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From: "Jike Song" <albcamus@gmail.com>
To: "H. Peter Anvin" <hpa@zytor.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 14:40:37 +0800	[thread overview]
Message-ID: <df9815e70810292340g52d38e83t47dffd02125b4fe3@mail.gmail.com> (raw)
In-Reply-To: <49093012.7010301@zytor.com>

On Thu, Oct 30, 2008 at 11:54 AM, H. Peter Anvin <hpa@zytor.com> wrote:
> Jike Song wrote:
>>
>> Besides, by looking at the inline assembly in kernel,  I found lots of
>> codes like this:
>>
>>         static inline void atomic_add(int i, atomic_t *v)
>>         {
>>               asm volatile(LOCK_PREFIX "addl %1,%0"
>>                            : "=m" (v->counter)
>>                            : "ir" (i), "m" (v->counter));
>>         }
>>
>>
>> Yes, it works. But a little ugly..  Should this be cleaned-up with the
>> following?
>>
>>         : "+m" (v->counter)
>>         : "ir" (i)
>>
>> If you agrees, I'll send out the patch; otherwise I won't wasting your time ;-)
>>
>
> Please don't change them just to change them, if there is no actual
> error.  You never know when you're going to trigger a new bug in some
> weird version of gcc.
>
>        -hpa

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)

-- 
Thanks,
Jike

  reply	other threads:[~2008-10-30  6:40 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 [this message]
2008-10-30 14:51         ` H. Peter Anvin
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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