linux-kernel - Re: [patch] powerpc: change u64/s64 to a long long integer type

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Message-Id: <20081222151338.3b6ef997.akpm@linux-foundation.org>
Date:	Mon, 22 Dec 2008 15:13:38 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Sam Ravnborg <sam@...nborg.org>
Cc:	mingo@...e.hu, sfr@...b.auug.org.au, linux-kernel@...r.kernel.org,
	kenchen@...gle.com, paulus@...ba.org, tglx@...utronix.de,
	hpa@...or.com, linux-next@...r.kernel.org, davem@...emloft.net
Subject: Re: [patch] powerpc: change u64/s64 to a long long integer type

On Tue, 23 Dec 2008 00:00:35 +0100
Sam Ravnborg <sam@...nborg.org> wrote:

> On Mon, Dec 22, 2008 at 02:43:19PM -0800, Andrew Morton wrote:
> > On Mon, 22 Dec 2008 09:03:41 +0100
> > Ingo Molnar <mingo@...e.hu> wrote:
> > 
> > > Subject: powerpc: change u64/s64 to a long long integer type
> > 
> > <applause>
> > 
> > There are lots of other architctures that need doing though.
> 
> I have missed the introduction.
> Can you explain why?

People keep on doing

	printk("%llu", some_u64);

testing it only on x86_64 and this generates a warning storm on
powerpc, sparc64, etc.  Because they use `long', not `long long'.

And not just a little bit - this bug gets repeated maybe ten times per
week - it's insane.

If we make all architectures use `long long' then the above code
becomes correct and warning-free on all architectures.

And we then get to remove all the open-coded (unsigned long long) casts
which we added all over the tree (hundreds of them).

> I have done a bit of sparc hacking lately and was wondering if
> sparc needs something similar.
> 
> cd arch/sparc
> git grep u64 | grep -v __u64 | wc -l
> 448
> 
> [On the unified tree]

Yes, quite a few 64-bit architectures are using `long' for their
s64/u64 types.  We should convert them all to `long long'.

That's quite trivial to do, but it causes a lot of warnings due to code
in arch-speciic files which does

	printk("%lu", some_u64);

which will then generate a warning.  Or an error if the archtiecture
uses -Werror, which several do.  So we need to simultaneously convert
all those to %llu.  (Or %Lu, which saves a byte :))

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