Assert that the range passed to landinsert is not empty.

Assert that the range passed to ArenaFreeLandInsert is not empty.
Assert that there's address space left over in a chunk after the overheads have been accounted for.

Copied from Perforce
 Change: 190920
 ServerID: perforce.ravenbrook.com

mps/code/arena.c

@@ -949,6 +949,7 @@ Res ArenaFreeLandInsert(Arena arena, Addr base, Addr limit)
   Res res;
 
   AVERT(Arena, arena);
+  AVER(base < limit);
 
   RangeInit(&range, base, limit);
   res = arenaFreeLandInsertExtend(&oldRange, arena, &range);

mps/code/land.c

@@ -198,6 +198,7 @@ Res LandInsert(Range rangeReturn, Land land, Range range)
   AVERT(Land, land);
   AVERT(Range, range);
   AVER(RangeIsAligned(range, land->alignment));
+  AVER(!RangeIsEmpty(range));
   landEnter(land);
 
   res = (*land->class->insert)(rangeReturn, land, range);

mps/code/tract.c

@@ -174,6 +174,7 @@ Res ChunkInit(Chunk chunk, Arena arena, Addr base, Addr limit, Size reserved,
   Count pages;
   Shift pageShift;
   Size pageTableSize;
+  Addr allocBase;
   void *p;
   Res res;
 
@@ -219,12 +220,14 @@ Res ChunkInit(Chunk chunk, Arena arena, Addr base, Addr limit, Size reserved,
   /* Init allocTable after class init, because it might be mapped there. */
   BTResRange(chunk->allocTable, 0, pages);
 
+  /* Check that there is some usable address space remaining in the chunk. */
+  allocBase = PageIndexBase(chunk, chunk->allocBase);
+  AVER(allocBase < chunk->limit);
+
   /* Add the chunk's free address space to the arena's freeLand, so that
      we can allocate from it. */
   if (arena->hasFreeLand) {
-    res = ArenaFreeLandInsert(arena,
-                              PageIndexBase(chunk, chunk->allocBase),
-                              chunk->limit);
+    res = ArenaFreeLandInsert(arena, allocBase, chunk->limit);
     if (res != ResOK)
       goto failLandInsert;
   }