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    SubjectRe: [PATCH 0/5][RFC] kprobes/ftrace: Have kprobes use ftrace on ftrace nops
    Hi Steven,

    Thanks for this nice feature!

    (2011/08/11 1:22), Steven Rostedt wrote:
    > Hi All,
    > I started working on adding the -mfentry switch to ftrace, which
    > allows us to remove the frame pointers requirement from function tracing
    > as well as makes mcount (fentry) work just better.
    > But when I did this in another branch, I noticed that I broke kprobes
    > in its most common usage. The attaching a probe at the beginning of
    > a function to use get to its parameters.
    > So I started this branch. This branch is to have kprobes use ftrace
    > directly when a probe is attached to a ftrace nop. Currently, kprobes
    > will just error when that happens. With this patch set, it will hook
    > into the ftrace infrastructure and use ftrace instead. This is more
    > like an optimized probe as no breakpoints need to be set. A call to
    > the function is done directly via the mcount trampoline. If ftrace
    > pt_regs is implemented for an arch, kprobes gets this feature for free.

    I agreed this idea, this looks good to me too :)
    With -fentry, this can improve dynamic trace events very much.

    BTW (OT), it seems that current kprobe data structure becomes a bit
    fat. Maybe what we need is just a "holder of hooking handler" as
    what ftrace provides, not a full storage data structure of copied
    instrucutions. Perhaps, we'd better diet the kprobe structure for
    transparency of hooking infrastructure.

    > The first patch is just a clean up that I need to push out to get rid
    > of the annoying compile warning about initialized variables that
    > gcc can't tell have been initialized.
    > The next two patches have ftrace pass both the ftrace_ops structure
    > and the pt_regs to the callback function that is registered with ftrace.
    > The last two patches have kprobes interact with ftrace and use the
    > ftrace infrastructure instead.
    > I only did this for x86_64, and will do it for x86_32 and PPC64 if everyone
    > agrees with this approach. Then I could find people to do it for other
    > archs :)

    OK, I'll review this soon!

    Thank you!

    Masami HIRAMATSU
    Software Platform Research Dept. Linux Technology Center
    Hitachi, Ltd., Yokohama Research Laboratory

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