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    SubjectRe: [PATCH 04/15] ftrace: pack event structures.
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    On Tue, 2011-03-08 at 22:39 -0800, David Miller wrote:
    > From: Steven Rostedt <rostedt@goodmis.org>
    > Date: Tue, 08 Mar 2011 18:30:03 -0500
    >
    > > I'm going back through this patch set and looking to incorporate it into
    > > 2.6.39. But I know how touchy sparc is with "packed" data structures. Do
    > > you see this patch as hurting sparc?
    > >
    > > I wonder if we should change this to something like:
    > >
    > > #ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
    > > # define do_event_packed __attirbute__((packed))
    > > #else
    > > # define do_event_packed
    > > #endif
    > >
    > > and use "do_event_packed" instead?
    >
    > I think you should elide packed at all costs, and instead tell the compiler
    > what your intentions are by exposing the real types using unions or
    > similar instead of hiding it in an opaque way behind final char[] arrays.

    The problem here is not the issue of char[] but because of the way
    ftrace's header was 12 bytes and caused everything that had a 8byte word
    use another 4 bytes to align it. As I stated in another email, I think
    removing the "int lock_depth" from the ftrace header should solve this.

    David (Sharp), the reason for the "packed" was because of that extra 4
    bytes in the ftrace header, right? So removing the lock_depth should fix
    the issues that you've seen?

    -- Steve





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