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bug#24751: 26.0.50; Regex stack overflow not detected properly (gets "Va
bug#24751: 26.0.50; Regex stack overflow not detected properly (gets "Variable binding depth exceeds max-specpdl-size")
Mon, 02 Jan 2017 17:24:26 +0200
> From: address@hidden
> Cc: address@hidden
> Date: Sun, 01 Jan 2017 23:49:46 -0500
> 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?
How about the below?
--- src/regex.c~0 2016-12-11 06:39:19.000000000 +0200
+++ src/regex.c 2017-01-02 12:40:44.266517100 +0200
@@ -1195,24 +1195,28 @@
gettext_noop ("Range striding over charsets") /* REG_ERANGEX */
-/* Avoiding alloca during matching, to placate r_alloc. */
+/* Whether to allocate memory during matching. */
-/* 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
- Here's another reason to avoid allocation: Emacs
- processes input from X in a signal handler; processing X input may
- call malloc; if input arrives while a matching routine is calling
- malloc, then we're scrod. But Emacs can't just block input while
- calling matching routines; then we don't notice interrupts when
- they come in. So, Emacs blocks input around all regexp calls
- except the matching calls, which it leaves unprotected, in the
- faith that they will not malloc. */
+/* Define MATCH_MAY_ALLOCATE to allow the searching and matching
+ functions allocate memory for the failure stack and registers.
+ Normally should be defined, because otherwise searching and
+ matching routines will have much smaller memory resources at their
+ disposal, and therefore might fail to handle complex regexps.
+ Therefore undefine MATCH_MAY_ALLOCATE only in the following
+ exceptional situations:
+ . When running on a system where memory is at premium.
+ . When alloca cannot be used at all, perhaps due to bugs in
+ its implementation, or its being unavailable, or due to a
+ very small stack size. This requires to define REGEX_MALLOC
+ to use malloc instead, which in turn could lead to memory
+ leaks if search is interrupted by a signal. (For these
+ reasons, defining REGEX_MALLOC when building Emacs
+ automatically undefines MATCH_MAY_ALLOCATE, but outside
+ Emacs you may not care about memory leaks.) If you want to
+ prevent the memory leaks, undefine MATCH_MAY_ALLOCATE.
+ . When code that calls the searching and matching functions
+ cannot allow memory allocation, for whatever reasons. */
/* Normally, this is fine. */