kernel - Re: [PATCH] z3fold: use %z modifier for format string

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Date:   Fri, 25 Nov 2016 08:38:25 +0100
From:   Vitaly Wool <vitalywool@...il.com>
To:     Joe Perches <joe@...ches.com>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dan Streetman <ddstreet@...e.org>,
        zhong jiang <zhongjiang@...wei.com>,
        Linux-MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] z3fold: use %z modifier for format string

Hi Joe,

On Thu, Nov 24, 2016 at 6:08 PM, Joe Perches <joe@...ches.com> wrote:
> On Thu, 2016-11-24 at 17:31 +0100, Arnd Bergmann wrote:
>> Printing a size_t requires the %zd format rather than %d:
>>
>> mm/z3fold.c: In function ‘init_z3fold’:
>> include/linux/kern_levels.h:4:18: error: format ‘%d’ expects argument of type ‘int’, but argument 2 has type ‘long unsigned int’ [-Werror=format=]
>>
>> Fixes: 50a50d2676c4 ("z3fold: don't fail kernel build if z3fold_header is too big")
>> Signed-off-by: Arnd Bergmann <arnd@...db.de>
>> ---
>>  mm/z3fold.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/mm/z3fold.c b/mm/z3fold.c
>> index e282ba073e77..66ac7a7dc934 100644
>> --- a/mm/z3fold.c
>> +++ b/mm/z3fold.c
>> @@ -884,7 +884,7 @@ static int __init init_z3fold(void)
>>  {
>>       /* Fail the initialization if z3fold header won't fit in one chunk */
>>       if (sizeof(struct z3fold_header) > ZHDR_SIZE_ALIGNED) {
>> -             pr_err("z3fold: z3fold_header size (%d) is bigger than "
>> +             pr_err("z3fold: z3fold_header size (%zd) is bigger than "
>>                       "the chunk size (%d), can't proceed\n",
>>                       sizeof(struct z3fold_header) , ZHDR_SIZE_ALIGNED);
>>               return -E2BIG;
>
> The embedded "z3fold: " prefix here should be removed
> as there's a pr_fmt that also adds it.
>
> The test looks like it should be a BUILD_BUG_ON rather
> than any runtime test too.

It used to be BUILD_BUG_ON but we deliberately changed that because
sizeof(spinlock_t) gets bloated in debug builds, so it just won't
build with default CHUNK_SIZE.

~vitaly