Messages in this thread | | | Subject | Re: [PATCH 0/5][RFC] kprobes/ftrace: Have kprobes use ftrace on ftrace nops | From | Steven Rostedt <> | Date | Wed, 10 Aug 2011 20:34:02 -0400 |
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On Thu, 2011-08-11 at 09:21 +0900, Masami Hiramatsu wrote: > 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.
Sure, I can make the ftrace_ops field in kprobes dynamically allocated instead. That shouldn't be an issue.
> > > 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!
Thanks!
-- Steve
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