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    SubjectRe: Linux 3.3-rc4
    On 02/20/2012 09:06 PM, Linus Torvalds wrote:
    > On Mon, Feb 20, 2012 at 8:52 PM, Ian Kent <> wrote:
    >> I think the patch attached to your original post needs a little work if
    >> that is to be used. Correct me if I'm wrong but AFAICT there are more
    >> architectures that use 8-byte alignment than just x86-64, such as alpha,
    >> ia64 and ppc64 and I believe they may also be used in a compat mode.
    > The only issue is compat mode, and afaik, all other architectures
    > except for x86-32 do __u64 with natural alignment.
    > So all 64-bit architectures use natural alignment, the only issue is
    > the alignment of __u64 in 32-bit mode.
    > So it really is *not* about 8-byte alignment. Quite the reverse. It's
    > about 4-byte alignment of 64-bit entities, and I suspect x86-32 is the
    > only one that does that.
    > See "compat_u64", and notice how only in arch/x86/include/asm/compat.h
    > do we have
    > typedef u64 __attribute__((aligned(4))) compat_u64;
    > So it really is limited to only x86.

    m68k has alignment 2 for 32- and 64-bit quantities, so it's not just
    x86; the only reason you don't see that one is because m68k doesn't have
    a compat layer to worry about.

    Holes are highly undesirable for another reason: they create security
    holes where kernel information leaks out.


    H. Peter Anvin, Intel Open Source Technology Center
    I work for Intel. I don't speak on their behalf.

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