Fix an assertion-failure in memarea_alloc() on 64-bit platforms.

The trick is that we should assert that our next_mem pointer has not
run off the end of the array _before_ we realign the pointer, since
doing that could take us over the end... but only if we're on a system
where malloc() gives us ram in increments smaller than sizeof(void*).

ChangeLog

@@ -12,7 +12,12 @@ Changes in version 0.2.1.15??? - ????-??-??
       directory authority.  Fixes part of bug 932.
     - When we change to or from being a bridge, reset our counts of
       client usage by country.  Fixes bug 932.
-    - Fix a bug that made stream bandwidth get misreported to the controller.
+    - Fix a bug that made stream bandwidth get misreported to the
+      controller.
+    - Fix an assertion failure on 64-bit platforms when we allocated
+      memory right up to the end of a memarea, then realigned the
+      memory one step beyond the end.  Fixes a possible cause of bug
+      930.
 
 
 Changes in version 0.2.1.14-rc - 2009-04-12

src/common/memarea.c

@@ -182,6 +182,8 @@ memarea_alloc(memarea_t *area, size_t sz)
   memarea_chunk_t *chunk = area->first;
   char *result;
   tor_assert(chunk);
+  if (sz == 0)
+    sz = 1;
   if (chunk->next_mem+sz > chunk->u.mem+chunk->mem_size) {
     if (sz+CHUNK_HEADER_SIZE >= CHUNK_SIZE) {
       /* This allocation is too big.  Stick it in a special chunk, and put
@@ -198,10 +200,11 @@ memarea_alloc(memarea_t *area, size_t sz)
     tor_assert(chunk->mem_size >= sz);
   }
   result = chunk->next_mem;
-  chunk->next_mem = realign_pointer(chunk->next_mem + sz);
+  chunk->next_mem = chunk->next_mem + sz;
   // XXXX021 remove these once bug 930 is solved.
   tor_assert(chunk->next_mem >= chunk->u.mem);
   tor_assert(chunk->next_mem <= chunk->u.mem+chunk->mem_size);
+  chunk->next_mem = realign_pointer(chunk->next_mem);
   return result;
 }
 
@@ -272,7 +275,8 @@ memarea_assert_ok(memarea_t *area)
 
   for (chunk = area->first; chunk; chunk = chunk->next_chunk) {
     tor_assert(chunk->next_mem >= chunk->u.mem);
-    tor_assert(chunk->next_mem <= chunk->u.mem+chunk->mem_size+MEMAREA_ALIGN);
+    tor_assert(chunk->next_mem <=
+          (char*) realign_pointer(chunk->u.mem+chunk->mem_size));
   }
 }