bug#40661: Crash in regex search during redisplay

[Daniel Colascione]

On April 16, 2020 9:33:16 AM PDT, Eli Zaretskii <eliz@gnu.org> wrote:
>> Date: Thu, 16 Apr 2020 18:36:36 +0300
>> From: Eli Zaretskii <eliz@gnu.org>
>> Cc: 40661@debbugs.gnu.org
>> 
>> Looks like GC sometimes kicks in while we are inside re_search_2
>
>Or not.  I cannot get a breakpoint inside GC to fire while we are in
>search_buffer_re, so maybe my hypothesis was wrong.  Although the
>symptoms are all there: when the segfault hits, the pointers passed to
>re_search_2 are invalid, but BEGV_ADDR and GAP_END_ADDR, from which
>they are supposed to be computed, are valid (and different).  And the
>patch does seem to avoid the segfaults.  But maybe it's just a
>coincidence or a side effect...

Try using rr and see where those pointers came from