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From: "H. Peter Anvin" <hpa@zytor.com>
To: Jike Song <albcamus@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>,
	tglx@linutronix.de, mingo@redhat.com,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] x86: fix inline assembly constraints
Date: Thu, 30 Oct 2008 07:51:05 -0700	[thread overview]
Message-ID: <4909C9D9.7040105@zytor.com> (raw)
In-Reply-To: <df9815e70810292340g52d38e83t47dffd02125b4fe3@mail.gmail.com>

Jike Song wrote:
> 
> Yes, sometimes gcc did have bugs with its obscure inline asm
> conventions. But I think the change of x86-64 atomic operations should
> be OK. Anyway, the "+" constraint is more clear than a "=m" output and
>  a "m" input.
> 
> The 32-bit atomic ops were already changed to "+m".(commit
> b862f3b099f3ea672c7438c0b282ce8201d39dfc)
> 

You *THINK*.  It's very easy to *THINK* that gcc won't do something
utterly moronic, and you'd be wrong.

Just changing it for the sake of churn is pointless... if there is a
bug, then we have to take the risk anyway, but if it is already correct,
then there is no point in provoking a bug.  Not *your* bug, because your
code is correct, but gcc's bug.

FWIW, the reason that code doesn't use "+m" is because a version of gcc
which we no longer support didn't handle it.  That by itself isn't a
reason to keep it, but there is also no reason to just "tidy" it, IMNSHO.

	-hpa

  reply	other threads:[~2008-10-30 14:53 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-10-29 16:32 Jike Song
2008-10-29 16:32 ` Jike Song
2008-10-29 16:34 ` Ingo Molnar
2008-10-30  2:31   ` Jike Song
2008-10-30  3:54     ` H. Peter Anvin
2008-10-30  6:40       ` Jike Song
2008-10-30 14:51         ` H. Peter Anvin [this message]
2008-10-30 19:29     ` Ingo Molnar
2008-10-31  2:12       ` Jike Song
     [not found] <fa.IZJ3RdF6xWbbMqWVWyYRstzZBsk@ifi.uio.no>
     [not found] ` <fa.L4yER0Vo1brqQzpHIySgWqUN5UM@ifi.uio.no>
     [not found]   ` <fa.rs0w7okAn1If1ilwD81OTzT4rKg@ifi.uio.no>
2008-10-30  3:52     ` Robert Hancock

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