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