From: masami.hiramatsu.pt@hitachi•com (Masami Hiramatsu)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH RFC 2/6] arm64: Kprobes with single stepping support
Date: Tue, 12 Nov 2013 02:32:52 +0900 [thread overview]
Message-ID: <528114C4.5000506@hitachi.com> (raw)
In-Reply-To: <20131111105812.GC28302@mudshark.cambridge.arm.com>
(2013/11/11 19:58), Will Deacon wrote:
> On Mon, Nov 11, 2013 at 10:51:52AM +0000, Masami Hiramatsu wrote:
>> (2013/11/11 16:54), Masami Hiramatsu wrote:
>>>>>> In fact, how do you avoid a race with hardware breakpoints? E.g., somebody
>>>>>> places a hardware breakpoint on an instruction in the kernel for which
>>>>>> kprobes has patched in a brk. We take the hardware breakpoint, disable the
>>>>>> breakpoint and set up a single step before returning to the brk. The brk
>>>>>> then traps, but we must take care not to disable single-step and/or unmask
>>>>>> debug exceptions, because that will cause the hardware breakpoint code to
>>>>>> re-arm its breakpoint before we've stepped off the brk instruction.
>>>>>
>>>>> Hmm, frankly to say, this kind of race issue is not seriously discussed
>>>>> on x86 too, since kgdb is still a special tool (not used on the production
>>>>> system).
>>>>> I think under such situation kgdb operator must have full control of the
>>>>> system, and he can (and has to) avoid such kind of race.
>>>> Masami,
>>>>
>>>> Hmm I think in same lines, but not sure if we expect kprobes to be
>>>> able to work fool-proof along with kgdb or hw breakpoints ?
>>>
>>> For hw breakpoint, yes, we finally get check each other to safely
>>> use it even if one rejects the other one at some points(address).
>>> Since the hw breakpoint is already open for normal user via perf,
>>> we should do it. But the policy still needs to be discussed.
>>
>> 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
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)
Thank you,
--
Masami HIRAMATSU
IT Management Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt at hitachi.com
next prev parent reply other threads:[~2013-11-11 17:32 UTC|newest]
Thread overview: 49+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-10-17 11:17 [PATCH RFC v2 0/6] ARM64: Add kernel probes(Kprobes) support Sandeepa Prabhu
2013-10-17 11:17 ` [PATCH RFC v4 1/6] arm64: support single-step and breakpoint handler hooks Sandeepa Prabhu
2013-10-25 15:22 ` Will Deacon
2013-12-03 14:33 ` Sandeepa Prabhu
2013-12-03 19:44 ` Will Deacon
2013-10-17 11:17 ` [PATCH RFC 2/6] arm64: Kprobes with single stepping support Sandeepa Prabhu
2013-11-08 16:56 ` Will Deacon
2013-11-09 9:10 ` Masami Hiramatsu
2013-11-11 5:39 ` Sandeepa Prabhu
2013-11-11 7:54 ` Masami Hiramatsu
2013-11-11 10:51 ` Masami Hiramatsu
2013-11-11 10:58 ` Will Deacon
2013-11-11 17:32 ` Masami Hiramatsu [this message]
2013-11-12 6:23 ` Sandeepa Prabhu
2013-11-12 7:27 ` Masami Hiramatsu
2013-11-12 8:44 ` Sandeepa Prabhu
2013-11-12 10:17 ` Masami Hiramatsu
2013-11-12 10:55 ` Sandeepa Prabhu
2013-11-12 14:11 ` Masami Hiramatsu
2013-11-12 16:59 ` Steven Rostedt
2013-11-13 16:05 ` Masami Hiramatsu
[not found] ` <CA+b37P1sNsEXrJFfVL51sZ-SeGNCBiwXnOwCiFY8CBwSXPw+mQ@mail.gmail.com>
2013-11-13 7:08 ` Sandeepa Prabhu
2013-11-13 14:07 ` Masami Hiramatsu
2013-11-13 14:31 ` Will Deacon
2013-11-13 15:55 ` Sandeepa Prabhu
2013-11-15 16:39 ` Will Deacon
2013-11-18 6:55 ` Sandeepa Prabhu
2013-11-18 8:51 ` Sandeepa Prabhu
2013-11-13 13:58 ` Peter Zijlstra
2013-11-13 14:20 ` Will Deacon
2013-11-11 5:35 ` Sandeepa Prabhu
2013-11-11 11:21 ` Will Deacon
2013-11-12 6:52 ` Sandeepa Prabhu
2013-11-15 16:37 ` Will Deacon
2013-11-18 6:43 ` Sandeepa Prabhu
2013-10-17 11:17 ` [PATCH RFC 3/6] arm64: Kprobes instruction simulation support Sandeepa Prabhu
2013-11-08 17:03 ` Will Deacon
2013-11-11 5:58 ` Sandeepa Prabhu
2013-10-17 11:17 ` [PATCH RFC 4/6] arm64: Add kernel return probes support(kretprobes) Sandeepa Prabhu
2013-11-08 17:04 ` Will Deacon
2013-11-11 4:29 ` Sandeepa Prabhu
2013-11-11 7:53 ` AKASHI Takahiro
2013-11-11 8:55 ` Sandeepa Prabhu
2013-10-17 11:17 ` [PATCH RFC 5/6] arm64: Enable kprobes support for arm64 platform Sandeepa Prabhu
2013-10-17 11:17 ` [PATCH RFC 6/6] kprobes: Add cases for arm and arm64 in sample module Sandeepa Prabhu
2013-10-25 15:24 ` Will Deacon
2013-11-06 11:05 ` Sandeepa Prabhu
2013-10-18 8:32 ` [PATCH RFC v2 0/6] ARM64: Add kernel probes(Kprobes) support Masami Hiramatsu
2013-10-21 4:17 ` Sandeepa Prabhu
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