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

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Message-ID: <CA+8MBbK_nfOhZGsd5wU-hyiwh3pHS5c42eiBfxLpCjDgBKUqJg@mail.gmail.com>
Date:	Mon, 10 Jun 2013 15:26:26 -0700
From:	Tony Luck <tony.luck@...il.com>
To:	Chen Gang <gang.chen@...anux.com>
Cc:	Richard Henderson <rth@...ddle.net>, ink@...assic.park.msu.ru,
	Matt Turner <mattst88@...il.com>,
	"dhowells@...hat.com" <dhowells@...hat.com>,
	"Yu, Fenghua" <fenghua.yu@...el.com>,
	yasutake.koichi@...panasonic.com, 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 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.

-Tony Luck
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