Re: [RFC][PATCH 0/5] arch: atomic rework

[David Lang]

On Tue, 18 Feb 2014, Torvald Riegel wrote:

> On Tue, 2014-02-18 at 22:40 +0100, Peter Zijlstra wrote:
> > On Tue, Feb 18, 2014 at 10:21:56PM +0100, Torvald Riegel wrote:
> > > Well, that's how atomics that aren't volatile are defined in the
> > > standard.  I can see that you want something else too, but that doesn't
> > > mean that the other thing is broken.
> >
> > Well that other thing depends on being able to see the entire program at
> > compile time. PaulMck already listed various ways in which this is
> > not feasible even for normal userspace code.
> >
> > In particular; DSOs and JITs were mentioned.
>
> No it doesn't depend on whole-program analysis being possible.  Because
> if it isn't, then a correct compiler will just not do certain
> optimizations simply because it can't prove properties required for the
> optimization to hold.  With the exception of access to objects via magic
> numbers (e.g., fixed and known addresses (see my reply to Paul), which
> are outside of the semantics specified in the standard), I don't see a
> correctness problem here.

Are you really sure that the compiler can figure out every possible thing that a 
loadable module or JITed code can access? That seems like a pretty strong claim.

David Lang
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