1 files changed, 22 insertions, 10 deletions

diff --git a/src/alloc.c b/src/alloc.c
index 28c9b51dab4..0f105f87207 100644
--- a/src/alloc.c
+++ b/src/alloc.c
@@ -761,13 +761,17 @@ xnrealloc (void *pa, ptrdiff_t nitems, ptrdiff_t item_size)
    infinity.
 
    If PA is null, then allocate a new array instead of reallocating
-   the old one.  Thus, to grow an array A without saving its old
-   contents, invoke xfree (A) immediately followed by xgrowalloc (0,
-   &NITEMS, ...).
+   the old one.
 
    Block interrupt input as needed.  If memory exhaustion occurs, set
    *NITEMS to zero if PA is null, and signal an error (i.e., do not
-   return).  */
+   return).
+
+   Thus, to grow an array A without saving its old contents, do
+   { xfree (A); A = NULL; A = xpalloc (NULL, &AITEMS, ...); }.
+   The A = NULL avoids a dangling pointer if xpalloc exhausts memory
+   and signals an error, and later this code is reexecuted and
+   attempts to free A.  */
 
 void *
 xpalloc (void *pa, ptrdiff_t *nitems, ptrdiff_t nitems_incr_min,
@@ -822,12 +826,7 @@ xstrdup (const char *s)
 Lisp_Object
 safe_alloca_unwind (Lisp_Object arg)
 {
-  register struct Lisp_Save_Value *p = XSAVE_VALUE (arg);
-
-  p->dogc = 0;
-  xfree (p->pointer);
-  p->pointer = 0;
-  free_misc (arg);
+  free_save_value (arg);
   return Qnil;
 }
 
@@ -3361,6 +3360,19 @@ make_save_value (void *pointer, ptrdiff_t integer)
   return val;
 }
 
+/* Free a Lisp_Misc_Save_Value object.  */
+
+void
+free_save_value (Lisp_Object save)
+{
+  register struct Lisp_Save_Value *p = XSAVE_VALUE (save);
+
+  p->dogc = 0;
+  xfree (p->pointer);
+  p->pointer = NULL;
+  free_misc (save);
+}
+
 /* Return a Lisp_Misc_Overlay object with specified START, END and PLIST.  */
 
 Lisp_Object