kernel/gcov/gcc_3_4.c: use struct_size() in kzalloc()

One of the more common cases of allocation size calculations is finding
the size of a structure that has a zero-sized array at the end, along
with memory for some number of elements for that array.  For example:

  struct foo {
      int stuff;
      void *entry[];
  };

  instance = kzalloc(sizeof(struct foo) + sizeof(void *) * count, GFP_KERNEL);

Instead of leaving these open-coded and prone to type mistakes, we can
now use the new struct_size() helper:

  instance = kzalloc(struct_size(instance, entry, count), GFP_KERNEL);

This code was detected with the help of Coccinelle.

Link: http://lkml.kernel.org/r/20190109172445.GA15908@embeddedorSigned-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Reviewed-by: Peter Oberparleiter <oberpar@linux.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/gcov/gcc_3_4.c

@@ -245,8 +245,7 @@ struct gcov_info *gcov_info_dup(struct gcov_info *info)
 
 	/* Duplicate gcov_info. */
 	active = num_counter_active(info);
-	dup = kzalloc(sizeof(struct gcov_info) +
-		      sizeof(struct gcov_ctr_info) * active, GFP_KERNEL);
+	dup = kzalloc(struct_size(dup, counts, active), GFP_KERNEL);
 	if (!dup)
 		return NULL;
 	dup->version		= info->version;
@@ -364,8 +363,7 @@ struct gcov_iterator *gcov_iter_new(struct gcov_info *info)
 {
 	struct gcov_iterator *iter;
 
-	iter = kzalloc(sizeof(struct gcov_iterator) +
-		       num_counter_active(info) * sizeof(struct type_info),
+	iter = kzalloc(struct_size(iter, type_info, num_counter_active(info)),
 		       GFP_KERNEL);
 	if (iter)
 		iter->info = info;