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Date: Tue, 01 Mar 2011 10:30:39 +0000 From: Will Deacon <will.deacon@....com> To: David Brown <davidb@...eaurora.org> Cc: Stephen Boyd <sboyd@...eaurora.org>, linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org Subject: Re: [PATCH 1/4] msm: scm: Mark inline asm as volatile Hi David, On Sun, 2011-02-27 at 17:38 +0000, David Brown wrote: > Per the gcc manual: > > If your assembler instructions access memory in an unpredictable > fashion, add `memory' to the list of clobbered registers. This will > cause GCC to not keep memory values cached in registers across the > assembler instruction and not optimize stores or loads to that > memory. You will also want to add the `volatile' keyword if the > memory affected is not listed in the inputs or outputs of the `asm', > as the `memory' clobber does not count as a side-effect of the `asm'. > If you know how large the accessed memory is, you can add it as input > or output but if this is not known, you should add `memory'. As an > example, if you access ten bytes of a string, you can use a memory > input like: > Right, so if you neglected to check the output from the smc block then it would be a candidate for removal even with a memory clobber. Now I see why you want a volatile in there! For what it's worth: Acked-by: Will Deacon <will.deacon@....com> Will -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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