458b0977787edbad699d18590dacb10db95de165
[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.
11
12 The latest version of this document can be found at:
13
14 git tree: git://git.efficios.com/ctf.git
15 gitweb: http://git.efficios.com/?p=ctf.git
16
17 A reference implementation of a library to read and write this trace format is
18 being implemented within the BabelTrace project, a converter between trace
19 formats. The development tree is available at:
20
21 git tree: git://git.efficios.com/babeltrace.git
22 gitweb: http://git.efficios.com/?p=babeltrace.git
23
24
25 1. Preliminary definitions
26
27 - Event Trace: An ordered sequence of events.
28 - Event Stream: An ordered sequence of events, containing a subset of the
29 trace event types.
30 - Event Packet: A sequence of physically contiguous events within an event
31 stream.
32 - Event: This is the basic entry in a trace. (aka: a trace record).
33 - An event identifier (ID) relates to the class (a type) of event within
34 an event stream.
35 e.g. event: irq_entry.
36 - An event (or event record) relates to a specific instance of an event
37 class.
38 e.g. event: irq_entry, at time X, on CPU Y
39 - Source Architecture: Architecture writing the trace.
40 - Reader Architecture: Architecture reading the trace.
41
42
43 2. High-level representation of a trace
44
45 A trace is divided into multiple event streams. Each event stream contains a
46 subset of the trace event types.
47
48 The final output of the trace, after its generation and optional transport over
49 the network, is expected to be either on permanent or temporary storage in a
50 virtual file system. Because each event stream is appended to while a trace is
51 being recorded, each is associated with a separate file for output. Therefore,
52 a stored trace can be represented as a directory containing one file per stream.
53
54 A metadata event stream contains information on trace event types. It describes:
55
56 - Trace version.
57 - Types available.
58 - Per-stream event header description.
59 - Per-stream event header selection.
60 - Per-stream event context fields.
61 - Per-event
62 - Event type to stream mapping.
63 - Event type to name mapping.
64 - Event type to ID mapping.
65 - Event fields description.
66
67
68 3. Event stream
69
70 An event stream is divided in contiguous event packets of variable size. These
71 subdivisions have a variable size. An event packet can contain a certain amount
72 of padding at the end. The rationale for the event stream design choices is
73 explained in Appendix B. Stream Header Rationale.
74
75 An event stream is divided in contiguous event packets of variable size. These
76 subdivisions have a variable size. An event packet can contain a certain amount
77 of padding at the end. The stream header is repeated at the beginning of each
78 event packet.
79
80 The event stream header will therefore be referred to as the "event packet
81 header" throughout the rest of this document.
82
83
84 4. Types
85
86 Types are organized as type classes. Each type class belong to either of two
87 kind of types: basic types or compound types.
88
89 4.1 Basic types
90
91 A basic type is a scalar type, as described in this section. It includes
92 integers, GNU/C bitfields, enumerations, and floating point values.
93
94 4.1.1 Type inheritance
95
96 Type specifications can be inherited to allow deriving types from a
97 type class. For example, see the uint32_t named type derived from the "integer"
98 type class below ("Integers" section). Types have a precise binary
99 representation in the trace. A type class has methods to read and write these
100 types, but must be derived into a type to be usable in an event field.
101
102 4.1.2 Alignment
103
104 We define "byte-packed" types as aligned on the byte size, namely 8-bit.
105 We define "bit-packed" types as following on the next bit, as defined by the
106 "bitfields" section.
107
108 All basic types, except bitfields, are either aligned on an architecture-defined
109 specific alignment or byte-packed, depending on the architecture preference.
110 Architectures providing fast unaligned write byte-packed basic types to save
111 space, aligning each type on byte boundaries (8-bit). Architectures with slow
112 unaligned writes align types on specific alignment values. If no specific
113 alignment is declared for a type nor its parents, it is assumed to be bit-packed
114 for bitfields and byte-packed for other types.
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 If a numeric value is encountered between < >, it represents the integer type
278 size used to hold the enumeration, in bits.
279
280 enum name <integer_type OR size> {
281 somestring = start_value1 ... end_value1,
282 "other string" = start_value2 ... end_value2,
283 yet_another_string, /* will be assigned to end_value2 + 1 */
284 "some other string" = value,
285 ...
286 };
287
288 If the values are omitted, the enumeration starts at 0 and increment of 1 for
289 each entry:
290
291 enum name <32> {
292 ZERO,
293 ONE,
294 TWO,
295 TEN = 10,
296 ELEVEN,
297 };
298
299 Overlapping ranges within a single enumeration are implementation defined.
300
301 A nameless enumeration can be declared as a field type or as part of a typedef:
302
303 enum <integer_type> {
304 ...
305 }
306
307
308 4.2 Compound types
309
310 Compound are aggregation of type declarations. Compound types include
311 structures, variant, arrays, sequences, and strings.
312
313 4.2.1 Structures
314
315 Structures are aligned on the largest alignment required by basic types
316 contained within the structure. (This follows the ISO/C standard for structures)
317
318 Metadata representation of a named structure:
319
320 struct name {
321 field_type field_name;
322 field_type field_name;
323 ...
324 };
325
326 Example:
327
328 struct example {
329 integer { /* Nameless type */
330 size = 16;
331 signed = true;
332 align = 16;
333 } first_field_name;
334 uint64_t second_field_name; /* Named type declared in the metadata */
335 };
336
337 The fields are placed in a sequence next to each other. They each possess a
338 field name, which is a unique identifier within the structure.
339
340 A nameless structure can be declared as a field type or as part of a typedef:
341
342 struct {
343 ...
344 }
345
346 4.2.2 Variants (Discriminated/Tagged Unions)
347
348 A CTF variant is a selection between different types. A CTF variant must always
349 be defined within the scope of a structure or within fields contained within a
350 structure (defined recursively). A "tag" enumeration field must appear in either
351 the same lexical scope or an uppermost scope, prior to the variant field (in
352 field declaration order). The type selection is indicated by the mapping from
353 the enumeration value to the string used as variant type selector. The field to
354 use as tag is specified by the "tag_field", specified between "< >" after the
355 "variant" keyword for unnamed variants, and after "variant name" for named
356 variants.
357
358 The alignment of the variant is the alignment of the type as selected by the tag
359 value for the specific instance of the variant. The alignment of the type
360 containing the variant is independent of the variant alignment. The size of the
361 variant is the size as selected by the tag value for the specific instance of
362 the variant.
363
364 A named variant declaration followed by its definition within a structure
365 declaration:
366
367 variant name {
368 field_type sel1;
369 field_type sel2;
370 field_type sel3;
371 ...
372 };
373
374 struct {
375 enum <integer_type or size> { sel1, sel2, sel3, ... } tag_field;
376 ...
377 variant name <tag_field> v;
378 }
379
380 An unnamed variant definition within a structure is expressed by the following
381 metadata:
382
383 struct {
384 enum <integer_type or size> { sel1, sel2, sel3, ... } tag_field;
385 ...
386 variant <tag_field> {
387 field_type sel1;
388 field_type sel2;
389 field_type sel3;
390 ...
391 } v;
392 }
393
394 Example of a named variant within a sequence that refers to a single tag field:
395
396 variant example {
397 uint32_t a;
398 uint64_t b;
399 short c;
400 };
401
402 struct {
403 enum <uint2_t> { a, b, c } choice;
404 variant example <choice> v[unsigned int];
405 }
406
407 Example of an unnamed variant:
408
409 struct {
410 enum <uint2_t> { a, b, c, d } choice;
411 /* Unrelated fields can be added between the variant and its tag */
412 int32_t somevalue;
413 variant <choice> {
414 uint32_t a;
415 uint64_t b;
416 short c;
417 struct {
418 unsigned int field1;
419 uint64_t field2;
420 } d;
421 } s;
422 }
423
424 Example of an unnamed variant within an array:
425
426 struct {
427 enum <uint2_t> { a, b, c } choice;
428 variant <choice> {
429 uint32_t a;
430 uint64_t b;
431 short c;
432 } v[10];
433 }
434
435 Example of a variant type definition within a structure, where the defined type
436 is then declared within an array of structures. This variant refers to a tag
437 located in an upper lexical scope. This example clearly shows that a variant
438 type definition referring to the tag "x" uses the closest preceding field from
439 the lexical scope of the type definition.
440
441 struct {
442 enum <uint2_t> { a, b, c, d } x;
443
444 typedef variant <x> { /*
445 * "x" refers to the preceding "x" enumeration in the
446 * lexical scope of the type definition.
447 */
448 uint32_t a;
449 uint64_t b;
450 short c;
451 } example_variant;
452
453 struct {
454 enum <int> { x, y, z } x; /* This enumeration is not used by "v". */
455 example_variant v; /*
456 * "v" uses the "enum <uint2_t> { a, b, c, d }"
457 * tag.
458 */
459 } a[10];
460 }
461
462 4.2.3 Arrays
463
464 Arrays are fixed-length. Their length is declared in the type declaration within
465 the metadata. They contain an array of "inner type" elements, which can refer to
466 any type not containing the type of the array being declared (no circular
467 dependency). The length is the number of elements in an array.
468
469 Metadata representation of a named array:
470
471 typedef elem_type name[length];
472
473 A nameless array can be declared as a field type within a structure, e.g.:
474
475 uint8_t field_name[10];
476
477
478 4.2.4 Sequences
479
480 Sequences are dynamically-sized arrays. They start with an integer that specify
481 the length of the sequence, followed by an array of "inner type" elements.
482 The length is the number of elements in the sequence.
483
484 Metadata representation for a named sequence:
485
486 typedef elem_type name[length_type];
487
488 A nameless sequence can be declared as a field type, e.g.:
489
490 long field_name[int];
491
492 The length type follows the integer types specifications, and the sequence
493 elements follow the "array" specifications.
494
495 4.2.5 Strings
496
497 Strings are an array of bytes of variable size and are terminated by a '\0'
498 "NULL" character. Their encoding is described in the metadata. In absence of
499 encoding attribute information, the default encoding is UTF-8.
500
501 Metadata representation of a named string type:
502
503 typealias string {
504 encoding = UTF8 OR ASCII;
505 } : name;
506
507 A nameless string type can be declared as a field type:
508
509 string field_name; /* Use default UTF8 encoding */
510
511 5. Event Packet Header
512
513 The event packet header consists of two part: one is mandatory and have a fixed
514 layout. The second part, the "event packet context", has its layout described in
515 the metadata.
516
517 - Aligned on page size. Fixed size. Fields either aligned or packed (depending
518 on the architecture preference).
519 No padding at the end of the event packet header. Native architecture byte
520 ordering.
521
522 Fixed layout (event packet header):
523
524 - Magic number (CTF magic numbers: 0xC1FC1FC1 and its reverse endianness
525 representation: 0xC11FFCC1) It needs to have a non-symmetric bytewise
526 representation. Used to distinguish between big and little endian traces (this
527 information is determined by knowing the endianness of the architecture
528 reading the trace and comparing the magic number against its value and the
529 reverse, 0xC11FFCC1). This magic number specifies that we use the CTF metadata
530 description language described in this document. Different magic numbers
531 should be used for other metadata description languages.
532 - Trace UUID, used to ensure the event packet match the metadata used.
533 (note: we cannot use a metadata checksum because metadata can be appended to
534 while tracing is active)
535 - Stream ID, used as reference to stream description in metadata.
536
537 Metadata-defined layout (event packet context):
538
539 - Event packet content size (in bytes).
540 - Event packet size (in bytes, includes padding).
541 - Event packet content checksum (optional). Checksum excludes the event packet
542 header.
543 - Per-stream event packet sequence count (to deal with UDP packet loss). The
544 number of significant sequence counter bits should also be present, so
545 wrap-arounds are deal with correctly.
546 - Timestamp at the beginning and timestamp at the end of the event packet.
547 Both timestamps are written in the packet header, but sampled respectively
548 while (or before) writing the first event and while (or after) writing the
549 last event in the packet. The inclusive range between these timestamps should
550 include all event timestamps assigned to events contained within the packet.
551 - Events discarded count
552 - Snapshot of a per-stream free-running counter, counting the number of
553 events discarded that were supposed to be written in the stream prior to
554 the first event in the event packet.
555 * Note: producer-consumer buffer full condition should fill the current
556 event packet with padding so we know exactly where events have been
557 discarded.
558 - Lossless compression scheme used for the event packet content. Applied
559 directly to raw data. New types of compression can be added in following
560 versions of the format.
561 0: no compression scheme
562 1: bzip2
563 2: gzip
564 3: xz
565 - Cypher used for the event packet content. Applied after compression.
566 0: no encryption
567 1: AES
568 - Checksum scheme used for the event packet content. Applied after encryption.
569 0: no checksum
570 1: md5
571 2: sha1
572 3: crc32
573
574 5.1 Event Packet Header Fixed Layout Description
575
576 struct event_packet_header {
577 uint32_t magic;
578 uint8_t trace_uuid[16];
579 uint32_t stream_id;
580 };
581
582 5.2 Event Packet Context Description
583
584 Event packet context example. These are declared within the stream declaration
585 in the metadata. All these fields are optional except for "content_size" and
586 "packet_size", which must be present in the context.
587
588 An example event packet context type:
589
590 struct event_packet_context {
591 uint64_t timestamp_begin;
592 uint64_t timestamp_end;
593 uint32_t checksum;
594 uint32_t stream_packet_count;
595 uint32_t events_discarded;
596 uint32_t cpu_id;
597 uint32_t/uint16_t content_size;
598 uint32_t/uint16_t packet_size;
599 uint8_t stream_packet_count_bits; /* Significant counter bits */
600 uint8_t compression_scheme;
601 uint8_t encryption_scheme;
602 uint8_t checksum_scheme;
603 };
604
605
606 6. Event Structure
607
608 The overall structure of an event is:
609
610 1 - Stream Packet Context (as specified by the stream metadata)
611 2 - Event Header (as specifed by the stream metadata)
612 3 - Stream Event Context (as specified by the stream metadata)
613 4 - Event Context (as specified by the event metadata)
614 5 - Event Payload (as specified by the event metadata)
615
616 6.1 Lexical Scope
617
618 For variant tag definition only, the lexical scope of each structure (stream
619 packet context, header, stream event context, event context and payload) is
620 extended in the following way: lower levels (e.g. 3) can refer to fields defined
621 in prior levels (e.g. 2 and 1). The field in the closest level has priority in
622 case of field name conflict.
623
624 This allows, for instance, the event context to define a variant refering to the
625 "id" field of the event header as selector.
626
627 6.2 Event Header
628
629 Event headers can be described within the metadata. We hereby propose, as an
630 example, two types of events headers. Type 1 accommodates streams with less than
631 31 event IDs. Type 2 accommodates streams with 31 or more event IDs.
632
633 One major factor can vary between streams: the number of event IDs assigned to
634 a stream. Luckily, this information tends to stay relatively constant (modulo
635 event registration while trace is being recorded), so we can specify different
636 representations for streams containing few event IDs and streams containing
637 many event IDs, so we end up representing the event ID and timestamp as densely
638 as possible in each case.
639
640 The header is extended in the rare occasions where the information cannot be
641 represented in the ranges available in the standard event header. They are also
642 used in the rare occasions where the data required for a field could not be
643 collected: the flag corresponding to the missing field within the missing_fields
644 array is then set to 1.
645
646 Types uintX_t represent an X-bit unsigned integer.
647
648
649 6.2.1 Type 1 - Few event IDs
650
651 - Aligned on 32-bit (or 8-bit if byte-packed, depending on the architecture
652 preference).
653 - Native architecture byte ordering.
654 - For "compact" selection
655 - Fixed size: 32 bits.
656 - For "extended" selection
657 - Size depends on the architecture and variant alignment.
658
659 struct event_header_1 {
660 /*
661 * id: range: 0 - 30.
662 * id 31 is reserved to indicate an extended header.
663 */
664 enum <uint5_t> { compact = 0 ... 30, extended = 31 } id;
665 variant <id> {
666 struct {
667 uint27_t timestamp;
668 } compact;
669 struct {
670 uint32_t id; /* 32-bit event IDs */
671 uint64_t timestamp; /* 64-bit timestamps */
672 } extended;
673 } v;
674 };
675
676
677 6.2.2 Type 2 - Many event IDs
678
679 - Aligned on 16-bit (or 8-bit if byte-packed, depending on the architecture
680 preference).
681 - Native architecture byte ordering.
682 - For "compact" selection
683 - Size depends on the architecture and variant alignment.
684 - For "extended" selection
685 - Size depends on the architecture and variant alignment.
686
687 struct event_header_2 {
688 /*
689 * id: range: 0 - 65534.
690 * id 65535 is reserved to indicate an extended header.
691 */
692 enum <uint16_t> { compact = 0 ... 65534, extended = 65535 } id;
693 variant <id> {
694 struct {
695 uint32_t timestamp;
696 } compact;
697 struct {
698 uint32_t id; /* 32-bit event IDs */
699 uint64_t timestamp; /* 64-bit timestamps */
700 } extended;
701 } v;
702 };
703
704
705 6.2 Event Context
706
707 The event context contains information relative to the current event. The choice
708 and meaning of this information is specified by the metadata "stream" and
709 "event" information. The "stream" context is applied to all events within the
710 stream. The "stream" context structure follows the event header. The "event"
711 context is applied to specific events. Its structure follows the "stream"
712 context stucture.
713
714 An example of stream-level event context is to save the event payload size with
715 each event, or to save the current PID with each event. These are declared
716 within the stream declaration within the metadata:
717
718 stream {
719 ...
720 event {
721 ...
722 context := struct {
723 uint pid;
724 uint16_t payload_size;
725 };
726 }
727 };
728
729 An example of event-specific event context is to declare a bitmap of missing
730 fields, only appended after the stream event context if the extended event
731 header is selected. NR_FIELDS is the number of fields within the event (a
732 numeric value).
733
734 event {
735 context = struct {
736 variant <id> {
737 struct { } compact;
738 struct {
739 uint1_t missing_fields[NR_FIELDS]; /* missing event fields bitmap */
740 } extended;
741 } v;
742 };
743 ...
744 }
745
746 6.3 Event Payload
747
748 An event payload contains fields specific to a given event type. The fields
749 belonging to an event type are described in the event-specific metadata
750 within a structure type.
751
752 6.3.1 Padding
753
754 No padding at the end of the event payload. This differs from the ISO/C standard
755 for structures, but follows the CTF standard for structures. In a trace, even
756 though it makes sense to align the beginning of a structure, it really makes no
757 sense to add padding at the end of the structure, because structures are usually
758 not followed by a structure of the same type.
759
760 This trick can be done by adding a zero-length "end" field at the end of the C
761 structures, and by using the offset of this field rather than using sizeof()
762 when calculating the size of a structure (see Appendix "A. Helper macros").
763
764 6.3.2 Alignment
765
766 The event payload is aligned on the largest alignment required by types
767 contained within the payload. (This follows the ISO/C standard for structures)
768
769
770 7. Metadata
771
772 The meta-data is located in a stream named "metadata". It is made of "event
773 packets", which each start with an event packet header. The event type within
774 the metadata stream have no event header nor event context. Each event only
775 contains a null-terminated "string" payload, which is a metadata description
776 entry. The events are packed one next to another. Each event packet start with
777 an event packet header, which contains, amongst other fields, the magic number
778 and trace UUID.
779
780 The metadata can be parsed by reading through the metadata strings, skipping
781 newlines and null-characters. Type names are made of a single identifier, and
782 can be surrounded by prefix/postfix. Text contained within "/*" and "*/", as
783 well as within "//" and end of line, are treated as comments. Boolean values can
784 be represented as true, TRUE, or 1 for true, and false, FALSE, or 0 for false.
785
786 Each of "trace", "stream", "event", "struct" and "variant" have their own
787 nestable declaration scope, within which types can be declared using "typedef"
788 and "typealias". An innermost declaration scope can refer to type declared
789 within its container lexical scope prior to the innermost declaration scope.
790 Redefinition of a typedef or typealias, or hiding an uppermost definition, is
791 not valid.
792
793 The grammar representing the CTF metadata is presented in
794 Appendix C. CTF Metadata Grammar.
795
796 trace {
797 major = value; /* Trace format version */
798 minor = value;
799 uuid = value; /* Trace UUID */
800 word_size = value;
801 };
802
803 stream {
804 id = stream_id;
805 /* Type 1 - Few event IDs; Type 2 - Many event IDs. See section 6.2. */
806 event.header := event_header_1 OR event_header_2;
807 event.context := struct {
808 ...
809 };
810 packet.context := struct {
811 ...
812 };
813 };
814
815 event {
816 name = event_name;
817 id = value; /* Numeric identifier within the stream */
818 stream = stream_id;
819 context := struct {
820 ...
821 };
822 fields := struct {
823 ...
824 };
825 };
826
827 /* More detail on types in section 4. Types */
828
829 /*
830 * Named types:
831 *
832 * Type declarations behave similarly to the C standard.
833 */
834
835 typedef aliased_type_prefix aliased_type new_type aliased_type_postfix;
836
837 /* e.g.: typedef struct example new_type_name[10]; */
838
839 /*
840 * typealias
841 *
842 * The "typealias" declaration can be used to give a name (including
843 * prefix/postfix) to a type. It should also be used to map basic C types
844 * (float, int, unsigned long, ...) to a CTF type. Typealias is a superset of
845 * "typedef": it also allows assignment of a simple variable identifier to a
846 * type.
847 */
848
849 typealias type_class {
850 ...
851 } : new_type_prefix new_type new_type_postfix;
852
853 /*
854 * e.g.:
855 * typealias integer {
856 * size = 32;
857 * align = 32;
858 * signed = false;
859 * } : struct page *;
860 *
861 * typealias integer {
862 * size = 32;
863 * align = 32;
864 * signed = true;
865 * } : int;
866 */
867
868 struct name {
869 ...
870 };
871
872 variant name {
873 ...
874 };
875
876 enum name <integer_type or size> {
877 ...
878 };
879
880
881 /*
882 * Unnamed types, contained within compound type fields, typedef or typealias.
883 */
884
885 struct {
886 ...
887 }
888
889 variant {
890 ...
891 }
892
893 enum <integer_type or size> {
894 ...
895 }
896
897 typedef type new_type[length];
898
899 struct {
900 type field_name[length];
901 }
902
903 typedef type new_type[length_type];
904
905 struct {
906 type field_name[length_type];
907 }
908
909 integer {
910 ...
911 }
912
913 floating_point {
914 ...
915 }
916
917 struct {
918 integer_type field_name:size; /* GNU/C bitfield */
919 }
920
921 struct {
922 string field_name;
923 }
924
925
926 A. Helper macros
927
928 The two following macros keep track of the size of a GNU/C structure without
929 padding at the end by placing HEADER_END as the last field. A one byte end field
930 is used for C90 compatibility (C99 flexible arrays could be used here). Note
931 that this does not affect the effective structure size, which should always be
932 calculated with the header_sizeof() helper.
933
934 #define HEADER_END char end_field
935 #define header_sizeof(type) offsetof(typeof(type), end_field)
936
937
938 B. Stream Header Rationale
939
940 An event stream is divided in contiguous event packets of variable size. These
941 subdivisions allow the trace analyzer to perform a fast binary search by time
942 within the stream (typically requiring to index only the event packet headers)
943 without reading the whole stream. These subdivisions have a variable size to
944 eliminate the need to transfer the event packet padding when partially filled
945 event packets must be sent when streaming a trace for live viewing/analysis.
946 An event packet can contain a certain amount of padding at the end. Dividing
947 streams into event packets is also useful for network streaming over UDP and
948 flight recorder mode tracing (a whole event packet can be swapped out of the
949 buffer atomically for reading).
950
951 The stream header is repeated at the beginning of each event packet to allow
952 flexibility in terms of:
953
954 - streaming support,
955 - allowing arbitrary buffers to be discarded without making the trace
956 unreadable,
957 - allow UDP packet loss handling by either dealing with missing event packet
958 or asking for re-transmission.
959 - transparently support flight recorder mode,
960 - transparently support crash dump.
961
962 The event stream header will therefore be referred to as the "event packet
963 header" throughout the rest of this document.
964
965 C. CTF Metadata Grammar
966
967 /*
968 * Common Trace Format (CTF) Metadata Grammar.
969 *
970 * Inspired from the C99 grammar:
971 * http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1124.pdf (Annex A)
972 *
973 * Specialized for CTF needs by including only constant and declarations from
974 * C99 (excluding function declarations), and by adding support for variants,
975 * sequences and CTF-specific specifiers.
976 */
977
978 1) Lexical grammar
979
980 1.1) Lexical elements
981
982 token:
983 keyword
984 identifier
985 constant
986 string-literal
987 punctuator
988
989 1.2) Keywords
990
991 keyword: is one of
992
993 const
994 char
995 double
996 enum
997 event
998 floating_point
999 float
1000 integer
1001 int
1002 long
1003 short
1004 signed
1005 stream
1006 string
1007 struct
1008 trace
1009 typealias
1010 typedef
1011 unsigned
1012 variant
1013 void
1014 _Bool
1015 _Complex
1016 _Imaginary
1017
1018
1019 1.3) Identifiers
1020
1021 identifier:
1022 identifier-nondigit
1023 identifier identifier-nondigit
1024 identifier digit
1025
1026 identifier-nondigit:
1027 nondigit
1028 universal-character-name
1029 any other implementation-defined characters
1030
1031 nondigit:
1032 _
1033 [a-zA-Z] /* regular expression */
1034
1035 digit:
1036 [0-9] /* regular expression */
1037
1038 1.4) Universal character names
1039
1040 universal-character-name:
1041 \u hex-quad
1042 \U hex-quad hex-quad
1043
1044 hex-quad:
1045 hexadecimal-digit hexadecimal-digit hexadecimal-digit hexadecimal-digit
1046
1047 1.5) Constants
1048
1049 constant:
1050 integer-constant
1051 enumeration-constant
1052 character-constant
1053
1054 integer-constant:
1055 decimal-constant integer-suffix-opt
1056 octal-constant integer-suffix-opt
1057 hexadecimal-constant integer-suffix-opt
1058
1059 decimal-constant:
1060 nonzero-digit
1061 decimal-constant digit
1062
1063 octal-constant:
1064 0
1065 octal-constant octal-digit
1066
1067 hexadecimal-constant:
1068 hexadecimal-prefix hexadecimal-digit
1069 hexadecimal-constant hexadecimal-digit
1070
1071 hexadecimal-prefix:
1072 0x
1073 0X
1074
1075 nonzero-digit:
1076 [1-9]
1077
1078 integer-suffix:
1079 unsigned-suffix long-suffix-opt
1080 unsigned-suffix long-long-suffix
1081 long-suffix unsigned-suffix-opt
1082 long-long-suffix unsigned-suffix-opt
1083
1084 unsigned-suffix:
1085 u
1086 U
1087
1088 long-suffix:
1089 l
1090 L
1091
1092 long-long-suffix:
1093 ll
1094 LL
1095
1096 digit-sequence:
1097 digit
1098 digit-sequence digit
1099
1100 hexadecimal-digit-sequence:
1101 hexadecimal-digit
1102 hexadecimal-digit-sequence hexadecimal-digit
1103
1104 enumeration-constant:
1105 identifier
1106 string-literal
1107
1108 character-constant:
1109 ' c-char-sequence '
1110 L' c-char-sequence '
1111
1112 c-char-sequence:
1113 c-char
1114 c-char-sequence c-char
1115
1116 c-char:
1117 any member of source charset except single-quote ('), backslash
1118 (\), or new-line character.
1119 escape-sequence
1120
1121 escape-sequence:
1122 simple-escape-sequence
1123 octal-escape-sequence
1124 hexadecimal-escape-sequence
1125 universal-character-name
1126
1127 simple-escape-sequence: one of
1128 \' \" \? \\ \a \b \f \n \r \t \v
1129
1130 octal-escape-sequence:
1131 \ octal-digit
1132 \ octal-digit octal-digit
1133 \ octal-digit octal-digit octal-digit
1134
1135 hexadecimal-escape-sequence:
1136 \x hexadecimal-digit
1137 hexadecimal-escape-sequence hexadecimal-digit
1138
1139 1.6) String literals
1140
1141 string-literal:
1142 " s-char-sequence-opt "
1143 L" s-char-sequence-opt "
1144
1145 s-char-sequence:
1146 s-char
1147 s-char-sequence s-char
1148
1149 s-char:
1150 any member of source charset except double-quote ("), backslash
1151 (\), or new-line character.
1152 escape-sequence
1153
1154 1.7) Punctuators
1155
1156 punctuator: one of
1157 [ ] ( ) { } . -> * + - < > : ; ... = ,
1158
1159
1160 2) Phrase structure grammar
1161
1162 primary-expression:
1163 identifier
1164 constant
1165 string-literal
1166 ( unary-expression )
1167
1168 postfix-expression:
1169 primary-expression
1170 postfix-expression [ unary-expression ]
1171 postfix-expression . identifier
1172 postfix-expressoin -> identifier
1173
1174 unary-expression:
1175 postfix-expression
1176 unary-operator postfix-expression
1177
1178 unary-operator: one of
1179 + -
1180
1181 assignment-operator:
1182 =
1183
1184 constant-expression:
1185 unary-expression
1186
1187 constant-expression-range:
1188 constant-expression ... constant-expression
1189
1190 2.2) Declarations:
1191
1192 declaration:
1193 declaration-specifiers ;
1194 declaration-specifiers storage-class-specifier declaration-specifiers declarator-list ;
1195 ctf-specifier ;
1196
1197 declaration-specifiers:
1198 type-specifier declaration-specifiers-opt
1199 type-qualifier declaration-specifiers-opt
1200
1201 declarator-list:
1202 declarator
1203 declarator-list , declarator
1204
1205 abstract-declarator-list:
1206 abstract-declarator
1207 abstract-declarator-list , abstract-declarator
1208
1209 storage-class-specifier:
1210 typedef
1211
1212 type-specifier:
1213 void
1214 char
1215 short
1216 int
1217 long
1218 float
1219 double
1220 signed
1221 unsigned
1222 _Bool
1223 _Complex
1224 struct-specifier
1225 variant-specifier
1226 enum-specifier
1227 typedef-name
1228 ctf-type-specifier
1229
1230 struct-specifier:
1231 struct identifier-opt { struct-or-variant-declaration-list-opt }
1232 struct identifier
1233
1234 struct-or-variant-declaration-list:
1235 struct-or-variant-declaration
1236 struct-or-variant-declaration-list struct-or-variant-declaration
1237
1238 struct-or-variant-declaration:
1239 specifier-qualifier-list struct-or-variant-declarator-list ;
1240 declaration-specifiers storage-class-specifier declaration-specifiers declarator-list ;
1241 typealias declaration-specifiers abstract-declarator-list : declaration-specifiers abstract-declarator-list ;
1242 typealias declaration-specifiers abstract-declarator-list : declarator-list ;
1243
1244 specifier-qualifier-list:
1245 type-specifier specifier-qualifier-list-opt
1246 type-qualifier specifier-qualifier-list-opt
1247
1248 struct-or-variant-declarator-list:
1249 struct-or-variant-declarator
1250 struct-or-variant-declarator-list , struct-or-variant-declarator
1251
1252 struct-or-variant-declarator:
1253 declarator
1254 declarator-opt : constant-expression
1255
1256 variant-specifier:
1257 variant identifier-opt variant-tag-opt { struct-or-variant-declaration-list }
1258 variant identifier variant-tag
1259
1260 variant-tag:
1261 < identifier >
1262
1263 enum-specifier:
1264 enum identifier-opt { enumerator-list }
1265 enum identifier-opt { enumerator-list , }
1266 enum identifier
1267 enum identifier-opt < declaration-specifiers > { enumerator-list }
1268 enum identifier-opt < declaration-specifiers > { enumerator-list , }
1269 enum identifier < declaration-specifiers >
1270 enum identifier-opt < integer-constant > { enumerator-list }
1271 enum identifier-opt < integer-constant > { enumerator-list , }
1272 enum identifier < integer-constant >
1273
1274 enumerator-list:
1275 enumerator
1276 enumerator-list , enumerator
1277
1278 enumerator:
1279 enumeration-constant
1280 enumeration-constant = constant-expression
1281 enumeration-constant = constant-expression-range
1282
1283 type-qualifier:
1284 const
1285
1286 declarator:
1287 pointer-opt direct-declarator
1288
1289 direct-declarator:
1290 identifier
1291 ( declarator )
1292 direct-declarator [ type-specifier ]
1293 direct-declarator [ constant-expression ]
1294
1295 abstract-declarator:
1296 pointer-opt direct-abstract-declarator
1297
1298 direct-abstract-declarator:
1299 identifier-opt
1300 ( abstract-declarator )
1301 direct-abstract-declarator [ type-specifier ]
1302 direct-abstract-declarator [ constant-expression ]
1303 direct-abstract-declarator [ ]
1304
1305 pointer:
1306 * type-qualifier-list-opt
1307 * type-qualifier-list-opt pointer
1308
1309 type-qualifier-list:
1310 type-qualifier
1311 type-qualifier-list type-qualifier
1312
1313 typedef-name:
1314 identifier
1315
1316 2.3) CTF-specific declarations
1317
1318 ctf-specifier:
1319 event { ctf-assignment-expression-list-opt }
1320 stream { ctf-assignment-expression-list-opt }
1321 trace { ctf-assignment-expression-list-opt }
1322 typealias declaration-specifiers abstract-declarator-list : declaration-specifiers abstract-declarator-list ;
1323 typealias declaration-specifiers abstract-declarator-list : declarator-list ;
1324
1325 ctf-type-specifier:
1326 floating_point { ctf-assignment-expression-list-opt }
1327 integer { ctf-assignment-expression-list-opt }
1328 string { ctf-assignment-expression-list-opt }
1329
1330 ctf-assignment-expression-list:
1331 ctf-assignment-expression
1332 ctf-assignment-expression-list ; ctf-assignment-expression
1333
1334 ctf-assignment-expression:
1335 unary-expression assignment-operator unary-expression
1336 unary-expression type-assignment-operator type-specifier
1337 declaration-specifiers storage-class-specifier declaration-specifiers declarator-list
1338 typealias declaration-specifiers abstract-declarator-list : declaration-specifiers abstract-declarator-list
1339 typealias declaration-specifiers abstract-declarator-list : declarator-list
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