pahole: Introduce --flat_array

CTF doesn't have support for multiple array dimensions, so it flattens
the arrays.

This caused a large number of false positives in ctfdwdiff, so introduce
this conf_fprintf option, use it in pahole and ctfdwdiff.

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

ctfdwdiff

@@ -6,8 +6,8 @@ ctf=/tmp/$obj.ctf.c
 dwarf=/tmp/$obj.dwarf.c
 pahole -Z $obj
 pahole -F ctf $obj > $ctf
-pahole -F dwarf $obj > $dwarf
-diff -u $ctf $dwarf > $diff
+pahole --flat_arrays -F dwarf $obj > $dwarf
+diff -up $ctf $dwarf > $diff
 if [ -s $diff ] ; then
 	# vim /tmp/$obj.diff
 	exit 0

dwarves.c

@@ -273,14 +273,26 @@ static size_t array_type__fprintf(const struct tag *tag_self,
 	struct array_type *self = tag__array_type(tag_self);
 	struct tag *type = cu__type(cu, tag_self->type);
 	size_t printed;
+	unsigned long long flat_dimensions = 0;
 	int i;
 
 	if (type == NULL)
 		return tag__id_not_found_fprintf(fp, tag_self->type);
 
 	printed = type__fprintf(type, cu, name, conf, fp);
-	for (i = 0; i < self->dimensions; ++i)
-		printed += fprintf(fp, "[%u]", self->nr_entries[i]);
+	for (i = 0; i < self->dimensions; ++i) {
+		if (conf->flat_arrays) {
+			if (!flat_dimensions)
+				flat_dimensions = self->nr_entries[i];
+			else
+				flat_dimensions *= self->nr_entries[i];
+		} else
+			printed += fprintf(fp, "[%u]", self->nr_entries[i]);
+	}
+
+	if (conf->flat_arrays)
+		printed += fprintf(fp, "[%llu]", flat_dimensions);
+
 	return printed;
 }
 

dwarves.h

@@ -41,6 +41,10 @@ struct conf_load {
 	char			*format_path;
 };
 
+/** struct conf_fprintf - hints to the __fprintf routines
+ *
+ * @flat_arrays - a->foo[10][2] becomes a->foo[20]
+ */
 struct conf_fprintf {
 	const char *prefix;
 	const char *suffix;
@@ -58,6 +62,7 @@ struct conf_fprintf {
 	uint8_t	   show_only_data_members:1;
 	uint8_t	   no_semicolon:1;
 	uint8_t	   show_first_biggest_size_base_type_member:1;
+	uint8_t	   flat_arrays:1;
 };
 
 struct cus {

man-pages/pahole.1

@@ -159,6 +159,12 @@ Show how many times struct was defined.
 .B \-u, \-\-defined_in
 Show CUs where CLASS_NAME (-C) is defined.
 
+.TP
+.B     \-\-flat_arrays
+Flatten arrays, so that array[10][2] becomes array[20].
+Useful when generating from both CTF and DWARF encodings
+for the same binary for testing purposes.
+
 .TP
 .B \-V, \-\-verbose
 be verbose

pahole.c

@@ -703,6 +703,8 @@ static void print_containers(const struct cu *cu, uint16_t type, int ident)
 /* Name and version of program.  */
 ARGP_PROGRAM_VERSION_HOOK_DEF = dwarves_print_version;
 
+#define ARGP_flat_arrays     300
+
 static const struct argp_option pahole__options[] = {
 	{
 		.name = "bit_holes",
@@ -900,6 +902,11 @@ static const struct argp_option pahole__options[] = {
 		.key  = 'Z',
 		.doc  = "Encode as CTF",
 	},
+	{
+		.name = "flat_arrays",
+		.key  = ARGP_flat_arrays,
+		.doc  = "Flat arrays",
+	},
 	{
 		.name = NULL,
 	}
@@ -968,9 +975,8 @@ static error_t pahole__options_parser(int key, char *arg,
 		if (!global_verbose)
 			formatter = class_name_formatter;
 		break;
-	case 'Z':
-		ctf_encode = 1;
-		break;
+	case 'Z': ctf_encode = 1;			break;
+	case ARGP_flat_arrays: conf.flat_arrays = 1;	break;
 	default:
 		return ARGP_ERR_UNKNOWN;
 	}