1 files changed, 31 insertions, 0 deletions

diff --git a/src/lisp.h b/src/lisp.h
index 4ea0e52efb7..dc78e524213 100644
--- a/src/lisp.h
+++ b/src/lisp.h
@@ -3246,6 +3246,37 @@ extern Lisp_Object Vdirectory_sep_char;
          : Fcons ((el), (check)))))
 
 
+/* SAFE_ALLOCA normally allocates memory on the stack, but if size is
+   larger than MAX_ALLOCA, use xmalloc to avoid overflowing the stack.  */
+
+#define MAX_ALLOCA 16*1024
+
+extern Lisp_Object safe_alloca_unwind (Lisp_Object);
+
+#define USE_SAFE_ALLOCA                 \
+  int sa_count = SPECPDL_INDEX ()
+
+#define SAFE_ALLOCA(buf, type, size)                      \
+  do {                                                    \
+    if ((size) < MAX_ALLOCA)                              \
+      buf = (type) alloca (size);                         \
+    else                                                  \
+      {                                                   \
+        buf = (type) xmalloc (size);                      \
+        record_unwind_protect (safe_alloca_unwind,        \
+                               make_save_value (buf, 0)); \
+      }                                                   \
+  } while (0)
+
+#define SAFE_FREE(size)                 \
+  do {                                  \
+    if ((size) >= MAX_ALLOCA)           \
+      unbind_to (sa_count, Qnil);       \
+  } while (0)
+
+
+
+
 #endif /* EMACS_LISP_H */
 
 /* arch-tag: 9b2ed020-70eb-47ac-94ee-e1c2a5107d5e