[PATCH 2/2] pahole: Add --padding N to show only structs with N bytes of padding at its end

[Arnaldo Carvalho de Melo <acme@kernel.org>]

From: Arnaldo Carvalho de Melo <acme@redhat.com>

Example usage:

  $ pahole --padding 4 --with_flexible_array
  <SNIP>
  struct netprio_map {
          struct callback_head       rcu;                  /*     0    16 */
          u32                        priomap_len;          /*    16     4 */
          u32                        priomap[];            /*    20     0 */

          /* size: 24, cachelines: 1, members: 3 */
          /* padding: 4 */
          /* last cacheline: 24 bytes */
  };
  <SNIP>

Cc: "Gustavo A. R. Silva" <gustavoars@kernel.org>
Cc: Willy Tarreau <w@1wt.eu>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
 man-pages/pahole.1 | 4 ++++
 pahole.c           | 7 ++++++-
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/man-pages/pahole.1 b/man-pages/pahole.1
index 840f8e13807ba1be..b3e6632bdbf6b561 100644
--- a/man-pages/pahole.1
+++ b/man-pages/pahole.1
@@ -223,6 +223,10 @@ Find pointers to CLASS_NAME.
 .B \-H, \-\-holes=NR_HOLES
 Show only structs with at least NR_HOLES holes.
 
+.TP
+.B \-\-padding=SIZE_PADDING
+Show only structs with SIZE_PADDING bytes of padding at its end.
+
 .TP
 .B \-\-padding_ge=SIZE_PADDING
 Show only structs with at least SIZE_PADDING bytes of padding at its end.
diff --git a/pahole.c b/pahole.c
index 56b0ca0c55993100..780f0c4eacfe2ee8 100644
--- a/pahole.c
+++ b/pahole.c
@@ -60,6 +60,7 @@ static char *decl_exclude_prefix;
 static size_t decl_exclude_prefix_len;
 
 static uint16_t nr_holes;
+static uint16_t end_padding;
 static uint16_t end_padding_ge;
 static uint16_t nr_bit_holes;
 static uint16_t hole_size_ge;
@@ -825,7 +826,8 @@ static struct class *class__filter(struct class *class, struct cu *cu,
 	 * that need finding holes, like --packable, --nr_holes, etc
 	 */
 	if (!tag__is_struct(tag))
-		return (just_structs || show_packable || nr_holes || nr_bit_holes || hole_size_ge || end_padding_ge) ? NULL : class;
+		return (just_structs || show_packable || nr_holes || nr_bit_holes || hole_size_ge ||
+			end_padding_ge || end_padding) ? NULL : class;
 
 	if (tag->top_level)
 		class__find_holes(class);
@@ -833,6 +835,7 @@ static struct class *class__filter(struct class *class, struct cu *cu,
 	if (class->nr_holes < nr_holes ||
 	    class->padding < end_padding_ge ||
 	    class->nr_bit_holes < nr_bit_holes ||
+	    (end_padding != 0 && class->padding != end_padding) ||
 	    (hole_size_ge != 0 && !class__has_hole_ge(class, hole_size_ge)))
 		return NULL;
 
@@ -1242,6 +1245,7 @@ ARGP_PROGRAM_VERSION_HOOK_DEF = dwarves_print_version;
 #define ARGP_reproducible_build 345
 #define ARGP_running_kernel_vmlinux 346
 #define ARG_PADDING_GE		   347
+#define ARG_PADDING		   348
 
 /* --btf_features=feature1[,feature2,..] allows us to specify
  * a list of requested BTF features or "default" to enable all default
@@ -1894,6 +1898,7 @@ static error_t pahole__options_parser(int key, char *arg,
 		  class_name = arg;			break;
 	case 'F': conf_load.format_path = arg;		break;
 	case 'H': nr_holes = atoi(arg);			break;
+	case ARG_PADDING: end_padding = atoi(arg);	break;
 	case ARG_PADDING_GE: end_padding_ge = atoi(arg); break;
 	case 'I': conf.show_decl_info = 1;
 		  conf_load.extra_dbg_info = 1;		break;
-- 
2.46.0