linux-kernel - Re: [Suggestion] arch/*/include/asm/bitops.h: about __set

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Message-ID: <CAMuHMdWVx79L=ErRkNMide6xNqQt1RQr0psN8nqoADeV0h768A@mail.gmail.com>
Date:	Tue, 11 Jun 2013 09:32:39 +0200
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Tony Luck <tony.luck@...il.com>
Cc:	Chen Gang <gang.chen@...anux.com>,
	Richard Henderson <rth@...ddle.net>,
	Ivan Kokshaysky <ink@...assic.park.msu.ru>,
	Matt Turner <mattst88@...il.com>,
	"dhowells@...hat.com" <dhowells@...hat.com>,
	"Yu, Fenghua" <fenghua.yu@...el.com>,
	Koichi Yasutake <yasutake.koichi@...panasonic.com>,
	alpha <linux-alpha@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-ia64@...r.kernel.org" <linux-ia64@...r.kernel.org>,
	linux-am33-list@...hat.com, Linux-Arch <linux-arch@...r.kernel.org>
Subject: Re: [Suggestion] arch/*/include/asm/bitops.h: about __set_bit() API.

On Tue, Jun 11, 2013 at 12:26 AM, Tony Luck <tony.luck@...il.com> wrote:
> On Sat, Jun 8, 2013 at 3:08 AM, Chen Gang <gang.chen@...anux.com> wrote:
>> using 'unsigned int *', implicitly:
>>   ./ia64/include/asm/bitops.h:63:__set_bit (int nr, volatile void *addr)
>
> There is some downside on ia64 to your suggestion.  If "addr" is properly
> aligned for an "int", but misaligned for a long ... i.e. addr%8 == 4, then I'll
> take an unaligned reference trap if I work with long* where the current code
> working with int* does not.
>
> Now perhaps all the callers do guarantee long* alignment?  But I don't know.
>
> Apart from uniformity, there doesn't see to be any upside to changing this.

The address pointers have been supposed to be "long *" for a very long time.
Probably alpha (the second official Linux platform) did it
differently, and never
standardized to "long *".

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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