Messages in this thread | | | Date | Fri, 20 Feb 2015 22:25:33 +0900 | From | Masami Hiramatsu <> | Subject | Re: [PATCH 1/2] kprobes/x86: Use 5-byte NOP when the code might be modified by ftrace |
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(2015/02/20 21:52), Ingo Molnar wrote: > > * Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com> wrote: > >> (2015/02/20 19:26), Ingo Molnar wrote: >>> >>> * Petr Mladek <pmladek@suse.cz> wrote: >>> >>>> can_probe() checks if the given address points to the >>>> beginning of an instruction. It analyzes all the >>>> instructions from the beginning of the function until the >>>> given address. The code might be modified by another >>>> Kprobe. In this case, the current code is read into a >>>> buffer, int3 breakpoint is replaced by the saved opcode >>>> in the buffer, and can_probe() analyzes the buffer >>>> instead. >>>> >>>> [...] >>> >>> Had to drop this patch due to build failures on 32-bit x86: >>> >>> arch/x86/kernel/kprobes/core.c:258:40: error: ‘MCOUNT_INSN_SIZE’ undeclared (first use in this function) >> >> Oops, MCOUNT_INSN_SIZE actually depends on >> CONFIG_FUNCTION_TRACER... I think we can use 5 instead of >> that since we are copying NOP_ATOMIC5. > > Or just make the define more widely available? It's not > like the size changes from disabling the function tracer.
Yeah, it could be. Actually, to tell the truth, if CONFIG_FUNCTION_TRACER=n, ftrace_location() always returns 0, so the 2nd memcpy never be executed (it should be disappeared by optimization). Thus *this* issue is very local one, and I thought we'd better fix this locally. :)
Thank you,
-- Masami HIRAMATSU Software Platform Research Dept. Linux Technology Research Center Hitachi, Ltd., Yokohama Research Laboratory E-mail: masami.hiramatsu.pt@hitachi.com
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