From: Paul Eggert <eggert@cs.ucla.edu>
Date: Thu, 9 Oct 2014 06:54:10 +0000 (-0700)
Subject: * lisp.h (USE_STACK_STRING): Now true only if USE_STACK CONS.
X-Git-Tag: emacs-25.0.90~2635^2~679^2~91
X-Git-Url: http://git.eshelyaron.com/gitweb/?a=commitdiff_plain;h=8881986b3e227f46d8a7d6766b41802bcfc2517c;p=emacs.git

* lisp.h (USE_STACK_STRING): Now true only if USE_STACK CONS.

On x86 platforms this works around GCC bug 63495
<https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63495>,
and more generally should fix a portability problem in Emacs.
Problem reported by Stefan Monnier in:
http://lists.gnu.org/archive/html/emacs-devel/2014-10/msg00261.html
---

diff --git a/src/ChangeLog b/src/ChangeLog
index e01c70f3dce..a38df05518d 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,12 @@
+2014-10-09  Paul Eggert  <eggert@cs.ucla.edu>
+
+	* lisp.h (USE_STACK_STRING): Now true only if USE_STACK CONS.
+	On x86 platforms this works around GCC bug 63495
+	<https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63495>,
+	and more generally should fix a portability problem in Emacs.
+	Problem reported by Stefan Monnier in:
+	http://lists.gnu.org/archive/html/emacs-devel/2014-10/msg00261.html
+
 2014-10-08  Leo Liu  <sdl.web@gmail.com>
 
 	Enhance terpri to allow conditionally output a newline.  (Bug#18652)
diff --git a/src/lisp.h b/src/lisp.h
index 0425744b301..9e4cc5fdc53 100644
--- a/src/lisp.h
+++ b/src/lisp.h
@@ -4615,13 +4615,16 @@ union Aligned_String
   double d; intmax_t i; void *p;
 };
 
-/* True for stack-based cons and string implementations.  */
+/* True for stack-based cons and string implementations, respectively.
+   Use stack-based strings only if stack-based cons also works.
+   Otherwise, STACK_CONS would create heap-based cons cells that
+   could point to stack-based strings, which is a no-no.  */
 
 enum
   {
     USE_STACK_CONS = (USE_STACK_LISP_OBJECTS
 		      && alignof (union Aligned_Cons) % GCALIGNMENT == 0),
-    USE_STACK_STRING = (USE_STACK_LISP_OBJECTS
+    USE_STACK_STRING = (USE_STACK_CONS
 			&& alignof (union Aligned_String) % GCALIGNMENT == 0)
   };