------------------------------------------------------------
revno: 107358
committer: Paul Eggert <eggert@xxxxxxxxxxx>
branch nick: trunk
timestamp: Mon 2012-02-20 15:09:58 -0800
message:
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 HorÃk. 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.
modified:
src/ChangeLog
src/lisp.h
src/mem-limits.h
=== modified file 'src/ChangeLog'
--- a/src/ChangeLog 2012-02-19 09:58:23 +0000
+++ b/src/ChangeLog 2012-02-20 23:09:58 +0000
@@ -1,3 +1,17 @@
+2012-02-20 Paul Eggert <eggert@xxxxxxxxxxx>
+
+ 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 HorÃk. 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@xxxxxxx>

* fileio.c (Ffile_name_directory, Ffile_name_nondirectory)

=== modified file 'src/lisp.h'
--- a/src/lisp.h 2012-01-19 07:21:25 +0000
+++ b/src/lisp.h 2012-02-20 23:09:58 +0000
@@ -168,6 +168,10 @@
#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 @@
|| 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 @@
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

=== modified file 'src/mem-limits.h'
--- a/src/mem-limits.h 2012-01-19 07:21:25 +0000
+++ b/src/mem-limits.h 2012-02-20 23:09:58 +0000
@@ -34,7 +34,7 @@
#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) \

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