Xenial's gdb 7.11 breaks rr

Robert O'Callahan robert at ocallahan.org
Sat May 14 00:14:33 UTC 2016


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?

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.

Rob
-- 
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