Merge from origin/emacs-25

b73f466 * lisp/cus-start.el (exec-path): Handle nil elements.  (Bug#2...
55ebb70 Catch the imenu-unavailable error in sh-mode completion table
993acb5 ; Minor fix for last change in characters.el
30c4bb5 More char-width fixes
4eb4463 Fix char-width-table values for some Emoji
528997d Keep point when switching from and to *terminal* buffer
2130005 * INSTALL: Use correct Emacs release number 25.
10835b1 Avoid crashes due to objects read with the #n=object form
4de671d Improve doc string of 'completion-at-point-functions'
ceb46f0 Fix crash in evaluating functions
d8374c4 * src/filelock.c (current_lock_owner): Update comment.

1 files changed, 12 insertions, 1 deletions

diff --git a/src/lread.c b/src/lread.c
index 10eec3b1be0..58d518ce40b 100644
--- a/src/lread.c
+++ b/src/lread.c
@@ -2917,7 +2917,18 @@ read1 (Lisp_Object readcharfun, int *pch, bool first_in_list)
 		  if (c == '=')
 		    {
 		      /* Make a placeholder for #n# to use temporarily.  */
-		      AUTO_CONS (placeholder, Qnil, Qnil);
+		      /* Note: We used to use AUTO_CONS to allocate
+			 placeholder, but that is a bad idea, since it
+			 will place a stack-allocated cons cell into
+			 the list in read_objects, which is a
+			 staticpro'd global variable, and thus each of
+			 its elements is marked during each GC.  A
+			 stack-allocated object will become garbled
+			 when its stack slot goes out of scope, and
+			 some other function reuses it for entirely
+			 different purposes, which will cause crashes
+			 in GC.  */
+		      Lisp_Object placeholder = Fcons (Qnil, Qnil);
 		      Lisp_Object cell = Fcons (make_number (n), placeholder);
 		      read_objects = Fcons (cell, read_objects);