Messages in this thread | | | Date | Wed, 09 May 2012 17:12:13 +0900 | From | Masami Hiramatsu <> | Subject | Re: [PATCH 6/9][RFC] kprobes: Allow probe on ftrace reserved text (but move it) |
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(2012/05/09 14:53), Masami Hiramatsu wrote: > (2012/05/08 22:04), Steven Rostedt wrote: >> Note, the big difference with using ftrace optimization and normal >> kprobe jump optimization is that the ftrace one can be used on a preempt >> kernel. But this code is still under development. I want to get a >> solution for the current code (this patch set) now. It would be nice if >> it was ready for 3.5. > > I doubt that we can really do this. If this is possible, I can make > jump optimization work with preemptive kernel.
Now I'm clear that it can be done only with ftrace-nop. What I concerned with is out-of-line execution buffer releasing timing. but with the ftrace-nop, we don't need to do that.
Theoretically, that will be done in following steps;
1. call mcount (w/ push call-site address+5) 2. mcount calls ftrace handlers 3. mcount makes pt_regs on the stack - on x86-32, regs->cs should be the call-site address+5, since regs->sp must be the top of original stack. - on x86-64, it is enough that regs->sp points the top of original stack. 4. mcount store call-site address+5 to %ax 5. mcount calls new-optprobe handler (which returns call-site address+5) 6. mcount restores registers 7. mcount returns to the call-site address+5.
Between 6 and 7, original opt-probe has to do out-of-line execution, but this ftrace-based one doesn't need to do that. In that case, we don't need to allocate nor to release out-of-line execution buffer for this probe.
Thank you!
-- Masami HIRAMATSU Software Platform Research Dept. Linux Technology Center Hitachi, Ltd., Yokohama Research Laboratory E-mail: masami.hiramatsu.pt@hitachi.com
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