Add tests to check "freed memory fill" behaviour in debug mode

test/test-api.c

@@ -79,6 +79,7 @@ bool test_stl_allocator2(void);
 bool check_zero_init(uint8_t* p, size_t size);
 #if MI_DEBUG >= 2
 bool check_debug_fill_uninit(uint8_t* p, size_t size);
+bool check_debug_fill_freed(uint8_t* p, size_t size);
 #endif
 
 // ---------------------------------------------------------------------------
@@ -352,6 +353,22 @@ int main(void) {
     result &= check_debug_fill_uninit(p, malloc_size);
     mi_free(p);
   });
+
+
+  CHECK_BODY("fill-freed-small", {
+    size_t malloc_size = MI_SMALL_SIZE_MAX / 2;
+    uint8_t* p = (uint8_t*)mi_malloc(malloc_size);
+    mi_free(p);
+    // First sizeof(void*) bytes will contain housekeeping data, skip these
+    result = check_debug_fill_freed(p + sizeof(void*), malloc_size - sizeof(void*));
+  });
+  CHECK_BODY("fill-freed-large", {
+    size_t malloc_size = MI_SMALL_SIZE_MAX * 2;
+    uint8_t* p = (uint8_t*)mi_malloc(malloc_size);
+    mi_free(p);
+    // First sizeof(void*) bytes will contain housekeeping data, skip these
+    result = check_debug_fill_freed(p + sizeof(void*), malloc_size - sizeof(void*));
+  });
 #endif
 
 
@@ -554,4 +571,15 @@ bool check_debug_fill_uninit(uint8_t* p, size_t size) {
   }
   return result;
 }
+
+bool check_debug_fill_freed(uint8_t* p, size_t size) {
+  if(!p)
+    return false;
+
+  bool result = true;
+  for (size_t i = 0; i < size; ++i) {
+    result &= p[i] == MI_DEBUG_FREED;
+  }
+  return result;
+}
 #endif