commit a40c73351c7aa2b990274122539a36fd3506cf79

Author: Paul Eggert <eggert@cs.ucla.edu>

Date:   Mon Feb 20 15:09:58 2012 -0800

    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.

diff --git a/src/lisp.h b/src/lisp.h

index 366d24a..8bfd707 100644

--- a/src/lisp.h

+++ b/src/lisp.h

@@ -168,6 +168,10 @@ extern int suppress_checking EXTERNALLY_VISIBLE;

 #define GCTYPEBITS 3

 #endif

+#ifndef VALBITS

+#define VALBITS (BITS_PER_EMACS_INT - GCTYPEBITS)

+#endif

+

 #ifndef NO_DECL_ALIGN

 # ifndef DECL_ALIGN

 #  if HAVE_ATTRIBUTE_ALIGNED

@@ -191,7 +195,15 @@ extern int suppress_checking EXTERNALLY_VISIBLE;

      || defined DARWIN_OS || defined __sun)

 /* We also need to be able to specify mult-of-8 alignment on static vars.  */

 # if defined DECL_ALIGN

-#  define USE_LSB_TAG

+/* mark_maybe_object assumes that EMACS_INT values are contiguous,

+   but this is not true on some hosts where EMACS_INT is wider than a pointer,

+   as they may allocate the halves of an EMACS_INT separately.

+   On these hosts USE_LSB_TAG is not needed because the top bits of an

+   EMACS_INT are unused, so define USE_LSB_TAG only on hosts where it

+   might be useful.  */

+#  if UINTPTR_MAX >> VALBITS != 0

+#   define USE_LSB_TAG

+#  endif

 # endif

 #endif

@@ -309,11 +321,6 @@ enum Lisp_Fwd_Type

     Lisp_Fwd_Kboard_Obj,	/* Fwd to a Lisp_Object field of kboards.  */

   };

-/* These values are overridden by the m- file on some machines.  */

-#ifndef VALBITS

-#define VALBITS (BITS_PER_EMACS_INT - GCTYPEBITS)

-#endif

-

 #ifdef USE_LISP_UNION_TYPE

 #ifndef WORDS_BIGENDIAN

diff --git a/src/mem-limits.h b/src/mem-limits.h

index 472e591..244592a 100644

--- a/src/mem-limits.h

+++ b/src/mem-limits.h

@@ -34,7 +34,7 @@ extern int etext;

 #endif

 extern char *start_of_data (void);

-#if defined USE_LSB_TAG

+#if defined USE_LSB_TAG || UINTPTR_MAX >> VALBITS == 0

 #define EXCEEDS_LISP_PTR(ptr) 0

 #elif defined DATA_SEG_BITS

 #define EXCEEDS_LISP_PTR(ptr) \