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:

>> From: npostavs@users.sourceforge.net
>> Cc: 24751@debbugs.gnu.org
>> Date: Sun, 01 Jan 2017 13:33:35 -0500
>> 
>> 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.
>> 
>> Is there ever any case where REGEX_MALLOC is defined?  I can't see where
>> it happens.
>
> I don't understand the question.  You can compile regex.c with the
> "-DREGEX_MALLOC" option whenever you like.  We don't do that,
                                              ^^^^^^^^^^^^^^^^

Thanks, that's what I was wondering about in my question.

>
>> I don't understand why you say relocation is dependent on
>> REGEX_MALLOC, I thought only REL_ALLOC affects that.
>
> REL_ALLOC determines whether ralloc.c is compiled in, which I
> mentioned above.

But if REL_ALLOC is defined, then SAFE_ALLOCA could cause relocation
(via malloc) regardless of whether REGEX_MALLOC is defined or not, no?