linux-kernel - Re: [git pull] core kernel updates for v2.6.28

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Message-ID: <c62985530810161616ycd3daddu61c0bbc36908fff8@mail.gmail.com>
Date:	Fri, 17 Oct 2008 01:16:09 +0200
From:	"Frédéric Weisbecker" <fweisbec@...il.com>
To:	"Linus Torvalds" <torvalds@...ux-foundation.org>
Cc:	"Ingo Molnar" <mingo@...e.hu>,
	"Benjamin Herrenschmidt" <benh@...nel.crashing.org>,
	"Kumar Gala" <galak@...nel.crashing.org>,
	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Jeremy Fitzhardinge" <jeremy@...p.org>,
	"Becky Bruce" <becky.bruce@...escale.com>
Subject: Re: [git pull] core kernel updates for v2.6.28

2008/10/17 Linus Torvalds <torvalds@...ux-foundation.org>:
> Well, the thing is, on 32-bit x86, ptrdiff_t is "int". And on 64-bit, it's
> "long". And on some (most?) other architectures, it's "long" regardless of
> whether it's 32-bit or 64-bit.
>
> So you fixed a warnign on x86-32, but you introduced it just about
> everywhere else.
>
> And it so happens that the old use of "%ld" was better than "%d", because
> regardless of the exact type of ptrdiff_t, with gcc it is essentially
> always going to be at least the same _size_ as "long". IOW, even when it's
> "int", it will always print out correctly with "%ld", despite the format
> warning. IOW, the type may be "wrong" from a C standards standpoint, but
> it will work in practice.
>
> In contrast, using "%d" can actually print it out wrong, because it will
> be literally the wrong physical size, not just a type issue on a C level.
> So depending on calling conventions, you might end up with the upper bits
> cleared, or even the wrong bits printed out.
>
> Using "%td" is always right, assuming the underlying printing library is
> recent enough to know about it. And the kernel has known about %td for the
> last three years.
>
>                        Linus

Oops you're right my fix made things worst than before.
I will be aware of this %td for the future.

Thanks for the explanations Linus.
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