From 986a3b58a86984e80a7fec5234a3a4d814139aa6 Mon Sep 17 00:00:00 2001
From: Arnaldo Carvalho de Melo <acme@redhat.com>
Date: Mon, 15 Apr 2019 13:55:34 -0300
Subject: [PATCH] fprintf: Only add bitfield forced paddings when alignment
 info available

I.e. BTF doesn't have DW_AT_alignment, so avoid emitting the bitfield
for padding at the end:

  $ pahole -F btf -C rseq examples/tcp.o
  struct rseq {
	  __u32                      cpu_id_start;         /*     0     4 */
	  __u32                      cpu_id;               /*     4     4 */
  	union {
  		__u64              ptr64;                /*     8     8 */
  		__u64              ptr;                  /*     8     8 */
  	} rseq_cs;                                       /*     8     8 */
  	__u32                      flags;                /*    16     4 */

  	/* Force padding: */
  	__u32                      :32;
  	__u32                      :32;
  	__u32                      :32;

  	/* size: 32, cachelines: 1, members: 4 */
  	/* padding: 12 */
  	/* last cacheline: 32 bytes */
  };
  $

After:

  $ pahole -F btf -C rseq examples/tcp.o
  struct rseq {
	__u32                      cpu_id_start;         /*     0     4 */
	__u32                      cpu_id;               /*     4     4 */
	union {
		__u64              ptr64;                /*     8     8 */
		__u64              ptr;                  /*     8     8 */
	} rseq_cs;                                       /*     8     8 */
	__u32                      flags;                /*    16     4 */

	/* size: 32, cachelines: 1, members: 4 */
	/* padding: 12 */
	/* last cacheline: 32 bytes */
  };
  $

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
 dwarves_fprintf.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/dwarves_fprintf.c b/dwarves_fprintf.c
index 34073d1..9d493ab 100644
--- a/dwarves_fprintf.c
+++ b/dwarves_fprintf.c
@@ -1596,7 +1596,11 @@ static size_t __class__fprintf(struct class *class, const struct cu *cu,
 		last = pos;
 	}
 
-	if (class->padding != 0 && type->alignment == 0) {
+	/*
+	 * BTF doesn't have alignment info, for now use this infor from the loader
+	 * to avoid adding the forced bitfield paddings and have btfdiff happy.
+	 */
+	if (class->padding != 0 && type->alignment == 0 && conf->has_alignment_info) {
 		tag_pos = cu__type(cu, last->tag.type);
 		size = tag__size(tag_pos, cu);