linux-kernel - Re: [PATCH] mtd: nand: Use ULL-suffix for big u64 constant

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Date:	Mon, 11 Aug 2014 20:51:51 +0200
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Brian Norris <computersforpeace@...il.com>
Cc:	Boris BREZILLON <boris.brezillon@...e-electrons.com>,
	MTD Maling List <linux-mtd@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mtd: nand: Use ULL-suffix for big u64 constant

Hi Brian,

On Mon, Aug 11, 2014 at 7:50 PM, Brian Norris
<computersforpeace@...il.com> wrote:
> On Sat, Aug 09, 2014 at 07:07:53PM +0200, Geert Uytterhoeven wrote:
>> drivers/mtd/nand/nand_timings.c:45: warning: integer constant is too large for ‘long’ type
>
> On what compiler / static analyzer?

Any 32-bit version of gcc at the standard warning level, at least
until gcc 4.4.7.
With gcc 4.6 it's indeed gone.

>> Signed-off-by: Geert Uytterhoeven <geert@...ux-m68k.org>
>> ---
>>  drivers/mtd/nand/nand_timings.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/mtd/nand/nand_timings.c b/drivers/mtd/nand/nand_timings.c
>> index 8b36253420fa..e81470a8ac67 100644
>> --- a/drivers/mtd/nand/nand_timings.c
>> +++ b/drivers/mtd/nand/nand_timings.c
>> @@ -42,7 +42,7 @@ static const struct nand_sdr_timings onfi_sdr_timings[] = {
>>               .tRHZ_max = 200000,
>>               .tRLOH_min = 0,
>>               .tRP_min = 50000,
>> -             .tRST_max = 250000000000,
>> +             .tRST_max = 250000000000ULL,
>
> See [1] and [2]. I'm pretty sure it is a bug in your tool to warn about

Yes, I saw those, after I had created my patch. I decided to send it anyway ;-)

> this. The C standard seems pretty clear that the large literal constant
> is automatically promoted to a sufficiently large type, so AIUI there
> should be no need for such a warning. A standards-compliant compiler
> will do the right thing.

Actually I didn't know there existed versions of gcc that did _not_ give
this warning. This seems to be a recent thing on gcc for 32-bit targets.
For 64-bit targets, apparently it only gives a warning if the constant
is that large that it can no longer fit in a 64-bit signed integer.

> However, I could be convinced to apply this, if only to satisfy broken
> tools and to avoid addressing this question over and over...

So please apply. Too many people are still using 32-bit targets and
gcc < 4.6.

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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