Avoid calling Standard C string/array functions with NULL arguments

glibc string.h declares memcpy() with attribute(nonnull(1,2)), causing
calls with NULL arguments to be treated as undefined behaviour.
This is consistent with ISO C99 and C11, which state that passing 0
to string functions as an array length does not remove the requirement
that the pointer to the array is a valid pointer.
gcc -fsanitize=undefined catches this while running OSTree's test suite.

Similarly, running the GLib test suite reports similar issues for
qsort(), memmove(), memcmp().

Signed-off-by: Simon McVittie <smcv@debian.org>
Bug: https://bugzilla.gnome.org/show_bug.cgi?id=775510
Reviewed-by: Colin Walters

gio/gconverterinputstream.c

@@ -262,7 +262,9 @@ buffer_read (Buffer *buffer,
 	     char *dest,
 	     gsize count)
 {
-  memcpy (dest, buffer->data + buffer->start, count);
+  if (count != 0)
+    memcpy (dest, buffer->data + buffer->start, count);
+
   buffer_consumed (buffer, count);
 }
 
@@ -293,9 +295,11 @@ grow_buffer (Buffer *buffer)
   data = g_malloc (size);
   in_buffer = buffer_data_size (buffer);
 
-  memcpy (data,
+  if (in_buffer != 0)
-	  buffer->data + buffer->start,
+    memcpy (data,
-	  in_buffer);
+            buffer->data + buffer->start,
+            in_buffer);
+
   g_free (buffer->data);
   buffer->data = data;
   buffer->end -= buffer->start;

gio/gconverteroutputstream.c

@@ -300,9 +300,11 @@ grow_buffer (Buffer *buffer)
   data = g_malloc (size);
   in_buffer = buffer_data_size (buffer);
 
-  memcpy (data,
+  if (in_buffer != 0)
-	  buffer->data + buffer->start,
+    memcpy (data,
-	  in_buffer);
+            buffer->data + buffer->start,
+            in_buffer);
+
   g_free (buffer->data);
   buffer->data = data;
   buffer->end -= buffer->start;

gio/gdesktopappinfo.c

@@ -506,7 +506,8 @@ add_token_result (const gchar *app_name,
 static void
 merge_token_results (gboolean first)
 {
-  qsort (static_token_results, static_token_results_size, sizeof (struct search_result), compare_results);
+  if (static_token_results_size != 0)
+    qsort (static_token_results, static_token_results_size, sizeof (struct search_result), compare_results);
 
   /* If this is the first token then we are basically merging a list with
    * itself -- we only perform de-duplication.
@@ -606,7 +607,8 @@ reset_total_search_results (void)
 static void
 sort_total_search_results (void)
 {
-  qsort (static_total_results, static_total_results_size, sizeof (struct search_result), compare_categories);
+  if (static_total_results_size != 0)
+    qsort (static_total_results, static_total_results_size, sizeof (struct search_result), compare_categories);
 }
 
 static void
@@ -620,9 +622,10 @@ merge_directory_results (void)
       static_total_results = g_renew (struct search_result, static_total_results, static_total_results_allocated);
     }
 
-  memcpy (static_total_results + static_total_results_size,
+  if (static_total_results + static_total_results_size != 0)
-          static_search_results,
+    memcpy (static_total_results + static_total_results_size,
-          static_search_results_size * sizeof (struct search_result));
+            static_search_results,
+            static_search_results_size * sizeof (struct search_result));
 
   static_total_results_size += static_search_results_size;
 

gio/gunixsocketaddress.c

@@ -116,7 +116,9 @@ g_unix_socket_address_set_property (GObject      *object,
 	  /* Clip to fit in UNIX_PATH_MAX with zero termination or first byte */
 	  len = MIN (array->len, UNIX_PATH_MAX-1);
 
-	  memcpy (address->priv->path, array->data, len);
+	  if (len != 0)
+	    memcpy (address->priv->path, array->data, len);
+
 	  address->priv->path[len] = 0; /* Ensure null-terminated */
 	  address->priv->path_len = len;
 	}

gio/gvdb/gvdb-builder.c

@@ -291,7 +291,8 @@ file_builder_add_string (FileBuilder *fb,
   chunk->offset = fb->offset;
   chunk->size = length;
   chunk->data = g_malloc (length);
-  memcpy (chunk->data, string, length);
+  if (length != 0)
+    memcpy (chunk->data, string, length);
 
   *start = guint32_to_le (fb->offset);
   *size = guint16_to_le (length);

glib/garray.c

@@ -415,6 +415,9 @@ g_array_append_vals (GArray       *farray,
 
   g_return_val_if_fail (array, NULL);
 
+  if (len == 0)
+    return farray;
+
   g_array_maybe_expand (array, len);
 
   memcpy (g_array_elt_pos (array, array->len), data, 
@@ -468,6 +471,9 @@ g_array_prepend_vals (GArray        *farray,
 
   g_return_val_if_fail (array, NULL);
 
+  if (len == 0)
+    return farray;
+
   g_array_maybe_expand (array, len);
 
   memmove (g_array_elt_pos (array, len), g_array_elt_pos (array, 0),
@@ -517,6 +523,9 @@ g_array_insert_vals (GArray        *farray,
 
   g_return_val_if_fail (array, NULL);
 
+  if (len == 0)
+    return farray;
+
   g_array_maybe_expand (array, len);
 
   memmove (g_array_elt_pos (array, len + index_),

glib/goption.c

@@ -2361,7 +2361,10 @@ g_option_group_add_entries (GOptionGroup       *group,
 
   group->entries = g_renew (GOptionEntry, group->entries, group->n_entries + n_entries);
 
-  memcpy (group->entries + group->n_entries, entries, sizeof (GOptionEntry) * n_entries);
+  /* group->entries could be NULL in the trivial case where we add no
+   * entries to no entries */
+  if (n_entries != 0)
+    memcpy (group->entries + group->n_entries, entries, sizeof (GOptionEntry) * n_entries);
 
   for (i = group->n_entries; i < group->n_entries + n_entries; i++)
     {

glib/gstrfuncs.c

@@ -386,7 +386,7 @@ g_memdup (gconstpointer mem,
 {
   gpointer new_mem;
 
-  if (mem)
+  if (mem && byte_size != 0)
     {
       new_mem = g_malloc (byte_size);
       memcpy (new_mem, mem, byte_size);

glib/gtestutils.h

@@ -74,7 +74,7 @@ typedef void (*GTestFixtureFunc) (gpointer      fixture,
                                              if (__l1 != __l2) \
                                                g_assertion_message_cmpnum (G_LOG_DOMAIN, __FILE__, __LINE__, G_STRFUNC, \
                                                                            #l1 " (len(" #m1 ")) == " #l2 " (len(" #m2 "))", __l1, "==", __l2, 'i'); \
-                                             else if (memcmp (__m1, __m2, __l1) != 0) \
+                                             else if (__l1 != 0 && memcmp (__m1, __m2, __l1) != 0) \
                                                g_assertion_message (G_LOG_DOMAIN, __FILE__, __LINE__, G_STRFUNC, \
                                                                     "assertion failed (" #m1 " == " #m2 ")"); \
                                         } G_STMT_END

gobject/gtype.c

@@ -3550,7 +3550,8 @@ g_type_children (GType  type,
       
       G_READ_LOCK (&type_rw_lock);	/* ->children is relocatable */
       children = g_new (GType, node->n_children + 1);
-      memcpy (children, node->children, sizeof (GType) * node->n_children);
+      if (node->n_children != 0)
+        memcpy (children, node->children, sizeof (GType) * node->n_children);
       children[node->n_children] = 0;
       
       if (n_children)