rr debbugger

Garming Sam garming at catalyst.net.nz
Tue Apr 11 23:17:39 UTC 2017

One thing to add, using checkpoint in the rr gdb debugger is
particularly nice. Instead of running from the beginning, you can make a
checkpoint right before the failure and restart from that point. In a
long-running situation, this is great for gathering information, and
particularly when the reverse debugging does not work entirely (e.g.
optimized code or rr bugs).

I also have some ideas about a rr gdb command which would be useful for
following IRPC messages between processes. As it is, I haven't really
seen a good way of cycling through processes with rr and I don't see any
reason it can't be done.



On 12/04/17 10:10, Garming Sam via samba-technical wrote:
> Hi,
> I've talked to the lead developer in person before (he's a New
> Zealander) and I've debugged a few issues with it on Samba. I worked
> with him about a year ago to fix some of the syscalls which were
> required to run make test, like some interactions with socket wrapper.
> If you manage to find any replay divergences with make test TESTS="..."
> , he can actually figure it out from there (provided it doesn't take too
> long to reproduce).
> When I was playing around with it, there were still issues mmap and some
> of the caches, so TDB_NOMMAP made it fairly reliable as well as wiping
> any caches between runs. I see some of those have now been fixed, which
> is nice.
> It would be nice to run rr over a large number of intermittently failing
> tests (using chaos mode as well to produce different scheduling), but
> part of the problem with failures on these tests is that they have
> dependencies on earlier state during the full make test. There's still
> lots of work before we could actually get make test running entirely
> under rr, but it would be rather useful for these failures (despite the
> fact that replaying to that point would take a long time).
> Cheers,
> Garming
> On 12/04/17 03:59, Aurélien Aptel via samba-technical wrote:
>> Hi,
>> There is a group of people at mozilla working on a very interesting
>> project, the rr debugger. It allows you to record the non-deterministic
>> parts of a program run (syscall results) and replay them
>> deterministicly. This means you can finally use breakpoints without
>> trigerring timeouts on the client side. You can also reverse-debug:
>> start from the crash and go backward.
>> It wasn't working on smbd but after opening a couple of issues and
>> working on one I was able to use it. Other syscall might have to be
>> implemented depending on what you try to run.
>> http://rr-project.org/
>> You might want to pull from here to get an extra quotactl syscall
>> implemented:
>> https://github.com/aaptel/rr.git on the branch quotactl-xgetqstat
>> Cheers,

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