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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>
This commit is contained in:
Arnaldo Carvalho de Melo 2019-04-15 13:55:34 -03:00
parent 49c27bdd66
commit 986a3b58a8
1 changed files with 5 additions and 1 deletions
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6
dwarves_fprintf.c
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@ -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);