(2013/11/12 17:44), Sandeepa Prabhu wrote: > On 12 November 2013 12:57, Masami Hiramatsu > <masami.hiramatsu...@hitachi.com> wrote: >> (2013/11/12 15:23), Sandeepa Prabhu wrote: >>>>>> OK, I've ensured that the hw_breakpoint (from perf) can work >>>>>> with kprobes (from ftrace) at the same address on x86. >>>>>> So if arm64 already support hw_breakpoint on perf, kprobes should >>>>>> work with it. >>>>> >>>>> Single-stepping on x86 is different to the step behaviour on arm64 afaik. >>>>> On >>>>> ARM, we have to manually remove the breakpoint, perform a single-step, >>>>> then >>>>> add the breakpoint again. If we re-enable debug exceptions in the kprobe >>>>> handler, the step will complete early and we'll never step off the >>>>> breakpoint. >>>> >>>> I'm unsure about arm64's debug feature behavior, what does happen when >>>> it performs a single-step on sw-breakpoint? >>>> >>>>> Sandeepa: I think you need to retry Masami's test on the arm64 model, >>>>> since >>>>> I'm fairly sure it won't work as expected without some additional code. >>>> >>>> OK, anyway, for testing same one, we need to port ftrace first. So the next >> >> Sorry for confusion, s/next/fallback is what I meant. Making a kprobe module >> can be done without ftrace port. > Yes, got it, all my verification until now are done using sample > modules only, looking out for perf (or some other mechanism: ptrace?) > that uses v8 hw breakpoint.
Yes, kprobe vs. perf and uprobe vs. ptrace :) >>>> plan is to make a kprobe module to put a probe (which just printk >>>> something) >>>> on a specific function (e.g. vfs_symlink), and run perf record with >>>> hw-breakpoint as below >>>> >>>> $ perf record -e "mem:0xXXXXXX:k" ln -s /dev/null /tmp/foo >>>> >>>> Note that 0xXXXXXX is the address of vfs_symlink. >>>> >>>> After that, you can see the message in dmesg and also check the perf result >>>> with "sudo perf script --dump" (you can find a PERF_RECORD_SAMPLE entry if >>>> it works) >>> Thanks for steps, ARM64 ftrace patches are under review on arm mailing >>> list, I can contact the (linaro) developer implementing ftrace on >>> what's supported and then figure-out a way to test this concurrency of >>> kprobes breakpoint and hardware breakpoint. >> >> Would you mean this? :) >> http://www.spinics.net/lists/arm-kernel/msg278477.html >> >> Wow, it seems that this also has some works around instruction >> manipulation (and confusable filenames...) > I referred to: http://lwn.net/Articles/572323/ which is another > implementation and on LAKML OK, I'll check that (and looks good at a glance). By the way, I concern about Linaro guys who looks working a bit far from the LKML and original feature maintainers. Please contact them, I'm sure they don't bite your hand :) BTW, I'm currently trying a general housecleaning of __kprobes annotations. It may also have impact on your patch. https://lkml.org/lkml/2013/11/8/187 Thank you, -- Masami HIRAMATSU IT Management Research Dept. Linux Technology Center Hitachi, Ltd., Yokohama Research Laboratory E-mail: masami.hiramatsu...@hitachi.com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
