[Emacs-diffs] trunk r117838: Fix bug uncovered by changing alloca to auto buffer.

[Paul Eggert]

------------------------------------------------------------
revno: 117838
revision-id: address@hidden
parent: address@hidden
fixes bug: http://debbugs.gnu.org/18410
committer: Paul Eggert <address@hidden>
branch nick: trunk
timestamp: Sun 2014-09-07 15:27:59 -0700
message:
  Fix bug uncovered by changing alloca to auto buffer.
  
  * coding.c (growable_destination): New function.
  (produce_chars): Use it for sanity checks.  Do not fiddle with
  dst_end if the source and destination are both nil, as it's
  the caller's responsibility to avoid overlap.
  * keyboard.c (read_decoded_event_from_main_queue):
  The destination must be MAX_MULTIBYTE_LENGTH times the max source
  length, not 4 times, to prevent decode_coding_c_string from trying
  to reallocate a destination.  This removes the need for the FIXME.
modified:
  src/ChangeLog                  changelog-20091113204419-o5vbwnq5f7feedwu-1438
  src/coding.c                   coding.c-20091113204419-o5vbwnq5f7feedwu-1077
  src/keyboard.c                 keyboard.c-20091113204419-o5vbwnq5f7feedwu-449

=== modified file 'src/ChangeLog'
--- a/src/ChangeLog     2014-09-07 20:31:18 +0000
+++ b/src/ChangeLog     2014-09-07 22:27:59 +0000
@@ -1,5 +1,15 @@
 2014-09-07  Paul Eggert  <address@hidden>
 
+       Fix bug uncovered by changing alloca to auto buffer (Bug#18410).
+       * coding.c (growable_destination): New function.
+       (produce_chars): Use it for sanity checks.  Do not fiddle with
+       dst_end if the source and destination are both nil, as it's
+       the caller's responsibility to avoid overlap.
+       * keyboard.c (read_decoded_event_from_main_queue):
+       The destination must be MAX_MULTIBYTE_LENGTH times the max source
+       length, not 4 times, to prevent decode_coding_c_string from trying
+       to reallocate a destination.  This removes the need for the FIXME.
+
        * callproc.c (exec_failed) [DOS_NT]: Define a dummy.
        All callers simplified.  Add a comment about exec_failed, vfork,
        and alloca.

=== modified file 'src/coding.c'
--- a/src/coding.c      2014-09-07 07:04:01 +0000
+++ b/src/coding.c      2014-09-07 22:27:59 +0000
@@ -690,6 +690,14 @@
   XSETCDR (x, tmp);
 }
 
+/* True if CODING's destination can be grown.  */
+
+static bool
+growable_destination (struct coding_system *coding)
+{
+  return STRINGP (coding->dst_object) || BUFFERP (coding->dst_object);
+}
+
 
 /* Safely get one byte from the source text pointed by SRC which ends
    at SRC_END, and set C to that byte.  If there are not enough bytes
@@ -7019,8 +7027,10 @@
       int *buf = coding->charbuf;
       int *buf_end = buf + coding->charbuf_used;
 
-      if (EQ (coding->src_object, coding->dst_object))
+      if (EQ (coding->src_object, coding->dst_object)
+         && ! NILP (coding->dst_object))
        {
+         eassert (growable_destination (coding));
          coding_set_source (coding);
          dst_end = ((unsigned char *) coding->source) + coding->consumed;
        }
@@ -7059,6 +7069,7 @@
 
              if ((dst_end - dst) / MAX_MULTIBYTE_LENGTH < to_nchars)
                {
+                 eassert (growable_destination (coding));
                  if (((min (PTRDIFF_MAX, SIZE_MAX) - (buf_end - buf))
                       / MAX_MULTIBYTE_LENGTH)
                      < to_nchars)
@@ -7103,7 +7114,10 @@
       const unsigned char *src_end = src + coding->consumed;
 
       if (EQ (coding->dst_object, coding->src_object))
-       dst_end = (unsigned char *) src;
+       {
+         eassert (growable_destination (coding));
+         dst_end = (unsigned char *) src;
+       }
       if (coding->src_multibyte != coding->dst_multibyte)
        {
          if (coding->src_multibyte)
@@ -7119,6 +7133,7 @@
                  ONE_MORE_BYTE (c);
                  if (dst == dst_end)
                    {
+                     eassert (growable_destination (coding));
                      if (EQ (coding->src_object, coding->dst_object))
                        dst_end = (unsigned char *) src;
                      if (dst == dst_end)
@@ -7149,6 +7164,7 @@
 
                if (dst >= dst_end - 1)
                  {
+                   eassert (growable_destination (coding));
                    if (EQ (coding->src_object, coding->dst_object))
                      dst_end = (unsigned char *) src;
                    if (dst >= dst_end - 1)

=== modified file 'src/keyboard.c'
--- a/src/keyboard.c    2014-09-07 13:27:33 +0000
+++ b/src/keyboard.c    2014-09-07 22:27:59 +0000
@@ -2355,22 +2355,15 @@
              struct coding_system *coding
                = TERMINAL_KEYBOARD_CODING (terminal);
              unsigned char src[MAX_ENCODED_BYTES];
-             unsigned char dest[4 * sizeof src];
+             unsigned char dest[MAX_ENCODED_BYTES * MAX_MULTIBYTE_LENGTH];
              int i;
              for (i = 0; i < n; i++)
                src[i] = XINT (events[i]);
              if (meta_key != 2)
                for (i = 0; i < n; i++)
                  src[i] &= ~0x80;
-
-             /* FIXME: For some reason decode_coding_c_string requires a
-                fresh output buffer each time, and reusing the old buffer can
-                make Emacs dump core.  Avoid triggering the problem for now
-                by allocating a new buffer each time through the loop.  */
-             bool please_fixme = true;
-             coding->destination = please_fixme ? alloca (n * 4) : dest;
-
-             coding->dst_bytes = n * 4;
+             coding->destination = dest;
+             coding->dst_bytes = sizeof dest;
              decode_coding_c_string (coding, src, n, Qnil);
              eassert (coding->produced_char <= n);
              if (coding->produced_char == 0)