Re: Native compilation on MPS branch

[Andrea Corallo]

Gerd Möllmann <gerd.moellmann@gmail.com> writes:

> Andrea Corallo <acorallo@gnu.org> writes:
>
>> Dumb question: are you usnug rr to debug this?
>
> Not dumb at all :-). Last time I looked, which is now 10s ago, Homebrew
> still didn't offer rr. That's on arm, in case it matters.

IME rr is invaluable for debugging GC bugs, one can do things like
placing watch-points while doing reverse execution and discover
immediately where something was modified the last time.  You did a very
good job reaching this point of the development without rr.

Anyway I'll mention a trick I find extremely usefull to discover where
something was modified last time before a certain event without rr, I
apologize if you know it already but in case it might help some other
reader :)

1 When we crash we set a watch point on the memory we see got
unexpectedly modified
2 We set the ignore number of the watch-point to a very large number
3 We restart the execution of the program
4 When the program crashes again we can see how many time the watch point
was actually ignored
5 We subtract 1 to this number and we set it again as the ignore number
of the watch-point
6 We restart again and tada!! We are where that piece of memory was
modified for the last time :)

Hope this helps someone

  Andrea