Avoid buffer text relocations in calls to STRING_CHAR_* macros.

 src/charset.c (maybe_unify_char): Inhibit relocation of buffer text
 for the duration of call to load_charset, to avoid problems with
 callers of maybe_unify_char that access buffer text through C
 pointers.
 src/ralloc.c (r_alloc_inhibit_buffer_relocation): Increment and
 decrement the inhibition flag, instead of just setting or
 resetting it.

Fixes: debbugs:11519

3 files changed, 26 insertions, 1 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index 0b1ef220fc0..ec5725af2bc 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,14 @@
+2012-05-23  Eli Zaretskii  <eliz@gnu.org>
+
+        * charset.c (maybe_unify_char): Inhibit relocation of buffer text
+        for the duration of call to load_charset, to avoid problems with
+        callers of maybe_unify_char that access buffer text through C
+        pointers.
+
+        * ralloc.c (r_alloc_inhibit_buffer_relocation): Increment and
+        decrement the inhibition flag, instead of just setting or
+        resetting it.
+
 2012-05-24  Ken Brown  <kbrown@cornell.edu>
 
         * callproc.c (Fcall_process): Restore a line that was accidentally
diff --git a/src/charset.c b/src/charset.c
index 57e1603fc19..d287fc0bece 100644
--- a/src/charset.c
+++ b/src/charset.c
@@ -1641,6 +1641,12 @@ maybe_unify_char (int c, Lisp_Object val)
     return c;
 
   CHECK_CHARSET_GET_CHARSET (val, charset);
+#ifdef REL_ALLOC
+  /* The call to load_charset below can allocate memory, whcih screws
+     callers of this function through STRING_CHAR_* macros that hold C
+     pointers to buffer text, if REL_ALLOC is used.  */
+  r_alloc_inhibit_buffer_relocation (1);
+#endif
   load_charset (charset, 1);
   if (! inhibit_load_charset_map)
     {
@@ -1656,6 +1662,9 @@ maybe_unify_char (int c, Lisp_Object val)
       if (unified > 0)
         c = unified;
     }
+#ifdef REL_ALLOC
+  r_alloc_inhibit_buffer_relocation (0);
+#endif
   return c;
 }
 
diff --git a/src/ralloc.c b/src/ralloc.c
index db3638a54e6..2e4823dc6c1 100644
--- a/src/ralloc.c
+++ b/src/ralloc.c
@@ -1204,7 +1204,12 @@ r_alloc_reset_variable (POINTER *old, POINTER *new)
 void
 r_alloc_inhibit_buffer_relocation (int inhibit)
 {
-  use_relocatable_buffers = !inhibit;
+  if (use_relocatable_buffers < 0)
+    use_relocatable_buffers = 0;
+  if (inhibit)
+    use_relocatable_buffers++;
+  else if (use_relocatable_buffers > 0)
+    use_relocatable_buffers--;
 }