bug#24751: 26.0.50; Regex stack overflow not detected properly (gets "Variable binding depth exceeds max-specpdl-size")

[npostavs]

Eli Zaretskii <eliz@gnu.org> writes:

>> 
>> /* Define MATCH_MAY_ALLOCATE unless we need to make sure that the
>>    searching and matching functions should not call alloca.  On some
>>    systems, alloca is implemented in terms of malloc, and if we're
>>    using the relocating allocator routines, then malloc could cause a
>>    relocation, which might (if the strings being searched are in the
>>    ralloc heap) shift the data out from underneath the regexp
>>    routines.
>
>
> The first part is not obsolete, but its reasoning is backwards:
> SAFE_ALLOCA indeed can call malloc, but it could only cause relocation
> if REGEX_MALLOC is defined (and ralloc.c is compiled in).  And when
> you define REGEX_MALLOC, MATCH_MAY_ALLOCATE is undefined.  So the text
> there should be revised.

Everything you've said makes sense after your last message, but I'm
still unable to put it together and come up with a revised comment.
Could you make a suggestion?  Here are the rest of the changes.

v1-0001-Use-expanded-stack-during-regex-matches.patch
Description: patch