linux-kernel - Re: New bcache compiler warning (was: Re: bcache: Minor fixes from kbuild robot)

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Date:	Mon, 17 Feb 2014 22:11:51 +0100
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Randy Dunlap <rdunlap@...radead.org>
Cc:	Kent Overstreet <kmo@...erainc.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-bcache@...r.kernel.org
Subject: Re: New bcache compiler warning (was: Re: bcache: Minor fixes from
 kbuild robot)

On Mon, Feb 17, 2014 at 10:06 PM, Randy Dunlap <rdunlap@...radead.org> wrote:
> On 02/17/2014 01:00 PM, Geert Uytterhoeven wrote:
>> On Fri, Feb 14, 2014 at 8:04 PM, Linux Kernel Mailing List
>> <linux-kernel@...r.kernel.org> wrote:
>>>    bcache: Minor fixes from kbuild robot
>>
>>> diff --git a/drivers/md/bcache/bset.c b/drivers/md/bcache/bset.c
>>> index 4f6b594..3f74b4b 100644
>>> --- a/drivers/md/bcache/bset.c
>>> +++ b/drivers/md/bcache/bset.c
>>> @@ -23,7 +23,7 @@ void bch_dump_bset(struct btree_keys *b, struct bset *i, unsigned set)
>>>         for (k = i->start; k < bset_bkey_last(i); k = next) {
>>>                 next = bkey_next(k);
>>>
>>> -               printk(KERN_ERR "block %u key %zi/%u: ", set,
>>> +               printk(KERN_ERR "block %u key %li/%u: ", set,
>>>                        (uint64_t *) k - i->d, i->keys);
>>>
>>>                 if (b->ops->key_dump)
>>
>> On 32-bit (m68k):
>> drivers/md/bcache/bset.c: In function ‘bch_dump_bset’:
>> drivers/md/bcache/bset.c:27: warning: format ‘%li’ expects type ‘long
>> int’, but argument 3 has type ‘int’
>>
>> What are you trying to print here? It looks a bit strange to me.
>> Technically, the difference between two pointers is of type ptrdiff_.
>> The kernel had
>>
>> typedef __kernel_ptrdiff_t      ptrdiff_t;
>>
>> and
>>
>> #if __BITS_PER_LONG != 64
>> typedef unsigned int    __kernel_size_t;
>> typedef int             __kernel_ssize_t;
>> typedef int             __kernel_ptrdiff_t;
>> #else
>> typedef __kernel_ulong_t __kernel_size_t;
>> typedef __kernel_long_t __kernel_ssize_t;
>> typedef __kernel_long_t __kernel_ptrdiff_t;
>> #endif
>>
>> So I'd expect "%zi" to be the right way, and a quick test compile on
>> 32-bit (m68k)
>> and 64-bit (amd64) comfirms that. What was wrong with it?
>
> The kernel supports 't' (%t) for ptrdiff_t (same as glibc),
> so %ti should work (or %tu).

Yes, that compiles without warnings, too.

And after more decyphering, "(uint64_t *) k - i->d" seems to be positive,
so "%tu" should be OK.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
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