diff --git a/build_config.rb b/build_config.rb
index d379c7c..40f3b12 100644
--- a/build_config.rb
+++ b/build_config.rb
@@ -2,6 +2,7 @@ MRuby::CrossBuild.new ENV.fetch 'BUILD_NAME' do |conf|
   conf.toolchain :gcc
 
   conf.gem core: 'mruby-compiler'
+  conf.gem core: 'mruby-enumerator'
 
   conf.cc.flags      <<
     '-Wall'          <<
diff --git a/src/main.c b/src/main.c
index 429f9ba..71a70c6 100644
--- a/src/main.c
+++ b/src/main.c
@@ -40,6 +40,8 @@ void main(
     const uint32_t multiboot2_info_magic,
     const struct KernAux_Multiboot2_Info *const multiboot2_info
 ) {
+    kernaux_drivers_console_puts("========================================");
+
     kernaux_assert_cb = assert;
 
     ASSERT(multiboot2_info_magic == KERNAUX_MULTIBOOT2_INFO_MAGIC);
@@ -97,22 +99,41 @@ void assert(const char *const file, const int line, const char *const str)
 
 void *my_calloc(size_t nmemb, size_t size)
 {
-    return KernAux_Malloc_calloc(&allocator.malloc, nmemb, size);
+    void *const result = KernAux_Malloc_calloc(&allocator.malloc, nmemb, size);
+    if (result) {
+        kernaux_drivers_console_printf("calloc(%lu, %lu) = %p\n", nmemb, size, result);
+    } else if (nmemb * size != 0) {
+        kernaux_drivers_console_printf("!calloc(%lu, %lu)\n", nmemb, size);
+    }
+    return result;
 }
 
 void my_free(void *ptr)
 {
+    kernaux_drivers_console_printf("free(%p)\n", ptr);
     KernAux_Malloc_free(&allocator.malloc, ptr);
 }
 
 void *my_malloc(size_t size)
 {
-    return KernAux_Malloc_malloc(&allocator.malloc, size);
+    void *const result = KernAux_Malloc_malloc(&allocator.malloc, size);
+    if (result) {
+        kernaux_drivers_console_printf("malloc(%lu) = %p\n", size, result);
+    } else if (size != 0) {
+        kernaux_drivers_console_printf("!malloc(%lu)\n", size);
+    }
+    return result;
 }
 
 void *my_realloc(void *ptr, size_t size)
 {
-    return KernAux_Malloc_realloc(&allocator.malloc, ptr, size);
+    void *const result = KernAux_Malloc_realloc(&allocator.malloc, ptr, size);
+    if (result) {
+        kernaux_drivers_console_printf("realloc(%p, %lu) = %p\n", ptr, size, result);
+    } else if (size != 0) {
+        kernaux_drivers_console_printf("!realloc(%p, %lu)\n", ptr, size);
+    }
+    return result;
 }
 
 bool load_module(