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