[CRIU] [PATCH 2/3] dump: use breakpoints instead of tracing syscalls (v2)

[Christopher Covington]

On 09/19/2014 10:01 AM, Pavel Emelyanov wrote:
> On 09/17/2014 07:12 PM, Andrey Vagin wrote:
>> Currently CRIU traces syscalls to catch a moment, when sigreturn() is
>> called. Now we trace recv(cmd), close(logfd), close(cmdfd), sigreturn().
>>
>> We can reduce a number of steps by using hw breakpoints. A breakpoint is
>> set before sigreturn, so we will need to trace only it.
>>
>> v2: In the first version a breakpoint is set after sigreturn. In this
>> case we have a problem with signals. If a process has pending signals,
>> it will start to precess them after exiting from sigreturn(), but before
>> returning to userspace. So the breakpoint will not be triggered.
>>
>> And at the end Here are a few numbers how we catch sigreturn.
>> Before this patch criu executes 36 syscalls and gets 12 signals.
>> With this patch criu executes 18 syscalls and gets 5 signals.
>>
>> Signed-off-by: Andrey Vagin <avagin at openvz.org>
> 
> OK, applied, thanks a lot :)
> 
> Christopher, if it's possible, could you help us placing breakpoints
> into ARM parasite and restorer? :) This is quite good optimization,
> I think it makes sense to have one on ARM too.

I will look into this. Some Linux interfaces that I've used in the past that
may be available across architectures are:

Software breakpoint placement with uprobes. This requires debugfs.

https://lwn.net/Articles/499190/

Hardware breakpoint placement with perf_event_open.

https://github.com/deater/perf_event_tests/blob/master/tests/breakpoints/breakpoint_support.c

http://man7.org/linux/man-pages/man2/perf_event_open.2.html

Christopher

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