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Open Source and information security mailing list archives
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Date: Sat, 18 Aug 2007 02:04:35 +0200 From: Segher Boessenkool <segher@...nel.crashing.org> To: Satyam Sharma <satyam@...radead.org> Cc: Christoph Lameter <clameter@....com>, Paul Mackerras <paulus@...ba.org>, heiko.carstens@...ibm.com, horms@...ge.net.au, Stefan Richter <stefanr@...6.in-berlin.de>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, David Miller <davem@...emloft.net>, "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>, Ilpo Järvinen <ilpo.jarvinen@...sinki.fi>, ak@...e.de, cfriesen@...tel.com, rpjday@...dspring.com, Netdev <netdev@...r.kernel.org>, jesper.juhl@...il.com, linux-arch@...r.kernel.org, zlynx@....org, Andrew Morton <akpm@...ux-foundation.org>, schwidefsky@...ibm.com, Chris Snook <csnook@...hat.com>, Herbert Xu <herbert@...dor.apana.org.au>, 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 >>>> atomic_dec() writes >>>> to memory, so it _does_ have "volatile semantics", implicitly, as >>>> long as the compiler cannot optimise the atomic variable away >>>> completely -- any store counts as a side effect. >>> >>> I don't think an atomic_dec() implemented as an inline "asm volatile" >>> or one that uses a "forget" macro would have the same re-ordering >>> guarantees as an atomic_dec() that uses a volatile access cast. >> >> The "asm volatile" implementation does have exactly the same >> reordering guarantees as the "volatile cast" thing, > > I don't think so. "asm volatile" creates a side effect. Side effects aren't allowed to be reordered wrt sequence points. This is exactly the same reason as why "volatile accesses" cannot be reordered. >> if that is >> implemented by GCC in the "obvious" way. Even a "plain" asm() >> will do the same. > > Read the relevant GCC documentation. I did, yes. > [ of course, if the (latest) GCC documentation is *yet again* > wrong, then alright, not much I can do about it, is there. ] There was (and is) nothing wrong about the "+m" documentation, if that is what you are talking about. It could be extended now, to allow "+m" -- but that takes more than just "fixing" the documentation. Segher - To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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