[PATCH v3] c: Extend the -Wpadded message with actual padding size

gcc/ChangeLog:

	* stor-layout.cc (finalize_record_size): Extend warning message.

gcc/testsuite/ChangeLog:

	* c-c++-common/Wpadded.c: New test.

diff --git a/gcc/stor-layout.cc b/gcc/stor-layout.cc
index 765f22f68b9fea9f695764625bc6419b8825d29d..88923c4136bf2b95f86c4452e175d79b10228809 100644 (file)
--- a/gcc/stor-layout.cc
+++ b/gcc/stor-layout.cc
@@ -1781,7 +1781,12 @@ finalize_record_size (record_layout_info rli)
       && simple_cst_equal (unpadded_size, TYPE_SIZE (rli->t)) == 0
       && input_location != BUILTINS_LOCATION
       && !TYPE_ARTIFICIAL (rli->t))
-    warning (OPT_Wpadded, "padding struct size to alignment boundary");
+  {
+       tree pad_size
+         = size_binop (MINUS_EXPR, TYPE_SIZE_UNIT (rli->t), unpadded_size_unit);
+         warning (OPT_Wpadded,
+               "padding struct size to alignment boundary with %E bytes", pad_size);
+  }
 
   if (warn_packed && TREE_CODE (rli->t) == RECORD_TYPE
       && TYPE_PACKED (rli->t) && ! rli->packed_maybe_necessary

diff --git a/gcc/testsuite/c-c++-common/Wpadded.c b/gcc/testsuite/c-c++-common/Wpadded.c
new file mode 100644 (file)
index 0000000..c5be468
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/Wpadded.c
@@ -0,0 +1,14 @@
+/* { dg-do compile } */
+/* { dg-options "-Wpadded" } */
+
+/*
+ * The struct is on single line, because C++ compiler emits the -Wpadded
+ * warning at the first line of the struct definition, while the C compiler at
+ * the last line. This way the test passes on both.
+ *
+ * Attribute aligned is needed for the test to pass on targets where
+ * the default behaviour is to pack the struct and also on targets that align
+ * 4 byte fields to 2 byte boundary.
+ */
+struct S { __UINT32_TYPE__ i; char c; } __attribute__((aligned(4))); /* { dg-warning "padding struct size to alignment boundary with 3 bytes" } */
+