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bug#10042: VIRT_ADDR_VARIES fix for Emacs under valgrind etc.


From: Paul Eggert
Subject: bug#10042: VIRT_ADDR_VARIES fix for Emacs under valgrind etc.
Date: Sun, 13 Nov 2011 20:55:03 -0800
User-agent: Mozilla/5.0 (X11; Linux i686; rv:7.0.1) Gecko/20110929 Thunderbird/7.0.1

This is a followup to the thread that began at
<http://lists.gnu.org/archive/html/emacs-devel/2011-11/msg00081.html>.

This patch fixes a bug where Emacs won't run correctly
under valgrind.  As Andreas mentioned, without the patch Emacs
probably isn't all that safe even when run outside of valgrind.

# Bazaar merge directive format 2 (Bazaar 0.90)
# revision_id: address@hidden
# target_branch: bzr+ssh://address@hidden/emacs/trunk
# testament_sha1: 6e35062324740218b862c3bc27e0aed206fee1ee
# timestamp: 2011-11-13 20:42:27 -0800
# base_revision_id: address@hidden
# 
# Begin patch
=== modified file 'src/ChangeLog'
--- src/ChangeLog       2011-11-12 12:11:54 +0000
+++ src/ChangeLog       2011-11-14 04:35:22 +0000
@@ -1,3 +1,22 @@
+2011-11-14  Paul Eggert  <address@hidden>
+
+       Standardize on VIRT_ADDR_VARIES behavior; otherwise, valgrind
+       does not work on some platforms.  Problem reported by Andreas Schwab in
+       <http://lists.gnu.org/archive/html/emacs-devel/2011-11/msg00081.html>.
+       * puresize.h (pure, PURE_P): Always behave as if VIRT_ADDR_VARIES
+       is set, removing the need for VIRT_ADDRESS_VARIES.
+       (PURE_P): Use a more-efficient implementation that needs just one
+       comparison, not two: on x86-64 with GCC 4.6.2, this cut down the
+       number of instructions from 6 (xorl, cmpq, jge, xorl, cmpq, setge)
+       to 4 (xorl, subq, cmpq, setbe).
+       * alloc.c (pure): Always extern now, since that's the
+       VIRT_ADDR_VARIES behavior.
+       (PURE_POINTER_P): Use a single comparison, not two, for
+       consistency with the new puresize.h.
+       * lisp.h (PNTR_COMPARISON_TYPE): Remove; no longer needed.
+       * m/ibms390.h, m/intel386.h, m/template.h, s/cygwin.h, s/hpux10-20.h:
+       Remove VIRT_ADDR_VARIES no longer needed.
+
 2011-11-12  Eli Zaretskii  <address@hidden>
 
        * makefile.w32-in (HEAPSIZE): New variable, allows to build temacs

=== modified file 'src/alloc.c'
--- src/alloc.c 2011-11-07 05:37:49 +0000
+++ src/alloc.c 2011-11-10 08:14:27 +0000
@@ -203,9 +203,6 @@
    remapping on more recent systems because this is less important
    nowadays than in the days of small memories and timesharing.  */
 
-#ifndef VIRT_ADDR_VARIES
-static
-#endif
 EMACS_INT pure[(PURESIZE + sizeof (EMACS_INT) - 1) / sizeof (EMACS_INT)] = 
{1,};
 #define PUREBEG (char *) pure
 
@@ -222,10 +219,7 @@
 /* Value is non-zero if P points into pure space.  */
 
 #define PURE_POINTER_P(P)                                      \
-     (((PNTR_COMPARISON_TYPE) (P)                              \
-       < (PNTR_COMPARISON_TYPE) ((char *) purebeg + pure_size))        \
-      && ((PNTR_COMPARISON_TYPE) (P)                           \
-         >= (PNTR_COMPARISON_TYPE) purebeg))
+  ((uintptr_t) (P) - (uintptr_t) purebeg <= pure_size)
 
 /* Index in pure at which next pure Lisp object will be allocated.. */
 

=== modified file 'src/lisp.h'
--- src/lisp.h  2011-11-07 17:04:01 +0000
+++ src/lisp.h  2011-11-10 08:14:27 +0000
@@ -1877,9 +1877,6 @@
     CHECK_NATNUM (tmp);                        \
     XSETCDR ((x), tmp);                        \
   } while (0)
-
-/* Cast pointers to this type to compare them.  */
-#define PNTR_COMPARISON_TYPE uintptr_t
 
 /* Define a built-in function for calling from Lisp.
  `lname' should be the name to give the function in Lisp,

=== modified file 'src/m/ibms390.h'
--- src/m/ibms390.h     2011-02-16 01:35:20 +0000
+++ src/m/ibms390.h     2011-11-10 08:14:27 +0000
@@ -17,11 +17,6 @@
 You should have received a copy of the GNU General Public License
 along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 
-
-/* Define VIRT_ADDR_VARIES if the virtual addresses of
-   pure and impure space as loaded can vary, and even their
-   relative order cannot be relied on.
-
-   Otherwise Emacs assumes that text space precedes data space,
-   numerically.  */
-#define VIRT_ADDR_VARIES
+/* This file is a placeholder -- it does not contain any definitions.
+   At some point we should probably fix this by removing the file
+   and removing all uses of it.  */

=== modified file 'src/m/intel386.h'
--- src/m/intel386.h    2011-01-31 23:54:50 +0000
+++ src/m/intel386.h    2011-11-10 08:14:27 +0000
@@ -19,7 +19,6 @@
 
 
 #ifdef WINDOWSNT
-#define VIRT_ADDR_VARIES
 #define DATA_START     get_data_start ()
 #endif
 
@@ -28,4 +27,3 @@
 /* we cannot get the maximum address for brk */
 #define ULIMIT_BREAK_VALUE (32*1024*1024)
 #endif
-

=== modified file 'src/m/template.h'
--- src/m/template.h    2011-02-16 01:35:20 +0000
+++ src/m/template.h    2011-11-10 08:14:27 +0000
@@ -21,14 +21,6 @@
    does not define it automatically.
    Ones defined so far include m68k and many others */
 
-/* Define VIRT_ADDR_VARIES if the virtual addresses of
-   pure and impure space as loaded can vary, and even their
-   relative order cannot be relied on.
-
-   Otherwise Emacs assumes that text space precedes data space,
-   numerically.  */
-#define VIRT_ADDR_VARIES
-
 /* After adding support for a new machine, modify the large case
    statement in configure.in to recognize reasonable
    configuration names, and add a description of the system to

=== modified file 'src/puresize.h'
--- src/puresize.h      2011-06-09 19:08:29 +0000
+++ src/puresize.h      2011-11-10 08:14:27 +0000
@@ -75,21 +75,7 @@
 
 /* Define PURE_P.  */
 
-#ifdef VIRT_ADDR_VARIES
-/* For machines where text and data can go anywhere
-   in virtual memory.  */
-
 extern EMACS_INT pure[];
 
 #define PURE_P(obj) \
- ((PNTR_COMPARISON_TYPE) XPNTR (obj) < (PNTR_COMPARISON_TYPE) ((char *) pure + 
PURESIZE) \
-  && (PNTR_COMPARISON_TYPE) XPNTR (obj) >= (PNTR_COMPARISON_TYPE) pure)
-
-#else /* not VIRT_ADDR_VARIES */
-
-extern char my_edata[];
-
-#define PURE_P(obj) \
-  ((PNTR_COMPARISON_TYPE) XPNTR (obj) < (PNTR_COMPARISON_TYPE) my_edata)
-
-#endif /* VIRT_ADDRESS_VARIES */
+  ((uintptr_t) XPNTR (obj) - (uintptr_t) pure <= PURESIZE)

=== modified file 'src/s/cygwin.h'
--- src/s/cygwin.h      2011-03-17 05:15:08 +0000
+++ src/s/cygwin.h      2011-11-10 08:14:27 +0000
@@ -91,9 +91,6 @@
    why it needed to be changed.  */
 #define GC_MARK_STACK GC_MAKE_GCPROS_NOOPS
 
-/* Virtual addresses of pure and impure space can vary, as on Windows.  */
-#define VIRT_ADDR_VARIES
-
 /* Emacs supplies its own malloc, but glib (part of Gtk+) calls
    memalign and on Cygwin, that becomes the Cygwin-supplied memalign.
    As malloc is not the Cygwin malloc, the Cygwin memalign always

=== modified file 'src/s/hpux10-20.h'
--- src/s/hpux10-20.h   2011-11-11 23:17:16 +0000
+++ src/s/hpux10-20.h   2011-11-14 04:35:22 +0000
@@ -100,14 +100,6 @@
    header sections which lose when `static' is defined away, as it is
    on HP-UX.  (You get duplicate symbol errors on linking). */
 #undef _FILE_OFFSET_BITS
-
-/* Define VIRT_ADDR_VARIES if the virtual addresses of
-   pure and impure space as loaded can vary, and even their
-   relative order cannot be relied on.
-
-   Otherwise Emacs assumes that text space precedes data space,
-   numerically.  */
-#define VIRT_ADDR_VARIES
 
 /* The data segment on this machine always starts at address 0x40000000.  */
 #define DATA_SEG_BITS 0x40000000





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