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    SubjectRe: [PATCH 5/5] debug: BUILD_BUG_ON: error on non-const expressions
    >>> Boaz Harrosh <bharrosh@panasas.com> 01.09.08 16:21 >>>
    >> I have to admit that I'm surprise this compiles: You replace an expression
    >> with a statement, and hence you reduce the places where BUILD_BUG_ON()
    >> can validly be used.
    >
    >it is only an expression because of the (void)() cast, which is what
    >I'm trying to avoid.

    No, sizeof() alone is an expression, too. Also, by using a statement you'll
    have more problems with fixing BUILD_BUG_ON_ZERO(), which must be
    an expression.

    >> Of course you could wrap the whole thing in ({}),
    >
    >"do{}while(0)" is effectively an "{}" plus the added bonus
    >of demanding an ";" ;-)

    An expression likewise demands a terminating ; (or a continuation of the
    expression, i.e. by using an operator)

    >> Also, are you sure the compiler will eliminate the dead variable in all
    >> cases?
    >>
    >> Finally, using as common a variable as 'x' here seems dangerous, too:
    >> What if somewhere x is #define-d to something more complex than a
    >> simple identifier?
    >
    >No it is scoped in a dead do{}while(0). What gets optimized out most
    >is the do nothing do{}while(0). The inside is just ignored.

    I don't think compilers in general and gcc in particular work this way
    (i.e. automatically throwing away everything included in a dead block).

    Jan



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