Xenial's gdb 7.11 breaks rr

Kyle Huey me at kylehuey.com
Sat May 14 00:19:54 UTC 2016

On Fri, May 13, 2016 at 5:14 PM, Robert O'Callahan <robert at ocallahan.org>

> 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.

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.


- Kyle
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