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Message-ID: <alpine.LFD.0.999.0708180512300.3666@enigma.security.iitk.ac.in>
Date: Sat, 18 Aug 2007 05:21:42 +0530 (IST)
From: Satyam Sharma <satyam@...radead.org>
To: Segher Boessenkool <segher@...nel.crashing.org>
cc: Paul Mackerras <paulus@...ba.org>, heiko.carstens@...ibm.com,
horms@...ge.net.au,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
rpjday@...dspring.com, ak@...e.de, netdev@...r.kernel.org,
cfriesen@...tel.com, Nick Piggin <nickpiggin@...oo.com.au>,
linux-arch@...r.kernel.org, jesper.juhl@...il.com,
Andrew Morton <akpm@...ux-foundation.org>, zlynx@....org,
clameter@....com, schwidefsky@...ibm.com,
Chris Snook <csnook@...hat.com>,
Herbert Xu <herbert.xu@...hat.com>, davem@...emloft.net,
Linus Torvalds <torvalds@...ux-foundation.org>,
wensong@...ux-vs.org, wjiang@...ilience.com
Subject: Re: [PATCH 0/24] make atomic_read() behave consistently across all
architectures
On Sat, 18 Aug 2007, Segher Boessenkool wrote:
> > #define forget(a) __asm__ __volatile__ ("" :"=m" (a) :"m" (a))
> >
> > [ This is exactly equivalent to using "+m" in the constraints, as recently
> > explained on a GCC list somewhere, in response to the patch in my bitops
> > series a few weeks back where I thought "+m" was bogus. ]
>
> [It wasn't explained on a GCC list in response to your patch, as
> far as I can see -- if I missed it, please point me to an archived
> version of it].
http://gcc.gnu.org/ml/gcc-patches/2007-07/msg01758.html
is a follow-up in the thread on the gcc-patches@....gnu.org mailing list,
which began with:
http://gcc.gnu.org/ml/gcc-patches/2007-07/msg01677.html
that was posted by Jan Kubicka, as he quotes in that initial posting,
after I had submitted:
http://lkml.org/lkml/2007/7/23/252
which was a (wrong) patch to "rectify" what I thought was the "bogus"
"+m" constraint, as per the quoted extract from gcc docs (that was
given in that (wrong) patch's changelog).
That's when _I_ came to know how GCC interprets "+m", but probably
this has been explained on those lists multiple times. Who cares,
anyway?
> One last time: it isn't equivalent on older (but still supported
> by Linux) versions of GCC. Current versions of GCC allow it, but
> it has no documented behaviour at all, so use it at your own risk.
True.
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