CTF grammar: = -> assignment-operator
[ctf.git] / common-trace-format-proposal.txt
1
2 RFC: Common Trace Format (CTF) Proposal (pre-v1.7)
3
4 Mathieu Desnoyers, EfficiOS Inc.
5
6 The goal of the present document is to propose a trace format that suits the
7 needs of the embedded, telecom, high-performance and kernel communities. It is
8 based on the Common Trace Format Requirements (v1.4) document. It is designed to
9 allow traces to be natively generated by the Linux kernel, Linux user-space
10 applications written in C/C++, and hardware components. One major element of
11 CTF is the Trace Stream Description Language (TSDL) which flexibility
12 enables description of various binary trace stream layouts.
13
14 The latest version of this document can be found at:
15
16 git tree: git://git.efficios.com/ctf.git
17 gitweb: http://git.efficios.com/?p=ctf.git
18
19 A reference implementation of a library to read and write this trace format is
20 being implemented within the BabelTrace project, a converter between trace
21 formats. The development tree is available at:
22
23 git tree: git://git.efficios.com/babeltrace.git
24 gitweb: http://git.efficios.com/?p=babeltrace.git
25
26
27 1. Preliminary definitions
28
29 - Event Trace: An ordered sequence of events.
30 - Event Stream: An ordered sequence of events, containing a subset of the
31 trace event types.
32 - Event Packet: A sequence of physically contiguous events within an event
33 stream.
34 - Event: This is the basic entry in a trace. (aka: a trace record).
35 - An event identifier (ID) relates to the class (a type) of event within
36 an event stream.
37 e.g. event: irq_entry.
38 - An event (or event record) relates to a specific instance of an event
39 class.
40 e.g. event: irq_entry, at time X, on CPU Y
41 - Source Architecture: Architecture writing the trace.
42 - Reader Architecture: Architecture reading the trace.
43
44
45 2. High-level representation of a trace
46
47 A trace is divided into multiple event streams. Each event stream contains a
48 subset of the trace event types.
49
50 The final output of the trace, after its generation and optional transport over
51 the network, is expected to be either on permanent or temporary storage in a
52 virtual file system. Because each event stream is appended to while a trace is
53 being recorded, each is associated with a separate file for output. Therefore,
54 a stored trace can be represented as a directory containing one file per stream.
55
56 Meta-data description associated with the trace contains information on
57 trace event types expressed in the Trace Stream Description Language
58 (TSDL). This language describes:
59
60 - Trace version.
61 - Types available.
62 - Per-trace event header description.
63 - Per-stream event header description.
64 - Per-stream event context description.
65 - Per-event
66 - Event type to stream mapping.
67 - Event type to name mapping.
68 - Event type to ID mapping.
69 - Event context description.
70 - Event fields description.
71
72
73 3. Event stream
74
75 An event stream can be divided into contiguous event packets of variable
76 size. These subdivisions have a variable size. An event packet can
77 contain a certain amount of padding at the end. The stream header is
78 repeated at the beginning of each event packet. The rationale for the
79 event stream design choices is explained in Appendix B. Stream Header
80 Rationale.
81
82 The event stream header will therefore be referred to as the "event packet
83 header" throughout the rest of this document.
84
85
86 4. Types
87
88 Types are organized as type classes. Each type class belong to either of two
89 kind of types: basic types or compound types.
90
91 4.1 Basic types
92
93 A basic type is a scalar type, as described in this section. It includes
94 integers, GNU/C bitfields, enumerations, and floating point values.
95
96 4.1.1 Type inheritance
97
98 Type specifications can be inherited to allow deriving types from a
99 type class. For example, see the uint32_t named type derived from the "integer"
100 type class below ("Integers" section). Types have a precise binary
101 representation in the trace. A type class has methods to read and write these
102 types, but must be derived into a type to be usable in an event field.
103
104 4.1.2 Alignment
105
106 We define "byte-packed" types as aligned on the byte size, namely 8-bit.
107 We define "bit-packed" types as following on the next bit, as defined by the
108 "Integers" section.
109
110 Each basic type must specify its alignment, in bits. Examples of
111 possible alignments are: bit-packed (align = 1), byte-packed (align =
112 8), or word-aligned (e.g. align = 32 or align = 64). The choice depends
113 on the architecture preference and compactness vs performance trade-offs
114 of the implementation. Architectures providing fast unaligned write
115 byte-packed basic types to save space, aligning each type on byte
116 boundaries (8-bit). Architectures with slow unaligned writes align types
117 on specific alignment values. If no specific alignment is declared for a
118 type, it is assumed to be bit-packed for integers with size not multiple
119 of 8 bits and for gcc bitfields. All other basic types are byte-packed
120 by default. It is however recommended to always specify the alignment
121 explicitly. Alignment values must be power of two. Compound types are
122 aligned as specified in their individual specification.
123
124 TSDL meta-data attribute representation of a specific alignment:
125
126 align = value; /* value in bits */
127
128 4.1.3 Byte order
129
130 By default, the native endianness of the source architecture the trace is used.
131 Byte order can be overridden for a basic type by specifying a "byte_order"
132 attribute. Typical use-case is to specify the network byte order (big endian:
133 "be") to save data captured from the network into the trace without conversion.
134 If not specified, the byte order is native.
135
136 TSDL meta-data representation:
137
138 byte_order = native OR network OR be OR le; /* network and be are aliases */
139
140 4.1.4 Size
141
142 Type size, in bits, for integers and floats is that returned by "sizeof()" in C
143 multiplied by CHAR_BIT.
144 We require the size of "char" and "unsigned char" types (CHAR_BIT) to be fixed
145 to 8 bits for cross-endianness compatibility.
146
147 TSDL meta-data representation:
148
149 size = value; (value is in bits)
150
151 4.1.5 Integers
152
153 Signed integers are represented in two-complement. Integer alignment,
154 size, signedness and byte ordering are defined in the TSDL meta-data.
155 Integers aligned on byte size (8-bit) and with length multiple of byte
156 size (8-bit) correspond to the C99 standard integers. In addition,
157 integers with alignment and/or size that are _not_ a multiple of the
158 byte size are permitted; these correspond to the C99 standard bitfields,
159 with the added specification that the CTF integer bitfields have a fixed
160 binary representation. A MIT-licensed reference implementation of the
161 CTF portable bitfields is available at:
162
163 http://git.efficios.com/?p=babeltrace.git;a=blob;f=include/babeltrace/bitfield.h
164
165 Binary representation of integers:
166
167 - On little and big endian:
168 - Within a byte, high bits correspond to an integer high bits, and low bits
169 correspond to low bits.
170 - On little endian:
171 - Integer across multiple bytes are placed from the less significant to the
172 most significant.
173 - Consecutive integers are placed from lower bits to higher bits (even within
174 a byte).
175 - On big endian:
176 - Integer across multiple bytes are placed from the most significant to the
177 less significant.
178 - Consecutive integers are placed from higher bits to lower bits (even within
179 a byte).
180
181 This binary representation is derived from the bitfield implementation in GCC
182 for little and big endian. However, contrary to what GCC does, integers can
183 cross units boundaries (no padding is required). Padding can be explicitly
184 added (see 4.1.6 GNU/C bitfields) to follow the GCC layout if needed.
185
186 TSDL meta-data representation:
187
188 integer {
189 signed = true OR false; /* default false */
190 byte_order = native OR network OR be OR le; /* default native */
191 size = value; /* value in bits, no default */
192 align = value; /* value in bits */
193 /* based used for pretty-printing output, default: decimal. */
194 base = decimal OR dec OR OR d OR i OR u OR 10 OR hexadecimal OR hex OR x OR X OR p OR 16
195 OR octal OR oct OR o OR 8 OR binary OR b OR 2;
196 /* character encoding, default: none */
197 encoding = none or UTF8 or ASCII;
198 }
199
200 Example of type inheritance (creation of a uint32_t named type):
201
202 typealias integer {
203 size = 32;
204 signed = false;
205 align = 32;
206 } := uint32_t;
207
208 Definition of a named 5-bit signed bitfield:
209
210 typealias integer {
211 size = 5;
212 signed = true;
213 align = 1;
214 } := int5_t;
215
216 The character encoding field can be used to specify that the integer
217 must be printed as a text character when read. e.g.:
218
219 typealias integer {
220 size = 8;
221 align = 8;
222 signed = false;
223 encoding = UTF8;
224 } := utf_char;
225
226
227 4.1.6 GNU/C bitfields
228
229 The GNU/C bitfields follow closely the integer representation, with a
230 particularity on alignment: if a bitfield cannot fit in the current unit, the
231 unit is padded and the bitfield starts at the following unit. The unit size is
232 defined by the size of the type "unit_type".
233
234 TSDL meta-data representation:
235
236 unit_type name:size;
237
238 As an example, the following structure declared in C compiled by GCC:
239
240 struct example {
241 short a:12;
242 short b:5;
243 };
244
245 The example structure is aligned on the largest element (short). The second
246 bitfield would be aligned on the next unit boundary, because it would not fit in
247 the current unit.
248
249 4.1.7 Floating point
250
251 The floating point values byte ordering is defined in the TSDL meta-data.
252
253 Floating point values follow the IEEE 754-2008 standard interchange formats.
254 Description of the floating point values include the exponent and mantissa size
255 in bits. Some requirements are imposed on the floating point values:
256
257 - FLT_RADIX must be 2.
258 - mant_dig is the number of digits represented in the mantissa. It is specified
259 by the ISO C99 standard, section 5.2.4, as FLT_MANT_DIG, DBL_MANT_DIG and
260 LDBL_MANT_DIG as defined by <float.h>.
261 - exp_dig is the number of digits represented in the exponent. Given that
262 mant_dig is one bit more than its actual size in bits (leading 1 is not
263 needed) and also given that the sign bit always takes one bit, exp_dig can be
264 specified as:
265
266 - sizeof(float) * CHAR_BIT - FLT_MANT_DIG
267 - sizeof(double) * CHAR_BIT - DBL_MANT_DIG
268 - sizeof(long double) * CHAR_BIT - LDBL_MANT_DIG
269
270 TSDL meta-data representation:
271
272 floating_point {
273 exp_dig = value;
274 mant_dig = value;
275 byte_order = native OR network OR be OR le;
276 align = value;
277 }
278
279 Example of type inheritance:
280
281 typealias floating_point {
282 exp_dig = 8; /* sizeof(float) * CHAR_BIT - FLT_MANT_DIG */
283 mant_dig = 24; /* FLT_MANT_DIG */
284 byte_order = native;
285 align = 32;
286 } := float;
287
288 TODO: define NaN, +inf, -inf behavior.
289
290 Bit-packed, byte-packed or larger alignments can be used for floating
291 point values, similarly to integers.
292
293 4.1.8 Enumerations
294
295 Enumerations are a mapping between an integer type and a table of strings. The
296 numerical representation of the enumeration follows the integer type specified
297 by the meta-data. The enumeration mapping table is detailed in the enumeration
298 description within the meta-data. The mapping table maps inclusive value
299 ranges (or single values) to strings. Instead of being limited to simple
300 "value -> string" mappings, these enumerations map
301 "[ start_value ... end_value ] -> string", which map inclusive ranges of
302 values to strings. An enumeration from the C language can be represented in
303 this format by having the same start_value and end_value for each element, which
304 is in fact a range of size 1. This single-value range is supported without
305 repeating the start and end values with the value = string declaration.
306
307 enum name : integer_type {
308 somestring = start_value1 ... end_value1,
309 "other string" = start_value2 ... end_value2,
310 yet_another_string, /* will be assigned to end_value2 + 1 */
311 "some other string" = value,
312 ...
313 };
314
315 If the values are omitted, the enumeration starts at 0 and increment of 1 for
316 each entry:
317
318 enum name : unsigned int {
319 ZERO,
320 ONE,
321 TWO,
322 TEN = 10,
323 ELEVEN,
324 };
325
326 Overlapping ranges within a single enumeration are implementation defined.
327
328 A nameless enumeration can be declared as a field type or as part of a typedef:
329
330 enum : integer_type {
331 ...
332 }
333
334 Enumerations omitting the container type ": integer_type" use the "int"
335 type (for compatibility with C99). The "int" type must be previously
336 declared. E.g.:
337
338 typealias integer { size = 32; align = 32; signed = true } := int;
339
340 enum {
341 ...
342 }
343
344
345 4.2 Compound types
346
347 Compound are aggregation of type declarations. Compound types include
348 structures, variant, arrays, sequences, and strings.
349
350 4.2.1 Structures
351
352 Structures are aligned on the largest alignment required by basic types
353 contained within the structure. (This follows the ISO/C standard for structures)
354
355 TSDL meta-data representation of a named structure:
356
357 struct name {
358 field_type field_name;
359 field_type field_name;
360 ...
361 };
362
363 Example:
364
365 struct example {
366 integer { /* Nameless type */
367 size = 16;
368 signed = true;
369 align = 16;
370 } first_field_name;
371 uint64_t second_field_name; /* Named type declared in the meta-data */
372 };
373
374 The fields are placed in a sequence next to each other. They each possess a
375 field name, which is a unique identifier within the structure.
376
377 A nameless structure can be declared as a field type or as part of a typedef:
378
379 struct {
380 ...
381 }
382
383 Alignment for a structure compound type can be forced to a minimum value
384 by adding an "align" specifier after the declaration of a structure
385 body. This attribute is read as: align(value). The value is specified in
386 bits. The structure will be aligned on the maximum value between this
387 attribute and the alignment required by the basic types contained within
388 the structure. e.g.
389
390 struct {
391 ...
392 } align(32)
393
394 4.2.2 Variants (Discriminated/Tagged Unions)
395
396 A CTF variant is a selection between different types. A CTF variant must
397 always be defined within the scope of a structure or within fields
398 contained within a structure (defined recursively). A "tag" enumeration
399 field must appear in either the same lexical scope, prior to the variant
400 field (in field declaration order), in an upper lexical scope (see
401 Section 7.3.1), or in an upper dynamic scope (see Section 7.3.2). The
402 type selection is indicated by the mapping from the enumeration value to
403 the string used as variant type selector. The field to use as tag is
404 specified by the "tag_field", specified between "< >" after the
405 "variant" keyword for unnamed variants, and after "variant name" for
406 named variants.
407
408 The alignment of the variant is the alignment of the type as selected by the tag
409 value for the specific instance of the variant. The alignment of the type
410 containing the variant is independent of the variant alignment. The size of the
411 variant is the size as selected by the tag value for the specific instance of
412 the variant.
413
414 A named variant declaration followed by its definition within a structure
415 declaration:
416
417 variant name {
418 field_type sel1;
419 field_type sel2;
420 field_type sel3;
421 ...
422 };
423
424 struct {
425 enum : integer_type { sel1, sel2, sel3, ... } tag_field;
426 ...
427 variant name <tag_field> v;
428 }
429
430 An unnamed variant definition within a structure is expressed by the following
431 TSDL meta-data:
432
433 struct {
434 enum : integer_type { sel1, sel2, sel3, ... } tag_field;
435 ...
436 variant <tag_field> {
437 field_type sel1;
438 field_type sel2;
439 field_type sel3;
440 ...
441 } v;
442 }
443
444 Example of a named variant within a sequence that refers to a single tag field:
445
446 variant example {
447 uint32_t a;
448 uint64_t b;
449 short c;
450 };
451
452 struct {
453 enum : uint2_t { a, b, c } choice;
454 unsigned int seqlen;
455 variant example <choice> v[seqlen];
456 }
457
458 Example of an unnamed variant:
459
460 struct {
461 enum : uint2_t { a, b, c, d } choice;
462 /* Unrelated fields can be added between the variant and its tag */
463 int32_t somevalue;
464 variant <choice> {
465 uint32_t a;
466 uint64_t b;
467 short c;
468 struct {
469 unsigned int field1;
470 uint64_t field2;
471 } d;
472 } s;
473 }
474
475 Example of an unnamed variant within an array:
476
477 struct {
478 enum : uint2_t { a, b, c } choice;
479 variant <choice> {
480 uint32_t a;
481 uint64_t b;
482 short c;
483 } v[10];
484 }
485
486 Example of a variant type definition within a structure, where the defined type
487 is then declared within an array of structures. This variant refers to a tag
488 located in an upper lexical scope. This example clearly shows that a variant
489 type definition referring to the tag "x" uses the closest preceding field from
490 the lexical scope of the type definition.
491
492 struct {
493 enum : uint2_t { a, b, c, d } x;
494
495 typedef variant <x> { /*
496 * "x" refers to the preceding "x" enumeration in the
497 * lexical scope of the type definition.
498 */
499 uint32_t a;
500 uint64_t b;
501 short c;
502 } example_variant;
503
504 struct {
505 enum : int { x, y, z } x; /* This enumeration is not used by "v". */
506 example_variant v; /*
507 * "v" uses the "enum : uint2_t { a, b, c, d }"
508 * tag.
509 */
510 } a[10];
511 }
512
513 4.2.3 Arrays
514
515 Arrays are fixed-length. Their length is declared in the type
516 declaration within the meta-data. They contain an array of "inner type"
517 elements, which can refer to any type not containing the type of the
518 array being declared (no circular dependency). The length is the number
519 of elements in an array.
520
521 TSDL meta-data representation of a named array:
522
523 typedef elem_type name[length];
524
525 A nameless array can be declared as a field type within a structure, e.g.:
526
527 uint8_t field_name[10];
528
529 Arrays are always aligned on their element alignment requirement.
530
531 4.2.4 Sequences
532
533 Sequences are dynamically-sized arrays. They refer to a a "length"
534 unsigned integer field, which must appear in either the same lexical scope,
535 prior to the sequence field (in field declaration order), in an upper
536 lexical scope (see Section 7.3.1), or in an upper dynamic scope (see
537 Section 7.3.2). This length field represents the number of elements in
538 the sequence. The sequence per se is an array of "inner type" elements.
539
540 TSDL meta-data representation for a sequence type definition:
541
542 struct {
543 unsigned int length_field;
544 typedef elem_type typename[length_field];
545 typename seq_field_name;
546 }
547
548 A sequence can also be declared as a field type, e.g.:
549
550 struct {
551 unsigned int length_field;
552 long seq_field_name[length_field];
553 }
554
555 Multiple sequences can refer to the same length field, and these length
556 fields can be in a different upper dynamic scope:
557
558 e.g., assuming the stream.event.header defines:
559
560 stream {
561 ...
562 id = 1;
563 event.header := struct {
564 uint16_t seq_len;
565 };
566 };
567
568 event {
569 ...
570 stream_id = 1;
571 fields := struct {
572 long seq_a[stream.event.header.seq_len];
573 char seq_b[stream.event.header.seq_len];
574 };
575 };
576
577 The sequence elements follow the "array" specifications.
578
579 4.2.5 Strings
580
581 Strings are an array of bytes of variable size and are terminated by a '\0'
582 "NULL" character. Their encoding is described in the TSDL meta-data. In
583 absence of encoding attribute information, the default encoding is
584 UTF-8.
585
586 TSDL meta-data representation of a named string type:
587
588 typealias string {
589 encoding = UTF8 OR ASCII;
590 } := name;
591
592 A nameless string type can be declared as a field type:
593
594 string field_name; /* Use default UTF8 encoding */
595
596 Strings are always aligned on byte size.
597
598 5. Event Packet Header
599
600 The event packet header consists of two parts: the "event packet header"
601 is the same for all streams of a trace. The second part, the "event
602 packet context", is described on a per-stream basis. Both are described
603 in the TSDL meta-data. The packets are aligned on architecture-page-sized
604 addresses.
605
606 Event packet header (all fields are optional, specified by TSDL meta-data):
607
608 - Magic number (CTF magic number: 0xC1FC1FC1) specifies that this is a
609 CTF packet. This magic number is optional, but when present, it should
610 come at the very beginning of the packet.
611 - Trace UUID, used to ensure the event packet match the meta-data used.
612 (note: we cannot use a meta-data checksum in every cases instead of a
613 UUID because meta-data can be appended to while tracing is active)
614 This field is optional.
615 - Stream ID, used as reference to stream description in meta-data.
616 This field is optional if there is only one stream description in the
617 meta-data, but becomes required if there are more than one stream in
618 the TSDL meta-data description.
619
620 Event packet context (all fields are optional, specified by TSDL meta-data):
621
622 - Event packet content size (in bytes).
623 - Event packet size (in bytes, includes padding).
624 - Event packet content checksum (optional). Checksum excludes the event packet
625 header.
626 - Per-stream event packet sequence count (to deal with UDP packet loss). The
627 number of significant sequence counter bits should also be present, so
628 wrap-arounds are dealt with correctly.
629 - Time-stamp at the beginning and time-stamp at the end of the event packet.
630 Both timestamps are written in the packet header, but sampled respectively
631 while (or before) writing the first event and while (or after) writing the
632 last event in the packet. The inclusive range between these timestamps should
633 include all event timestamps assigned to events contained within the packet.
634 - Events discarded count
635 - Snapshot of a per-stream free-running counter, counting the number of
636 events discarded that were supposed to be written in the stream prior to
637 the first event in the event packet.
638 * Note: producer-consumer buffer full condition should fill the current
639 event packet with padding so we know exactly where events have been
640 discarded.
641 - Lossless compression scheme used for the event packet content. Applied
642 directly to raw data. New types of compression can be added in following
643 versions of the format.
644 0: no compression scheme
645 1: bzip2
646 2: gzip
647 3: xz
648 - Cypher used for the event packet content. Applied after compression.
649 0: no encryption
650 1: AES
651 - Checksum scheme used for the event packet content. Applied after encryption.
652 0: no checksum
653 1: md5
654 2: sha1
655 3: crc32
656
657 5.1 Event Packet Header Description
658
659 The event packet header layout is indicated by the trace packet.header
660 field. Here is a recommended structure type for the packet header with
661 the fields typically expected (although these fields are each optional):
662
663 struct event_packet_header {
664 uint32_t magic;
665 uint8_t uuid[16];
666 uint32_t stream_id;
667 };
668
669 trace {
670 ...
671 packet.header := struct event_packet_header;
672 };
673
674 If the magic number is not present, tools such as "file" will have no
675 mean to discover the file type.
676
677 If the uuid is not present, no validation that the meta-data actually
678 corresponds to the stream is performed.
679
680 If the stream_id packet header field is missing, the trace can only
681 contain a single stream. Its "id" field can be left out, and its events
682 don't need to declare a "stream_id" field.
683
684
685 5.2 Event Packet Context Description
686
687 Event packet context example. These are declared within the stream declaration
688 in the meta-data. All these fields are optional. If the packet size field is
689 missing, the whole stream only contains a single packet. If the content
690 size field is missing, the packet is filled (no padding). The content
691 and packet sizes include all headers.
692
693 An example event packet context type:
694
695 struct event_packet_context {
696 uint64_t timestamp_begin;
697 uint64_t timestamp_end;
698 uint32_t checksum;
699 uint32_t stream_packet_count;
700 uint32_t events_discarded;
701 uint32_t cpu_id;
702 uint32_t/uint16_t content_size;
703 uint32_t/uint16_t packet_size;
704 uint8_t stream_packet_count_bits; /* Significant counter bits */
705 uint8_t compression_scheme;
706 uint8_t encryption_scheme;
707 uint8_t checksum_scheme;
708 };
709
710
711 6. Event Structure
712
713 The overall structure of an event is:
714
715 1 - Stream Packet Context (as specified by the stream meta-data)
716 2 - Event Header (as specified by the stream meta-data)
717 3 - Stream Event Context (as specified by the stream meta-data)
718 4 - Event Context (as specified by the event meta-data)
719 5 - Event Payload (as specified by the event meta-data)
720
721 This structure defines an implicit dynamic scoping, where variants
722 located in inner structures (those with a higher number in the listing
723 above) can refer to the fields of outer structures (with lower number in
724 the listing above). See Section 7.3 TSDL Scopes for more detail.
725
726 6.1 Event Header
727
728 Event headers can be described within the meta-data. We hereby propose, as an
729 example, two types of events headers. Type 1 accommodates streams with less than
730 31 event IDs. Type 2 accommodates streams with 31 or more event IDs.
731
732 One major factor can vary between streams: the number of event IDs assigned to
733 a stream. Luckily, this information tends to stay relatively constant (modulo
734 event registration while trace is being recorded), so we can specify different
735 representations for streams containing few event IDs and streams containing
736 many event IDs, so we end up representing the event ID and time-stamp as
737 densely as possible in each case.
738
739 The header is extended in the rare occasions where the information cannot be
740 represented in the ranges available in the standard event header. They are also
741 used in the rare occasions where the data required for a field could not be
742 collected: the flag corresponding to the missing field within the missing_fields
743 array is then set to 1.
744
745 Types uintX_t represent an X-bit unsigned integer, as declared with
746 either:
747
748 typealias integer { size = X; align = X; signed = false } := uintX_t;
749
750 or
751
752 typealias integer { size = X; align = 1; signed = false } := uintX_t;
753
754 6.1.1 Type 1 - Few event IDs
755
756 - Aligned on 32-bit (or 8-bit if byte-packed, depending on the architecture
757 preference).
758 - Native architecture byte ordering.
759 - For "compact" selection
760 - Fixed size: 32 bits.
761 - For "extended" selection
762 - Size depends on the architecture and variant alignment.
763
764 struct event_header_1 {
765 /*
766 * id: range: 0 - 30.
767 * id 31 is reserved to indicate an extended header.
768 */
769 enum : uint5_t { compact = 0 ... 30, extended = 31 } id;
770 variant <id> {
771 struct {
772 uint27_t timestamp;
773 } compact;
774 struct {
775 uint32_t id; /* 32-bit event IDs */
776 uint64_t timestamp; /* 64-bit timestamps */
777 } extended;
778 } v;
779 } align(32); /* or align(8) */
780
781
782 6.1.2 Type 2 - Many event IDs
783
784 - Aligned on 16-bit (or 8-bit if byte-packed, depending on the architecture
785 preference).
786 - Native architecture byte ordering.
787 - For "compact" selection
788 - Size depends on the architecture and variant alignment.
789 - For "extended" selection
790 - Size depends on the architecture and variant alignment.
791
792 struct event_header_2 {
793 /*
794 * id: range: 0 - 65534.
795 * id 65535 is reserved to indicate an extended header.
796 */
797 enum : uint16_t { compact = 0 ... 65534, extended = 65535 } id;
798 variant <id> {
799 struct {
800 uint32_t timestamp;
801 } compact;
802 struct {
803 uint32_t id; /* 32-bit event IDs */
804 uint64_t timestamp; /* 64-bit timestamps */
805 } extended;
806 } v;
807 } align(16); /* or align(8) */
808
809
810 6.2 Event Context
811
812 The event context contains information relative to the current event.
813 The choice and meaning of this information is specified by the TSDL
814 stream and event meta-data descriptions. The stream context is applied
815 to all events within the stream. The stream context structure follows
816 the event header. The event context is applied to specific events. Its
817 structure follows the stream context structure.
818
819 An example of stream-level event context is to save the event payload size with
820 each event, or to save the current PID with each event. These are declared
821 within the stream declaration within the meta-data:
822
823 stream {
824 ...
825 event.context := struct {
826 uint pid;
827 uint16_t payload_size;
828 };
829 };
830
831 An example of event-specific event context is to declare a bitmap of missing
832 fields, only appended after the stream event context if the extended event
833 header is selected. NR_FIELDS is the number of fields within the event (a
834 numeric value).
835
836 event {
837 context = struct {
838 variant <id> {
839 struct { } compact;
840 struct {
841 uint1_t missing_fields[NR_FIELDS]; /* missing event fields bitmap */
842 } extended;
843 } v;
844 };
845 ...
846 }
847
848 6.3 Event Payload
849
850 An event payload contains fields specific to a given event type. The fields
851 belonging to an event type are described in the event-specific meta-data
852 within a structure type.
853
854 6.3.1 Padding
855
856 No padding at the end of the event payload. This differs from the ISO/C standard
857 for structures, but follows the CTF standard for structures. In a trace, even
858 though it makes sense to align the beginning of a structure, it really makes no
859 sense to add padding at the end of the structure, because structures are usually
860 not followed by a structure of the same type.
861
862 This trick can be done by adding a zero-length "end" field at the end of the C
863 structures, and by using the offset of this field rather than using sizeof()
864 when calculating the size of a structure (see Appendix "A. Helper macros").
865
866 6.3.2 Alignment
867
868 The event payload is aligned on the largest alignment required by types
869 contained within the payload. (This follows the ISO/C standard for structures)
870
871
872 7. Trace Stream Description Language (TSDL)
873
874 The Trace Stream Description Language (TSDL) allows expression of the
875 binary trace streams layout in a C99-like Domain Specific Language
876 (DSL).
877
878
879 7.1 Meta-data
880
881 The trace stream layout description is located in the trace meta-data.
882 The meta-data is itself located in a stream identified by its name:
883 "metadata".
884
885 The meta-data description can be expressed in two different formats:
886 text-only and packet-based. The text-only description facilitates
887 generation of meta-data and provides a convenient way to enter the
888 meta-data information by hand. The packet-based meta-data provides the
889 CTF stream packet facilities (checksumming, compression, encryption,
890 network-readiness) for meta-data stream generated and transported by a
891 tracer.
892
893 The text-only meta-data file is a plain text TSDL description.
894
895 The packet-based meta-data is made of "meta-data packets", which each
896 start with a meta-data packet header. The packet-based meta-data
897 description is detected by reading the magic number "0x75D11D57" at the
898 beginning of the file. This magic number is also used to detect the
899 endianness of the architecture by trying to read the CTF magic number
900 and its counterpart in reversed endianness. The events within the
901 meta-data stream have no event header nor event context. Each event only
902 contains a "sequence" payload, which is a sequence of bits using the
903 "trace.packet.header.content_size" field as a placeholder for its
904 length. The formatting of this sequence of bits is a plain-text
905 representation of the TSDL description. Each meta-data packet start with
906 a special packet header, specific to the meta-data stream, which
907 contains, exactly:
908
909 struct metadata_packet_header {
910 uint32_t magic; /* 0x75D11D57 */
911 uint8_t uuid[16]; /* Unique Universal Identifier */
912 uint32_t checksum; /* 0 if unused */
913 uint32_t content_size; /* in bits */
914 uint32_t packet_size; /* in bits */
915 uint8_t compression_scheme; /* 0 if unused */
916 uint8_t encryption_scheme; /* 0 if unused */
917 uint8_t checksum_scheme; /* 0 if unused */
918 };
919
920 The packet-based meta-data can be converted to a text-only meta-data by
921 concatenating all the strings in contains.
922
923 In the textual representation of the meta-data, the text contained
924 within "/*" and "*/", as well as within "//" and end of line, are
925 treated as comments. Boolean values can be represented as true, TRUE,
926 or 1 for true, and false, FALSE, or 0 for false. Within the string-based
927 meta-data description, the trace UUID is represented as a string of
928 hexadecimal digits and dashes "-". In the event packet header, the trace
929 UUID is represented as an array of bytes.
930
931
932 7.2 Declaration vs Definition
933
934 A declaration associates a layout to a type, without specifying where
935 this type is located in the event structure hierarchy (see Section 6).
936 This therefore includes typedef, typealias, as well as all type
937 specifiers. In certain circumstances (typedef, structure field and
938 variant field), a declaration is followed by a declarator, which specify
939 the newly defined type name (for typedef), or the field name (for
940 declarations located within structure and variants). Array and sequence,
941 declared with square brackets ("[" "]"), are part of the declarator,
942 similarly to C99. The enumeration base type is specified by
943 ": enum_base", which is part of the type specifier. The variant tag
944 name, specified between "<" ">", is also part of the type specifier.
945
946 A definition associates a type to a location in the event structure
947 hierarchy (see Section 6). This association is denoted by ":=", as shown
948 in Section 7.3.
949
950
951 7.3 TSDL Scopes
952
953 TSDL uses two different types of scoping: a lexical scope is used for
954 declarations and type definitions, and a dynamic scope is used for
955 variants references to tag fields and for sequence references to length
956 fields.
957
958 7.3.1 Lexical Scope
959
960 Each of "trace", "stream", "event", "struct" and "variant" have their own
961 nestable declaration scope, within which types can be declared using "typedef"
962 and "typealias". A root declaration scope also contains all declarations
963 located outside of any of the aforementioned declarations. An inner
964 declaration scope can refer to type declared within its container
965 lexical scope prior to the inner declaration scope. Redefinition of a
966 typedef or typealias is not valid, although hiding an upper scope
967 typedef or typealias is allowed within a sub-scope.
968
969 7.3.2 Dynamic Scope
970
971 A dynamic scope consists in the lexical scope augmented with the
972 implicit event structure definition hierarchy presented at Section 6.
973 The dynamic scope is used for variant tag and sequence length
974 definitions. It is used at definition time to look up the location of
975 the tag field associated with a variant, and to lookup up the location
976 of the length field associated with a sequence.
977
978 Therefore, variants (or sequences) in lower levels in the dynamic scope
979 (e.g. event context) can refer to a tag (or length) field located in
980 upper levels (e.g. in the event header) by specifying, in this case, the
981 associated tag with <header.field_name>. This allows, for instance, the
982 event context to define a variant referring to the "id" field of the
983 event header as selector.
984
985 The target dynamic scope must be specified explicitly when referring to
986 a field outside of the local static scope. The dynamic scope prefixes
987 are thus:
988
989 - Trace Packet Header: <trace.packet.header. >,
990 - Stream Packet Context: <stream.packet.context. >,
991 - Event Header: <stream.event.header. >,
992 - Stream Event Context: <stream.event.context. >,
993 - Event Context: <event.context. >,
994 - Event Payload: <event.fields. >.
995
996 Multiple declarations of the same field name within a single scope is
997 not valid. It is however valid to re-use the same field name in
998 different scopes. There is no possible conflict, because the dynamic
999 scope must be specified when a variant refers to a tag field located in
1000 a different dynamic scope.
1001
1002 The information available in the dynamic scopes can be thought of as the
1003 current tracing context. At trace production, information about the
1004 current context is saved into the specified scope field levels. At trace
1005 consumption, for each event, the current trace context is therefore
1006 readable by accessing the upper dynamic scopes.
1007
1008
1009 7.4 TSDL Examples
1010
1011 The grammar representing the TSDL meta-data is presented in Appendix C.
1012 TSDL Grammar. This section presents a rather lighter reading that
1013 consists in examples of TSDL meta-data, with template values.
1014
1015 The stream "id" can be left out if there is only one stream in the
1016 trace. The event "id" field can be left out if there is only one event
1017 in a stream.
1018
1019 trace {
1020 major = value; /* Trace format version */
1021 minor = value;
1022 uuid = "aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaaa"; /* Trace UUID */
1023 byte_order = be OR le; /* Endianness (required) */
1024 packet.header := struct {
1025 uint32_t magic;
1026 uint8_t uuid[16];
1027 uint32_t stream_id;
1028 };
1029 };
1030
1031 stream {
1032 id = stream_id;
1033 /* Type 1 - Few event IDs; Type 2 - Many event IDs. See section 6.1. */
1034 event.header := event_header_1 OR event_header_2;
1035 event.context := struct {
1036 ...
1037 };
1038 packet.context := struct {
1039 ...
1040 };
1041 };
1042
1043 event {
1044 name = event_name;
1045 id = value; /* Numeric identifier within the stream */
1046 stream_id = stream_id;
1047 context := struct {
1048 ...
1049 };
1050 fields := struct {
1051 ...
1052 };
1053 };
1054
1055 /* More detail on types in section 4. Types */
1056
1057 /*
1058 * Named types:
1059 *
1060 * Type declarations behave similarly to the C standard.
1061 */
1062
1063 typedef aliased_type_specifiers new_type_declarators;
1064
1065 /* e.g.: typedef struct example new_type_name[10]; */
1066
1067 /*
1068 * typealias
1069 *
1070 * The "typealias" declaration can be used to give a name (including
1071 * pointer declarator specifier) to a type. It should also be used to
1072 * map basic C types (float, int, unsigned long, ...) to a CTF type.
1073 * Typealias is a superset of "typedef": it also allows assignment of a
1074 * simple variable identifier to a type.
1075 */
1076
1077 typealias type_class {
1078 ...
1079 } := type_specifiers type_declarator;
1080
1081 /*
1082 * e.g.:
1083 * typealias integer {
1084 * size = 32;
1085 * align = 32;
1086 * signed = false;
1087 * } := struct page *;
1088 *
1089 * typealias integer {
1090 * size = 32;
1091 * align = 32;
1092 * signed = true;
1093 * } := int;
1094 */
1095
1096 struct name {
1097 ...
1098 };
1099
1100 variant name {
1101 ...
1102 };
1103
1104 enum name : integer_type {
1105 ...
1106 };
1107
1108
1109 /*
1110 * Unnamed types, contained within compound type fields, typedef or typealias.
1111 */
1112
1113 struct {
1114 ...
1115 }
1116
1117 struct {
1118 ...
1119 } align(value)
1120
1121 variant {
1122 ...
1123 }
1124
1125 enum : integer_type {
1126 ...
1127 }
1128
1129 typedef type new_type[length];
1130
1131 struct {
1132 type field_name[length];
1133 }
1134
1135 typedef type new_type[length_type];
1136
1137 struct {
1138 type field_name[length_type];
1139 }
1140
1141 integer {
1142 ...
1143 }
1144
1145 floating_point {
1146 ...
1147 }
1148
1149 struct {
1150 integer_type field_name:size; /* GNU/C bitfield */
1151 }
1152
1153 struct {
1154 string field_name;
1155 }
1156
1157
1158 A. Helper macros
1159
1160 The two following macros keep track of the size of a GNU/C structure without
1161 padding at the end by placing HEADER_END as the last field. A one byte end field
1162 is used for C90 compatibility (C99 flexible arrays could be used here). Note
1163 that this does not affect the effective structure size, which should always be
1164 calculated with the header_sizeof() helper.
1165
1166 #define HEADER_END char end_field
1167 #define header_sizeof(type) offsetof(typeof(type), end_field)
1168
1169
1170 B. Stream Header Rationale
1171
1172 An event stream is divided in contiguous event packets of variable size. These
1173 subdivisions allow the trace analyzer to perform a fast binary search by time
1174 within the stream (typically requiring to index only the event packet headers)
1175 without reading the whole stream. These subdivisions have a variable size to
1176 eliminate the need to transfer the event packet padding when partially filled
1177 event packets must be sent when streaming a trace for live viewing/analysis.
1178 An event packet can contain a certain amount of padding at the end. Dividing
1179 streams into event packets is also useful for network streaming over UDP and
1180 flight recorder mode tracing (a whole event packet can be swapped out of the
1181 buffer atomically for reading).
1182
1183 The stream header is repeated at the beginning of each event packet to allow
1184 flexibility in terms of:
1185
1186 - streaming support,
1187 - allowing arbitrary buffers to be discarded without making the trace
1188 unreadable,
1189 - allow UDP packet loss handling by either dealing with missing event packet
1190 or asking for re-transmission.
1191 - transparently support flight recorder mode,
1192 - transparently support crash dump.
1193
1194
1195 C. TSDL Grammar
1196
1197 /*
1198 * Common Trace Format (CTF) Trace Stream Description Language (TSDL) Grammar.
1199 *
1200 * Inspired from the C99 grammar:
1201 * http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1124.pdf (Annex A)
1202 * and c++1x grammar (draft)
1203 * http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2011/n3291.pdf (Annex A)
1204 *
1205 * Specialized for CTF needs by including only constant and declarations from
1206 * C99 (excluding function declarations), and by adding support for variants,
1207 * sequences and CTF-specific specifiers. Enumeration container types
1208 * semantic is inspired from c++1x enum-base.
1209 */
1210
1211 1) Lexical grammar
1212
1213 1.1) Lexical elements
1214
1215 token:
1216 keyword
1217 identifier
1218 constant
1219 string-literal
1220 punctuator
1221
1222 1.2) Keywords
1223
1224 keyword: is one of
1225
1226 align
1227 const
1228 char
1229 double
1230 enum
1231 event
1232 floating_point
1233 float
1234 integer
1235 int
1236 long
1237 short
1238 signed
1239 stream
1240 string
1241 struct
1242 trace
1243 typealias
1244 typedef
1245 unsigned
1246 variant
1247 void
1248 _Bool
1249 _Complex
1250 _Imaginary
1251
1252
1253 1.3) Identifiers
1254
1255 identifier:
1256 identifier-nondigit
1257 identifier identifier-nondigit
1258 identifier digit
1259
1260 identifier-nondigit:
1261 nondigit
1262 universal-character-name
1263 any other implementation-defined characters
1264
1265 nondigit:
1266 _
1267 [a-zA-Z] /* regular expression */
1268
1269 digit:
1270 [0-9] /* regular expression */
1271
1272 1.4) Universal character names
1273
1274 universal-character-name:
1275 \u hex-quad
1276 \U hex-quad hex-quad
1277
1278 hex-quad:
1279 hexadecimal-digit hexadecimal-digit hexadecimal-digit hexadecimal-digit
1280
1281 1.5) Constants
1282
1283 constant:
1284 integer-constant
1285 enumeration-constant
1286 character-constant
1287
1288 integer-constant:
1289 decimal-constant integer-suffix-opt
1290 octal-constant integer-suffix-opt
1291 hexadecimal-constant integer-suffix-opt
1292
1293 decimal-constant:
1294 nonzero-digit
1295 decimal-constant digit
1296
1297 octal-constant:
1298 0
1299 octal-constant octal-digit
1300
1301 hexadecimal-constant:
1302 hexadecimal-prefix hexadecimal-digit
1303 hexadecimal-constant hexadecimal-digit
1304
1305 hexadecimal-prefix:
1306 0x
1307 0X
1308
1309 nonzero-digit:
1310 [1-9]
1311
1312 integer-suffix:
1313 unsigned-suffix long-suffix-opt
1314 unsigned-suffix long-long-suffix
1315 long-suffix unsigned-suffix-opt
1316 long-long-suffix unsigned-suffix-opt
1317
1318 unsigned-suffix:
1319 u
1320 U
1321
1322 long-suffix:
1323 l
1324 L
1325
1326 long-long-suffix:
1327 ll
1328 LL
1329
1330 enumeration-constant:
1331 identifier
1332 string-literal
1333
1334 character-constant:
1335 ' c-char-sequence '
1336 L' c-char-sequence '
1337
1338 c-char-sequence:
1339 c-char
1340 c-char-sequence c-char
1341
1342 c-char:
1343 any member of source charset except single-quote ('), backslash
1344 (\), or new-line character.
1345 escape-sequence
1346
1347 escape-sequence:
1348 simple-escape-sequence
1349 octal-escape-sequence
1350 hexadecimal-escape-sequence
1351 universal-character-name
1352
1353 simple-escape-sequence: one of
1354 \' \" \? \\ \a \b \f \n \r \t \v
1355
1356 octal-escape-sequence:
1357 \ octal-digit
1358 \ octal-digit octal-digit
1359 \ octal-digit octal-digit octal-digit
1360
1361 hexadecimal-escape-sequence:
1362 \x hexadecimal-digit
1363 hexadecimal-escape-sequence hexadecimal-digit
1364
1365 1.6) String literals
1366
1367 string-literal:
1368 " s-char-sequence-opt "
1369 L" s-char-sequence-opt "
1370
1371 s-char-sequence:
1372 s-char
1373 s-char-sequence s-char
1374
1375 s-char:
1376 any member of source charset except double-quote ("), backslash
1377 (\), or new-line character.
1378 escape-sequence
1379
1380 1.7) Punctuators
1381
1382 punctuator: one of
1383 [ ] ( ) { } . -> * + - < > : ; ... = ,
1384
1385
1386 2) Phrase structure grammar
1387
1388 primary-expression:
1389 identifier
1390 constant
1391 string-literal
1392 ( unary-expression )
1393
1394 postfix-expression:
1395 primary-expression
1396 postfix-expression [ unary-expression ]
1397 postfix-expression . identifier
1398 postfix-expressoin -> identifier
1399
1400 unary-expression:
1401 postfix-expression
1402 unary-operator postfix-expression
1403
1404 unary-operator: one of
1405 + -
1406
1407 assignment-operator:
1408 =
1409
1410 type-assignment-operator:
1411 :=
1412
1413 constant-expression-range:
1414 unary-expression ... unary-expression
1415
1416 2.2) Declarations:
1417
1418 declaration:
1419 declaration-specifiers declarator-list-opt ;
1420 ctf-specifier ;
1421
1422 declaration-specifiers:
1423 storage-class-specifier declaration-specifiers-opt
1424 type-specifier declaration-specifiers-opt
1425 type-qualifier declaration-specifiers-opt
1426
1427 declarator-list:
1428 declarator
1429 declarator-list , declarator
1430
1431 abstract-declarator-list:
1432 abstract-declarator
1433 abstract-declarator-list , abstract-declarator
1434
1435 storage-class-specifier:
1436 typedef
1437
1438 type-specifier:
1439 void
1440 char
1441 short
1442 int
1443 long
1444 float
1445 double
1446 signed
1447 unsigned
1448 _Bool
1449 _Complex
1450 _Imaginary
1451 struct-specifier
1452 variant-specifier
1453 enum-specifier
1454 typedef-name
1455 ctf-type-specifier
1456
1457 align-attribute:
1458 align ( unary-expression )
1459
1460 struct-specifier:
1461 struct identifier-opt { struct-or-variant-declaration-list-opt } align-attribute-opt
1462 struct identifier align-attribute-opt
1463
1464 struct-or-variant-declaration-list:
1465 struct-or-variant-declaration
1466 struct-or-variant-declaration-list struct-or-variant-declaration
1467
1468 struct-or-variant-declaration:
1469 specifier-qualifier-list struct-or-variant-declarator-list ;
1470 declaration-specifiers-opt storage-class-specifier declaration-specifiers-opt declarator-list ;
1471 typealias declaration-specifiers abstract-declarator-list type-assignment-operator declaration-specifiers abstract-declarator-list ;
1472 typealias declaration-specifiers abstract-declarator-list type-assignment-operator declarator-list ;
1473
1474 specifier-qualifier-list:
1475 type-specifier specifier-qualifier-list-opt
1476 type-qualifier specifier-qualifier-list-opt
1477
1478 struct-or-variant-declarator-list:
1479 struct-or-variant-declarator
1480 struct-or-variant-declarator-list , struct-or-variant-declarator
1481
1482 struct-or-variant-declarator:
1483 declarator
1484 declarator-opt : unary-expression
1485
1486 variant-specifier:
1487 variant identifier-opt variant-tag-opt { struct-or-variant-declaration-list }
1488 variant identifier variant-tag
1489
1490 variant-tag:
1491 < identifier >
1492
1493 enum-specifier:
1494 enum identifier-opt { enumerator-list }
1495 enum identifier-opt { enumerator-list , }
1496 enum identifier
1497 enum identifier-opt : declaration-specifiers { enumerator-list }
1498 enum identifier-opt : declaration-specifiers { enumerator-list , }
1499
1500 enumerator-list:
1501 enumerator
1502 enumerator-list , enumerator
1503
1504 enumerator:
1505 enumeration-constant
1506 enumeration-constant assignment-operator unary-expression
1507 enumeration-constant assignment-operator constant-expression-range
1508
1509 type-qualifier:
1510 const
1511
1512 declarator:
1513 pointer-opt direct-declarator
1514
1515 direct-declarator:
1516 identifier
1517 ( declarator )
1518 direct-declarator [ unary-expression ]
1519
1520 abstract-declarator:
1521 pointer-opt direct-abstract-declarator
1522
1523 direct-abstract-declarator:
1524 identifier-opt
1525 ( abstract-declarator )
1526 direct-abstract-declarator [ unary-expression ]
1527 direct-abstract-declarator [ ]
1528
1529 pointer:
1530 * type-qualifier-list-opt
1531 * type-qualifier-list-opt pointer
1532
1533 type-qualifier-list:
1534 type-qualifier
1535 type-qualifier-list type-qualifier
1536
1537 typedef-name:
1538 identifier
1539
1540 2.3) CTF-specific declarations
1541
1542 ctf-specifier:
1543 event { ctf-assignment-expression-list-opt }
1544 stream { ctf-assignment-expression-list-opt }
1545 trace { ctf-assignment-expression-list-opt }
1546 typealias declaration-specifiers abstract-declarator-list type-assignment-operator declaration-specifiers abstract-declarator-list ;
1547 typealias declaration-specifiers abstract-declarator-list type-assignment-operator declarator-list ;
1548
1549 ctf-type-specifier:
1550 floating_point { ctf-assignment-expression-list-opt }
1551 integer { ctf-assignment-expression-list-opt }
1552 string { ctf-assignment-expression-list-opt }
1553
1554 ctf-assignment-expression-list:
1555 ctf-assignment-expression ;
1556 ctf-assignment-expression-list ctf-assignment-expression ;
1557
1558 ctf-assignment-expression:
1559 unary-expression assignment-operator unary-expression
1560 unary-expression type-assignment-operator type-specifier
1561 declaration-specifiers-opt storage-class-specifier declaration-specifiers-opt declarator-list
1562 typealias declaration-specifiers abstract-declarator-list type-assignment-operator declaration-specifiers abstract-declarator-list
1563 typealias declaration-specifiers abstract-declarator-list type-assignment-operator declarator-list
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