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    SubjectRe: Style question: Should one check for NULL pointers?
    Date
    Followup to:  <3F0EC9C9.4090307@inet.com>
    By author: Eli Carter <eli.carter@inet.com>
    In newsgroup: linux.dev.kernel
    > >
    > > Not really needed, since a segfault will produce almost as much
    > > information as a BUG_ON(). Certainly it will produce enough to let a
    > > developer know that the pointer was NULL.
    >
    > Your first message said, "I see no reason for pure paranoia,
    > particularly if it's not commented as such." A BUG_ON() call makes it
    > clear that the condition should never happen. Dereferencing a NULL
    > leaves the question of whether NULL is an unhandled case or invalid
    > input. BUG_ON() is an explicit paranoia check, and with a bit of
    > preprocessing magic, you could compile out all of those checks.
    >
    > So it documents invalid input conditions, allows you to eliminate the
    > checks in the name of speed or your personal preference, or use them to
    > help with debugging/testing.
    >

    ... but it also bloats the code, in this case, in many ways
    needlessly. You don't want to compile out all BUG_ON()'s, just the
    ones that wouldn't be checked for anyway.

    In fact, have a macro that explicitly tests for nullness by
    dereferencing a pointer might be a good idea; on most architectures it
    will be a lot cheaper than BUG_ON() (which usually requires an
    explicit test), and the compiler at least has a prayer at optimizing
    it out.

    -hpa
    --
    <hpa@transmeta.com> at work, <hpa@zytor.com> in private!
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