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    SubjectRe: [PATCH 00/16] mm: prepare for converting vm->vm_flags to 64-bit
    On Fri, 23 Mar 2012 02:52:05 +0400
    Konstantin Khlebnikov <khlebnikov@openvz.org> wrote:

    > >> Is this ok?
    > >
    > > Yes.
    > >
    > > The thing about __nocast is that it's so *very* very easy to lose it.
    > > For example, do this:
    > >
    > > typedef long __nocast long_t;
    > >
    > > int main(long_t a)
    > > {
    > > return a;
    > > }
    > >
    > > and you get the (expected) warning.
    > >
    > > HOWEVER. Now do "return a+1" instead, and the warning goes away. Why?
    > > Because the expression ends up having just the type "long", because
    > > the "a" mixed happily with the "1" (that was cast from 'int' to 'long'
    > > by the normal C type rules).
    > >
    > > That is arguably a bug, but this kind of thing really wasn't what
    > > __nocast was designed for. The __nocast design ended up being too
    > > weak, though, and we hardly use it in the kernel.
    > >
    >
    > Thanks. Looks like "__nocast" totally undocumented.
    > It would be nice to add something about this into Documentation/sparse.txt

    Yup, Chris has added this to his todo list (thanks!).


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