fprintf: Print number of holes in class member types

In addition to paddings, a hole/unused space at the end, inform about
holes in the middle of the structs of non-pointer members.

For instance, for 'struct task_struct' in the Linux kernel we get this
extra info:

  --- task_struct.before.c	2024-02-09 11:38:39.249638750 -0300
  +++ task_struct.after.c	2024-02-09 16:19:34.221134835 -0300
  @@ -29,6 +29,9 @@

   	/* --- cacheline 2 boundary (128 bytes) --- */
   	struct sched_entity        se;                   /*   128   256 */
  +
  +	/* XXX last struct has 3 holes */
  +
   	/* --- cacheline 6 boundary (384 bytes) --- */
   	struct sched_rt_entity     rt;                   /*   384    48 */
   	struct sched_dl_entity     dl;                   /*   432   224 */
  @@ -100,6 +103,9 @@
   	/* --- cacheline 35 boundary (2240 bytes) was 16 bytes ago --- */
   	struct list_head           tasks;                /*  2256    16 */
   	struct plist_node          pushable_tasks;       /*  2272    40 */
  +
  +	/* XXX last struct has 1 hole */
  +
   	/* --- cacheline 36 boundary (2304 bytes) was 8 bytes ago --- */
   	struct rb_node             pushable_dl_tasks;    /*  2312    24 */
   	struct mm_struct *         mm;                   /*  2336     8 */
  @@ -172,6 +178,9 @@
   	/* XXX last struct has 4 bytes of padding */

   	struct vtime               vtime;                /*  2744    48 */
  +
  +	/* XXX last struct has 1 hole */
  +
   	/* --- cacheline 43 boundary (2752 bytes) was 40 bytes ago --- */
   	atomic_t                   tick_dep_mask;        /*  2792     4 */

  @@ -396,9 +405,12 @@
   	/* --- cacheline 145 boundary (9280 bytes) --- */
   	struct thread_struct       thread __attribute__((__aligned__(64))); /*  9280  4416 */

  +	/* XXX last struct has 1 hole */
  +
   	/* size: 13696, cachelines: 214, members: 262 */
   	/* sum members: 13518, holes: 21, sum holes: 162 */
   	/* sum bitfield members: 82 bits, bit holes: 2, sum bit holes: 46 bits */
  +	/* member types with holes: 4, total of those holes: 6 */
   	/* paddings: 6, sum paddings: 49 */
   	/* forced alignments: 2, forced holes: 2, sum forced holes: 88 */
   };

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

1 files changed, 20 insertions, 1 deletions

diff --git a/dwarves_fprintf.c b/dwarves_fprintf.c
index 6ba0e9fc..1169d359 100644
--- a/dwarves_fprintf.c
+++ b/dwarves_fprintf.c
@@ -1464,6 +1464,8 @@ out:
 
 struct member_types_holes {
 	uint16_t nr_paddings;
+	uint16_t nr_with_holes;
+	uint16_t total_nr_holes;
 	uint32_t sum_paddings;
 };
 
@@ -1473,6 +1475,8 @@ static size_t class__fprintf_member_type_holes(struct class *class, const struct
 {
 	size_t printed = 0;
 	uint16_t padding;
+	uint8_t nr_holes;
+	bool first = true;
 	/*
 	 * We may not yet have looked for holes and paddings in this member's
 	 * struct type.
@@ -1481,7 +1485,9 @@ static size_t class__fprintf_member_type_holes(struct class *class, const struct
 	class__infer_packed_attributes(class, cu);
 
 	padding = class->padding;
-	if (!padding)
+	nr_holes = class->nr_holes;
+
+	if (!padding && !nr_holes)
 		return 0;
 
 	if (!(*newline)++) {
@@ -1496,6 +1502,14 @@ static size_t class__fprintf_member_type_holes(struct class *class, const struct
 		holes->sum_paddings += padding;
 
 		printed += fprintf(fp, " %d byte%s of padding", padding, padding != 1 ? "s" : "");
+		first = false;
+	}
+
+	if (nr_holes) {
+		++holes->nr_with_holes;
+		holes->total_nr_holes += nr_holes;
+
+		printed += fprintf(fp, "%s %d hole%s", first ? "" : ",", nr_holes, nr_holes != 1 ? "s" : "");
 	}
 
 	return printed + fprintf(fp, " */");
@@ -1859,6 +1873,11 @@ static size_t __class__fprintf(struct class *class, const struct cu *cu,
 		printed += fprintf(fp, "%.*s/* padding: %u */\n",
 				   cconf.indent,
 				   tabs, class->padding);
+	if (member_types_holes.nr_with_holes > 0) {
+		printed += fprintf(fp, "%.*s/* member types with holes: %u, total of those holes: %u */\n",
+				   cconf.indent, tabs,
+				   member_types_holes.nr_with_holes, member_types_holes.total_nr_holes);
+	}
 	if (member_types_holes.nr_paddings > 0)
 		printed += fprintf(fp, "%.*s/* paddings: %u, sum paddings: "
 				   "%u */\n",