Minor cleanup

include/ucore/slot_allocator.h

@@ -5,9 +5,10 @@
 #include <assert.h>
 
 //Free memory is reused to build a linked list of slots
-typedef struct UCSlot UCSlot;
-struct UCSlot {
-    UCSlot *next;
+typedef union  UCSlot  UCSlot;
+union UCSlot {
+    UCSlot *next;       // next free block (when not allocated)
+    uint8_t data[0];   // data when allocated
 };
 
 typedef struct UCSlotArena UCSlotArena;
@@ -71,7 +72,7 @@ static inline void *uc_slot_alloc(UCSlotArena *arena)
 #endif
     }
 
-    return slot;
+    return &slot->data[0];
 }
 /**
  * Free a slot.
@@ -84,7 +85,7 @@ static inline void uc_slot_free(UCSlotArena *arena, void *memory)
 #ifdef DEBUG
         for (const UCSlot *slot = arena->free_list ; slot = slot->next) {
             if (slot == mem) {
-                assert("Double free detected");
+                assert(0 && "Double free detected");
             }
         }
 #endif