Xenial's gdb 7.11 breaks rr

Kyle Huey me at kylehuey.com
Sat May 14 00:23:21 UTC 2016


On Fri, May 13, 2016 at 5:19 PM, Kyle Huey <me at kylehuey.com> wrote:

> On Fri, May 13, 2016 at 5:14 PM, Robert O'Callahan <robert at ocallahan.org>
> wrote:
>
>>
>> On Sat, May 14, 2016 at 12:09 PM, Kyle Huey <me at kylehuey.com> wrote:
>>
>>> STR:
>>>
>>> 1. Build tip rr (8566e3038892)
>>> 2. ./bin/rr record ./bin/reverse_continue_process_signal
>>> 3. ./bin/rr replay
>>> 4. c
>>> 5. Once, the program has reached the final SIGKILL, b 22
>>> 6. rc
>>>
>>> Broken versions of gdb appear to forget which direction execution is
>>> heading in when an intermediate (and uninteresting) signal is reported by
>>> rr to gdb and resume with a vCont instead of a bc which sends us back to
>>> the SIGKILL at the end.
>>>
>>> This is fixed on the gdb tip, but building gdb is sufficiently annoying,
>>> and there is enough intermediate breakage, that I did not pin down a fix
>>> range.  Downgrading gdb on Ubuntu is non-trivial as well, so I ended up
>>> having to build from source :/
>>>
>>> I encountered this debugging Firefox, where the SIGKILL was the shutdown
>>> hang timeout killer and the intermediate signal is a SIGCHLD.
>>>
>>
>> Yeah, and there's also
>> https://sourceware.org/bugzilla/show_bug.cgi?id=19855 :-(.
>>
>> Can we get the fix for your bug backported to 7.11.1? And maybe see if
>> Ubuntu will update gdb to 7.11.1 in Xenial?
>>
>
> I would have to identify what actually fixed it first.
>

Lest I sound too pessimistic here, I'm willing to do the work if getting it
uplifted seems plausible.  Do the gdb maintainers ship dot releases?  Does
Ubuntu take them?

For 19855 I think we'll need to have rr sniff the gdb version somehow and
>> stop doing 'maint target-async 0'. That'd let us avoid the hideous
>> workaround for https://sourceware.org/bugzilla/show_bug.cgi?id=18617 as
>> well.
>>
>
> Yuck.
>
> - Kyle
>

- Kyle
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