fprintf: Allow suppressing the inferred __attribute__((__packed__))

We use things like DW_AT_alignment, so not all of those attributes are
inferred by formats like BTF that lack that info, allow suppressing the
output and make btfdiff ask for both DWARF and BTF output to have this
suppressed.

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

btfdiff

@@ -20,8 +20,11 @@ ${pahole_bin} -F dwarf \
 	      --flat_arrays \
 	      --suppress_aligned_attribute \
 	      --suppress_force_paddings \
+	      --suppress_packed \
 	      --show_private_classes $file > $dwarf_output
-${pahole_bin} -F btf $file > $btf_output
+${pahole_bin} -F btf \
+	      --suppress_packed \
+	      $file > $btf_output
 
 diff -up $dwarf_output $btf_output
 

dwarves.h

@@ -79,6 +79,7 @@ struct conf_fprintf {
 	uint8_t	   suppress_aligned_attribute:1;
 	uint8_t	   suppress_offset_comment:1;
 	uint8_t	   suppress_force_paddings:1;
+	uint8_t	   suppress_packed:1;
 	uint8_t	   show_decl_info:1;
 	uint8_t	   show_only_data_members:1;
 	uint8_t	   no_semicolon:1;

dwarves_fprintf.c

@@ -825,7 +825,7 @@ static size_t class_member__fprintf(struct class_member *member, bool union_memb
 			int slen = cm_name ? (int)strlen(cm_name) : -1;
 			int size_spacing = 5;
 
-			if (tag__is_struct(type) && tag__class(type)->is_packed) {
+			if (tag__is_struct(type) && tag__class(type)->is_packed && !conf->suppress_packed) {
 				int packed_len = sizeof("__attribute__((__packed__))");
 				slen += packed_len;
 			}
@@ -1697,7 +1697,7 @@ static size_t __class__fprintf(struct class *class, const struct cu *cu,
 out:
 	printed += fprintf(fp, "%.*s}", indent, tabs);
 
-	if (class->is_packed)
+	if (class->is_packed && !conf->suppress_packed)
 		printed += fprintf(fp, " __attribute__((__packed__))");
 
 	if (cconf.suffix)

man-pages/pahole.1

@@ -182,6 +182,14 @@ Suppress bitfield forced padding at the end of structs, as this requires
 something like DWARF's DW_AT_alignment, so that one can compare BTF or CTF
 output, that don't have that info.
 
+.TP
+.B     \-\-suppress_packed
+
+Suppress the output of the inference of __attribute__((__packed__)), so that
+one can compare BTF or CTF output, the inference algorithm uses things like
+DW_AT_alignment, so until it is improved to infer that as well for BTF, allow
+disabling this output.
+
 .TP
 .B     \-\-fixup_silly_bitfields
 Converts silly bitfields such as "int foo:32" to plain "int foo".

pahole.c

@@ -753,6 +753,7 @@ ARGP_PROGRAM_VERSION_HOOK_DEF = dwarves_print_version;
 #define ARGP_hex_fmt		   305
 #define ARGP_suppress_aligned_attribute	306
 #define ARGP_suppress_force_paddings	307
+#define ARGP_suppress_packed	   308
 
 static const struct argp_option pahole__options[] = {
 	{
@@ -960,6 +961,11 @@ static const struct argp_option pahole__options[] = {
 		.key  = ARGP_suppress_force_paddings,
 		.doc  = "Suppress int :N paddings at the end",
 	},
+	{
+		.name = "suppress_packed",
+		.key  = ARGP_suppress_packed,
+		.doc  = "Suppress output of inferred __attribute__((__packed__))",
+	},
 	{
 		.name = "show_private_classes",
 		.key  = ARGP_show_private_classes,
@@ -1064,6 +1070,8 @@ static error_t pahole__options_parser(int key, char *arg,
 		conf.suppress_aligned_attribute = 1;	break;
 	case ARGP_suppress_force_paddings:
 		conf.suppress_force_paddings = 1;	break;
+	case ARGP_suppress_packed:
+		conf.suppress_packed = 1;		break;
 	case ARGP_show_private_classes:
 		show_private_classes = true;
 		conf.show_only_data_members = 1;	break;