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