Fix crash due to non-contiguous EMACS_INT (Bug#10780).

* lisp.h (VALBITS): Move definition up, so that USE_LSB_TAG can use it.
(USE_LSB_TAG): Do not define if UINTPTR_MAX >> VALBITS == 0.
It's useless in that case, and it can cause problems on hosts
that allocate halves of EMACS_INT values separately.
Reported by Dan Horák.  Diagnosed by Andreas Schwab in
<http://debbugs.gnu.org/cgi/bugreport.cgi?bug=10780#30>.
* mem-limits.h (EXCEEDS_LISP_PTR): Define to 0 on hosts where
UINTPTR_MAX >> VALBITS == 0.  This is required by the above change;
it avoids undefined behavior on hosts where shifting right by more
than the word width has undefined behavior.

1 files changed, 14 insertions, 0 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index 3716aee7d69..911799b2bd2 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,17 @@
+2012-02-20  Paul Eggert  <eggert@cs.ucla.edu>
+
+        Fix crash due to non-contiguous EMACS_INT (Bug#10780).
+        * lisp.h (VALBITS): Move definition up, so that USE_LSB_TAG can use it.
+        (USE_LSB_TAG): Do not define if UINTPTR_MAX >> VALBITS == 0.
+        It's useless in that case, and it can cause problems on hosts
+        that allocate halves of EMACS_INT values separately.
+        Reported by Dan Horák.  Diagnosed by Andreas Schwab in
+        <http://debbugs.gnu.org/cgi/bugreport.cgi?bug=10780#30>.
+        * mem-limits.h (EXCEEDS_LISP_PTR): Define to 0 on hosts where
+        UINTPTR_MAX >> VALBITS == 0.  This is required by the above change;
+        it avoids undefined behavior on hosts where shifting right by more
+        than the word width has undefined behavior.
+
 2012-02-19  Chong Yidong  <cyd@gnu.org>
 
         * fileio.c (Ffile_name_directory, Ffile_name_nondirectory)