From: Paul Eggert <eggert@day>
Date: Sat, 27 Jul 2019 17:24:19 +0000 (-0700)
Subject: Fix arithmetic overflow in GC consing count
X-Git-Tag: emacs-27.0.90~1817^2~65
X-Git-Url: http://git.eshelyaron.com/gitweb/?a=commitdiff_plain;h=c26469daa752baf276bcad61b042b218402547de;p=emacs.git

Fix arithmetic overflow in GC consing count

* src/alloc.c (allow_garbage_collection):
Redo expression to avoid signed arithmetic overflow
in an intermediate expression when CONSING is negative.
---

diff --git a/src/alloc.c b/src/alloc.c
index c17bdb719a9..5e089311a27 100644
--- a/src/alloc.c
+++ b/src/alloc.c
@@ -5498,7 +5498,7 @@ staticpro (Lisp_Object const *varaddress)
 static void
 allow_garbage_collection (intmax_t consing)
 {
-  consing_until_gc -= OBJECT_CT_MAX - consing;
+  consing_until_gc = consing - (OBJECT_CT_MAX - consing_until_gc);
   garbage_collection_inhibited--;
 }