Change typealias delimiter from : to typename
[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
72 amount of padding at the end. The stream header is repeated at the
73 beginning of each event packet. The rationale for the event stream
74 design choices is explained in Appendix B. Stream Header Rationale.
75
76 The event stream header will therefore be referred to as the "event packet
77 header" throughout the rest of this document.
78
79
80 4. Types
81
82 Types are organized as type classes. Each type class belong to either of two
83 kind of types: basic types or compound types.
84
85 4.1 Basic types
86
87 A basic type is a scalar type, as described in this section. It includes
88 integers, GNU/C bitfields, enumerations, and floating point values.
89
90 4.1.1 Type inheritance
91
92 Type specifications can be inherited to allow deriving types from a
93 type class. For example, see the uint32_t named type derived from the "integer"
94 type class below ("Integers" section). Types have a precise binary
95 representation in the trace. A type class has methods to read and write these
96 types, but must be derived into a type to be usable in an event field.
97
98 4.1.2 Alignment
99
100 We define "byte-packed" types as aligned on the byte size, namely 8-bit.
101 We define "bit-packed" types as following on the next bit, as defined by the
102 "Integers" section.
103
104 All basic types, except bitfields, are either aligned on an architecture-defined
105 specific alignment or byte-packed, depending on the architecture preference.
106 Architectures providing fast unaligned write byte-packed basic types to save
107 space, aligning each type on byte boundaries (8-bit). Architectures with slow
108 unaligned writes align types on specific alignment values. If no specific
109 alignment is declared for a type, it is assumed to be bit-packed for
110 integers with size not multiple of 8 bits and for gcc bitfields. All
111 other types are byte-packed.
112
113 Metadata attribute representation of a specific alignment:
114
115 align = value; /* value in bits */
116
117 4.1.3 Byte order
118
119 By default, the native endianness of the source architecture the trace is used.
120 Byte order can be overridden for a basic type by specifying a "byte_order"
121 attribute. Typical use-case is to specify the network byte order (big endian:
122 "be") to save data captured from the network into the trace without conversion.
123 If not specified, the byte order is native.
124
125 Metadata representation:
126
127 byte_order = native OR network OR be OR le; /* network and be are aliases */
128
129 4.1.4 Size
130
131 Type size, in bits, for integers and floats is that returned by "sizeof()" in C
132 multiplied by CHAR_BIT.
133 We require the size of "char" and "unsigned char" types (CHAR_BIT) to be fixed
134 to 8 bits for cross-endianness compatibility.
135
136 Metadata representation:
137
138 size = value; (value is in bits)
139
140 4.1.5 Integers
141
142 Signed integers are represented in two-complement. Integer alignment, size,
143 signedness and byte ordering are defined in the metadata. Integers aligned on
144 byte size (8-bit) and with length multiple of byte size (8-bit) correspond to
145 the C99 standard integers. In addition, integers with alignment and/or size that
146 are _not_ a multiple of the byte size are permitted; these correspond to the C99
147 standard bitfields, with the added specification that the CTF integer bitfields
148 have a fixed binary representation. A MIT-licensed reference implementation of
149 the CTF portable bitfields is available at:
150
151 http://git.efficios.com/?p=babeltrace.git;a=blob;f=include/babeltrace/bitfield.h
152
153 Binary representation of integers:
154
155 - On little and big endian:
156 - Within a byte, high bits correspond to an integer high bits, and low bits
157 correspond to low bits.
158 - On little endian:
159 - Integer across multiple bytes are placed from the less significant to the
160 most significant.
161 - Consecutive integers are placed from lower bits to higher bits (even within
162 a byte).
163 - On big endian:
164 - Integer across multiple bytes are placed from the most significant to the
165 less significant.
166 - Consecutive integers are placed from higher bits to lower bits (even within
167 a byte).
168
169 This binary representation is derived from the bitfield implementation in GCC
170 for little and big endian. However, contrary to what GCC does, integers can
171 cross units boundaries (no padding is required). Padding can be explicitely
172 added (see 4.1.6 GNU/C bitfields) to follow the GCC layout if needed.
173
174 Metadata representation:
175
176 integer {
177 signed = true OR false; /* default false */
178 byte_order = native OR network OR be OR le; /* default native */
179 size = value; /* value in bits, no default */
180 align = value; /* value in bits */
181 }
182
183 Example of type inheritance (creation of a uint32_t named type):
184
185 typealias integer {
186 size = 32;
187 signed = false;
188 align = 32;
189 } typename uint32_t;
190
191 Definition of a named 5-bit signed bitfield:
192
193 typealias integer {
194 size = 5;
195 signed = true;
196 align = 1;
197 } typename int5_t;
198
199 4.1.6 GNU/C bitfields
200
201 The GNU/C bitfields follow closely the integer representation, with a
202 particularity on alignment: if a bitfield cannot fit in the current unit, the
203 unit is padded and the bitfield starts at the following unit. The unit size is
204 defined by the size of the type "unit_type".
205
206 Metadata representation:
207
208 unit_type name:size:
209
210 As an example, the following structure declared in C compiled by GCC:
211
212 struct example {
213 short a:12;
214 short b:5;
215 };
216
217 The example structure is aligned on the largest element (short). The second
218 bitfield would be aligned on the next unit boundary, because it would not fit in
219 the current unit.
220
221 4.1.7 Floating point
222
223 The floating point values byte ordering is defined in the metadata.
224
225 Floating point values follow the IEEE 754-2008 standard interchange formats.
226 Description of the floating point values include the exponent and mantissa size
227 in bits. Some requirements are imposed on the floating point values:
228
229 - FLT_RADIX must be 2.
230 - mant_dig is the number of digits represented in the mantissa. It is specified
231 by the ISO C99 standard, section 5.2.4, as FLT_MANT_DIG, DBL_MANT_DIG and
232 LDBL_MANT_DIG as defined by <float.h>.
233 - exp_dig is the number of digits represented in the exponent. Given that
234 mant_dig is one bit more than its actual size in bits (leading 1 is not
235 needed) and also given that the sign bit always takes one bit, exp_dig can be
236 specified as:
237
238 - sizeof(float) * CHAR_BIT - FLT_MANT_DIG
239 - sizeof(double) * CHAR_BIT - DBL_MANT_DIG
240 - sizeof(long double) * CHAR_BIT - LDBL_MANT_DIG
241
242 Metadata representation:
243
244 floating_point {
245 exp_dig = value;
246 mant_dig = value;
247 byte_order = native OR network OR be OR le;
248 }
249
250 Example of type inheritance:
251
252 typealias floating_point {
253 exp_dig = 8; /* sizeof(float) * CHAR_BIT - FLT_MANT_DIG */
254 mant_dig = 24; /* FLT_MANT_DIG */
255 byte_order = native;
256 } typename float;
257
258 TODO: define NaN, +inf, -inf behavior.
259
260 4.1.8 Enumerations
261
262 Enumerations are a mapping between an integer type and a table of strings. The
263 numerical representation of the enumeration follows the integer type specified
264 by the metadata. The enumeration mapping table is detailed in the enumeration
265 description within the metadata. The mapping table maps inclusive value ranges
266 (or single values) to strings. Instead of being limited to simple
267 "value -> string" mappings, these enumerations map
268 "[ start_value ... end_value ] -> string", which map inclusive ranges of
269 values to strings. An enumeration from the C language can be represented in
270 this format by having the same start_value and end_value for each element, which
271 is in fact a range of size 1. This single-value range is supported without
272 repeating the start and end values with the value = string declaration.
273
274 enum name <integer_type> {
275 somestring = start_value1 ... end_value1,
276 "other string" = start_value2 ... end_value2,
277 yet_another_string, /* will be assigned to end_value2 + 1 */
278 "some other string" = value,
279 ...
280 };
281
282 If the values are omitted, the enumeration starts at 0 and increment of 1 for
283 each entry:
284
285 enum name <unsigned int> {
286 ZERO,
287 ONE,
288 TWO,
289 TEN = 10,
290 ELEVEN,
291 };
292
293 Overlapping ranges within a single enumeration are implementation defined.
294
295 A nameless enumeration can be declared as a field type or as part of a typedef:
296
297 enum <integer_type> {
298 ...
299 }
300
301
302 4.2 Compound types
303
304 Compound are aggregation of type declarations. Compound types include
305 structures, variant, arrays, sequences, and strings.
306
307 4.2.1 Structures
308
309 Structures are aligned on the largest alignment required by basic types
310 contained within the structure. (This follows the ISO/C standard for structures)
311
312 Metadata representation of a named structure:
313
314 struct name {
315 field_type field_name;
316 field_type field_name;
317 ...
318 };
319
320 Example:
321
322 struct example {
323 integer { /* Nameless type */
324 size = 16;
325 signed = true;
326 align = 16;
327 } first_field_name;
328 uint64_t second_field_name; /* Named type declared in the metadata */
329 };
330
331 The fields are placed in a sequence next to each other. They each possess a
332 field name, which is a unique identifier within the structure.
333
334 A nameless structure can be declared as a field type or as part of a typedef:
335
336 struct {
337 ...
338 }
339
340 4.2.2 Variants (Discriminated/Tagged Unions)
341
342 A CTF variant is a selection between different types. A CTF variant must
343 always be defined within the scope of a structure or within fields
344 contained within a structure (defined recursively). A "tag" enumeration
345 field must appear in either the same lexical scope, prior to the variant
346 field (in field declaration order), in an uppermost lexical scope (see
347 Section 7.2.1), or in an uppermost dynamic scope (see Section 7.2.2).
348 The type selection is indicated by the mapping from the enumeration
349 value to the string used as variant type selector. The field to use as
350 tag is specified by the "tag_field", specified between "< >" after the
351 "variant" keyword for unnamed variants, and after "variant name" for
352 named variants.
353
354 The alignment of the variant is the alignment of the type as selected by the tag
355 value for the specific instance of the variant. The alignment of the type
356 containing the variant is independent of the variant alignment. The size of the
357 variant is the size as selected by the tag value for the specific instance of
358 the variant.
359
360 A named variant declaration followed by its definition within a structure
361 declaration:
362
363 variant name {
364 field_type sel1;
365 field_type sel2;
366 field_type sel3;
367 ...
368 };
369
370 struct {
371 enum <integer_type> { sel1, sel2, sel3, ... } tag_field;
372 ...
373 variant name <tag_field> v;
374 }
375
376 An unnamed variant definition within a structure is expressed by the following
377 metadata:
378
379 struct {
380 enum <integer_type> { sel1, sel2, sel3, ... } tag_field;
381 ...
382 variant <tag_field> {
383 field_type sel1;
384 field_type sel2;
385 field_type sel3;
386 ...
387 } v;
388 }
389
390 Example of a named variant within a sequence that refers to a single tag field:
391
392 variant example {
393 uint32_t a;
394 uint64_t b;
395 short c;
396 };
397
398 struct {
399 enum <uint2_t> { a, b, c } choice;
400 variant example <choice> v[unsigned int];
401 }
402
403 Example of an unnamed variant:
404
405 struct {
406 enum <uint2_t> { a, b, c, d } choice;
407 /* Unrelated fields can be added between the variant and its tag */
408 int32_t somevalue;
409 variant <choice> {
410 uint32_t a;
411 uint64_t b;
412 short c;
413 struct {
414 unsigned int field1;
415 uint64_t field2;
416 } d;
417 } s;
418 }
419
420 Example of an unnamed variant within an array:
421
422 struct {
423 enum <uint2_t> { a, b, c } choice;
424 variant <choice> {
425 uint32_t a;
426 uint64_t b;
427 short c;
428 } v[10];
429 }
430
431 Example of a variant type definition within a structure, where the defined type
432 is then declared within an array of structures. This variant refers to a tag
433 located in an upper lexical scope. This example clearly shows that a variant
434 type definition referring to the tag "x" uses the closest preceding field from
435 the lexical scope of the type definition.
436
437 struct {
438 enum <uint2_t> { a, b, c, d } x;
439
440 typedef variant <x> { /*
441 * "x" refers to the preceding "x" enumeration in the
442 * lexical scope of the type definition.
443 */
444 uint32_t a;
445 uint64_t b;
446 short c;
447 } example_variant;
448
449 struct {
450 enum <int> { x, y, z } x; /* This enumeration is not used by "v". */
451 example_variant v; /*
452 * "v" uses the "enum <uint2_t> { a, b, c, d }"
453 * tag.
454 */
455 } a[10];
456 }
457
458 4.2.3 Arrays
459
460 Arrays are fixed-length. Their length is declared in the type declaration within
461 the metadata. They contain an array of "inner type" elements, which can refer to
462 any type not containing the type of the array being declared (no circular
463 dependency). The length is the number of elements in an array.
464
465 Metadata representation of a named array:
466
467 typedef elem_type name[length];
468
469 A nameless array can be declared as a field type within a structure, e.g.:
470
471 uint8_t field_name[10];
472
473
474 4.2.4 Sequences
475
476 Sequences are dynamically-sized arrays. They start with an integer that specify
477 the length of the sequence, followed by an array of "inner type" elements.
478 The length is the number of elements in the sequence.
479
480 Metadata representation for a named sequence:
481
482 typedef elem_type name[length_type];
483
484 A nameless sequence can be declared as a field type, e.g.:
485
486 long field_name[int];
487
488 The length type follows the integer types specifications, and the sequence
489 elements follow the "array" specifications.
490
491 4.2.5 Strings
492
493 Strings are an array of bytes of variable size and are terminated by a '\0'
494 "NULL" character. Their encoding is described in the metadata. In absence of
495 encoding attribute information, the default encoding is UTF-8.
496
497 Metadata representation of a named string type:
498
499 typealias string {
500 encoding = UTF8 OR ASCII;
501 } typename name;
502
503 A nameless string type can be declared as a field type:
504
505 string field_name; /* Use default UTF8 encoding */
506
507 5. Event Packet Header
508
509 The event packet header consists of two part: one is mandatory and have a fixed
510 layout. The second part, the "event packet context", has its layout described in
511 the metadata.
512
513 - Aligned on page size. Fixed size. Fields either aligned or packed (depending
514 on the architecture preference).
515 No padding at the end of the event packet header. Native architecture byte
516 ordering.
517
518 Fixed layout (event packet header):
519
520 - Magic number (CTF magic numbers: 0xC1FC1FC1 and its reverse endianness
521 representation: 0xC11FFCC1) It needs to have a non-symmetric bytewise
522 representation. Used to distinguish between big and little endian traces (this
523 information is determined by knowing the endianness of the architecture
524 reading the trace and comparing the magic number against its value and the
525 reverse, 0xC11FFCC1). This magic number specifies that we use the CTF metadata
526 description language described in this document. Different magic numbers
527 should be used for other metadata description languages.
528 - Trace UUID, used to ensure the event packet match the metadata used.
529 (note: we cannot use a metadata checksum because metadata can be appended to
530 while tracing is active)
531 - Stream ID, used as reference to stream description in metadata.
532
533 Metadata-defined layout (event packet context):
534
535 - Event packet content size (in bytes).
536 - Event packet size (in bytes, includes padding).
537 - Event packet content checksum (optional). Checksum excludes the event packet
538 header.
539 - Per-stream event packet sequence count (to deal with UDP packet loss). The
540 number of significant sequence counter bits should also be present, so
541 wrap-arounds are deal with correctly.
542 - Timestamp at the beginning and timestamp at the end of the event packet.
543 Both timestamps are written in the packet header, but sampled respectively
544 while (or before) writing the first event and while (or after) writing the
545 last event in the packet. The inclusive range between these timestamps should
546 include all event timestamps assigned to events contained within the packet.
547 - Events discarded count
548 - Snapshot of a per-stream free-running counter, counting the number of
549 events discarded that were supposed to be written in the stream prior to
550 the first event in the event packet.
551 * Note: producer-consumer buffer full condition should fill the current
552 event packet with padding so we know exactly where events have been
553 discarded.
554 - Lossless compression scheme used for the event packet content. Applied
555 directly to raw data. New types of compression can be added in following
556 versions of the format.
557 0: no compression scheme
558 1: bzip2
559 2: gzip
560 3: xz
561 - Cypher used for the event packet content. Applied after compression.
562 0: no encryption
563 1: AES
564 - Checksum scheme used for the event packet content. Applied after encryption.
565 0: no checksum
566 1: md5
567 2: sha1
568 3: crc32
569
570 5.1 Event Packet Header Fixed Layout Description
571
572 struct event_packet_header {
573 uint32_t magic;
574 uint8_t trace_uuid[16];
575 uint32_t stream_id;
576 };
577
578 5.2 Event Packet Context Description
579
580 Event packet context example. These are declared within the stream declaration
581 in the metadata. All these fields are optional except for "content_size" and
582 "packet_size", which must be present in the context.
583
584 An example event packet context type:
585
586 struct event_packet_context {
587 uint64_t timestamp_begin;
588 uint64_t timestamp_end;
589 uint32_t checksum;
590 uint32_t stream_packet_count;
591 uint32_t events_discarded;
592 uint32_t cpu_id;
593 uint32_t/uint16_t content_size;
594 uint32_t/uint16_t packet_size;
595 uint8_t stream_packet_count_bits; /* Significant counter bits */
596 uint8_t compression_scheme;
597 uint8_t encryption_scheme;
598 uint8_t checksum_scheme;
599 };
600
601
602 6. Event Structure
603
604 The overall structure of an event is:
605
606 1 - Stream Packet Context (as specified by the stream metadata)
607 2 - Event Header (as specified by the stream metadata)
608 3 - Stream Event Context (as specified by the stream metadata)
609 4 - Event Context (as specified by the event metadata)
610 5 - Event Payload (as specified by the event metadata)
611
612 This structure defines an implicit dynamic scoping, where variants
613 located in inner structures (those with a higher number in the listing
614 above) can refer to the fields of outer structures (with lower number in
615 the listing above). See Section 7.2 Metadata Scopes for more detail.
616
617 6.1 Event Header
618
619 Event headers can be described within the metadata. We hereby propose, as an
620 example, two types of events headers. Type 1 accommodates streams with less than
621 31 event IDs. Type 2 accommodates streams with 31 or more event IDs.
622
623 One major factor can vary between streams: the number of event IDs assigned to
624 a stream. Luckily, this information tends to stay relatively constant (modulo
625 event registration while trace is being recorded), so we can specify different
626 representations for streams containing few event IDs and streams containing
627 many event IDs, so we end up representing the event ID and timestamp as densely
628 as possible in each case.
629
630 The header is extended in the rare occasions where the information cannot be
631 represented in the ranges available in the standard event header. They are also
632 used in the rare occasions where the data required for a field could not be
633 collected: the flag corresponding to the missing field within the missing_fields
634 array is then set to 1.
635
636 Types uintX_t represent an X-bit unsigned integer.
637
638
639 6.1.1 Type 1 - Few event IDs
640
641 - Aligned on 32-bit (or 8-bit if byte-packed, depending on the architecture
642 preference).
643 - Native architecture byte ordering.
644 - For "compact" selection
645 - Fixed size: 32 bits.
646 - For "extended" selection
647 - Size depends on the architecture and variant alignment.
648
649 struct event_header_1 {
650 /*
651 * id: range: 0 - 30.
652 * id 31 is reserved to indicate an extended header.
653 */
654 enum <uint5_t> { compact = 0 ... 30, extended = 31 } id;
655 variant <id> {
656 struct {
657 uint27_t timestamp;
658 } compact;
659 struct {
660 uint32_t id; /* 32-bit event IDs */
661 uint64_t timestamp; /* 64-bit timestamps */
662 } extended;
663 } v;
664 };
665
666
667 6.1.2 Type 2 - Many event IDs
668
669 - Aligned on 16-bit (or 8-bit if byte-packed, depending on the architecture
670 preference).
671 - Native architecture byte ordering.
672 - For "compact" selection
673 - Size depends on the architecture and variant alignment.
674 - For "extended" selection
675 - Size depends on the architecture and variant alignment.
676
677 struct event_header_2 {
678 /*
679 * id: range: 0 - 65534.
680 * id 65535 is reserved to indicate an extended header.
681 */
682 enum <uint16_t> { compact = 0 ... 65534, extended = 65535 } id;
683 variant <id> {
684 struct {
685 uint32_t timestamp;
686 } compact;
687 struct {
688 uint32_t id; /* 32-bit event IDs */
689 uint64_t timestamp; /* 64-bit timestamps */
690 } extended;
691 } v;
692 };
693
694
695 6.2 Event Context
696
697 The event context contains information relative to the current event. The choice
698 and meaning of this information is specified by the metadata "stream" and
699 "event" information. The "stream" context is applied to all events within the
700 stream. The "stream" context structure follows the event header. The "event"
701 context is applied to specific events. Its structure follows the "stream"
702 context stucture.
703
704 An example of stream-level event context is to save the event payload size with
705 each event, or to save the current PID with each event. These are declared
706 within the stream declaration within the metadata:
707
708 stream {
709 ...
710 event {
711 ...
712 context := struct {
713 uint pid;
714 uint16_t payload_size;
715 };
716 }
717 };
718
719 An example of event-specific event context is to declare a bitmap of missing
720 fields, only appended after the stream event context if the extended event
721 header is selected. NR_FIELDS is the number of fields within the event (a
722 numeric value).
723
724 event {
725 context = struct {
726 variant <id> {
727 struct { } compact;
728 struct {
729 uint1_t missing_fields[NR_FIELDS]; /* missing event fields bitmap */
730 } extended;
731 } v;
732 };
733 ...
734 }
735
736 6.3 Event Payload
737
738 An event payload contains fields specific to a given event type. The fields
739 belonging to an event type are described in the event-specific metadata
740 within a structure type.
741
742 6.3.1 Padding
743
744 No padding at the end of the event payload. This differs from the ISO/C standard
745 for structures, but follows the CTF standard for structures. In a trace, even
746 though it makes sense to align the beginning of a structure, it really makes no
747 sense to add padding at the end of the structure, because structures are usually
748 not followed by a structure of the same type.
749
750 This trick can be done by adding a zero-length "end" field at the end of the C
751 structures, and by using the offset of this field rather than using sizeof()
752 when calculating the size of a structure (see Appendix "A. Helper macros").
753
754 6.3.2 Alignment
755
756 The event payload is aligned on the largest alignment required by types
757 contained within the payload. (This follows the ISO/C standard for structures)
758
759
760 7. Metadata
761
762 The meta-data is located in a stream identified by its name: "metadata".
763 It is made of "event packets", which each start with an event packet
764 header. The event type within the metadata stream have no event header
765 nor event context. Each event only contains a null-terminated "string"
766 payload, which is a metadata description entry. The events are packed
767 one next to another. Each event packet start with an event packet
768 header, which contains, amongst other fields, the magic number and trace
769 UUID. In the event packet header, the trace UUID is represented as an
770 array of bytes. Within the string-based metadata description, the trace
771 UUID is represented as a string of hexadecimal digits and dashes "-".
772
773 The metadata can be parsed by reading through the metadata strings,
774 skipping null-characters. Type names are made of a single identifier,
775 and can be surrounded by prefix/postfix. Text contained within "/*" and
776 "*/", as well as within "//" and end of line, are treated as comments.
777 Boolean values can be represented as true, TRUE, or 1 for true, and
778 false, FALSE, or 0 for false.
779
780
781 7.1 Declaration vs Definition
782
783 A declaration associates a layout to a type, without specifying where
784 this type is located in the event structure hierarchy (see Section 6).
785 This therefore includes typedef, typealias, as well as all type
786 specifiers. In certain circumstances (typedef, structure field and
787 variant field), a declaration is followed by a declarator, which specify
788 the newly defined type name (for typedef), or the field name (for
789 declarations located within structure and variants). Array and sequence,
790 declared with square brackets ("[" "]"), are part of the declarator,
791 similarly to C99. The enumeration type specifier and variant tag name
792 (both specified with "<" ">") are part of the type specifier.
793
794 A definition associates a type to a location in the event structure
795 hierarchy (see Section 6). This association is denoted by ":=", as shown
796 in Section 7.3.
797
798
799 7.2 Metadata Scopes
800
801 CTF metadata uses two different types of scoping: a lexical scope is
802 used for declarations and type definitions, and a dynamic scope is used
803 for variants references to tag fields.
804
805 7.2.1 Lexical Scope
806
807 Each of "trace", "stream", "event", "struct" and "variant" have their own
808 nestable declaration scope, within which types can be declared using "typedef"
809 and "typealias". A root declaration scope also contains all declarations
810 located outside of any of the aforementioned declarations. An inner
811 declaration scope can refer to type declared within its container
812 lexical scope prior to the inner declaration scope. Redefinition of a
813 typedef or typealias is not valid, although hiding an upper scope
814 typedef or typealias is allowed within a sub-scope.
815
816 7.2.2 Dynamic Scope
817
818 A dynamic scope consists in the lexical scope augmented with the
819 implicit event structure definition hierarchy presented at Section 6.
820 The dynamic scope is only used for variant tag definitions. It is used
821 at definition time to look up the location of the tag field associated
822 with a variant.
823
824 Therefore, variants in lower levels in the dynamic scope (e.g. event
825 context) can refer to a tag field located in upper levels (e.g. in the
826 event header) by specifying, in this case, the associated tag with
827 <header.field_name>. This allows, for instance, the event context to
828 define a variant referring to the "id" field of the event header as
829 selector.
830
831 The target dynamic scope must be specified explicitly when referring to
832 a field outside of the local static scope. The dynamic scope prefixes
833 are thus:
834
835 - Stream Packet Context: <stream.packet.context. >,
836 - Event Header: <stream.event.header. >,
837 - Stream Event Context: <stream.event.context. >,
838 - Event Context: <event.context. >,
839 - Event Payload: <event.fields. >.
840
841 Multiple declarations of the same field name within a single scope is
842 not valid. It is however valid to re-use the same field name in
843 different scopes. There is no possible conflict, because the dynamic
844 scope must be specified when a variant refers to a tag field located in
845 a different dynamic scope.
846
847 The information available in the dynamic scopes can be thought of as the
848 current tracing context. At trace production, information about the
849 current context is saved into the specified scope field levels. At trace
850 consumption, for each event, the current trace context is therefore
851 readable by accessing the upper dynamic scopes.
852
853
854 7.3 Metadata Examples
855
856 The grammar representing the CTF metadata is presented in
857 Appendix C. CTF Metadata Grammar. This section presents a rather ligher
858 reading that consists in examples of CTF metadata, with template values:
859
860 trace {
861 major = value; /* Trace format version */
862 minor = value;
863 uuid = "aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaaa"; /* Trace UUID */
864 word_size = value;
865 };
866
867 stream {
868 id = stream_id;
869 /* Type 1 - Few event IDs; Type 2 - Many event IDs. See section 6.1. */
870 event.header := event_header_1 OR event_header_2;
871 event.context := struct {
872 ...
873 };
874 packet.context := struct {
875 ...
876 };
877 };
878
879 event {
880 name = event_name;
881 id = value; /* Numeric identifier within the stream */
882 stream = stream_id;
883 context := struct {
884 ...
885 };
886 fields := struct {
887 ...
888 };
889 };
890
891 /* More detail on types in section 4. Types */
892
893 /*
894 * Named types:
895 *
896 * Type declarations behave similarly to the C standard.
897 */
898
899 typedef aliased_type_specifiers new_type_declarators;
900
901 /* e.g.: typedef struct example new_type_name[10]; */
902
903 /*
904 * typealias
905 *
906 * The "typealias" declaration can be used to give a name (including
907 * pointer declarator specifier) to a type. It should also be used to
908 * map basic C types (float, int, unsigned long, ...) to a CTF type.
909 * Typealias is a superset of "typedef": it also allows assignment of a
910 * simple variable identifier to a type. The keyword "typename" is
911 * reserved to separate the aliased type from the newly declared alias
912 * name.
913 */
914
915 typealias type_class {
916 ...
917 } typename type_specifiers type_declarator;
918
919 /*
920 * e.g.:
921 * typealias integer {
922 * size = 32;
923 * align = 32;
924 * signed = false;
925 * } typename struct page *;
926 *
927 * typealias integer {
928 * size = 32;
929 * align = 32;
930 * signed = true;
931 * } typename int;
932 */
933
934 struct name {
935 ...
936 };
937
938 variant name {
939 ...
940 };
941
942 enum name <integer_type> {
943 ...
944 };
945
946
947 /*
948 * Unnamed types, contained within compound type fields, typedef or typealias.
949 */
950
951 struct {
952 ...
953 }
954
955 variant {
956 ...
957 }
958
959 enum <integer_type> {
960 ...
961 }
962
963 typedef type new_type[length];
964
965 struct {
966 type field_name[length];
967 }
968
969 typedef type new_type[length_type];
970
971 struct {
972 type field_name[length_type];
973 }
974
975 integer {
976 ...
977 }
978
979 floating_point {
980 ...
981 }
982
983 struct {
984 integer_type field_name:size; /* GNU/C bitfield */
985 }
986
987 struct {
988 string field_name;
989 }
990
991
992 A. Helper macros
993
994 The two following macros keep track of the size of a GNU/C structure without
995 padding at the end by placing HEADER_END as the last field. A one byte end field
996 is used for C90 compatibility (C99 flexible arrays could be used here). Note
997 that this does not affect the effective structure size, which should always be
998 calculated with the header_sizeof() helper.
999
1000 #define HEADER_END char end_field
1001 #define header_sizeof(type) offsetof(typeof(type), end_field)
1002
1003
1004 B. Stream Header Rationale
1005
1006 An event stream is divided in contiguous event packets of variable size. These
1007 subdivisions allow the trace analyzer to perform a fast binary search by time
1008 within the stream (typically requiring to index only the event packet headers)
1009 without reading the whole stream. These subdivisions have a variable size to
1010 eliminate the need to transfer the event packet padding when partially filled
1011 event packets must be sent when streaming a trace for live viewing/analysis.
1012 An event packet can contain a certain amount of padding at the end. Dividing
1013 streams into event packets is also useful for network streaming over UDP and
1014 flight recorder mode tracing (a whole event packet can be swapped out of the
1015 buffer atomically for reading).
1016
1017 The stream header is repeated at the beginning of each event packet to allow
1018 flexibility in terms of:
1019
1020 - streaming support,
1021 - allowing arbitrary buffers to be discarded without making the trace
1022 unreadable,
1023 - allow UDP packet loss handling by either dealing with missing event packet
1024 or asking for re-transmission.
1025 - transparently support flight recorder mode,
1026 - transparently support crash dump.
1027
1028 The event stream header will therefore be referred to as the "event packet
1029 header" throughout the rest of this document.
1030
1031 C. CTF Metadata Grammar
1032
1033 /*
1034 * Common Trace Format (CTF) Metadata Grammar.
1035 *
1036 * Inspired from the C99 grammar:
1037 * http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1124.pdf (Annex A)
1038 *
1039 * Specialized for CTF needs by including only constant and declarations from
1040 * C99 (excluding function declarations), and by adding support for variants,
1041 * sequences and CTF-specific specifiers.
1042 */
1043
1044 1) Lexical grammar
1045
1046 1.1) Lexical elements
1047
1048 token:
1049 keyword
1050 identifier
1051 constant
1052 string-literal
1053 punctuator
1054
1055 1.2) Keywords
1056
1057 keyword: is one of
1058
1059 const
1060 char
1061 double
1062 enum
1063 event
1064 floating_point
1065 float
1066 integer
1067 int
1068 long
1069 short
1070 signed
1071 stream
1072 string
1073 struct
1074 trace
1075 typealias
1076 typedef
1077 typename
1078 unsigned
1079 variant
1080 void
1081 _Bool
1082 _Complex
1083 _Imaginary
1084
1085
1086 1.3) Identifiers
1087
1088 identifier:
1089 identifier-nondigit
1090 identifier identifier-nondigit
1091 identifier digit
1092
1093 identifier-nondigit:
1094 nondigit
1095 universal-character-name
1096 any other implementation-defined characters
1097
1098 nondigit:
1099 _
1100 [a-zA-Z] /* regular expression */
1101
1102 digit:
1103 [0-9] /* regular expression */
1104
1105 1.4) Universal character names
1106
1107 universal-character-name:
1108 \u hex-quad
1109 \U hex-quad hex-quad
1110
1111 hex-quad:
1112 hexadecimal-digit hexadecimal-digit hexadecimal-digit hexadecimal-digit
1113
1114 1.5) Constants
1115
1116 constant:
1117 integer-constant
1118 enumeration-constant
1119 character-constant
1120
1121 integer-constant:
1122 decimal-constant integer-suffix-opt
1123 octal-constant integer-suffix-opt
1124 hexadecimal-constant integer-suffix-opt
1125
1126 decimal-constant:
1127 nonzero-digit
1128 decimal-constant digit
1129
1130 octal-constant:
1131 0
1132 octal-constant octal-digit
1133
1134 hexadecimal-constant:
1135 hexadecimal-prefix hexadecimal-digit
1136 hexadecimal-constant hexadecimal-digit
1137
1138 hexadecimal-prefix:
1139 0x
1140 0X
1141
1142 nonzero-digit:
1143 [1-9]
1144
1145 integer-suffix:
1146 unsigned-suffix long-suffix-opt
1147 unsigned-suffix long-long-suffix
1148 long-suffix unsigned-suffix-opt
1149 long-long-suffix unsigned-suffix-opt
1150
1151 unsigned-suffix:
1152 u
1153 U
1154
1155 long-suffix:
1156 l
1157 L
1158
1159 long-long-suffix:
1160 ll
1161 LL
1162
1163 digit-sequence:
1164 digit
1165 digit-sequence digit
1166
1167 hexadecimal-digit-sequence:
1168 hexadecimal-digit
1169 hexadecimal-digit-sequence hexadecimal-digit
1170
1171 enumeration-constant:
1172 identifier
1173 string-literal
1174
1175 character-constant:
1176 ' c-char-sequence '
1177 L' c-char-sequence '
1178
1179 c-char-sequence:
1180 c-char
1181 c-char-sequence c-char
1182
1183 c-char:
1184 any member of source charset except single-quote ('), backslash
1185 (\), or new-line character.
1186 escape-sequence
1187
1188 escape-sequence:
1189 simple-escape-sequence
1190 octal-escape-sequence
1191 hexadecimal-escape-sequence
1192 universal-character-name
1193
1194 simple-escape-sequence: one of
1195 \' \" \? \\ \a \b \f \n \r \t \v
1196
1197 octal-escape-sequence:
1198 \ octal-digit
1199 \ octal-digit octal-digit
1200 \ octal-digit octal-digit octal-digit
1201
1202 hexadecimal-escape-sequence:
1203 \x hexadecimal-digit
1204 hexadecimal-escape-sequence hexadecimal-digit
1205
1206 1.6) String literals
1207
1208 string-literal:
1209 " s-char-sequence-opt "
1210 L" s-char-sequence-opt "
1211
1212 s-char-sequence:
1213 s-char
1214 s-char-sequence s-char
1215
1216 s-char:
1217 any member of source charset except double-quote ("), backslash
1218 (\), or new-line character.
1219 escape-sequence
1220
1221 1.7) Punctuators
1222
1223 punctuator: one of
1224 [ ] ( ) { } . -> * + - < > : ; ... = ,
1225
1226
1227 2) Phrase structure grammar
1228
1229 primary-expression:
1230 identifier
1231 constant
1232 string-literal
1233 ( unary-expression )
1234
1235 postfix-expression:
1236 primary-expression
1237 postfix-expression [ unary-expression ]
1238 postfix-expression . identifier
1239 postfix-expressoin -> identifier
1240
1241 unary-expression:
1242 postfix-expression
1243 unary-operator postfix-expression
1244
1245 unary-operator: one of
1246 + -
1247
1248 assignment-operator:
1249 =
1250
1251 type-assignment-operator:
1252 :=
1253
1254 constant-expression:
1255 unary-expression
1256
1257 constant-expression-range:
1258 constant-expression ... constant-expression
1259
1260 2.2) Declarations:
1261
1262 declaration:
1263 declaration-specifiers declarator-list-opt ;
1264 ctf-specifier ;
1265
1266 declaration-specifiers:
1267 storage-class-specifier declaration-specifiers-opt
1268 type-specifier declaration-specifiers-opt
1269 type-qualifier declaration-specifiers-opt
1270
1271 declarator-list:
1272 declarator
1273 declarator-list , declarator
1274
1275 abstract-declarator-list:
1276 abstract-declarator
1277 abstract-declarator-list , abstract-declarator
1278
1279 storage-class-specifier:
1280 typedef
1281
1282 type-specifier:
1283 void
1284 char
1285 short
1286 int
1287 long
1288 float
1289 double
1290 signed
1291 unsigned
1292 _Bool
1293 _Complex
1294 _Imaginary
1295 struct-specifier
1296 variant-specifier
1297 enum-specifier
1298 typedef-name
1299 ctf-type-specifier
1300
1301 struct-specifier:
1302 struct identifier-opt { struct-or-variant-declaration-list-opt }
1303 struct identifier
1304
1305 struct-or-variant-declaration-list:
1306 struct-or-variant-declaration
1307 struct-or-variant-declaration-list struct-or-variant-declaration
1308
1309 struct-or-variant-declaration:
1310 specifier-qualifier-list struct-or-variant-declarator-list ;
1311 declaration-specifiers storage-class-specifier declaration-specifiers declarator-list ;
1312 typealias declaration-specifiers abstract-declarator-list typename declaration-specifiers abstract-declarator-list ;
1313 typealias declaration-specifiers abstract-declarator-list typename declarator-list ;
1314
1315 specifier-qualifier-list:
1316 type-specifier specifier-qualifier-list-opt
1317 type-qualifier specifier-qualifier-list-opt
1318
1319 struct-or-variant-declarator-list:
1320 struct-or-variant-declarator
1321 struct-or-variant-declarator-list , struct-or-variant-declarator
1322
1323 struct-or-variant-declarator:
1324 declarator
1325 declarator-opt : constant-expression
1326
1327 variant-specifier:
1328 variant identifier-opt variant-tag-opt { struct-or-variant-declaration-list }
1329 variant identifier variant-tag
1330
1331 variant-tag:
1332 < identifier >
1333
1334 enum-specifier:
1335 enum identifier-opt { enumerator-list }
1336 enum identifier-opt { enumerator-list , }
1337 enum identifier
1338 enum identifier-opt < declaration-specifiers > { enumerator-list }
1339 enum identifier-opt < declaration-specifiers > { enumerator-list , }
1340 enum identifier < declaration-specifiers >
1341
1342 enumerator-list:
1343 enumerator
1344 enumerator-list , enumerator
1345
1346 enumerator:
1347 enumeration-constant
1348 enumeration-constant = constant-expression
1349 enumeration-constant = constant-expression-range
1350
1351 type-qualifier:
1352 const
1353
1354 declarator:
1355 pointer-opt direct-declarator
1356
1357 direct-declarator:
1358 identifier
1359 ( declarator )
1360 direct-declarator [ type-specifier ]
1361 direct-declarator [ constant-expression ]
1362
1363 abstract-declarator:
1364 pointer-opt direct-abstract-declarator
1365
1366 direct-abstract-declarator:
1367 identifier-opt
1368 ( abstract-declarator )
1369 direct-abstract-declarator [ type-specifier ]
1370 direct-abstract-declarator [ constant-expression ]
1371 direct-abstract-declarator [ ]
1372
1373 pointer:
1374 * type-qualifier-list-opt
1375 * type-qualifier-list-opt pointer
1376
1377 type-qualifier-list:
1378 type-qualifier
1379 type-qualifier-list type-qualifier
1380
1381 typedef-name:
1382 identifier
1383
1384 2.3) CTF-specific declarations
1385
1386 ctf-specifier:
1387 event { ctf-assignment-expression-list-opt }
1388 stream { ctf-assignment-expression-list-opt }
1389 trace { ctf-assignment-expression-list-opt }
1390 typealias declaration-specifiers abstract-declarator-list typename declaration-specifiers abstract-declarator-list ;
1391 typealias declaration-specifiers abstract-declarator-list typename declarator-list ;
1392
1393 ctf-type-specifier:
1394 floating_point { ctf-assignment-expression-list-opt }
1395 integer { ctf-assignment-expression-list-opt }
1396 string { ctf-assignment-expression-list-opt }
1397
1398 ctf-assignment-expression-list:
1399 ctf-assignment-expression
1400 ctf-assignment-expression-list ; ctf-assignment-expression
1401
1402 ctf-assignment-expression:
1403 unary-expression assignment-operator unary-expression
1404 unary-expression type-assignment-operator type-specifier
1405 declaration-specifiers storage-class-specifier declaration-specifiers declarator-list
1406 typealias declaration-specifiers abstract-declarator-list typename declaration-specifiers abstract-declarator-list
1407 typealias declaration-specifiers abstract-declarator-list typename declarator-list
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