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    SubjectRe: [PATCH 11/11] Use unreachable() in asm-generic/bug.h for !CONFIG_BUG case.
    Linus Torvalds wrote:
    > On Mon, 14 Sep 2009, David Daney wrote:
    >> The existing code just falls through to whatever happens to follow the BUG().
    > Brian was talking BUG_ON().
    > And the existing !CONFIG_BUG BUG_ON() is actually set up so that gcc will
    > just optimize it away entirely (yet give the same compile-time warnings as
    > the "real" BUG_ON() does).
    > Changing it to "if (cond) unreachable()" is likely to generate _more_
    > code, which is against the whole point of wanting to disable CONFIG_BUG.

    Yes, you are correct. I said the same thing in the log message for the

    Really it may be too early for this patch to be appropriate for your
    tree. GCC-4.5 will probably not be released for several more months,
    and it will be several years before a GCC with __builtin_unreachable()
    is being used by the majority of people compiling kernels.

    Ingo had suggested the approach of this patch as a way of eliminating
    many warnings when using !CONFIG_BUG. I think it clearly makes sense
    for compilers that support __builtin_unreachable(), but clearly it is
    not an unquestionable win if we end up generating larger code.

    With this particular patch, I don't really care if you merge it or not.
    Perhaps I shouldn't have made it part of the set.

    The rest of the set I think would make sense for 2.6.32 or 2.6.33.

    David Daney

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