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    SubjectRe: Linux 2.6.27.27


    On Mon, 20 Jul 2009, Linus Torvalds wrote:

    >
    >
    > On Mon, 20 Jul 2009, Greg KH wrote:
    >>
    >>>> Linus Torvalds (1):
    >>>> Don't use '-fwrapv' compiler option: it's buggy in gcc-4.1.x
    >>>
    >>> I'm very sorry to say that but 2.6.27.27 compiled with gcc-4.2.4
    >>> hangs during boot and it is caused by this fix.
    >>>
    >>> I extended http://bugzilla.kernel.org/show_bug.cgi?id=13012 with
    >>> additional info & .config.
    >>
    >> Wierd. Linus, any thoughts? Do we need to check the version of the
    >> compiler that we are using before turning that option off?
    >
    > Dang. That was what we hoped to avoid by not using -fwrapv - we didn't
    > know which compilers were buggy, although it _looked_ like just 4.1.x (I
    > have some dim memory of somebody suspecting a 4.2.x version too, but that
    > may have been just a "we know it should only be needed in 4.3.x, so maybe
    > we shouldn't use it in 4.2.x either").
    >
    > But it looks like the "buggy window" for -fno-strict-overflow is
    > potentially even _larger_ than it ever was with -fwrapv. And I suspect
    > that in both cases the real problem is that almost nobody ever uses either
    > optimization flag, so coverage is way way smaller.
    >
    > For now, I suspect we need to do something like this: go back to -fwrapv
    > (because it has gotten more testing), but limit it to 4.2.x and newer.
    >
    > However, it would be really good to figure out _why_ it breaks. It's
    > probably some specific configuration issue in addition to the particular
    > kernel vesion (and maybe it even needs some particular hardware to show
    > the bug - ie a specific driver that triggers it or whatever).

    No problem. Please let me know what should I do to help tracking this
    issue.

    Best regards,

    Krzysztof Olędzki
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