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

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* 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.
This commit is contained in:
Paul Eggert 2012-02-20 15:09:58 -08:00
parent 132b9726f6
commit 310f5bd429
3 changed files with 28 additions and 7 deletions
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14
src/ChangeLog
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@ -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)

19
src/lisp.h
View file

@ -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

2
src/mem-limits.h
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@ -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) \