libtraceevent: Add __rel_loc relative location attribute support

Add '__rel_loc' new dynamic data location attribute which encodes
the data location from the next to the field itself. This is similar
to the '__data_loc' but the location offset is not from the event
entry but from the next of the field.

This patch adds '__rel_loc' decoding support in the libtraceevent.

Link: https://lkml.kernel.org/r/163757343994.510314.13241077597729303802.stgit@devnote2

Cc: Beau Belgrave <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Cc: Tom Zanussi <[e-mail]>
Signed-off-by: Masami Hiramatsu <[e-mail]>
Signed-off-by: Steven Rostedt (VMware) <[e-mail]>

tools/lib/traceevent/event-parse.c

···
 	return 0;
 }
 
+static int field_is_relative_dynamic(struct tep_format_field *field)
+{
+	if (strncmp(field->type, "__rel_loc", 9) == 0)
+		return 1;
+
+	return 0;
+}
+
 static int field_is_long(struct tep_format_field *field)
 {
 	/* includes long long */
···
 			field->flags |= TEP_FIELD_IS_STRING;
 		if (field_is_dynamic(field))
 			field->flags |= TEP_FIELD_IS_DYNAMIC;
+		if (field_is_relative_dynamic(field))
+			field->flags |= TEP_FIELD_IS_DYNAMIC | TEP_FIELD_IS_RELATIVE;
 		if (field_is_long(field))
 			field->flags |= TEP_FIELD_IS_LONG;
 
···
 
 	arg->type = TEP_PRINT_STRING;
 	arg->string.string = token;
-	arg->string.offset = -1;
+	arg->string.field = NULL;
 
 	if (read_expected(TEP_EVENT_DELIM, ")") < 0)
 		goto out_err;
···
 
 	arg->type = TEP_PRINT_BITMASK;
 	arg->bitmask.bitmask = token;
-	arg->bitmask.offset = -1;
+	arg->bitmask.field = NULL;
 
 	if (read_expected(TEP_EVENT_DELIM, ")") < 0)
 		goto out_err;
···
 		free_token(token);
 		return process_int_array(event, arg, tok);
 	}
-	if (strcmp(token, "__get_str") == 0) {
+	if (strcmp(token, "__get_str") == 0 ||
+	    strcmp(token, "__get_rel_str") == 0) {
 		free_token(token);
 		return process_str(event, arg, tok);
 	}
-	if (strcmp(token, "__get_bitmask") == 0) {
+	if (strcmp(token, "__get_bitmask") == 0 ||
+	    strcmp(token, "__get_rel_bitmask") == 0) {
 		free_token(token);
 		return process_bitmask(event, arg, tok);
 	}
-	if (strcmp(token, "__get_dynamic_array") == 0) {
+	if (strcmp(token, "__get_dynamic_array") == 0 ||
+	    strcmp(token, "__get_rel_dynamic_array") == 0) {
 		free_token(token);
 		return process_dynamic_array(event, arg, tok);
 	}
-	if (strcmp(token, "__get_dynamic_array_len") == 0) {
+	if (strcmp(token, "__get_dynamic_array_len") == 0 ||
+	    strcmp(token, "__get_rel_dynamic_array_len") == 0) {
 		free_token(token);
 		return process_dynamic_array_len(event, arg, tok);
 	}
···
 	case TEP_PRINT_STRING: {
 		int str_offset;
 
-		if (arg->string.offset == -1) {
-			struct tep_format_field *f;
+		if (!arg->string.field)
+			arg->string.field = tep_find_any_field(event, arg->string.string);
+		if (!arg->string.field)
+			break;
 
-			f = tep_find_any_field(event, arg->string.string);
-			arg->string.offset = f->offset;
-		}
-		str_offset = data2host4(tep, *(unsigned int *)(data + arg->string.offset));
+		str_offset = data2host4(tep,
+				*(unsigned int *)(data + arg->string.field->offset));
 		str_offset &= 0xffff;
+		if (arg->string.field->flags & TEP_FIELD_IS_RELATIVE)
+			str_offset += arg->string.field->offset + arg->string.field->size;
 		print_str_to_seq(s, format, len_arg, ((char *)data) + str_offset);
 		break;
 	}
···
 		int bitmask_offset;
 		int bitmask_size;
 
-		if (arg->bitmask.offset == -1) {
-			struct tep_format_field *f;
-
-			f = tep_find_any_field(event, arg->bitmask.bitmask);
-			arg->bitmask.offset = f->offset;
-		}
-		bitmask_offset = data2host4(tep, *(unsigned int *)(data + arg->bitmask.offset));
+		if (!arg->bitmask.field)
+			arg->bitmask.field = tep_find_any_field(event, arg->bitmask.bitmask);
+		if (!arg->bitmask.field)
+			break;
+		bitmask_offset = data2host4(tep,
+				*(unsigned int *)(data + arg->bitmask.field->offset));
 		bitmask_size = bitmask_offset >> 16;
 		bitmask_offset &= 0xffff;
+		if (arg->bitmask.field->flags & TEP_FIELD_IS_RELATIVE)
+			bitmask_offset += arg->bitmask.field->offset + arg->bitmask.field->size;
 		print_bitmask_to_seq(tep, s, format, len_arg,
 				     data + bitmask_offset, bitmask_size);
 		break;
···
 			offset = val;
 			len = offset >> 16;
 			offset &= 0xffff;
+			if (field->flags & TEP_FIELD_IS_RELATIVE)
+				offset += field->offset + field->size;
 		}
 		if (field->flags & TEP_FIELD_IS_STRING &&
 		    is_printable_array(data + offset, len)) {
···
 					 data + offset, field->size);
 		*len = offset >> 16;
 		offset &= 0xffff;
+		if (field->flags & TEP_FIELD_IS_RELATIVE)
+			offset += field->offset + field->size;
 	} else
 		*len = field->size;
 

tools/lib/traceevent/event-parse.h

···
 	TEP_FIELD_IS_LONG	= 32,
 	TEP_FIELD_IS_FLAG	= 64,
 	TEP_FIELD_IS_SYMBOLIC	= 128,
+	TEP_FIELD_IS_RELATIVE	= 256,
 };
 
 struct tep_format_field {
···
 
 struct tep_print_arg_string {
 	char			*string;
-	int			offset;
+	struct tep_format_field *field;
 };
 
 struct tep_print_arg_bitmask {
 	char			*bitmask;
-	int			offset;
+	struct tep_format_field *field;
 };
 
 struct tep_print_arg_field {

tools/lib/traceevent/parse-filter.c

···
 
 		if (arg->str.field->flags & TEP_FIELD_IS_DYNAMIC) {
 			addr = *(unsigned int *)val;
-			val = record->data + (addr & 0xffff);
 			size = addr >> 16;
+			addr &= 0xffff;
+			if (arg->str.field->flags & TEP_FIELD_IS_RELATIVE)
+				addr += arg->str.field->offset + arg->str.field->size;
+			val = record->data + addr;
 		}
 
 		/*