Add scope semantic, add abstract declarations
[ctf.git] / common-trace-format-proposal.txt
1
2 RFC: Common Trace Format (CTF) Proposal (pre-v1.7)
3
4 Mathieu Desnoyers, EfficiOS Inc.
5
6 The goal of the present document is to propose a trace format that suits the
7 needs of the embedded, telecom, high-performance and kernel communities. It is
8 based on the Common Trace Format Requirements (v1.4) document. It is designed to
9 allow traces to be natively generated by the Linux kernel, Linux user-space
10 applications written in C/C++, and hardware components.
11
12 The latest version of this document can be found at:
13
14 git tree: git://git.efficios.com/ctf.git
15 gitweb: http://git.efficios.com/?p=ctf.git
16
17 A reference implementation of a library to read and write this trace format is
18 being implemented within the BabelTrace project, a converter between trace
19 formats. The development tree is available at:
20
21 git tree: git://git.efficios.com/babeltrace.git
22 gitweb: http://git.efficios.com/?p=babeltrace.git
23
24
25 1. Preliminary definitions
26
27 - Event Trace: An ordered sequence of events.
28 - Event Stream: An ordered sequence of events, containing a subset of the
29 trace event types.
30 - Event Packet: A sequence of physically contiguous events within an event
31 stream.
32 - Event: This is the basic entry in a trace. (aka: a trace record).
33 - An event identifier (ID) relates to the class (a type) of event within
34 an event stream.
35 e.g. event: irq_entry.
36 - An event (or event record) relates to a specific instance of an event
37 class.
38 e.g. event: irq_entry, at time X, on CPU Y
39 - Source Architecture: Architecture writing the trace.
40 - Reader Architecture: Architecture reading the trace.
41
42
43 2. High-level representation of a trace
44
45 A trace is divided into multiple event streams. Each event stream contains a
46 subset of the trace event types.
47
48 The final output of the trace, after its generation and optional transport over
49 the network, is expected to be either on permanent or temporary storage in a
50 virtual file system. Because each event stream is appended to while a trace is
51 being recorded, each is associated with a separate file for output. Therefore,
52 a stored trace can be represented as a directory containing one file per stream.
53
54 A metadata event stream contains information on trace event types. It describes:
55
56 - Trace version.
57 - Types available.
58 - Per-stream event header description.
59 - Per-stream event header selection.
60 - Per-stream event context fields.
61 - Per-event
62 - Event type to stream mapping.
63 - Event type to name mapping.
64 - Event type to ID mapping.
65 - Event fields description.
66
67
68 3. Event stream
69
70 An event stream is divided in contiguous event packets of variable size. These
71 subdivisions have a variable size. An event packet can contain a certain amount
72 of padding at the end. The rationale for the event stream design choices is
73 explained in Appendix B. Stream Header Rationale.
74
75 An event stream is divided in contiguous event packets of variable size. These
76 subdivisions have a variable size. An event packet can contain a certain amount
77 of padding at the end. The stream header is repeated at the beginning of each
78 event packet.
79
80 The event stream header will therefore be referred to as the "event packet
81 header" throughout the rest of this document.
82
83
84 4. Types
85
86 4.1 Basic types
87
88 A basic type is a scalar type, as described in this section.
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 typedef 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 typedef 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 typedef 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 string = 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 4.2 Compound types
304
305 4.2.1 Structures
306
307 Structures are aligned on the largest alignment required by basic types
308 contained within the structure. (This follows the ISO/C standard for structures)
309
310 Metadata representation of a named structure:
311
312 struct name {
313 field_type field_name;
314 field_type field_name;
315 ...
316 };
317
318 Example:
319
320 struct example {
321 integer { /* Nameless type */
322 size = 16;
323 signed = true;
324 align = 16;
325 } first_field_name;
326 uint64_t second_field_name; /* Named type declared in the metadata */
327 };
328
329 The fields are placed in a sequence next to each other. They each possess a
330 field name, which is a unique identifier within the structure.
331
332 A nameless structure can be declared as a field type or as part of a typedef:
333
334 struct {
335 ...
336 }
337
338 4.2.2 Variants (Discriminated/Tagged Unions)
339
340 A CTF variant is a selection between different types. A CTF variant must always
341 be defined within the scope of a structure or within fields contained within a
342 structure (defined recursively). A "tag" enumeration field must appear in either
343 the same lexical scope or an uppermost scope, prior to the variant field (in
344 field declaration order). The type selection is indicated by the mapping from
345 the enumeration value to the string used as variant type selector. The field to
346 use as tag is specified by the "tag_field", specified between "< >" after the
347 "variant" keyword for unnamed variants, and after "variant name" for named
348 variants.
349
350 The alignment of the variant is the alignment of the type as selected by the tag
351 value for the specific instance of the variant. The alignment of the type
352 containing the variant is independent of the variant alignment. The size of the
353 variant is the size as selected by the tag value for the specific instance of
354 the variant.
355
356 A named variant declaration followed by its definition within a structure
357 declaration:
358
359 variant name {
360 field_type sel1;
361 field_type sel2;
362 field_type sel3;
363 ...
364 };
365
366 struct {
367 enum <integer_type or size> { sel1, sel2, sel3, ... } tag_field;
368 ...
369 variant name <tag_field> v;
370 }
371
372 An unnamed variant definition within a structure is expressed by the following
373 metadata:
374
375 struct {
376 enum <integer_type or size> { sel1, sel2, sel3, ... } tag_field;
377 ...
378 variant <tag_field> {
379 field_type sel1;
380 field_type sel2;
381 field_type sel3;
382 ...
383 } v;
384 }
385
386 Example of a named variant within a sequence that refers to a single tag field:
387
388 variant example {
389 uint32_t a;
390 uint64_t b;
391 short c;
392 };
393
394 struct {
395 enum <uint2_t> { a, b, c } choice;
396 variant example <choice> v[unsigned int];
397 }
398
399 Example of an unnamed variant:
400
401 struct {
402 enum <uint2_t> { a, b, c, d } choice;
403 /* Unrelated fields can be added between the variant and its tag */
404 int32_t somevalue;
405 variant <choice> {
406 uint32_t a;
407 uint64_t b;
408 short c;
409 struct {
410 unsigned int field1;
411 uint64_t field2;
412 } d;
413 } s;
414 }
415
416 Example of an unnamed variant within an array:
417
418 struct {
419 enum <uint2_t> { a, b, c } choice;
420 variant <choice> {
421 uint32_t a;
422 uint64_t b;
423 short c;
424 } v[10];
425 }
426
427 Example of a variant type definition within a structure, where the defined type
428 is then declared within an array of structures. This variant refers to a tag
429 located in an upper lexical scope. This example clearly shows that a variant
430 type definition referring to the tag "x" uses the closest preceding field from
431 the lexical scope of the type definition.
432
433 struct {
434 enum <uint2_t> { a, b, c, d } x;
435
436 typedef variant <x> { /*
437 * "x" refers to the preceding "x" enumeration in the
438 * lexical scope of the type definition.
439 */
440 uint32_t a;
441 uint64_t b;
442 short c;
443 } example_variant;
444
445 struct {
446 enum <int> { x, y, z } x; /* This enumeration is not used by "v". */
447 example_variant v; /*
448 * "v" uses the "enum <uint2_t> { a, b, c, d }"
449 * tag.
450 */
451 } a[10];
452 }
453
454 4.2.3 Arrays
455
456 Arrays are fixed-length. Their length is declared in the type declaration within
457 the metadata. They contain an array of "inner type" elements, which can refer to
458 any type not containing the type of the array being declared (no circular
459 dependency). The length is the number of elements in an array.
460
461 Metadata representation of a named array:
462
463 typedef elem_type name[length];
464
465 A nameless array can be declared as a field type within a structure, e.g.:
466
467 uint8_t field_name[10];
468
469
470 4.2.4 Sequences
471
472 Sequences are dynamically-sized arrays. They start with an integer that specify
473 the length of the sequence, followed by an array of "inner type" elements.
474 The length is the number of elements in the sequence.
475
476 Metadata representation for a named sequence:
477
478 typedef elem_type name[length_type];
479
480 A nameless sequence can be declared as a field type, e.g.:
481
482 long field_name[int];
483
484 The length type follows the integer types specifications, and the sequence
485 elements follow the "array" specifications.
486
487 4.2.5 Strings
488
489 Strings are an array of bytes of variable size and are terminated by a '\0'
490 "NULL" character. Their encoding is described in the metadata. In absence of
491 encoding attribute information, the default encoding is UTF-8.
492
493 Metadata representation of a named string type:
494
495 typedef string {
496 encoding = UTF8 OR ASCII;
497 } name;
498
499 A nameless string type can be declared as a field type:
500
501 string field_name; /* Use default UTF8 encoding */
502
503 5. Event Packet Header
504
505 The event packet header consists of two part: one is mandatory and have a fixed
506 layout. The second part, the "event packet context", has its layout described in
507 the metadata.
508
509 - Aligned on page size. Fixed size. Fields either aligned or packed (depending
510 on the architecture preference).
511 No padding at the end of the event packet header. Native architecture byte
512 ordering.
513
514 Fixed layout (event packet header):
515
516 - Magic number (CTF magic numbers: 0xC1FC1FC1 and its reverse endianness
517 representation: 0xC11FFCC1) It needs to have a non-symmetric bytewise
518 representation. Used to distinguish between big and little endian traces (this
519 information is determined by knowing the endianness of the architecture
520 reading the trace and comparing the magic number against its value and the
521 reverse, 0xC11FFCC1). This magic number specifies that we use the CTF metadata
522 description language described in this document. Different magic numbers
523 should be used for other metadata description languages.
524 - Trace UUID, used to ensure the event packet match the metadata used.
525 (note: we cannot use a metadata checksum because metadata can be appended to
526 while tracing is active)
527 - Stream ID, used as reference to stream description in metadata.
528
529 Metadata-defined layout (event packet context):
530
531 - Event packet content size (in bytes).
532 - Event packet size (in bytes, includes padding).
533 - Event packet content checksum (optional). Checksum excludes the event packet
534 header.
535 - Per-stream event packet sequence count (to deal with UDP packet loss). The
536 number of significant sequence counter bits should also be present, so
537 wrap-arounds are deal with correctly.
538 - Timestamp at the beginning and timestamp at the end of the event packet.
539 Both timestamps are written in the packet header, but sampled respectively
540 while (or before) writing the first event and while (or after) writing the
541 last event in the packet. The inclusive range between these timestamps should
542 include all event timestamps assigned to events contained within the packet.
543 - Events discarded count
544 - Snapshot of a per-stream free-running counter, counting the number of
545 events discarded that were supposed to be written in the stream prior to
546 the first event in the event packet.
547 * Note: producer-consumer buffer full condition should fill the current
548 event packet with padding so we know exactly where events have been
549 discarded.
550 - Lossless compression scheme used for the event packet content. Applied
551 directly to raw data. New types of compression can be added in following
552 versions of the format.
553 0: no compression scheme
554 1: bzip2
555 2: gzip
556 3: xz
557 - Cypher used for the event packet content. Applied after compression.
558 0: no encryption
559 1: AES
560 - Checksum scheme used for the event packet content. Applied after encryption.
561 0: no checksum
562 1: md5
563 2: sha1
564 3: crc32
565
566 5.1 Event Packet Header Fixed Layout Description
567
568 struct event_packet_header {
569 uint32_t magic;
570 uint8_t trace_uuid[16];
571 uint32_t stream_id;
572 };
573
574 5.2 Event Packet Context Description
575
576 Event packet context example. These are declared within the stream declaration
577 in the metadata. All these fields are optional except for "content_size" and
578 "packet_size", which must be present in the context.
579
580 An example event packet context type:
581
582 struct event_packet_context {
583 uint64_t timestamp_begin;
584 uint64_t timestamp_end;
585 uint32_t checksum;
586 uint32_t stream_packet_count;
587 uint32_t events_discarded;
588 uint32_t cpu_id;
589 uint32_t/uint16_t content_size;
590 uint32_t/uint16_t packet_size;
591 uint8_t stream_packet_count_bits; /* Significant counter bits */
592 uint8_t compression_scheme;
593 uint8_t encryption_scheme;
594 uint8_t checksum_scheme;
595 };
596
597
598 6. Event Structure
599
600 The overall structure of an event is:
601
602 1 - Stream Packet Context (as specified by the stream metadata)
603 2 - Event Header (as specifed by the stream metadata)
604 3 - Stream Event Context (as specified by the stream metadata)
605 4 - Event Context (as specified by the event metadata)
606 5 - Event Payload (as specified by the event metadata)
607
608 6.1 Lexical Scope
609
610 For variant tag definition only, the lexical scope of each structure (stream
611 packet context, header, stream event context, event context and payload) is
612 extended in the following way: lower levels (e.g. 3) can refer to fields defined
613 in prior levels (e.g. 2 and 1). The field in the closest level has priority in
614 case of field name conflict.
615
616 This allows, for instance, the event context to define a variant refering to the
617 "id" field of the event header as selector.
618
619 6.2 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 6.2.1 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 6.2.2 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.
771
772 The metadata can be parsed by reading through the metadata strings, skipping
773 newlines and null-characters. Type names are made of a single identifier, and
774 can be surrounded by prefix/postfix. Text contained within "/*" and "*/", as
775 well as within "//" and end of line, are treated as comments. Boolean values can
776 be represented as true, TRUE, or 1 for true, and false, FALSE, or 0 for false.
777
778 Each of "trace", "stream", "event", "struct" and "variant" have their own
779 nestable declaration scope, within which types can be declared using "typedef"
780 and "typealias". An innermost declaration scope can refer to type declared
781 within its container lexical scope prior to the innermost declaration scope.
782
783 The grammar representing the CTF metadata is presented in
784 Appendix C. CTF Metadata Grammar.
785
786 trace {
787 major = value; /* Trace format version */
788 minor = value;
789 uuid = value; /* Trace UUID */
790 word_size = value;
791 };
792
793 stream {
794 id = stream_id;
795 /* Type 1 - Few event IDs; Type 2 - Many event IDs. See section 6.2. */
796 event.header := event_header_1 OR event_header_2;
797 event.context := struct {
798 ...
799 };
800 packet.context := struct {
801 ...
802 };
803 };
804
805 event {
806 name = event_name;
807 id = value; /* Numeric identifier within the stream */
808 stream = stream_id;
809 context := struct {
810 ...
811 };
812 fields := struct {
813 ...
814 };
815 };
816
817 /* More detail on types in section 4. Types */
818
819 /*
820 * Named types:
821 *
822 * Type declarations behave similarly to the C standard.
823 */
824
825 typedef aliased_type_prefix aliased_type new_type aliased_type_postfix;
826
827 /* e.g.: typedef struct example new_type_name[10]; */
828
829 /*
830 * typealias
831 *
832 * The "typealias" declaration can be used to give a name (including
833 * prefix/postfix) to a type.
834 */
835
836 typealias type_class {
837 ...
838 } : new_type_prefix new_type new_type_postfix;
839
840 /*
841 * e.g.:
842 * typealias integer {
843 * size = 32;
844 * align = 32;
845 * signed = false;
846 * } : struct page *;
847 */
848
849 struct name {
850 ...
851 };
852
853 variant name {
854 ...
855 };
856
857 enum name <integer_type or size> {
858 ...
859 };
860
861
862 /*
863 * Unnamed types, contained within compound type fields, typedef or typealias.
864 */
865
866 struct {
867 ...
868 }
869
870 variant {
871 ...
872 }
873
874 enum <integer_type or size> {
875 ...
876 }
877
878 typedef type new_type[length];
879
880 struct {
881 type field_name[length];
882 }
883
884 typedef type new_type[length_type];
885
886 struct {
887 type field_name[length_type];
888 }
889
890 integer {
891 ...
892 }
893
894 floating_point {
895 ...
896 }
897
898 struct {
899 integer_type field_name:size; /* GNU/C bitfield */
900 }
901
902 struct {
903 string field_name;
904 }
905
906
907 A. Helper macros
908
909 The two following macros keep track of the size of a GNU/C structure without
910 padding at the end by placing HEADER_END as the last field. A one byte end field
911 is used for C90 compatibility (C99 flexible arrays could be used here). Note
912 that this does not affect the effective structure size, which should always be
913 calculated with the header_sizeof() helper.
914
915 #define HEADER_END char end_field
916 #define header_sizeof(type) offsetof(typeof(type), end_field)
917
918
919 B. Stream Header Rationale
920
921 An event stream is divided in contiguous event packets of variable size. These
922 subdivisions allow the trace analyzer to perform a fast binary search by time
923 within the stream (typically requiring to index only the event packet headers)
924 without reading the whole stream. These subdivisions have a variable size to
925 eliminate the need to transfer the event packet padding when partially filled
926 event packets must be sent when streaming a trace for live viewing/analysis.
927 An event packet can contain a certain amount of padding at the end. Dividing
928 streams into event packets is also useful for network streaming over UDP and
929 flight recorder mode tracing (a whole event packet can be swapped out of the
930 buffer atomically for reading).
931
932 The stream header is repeated at the beginning of each event packet to allow
933 flexibility in terms of:
934
935 - streaming support,
936 - allowing arbitrary buffers to be discarded without making the trace
937 unreadable,
938 - allow UDP packet loss handling by either dealing with missing event packet
939 or asking for re-transmission.
940 - transparently support flight recorder mode,
941 - transparently support crash dump.
942
943 The event stream header will therefore be referred to as the "event packet
944 header" throughout the rest of this document.
945
946 C. CTF Metadata Grammar
947
948 /*
949 * Common Trace Format (CTF) Metadata Grammar.
950 *
951 * Inspired from the C99 grammar:
952 * http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1124.pdf (Annex A)
953 *
954 * Specialized for CTF needs by including only constant and declarations from
955 * C99 (excluding function declarations), and by adding support for variants,
956 * sequences and CTF-specific specifiers.
957 */
958
959 1) Lexical grammar
960
961 1.1) Lexical elements
962
963 token:
964 keyword
965 identifier
966 constant
967 string-literal
968 punctuator
969
970 1.2) Keywords
971
972 keyword: is one of
973
974 const
975 char
976 double
977 enum
978 event
979 floating_point
980 float
981 integer
982 int
983 long
984 short
985 signed
986 stream
987 string
988 struct
989 trace
990 typealias
991 typedef
992 unsigned
993 variant
994 void
995 _Bool
996 _Complex
997 _Imaginary
998
999
1000 1.3) Identifiers
1001
1002 identifier:
1003 identifier-nondigit
1004 identifier identifier-nondigit
1005 identifier digit
1006
1007 identifier-nondigit:
1008 nondigit
1009 universal-character-name
1010 any other implementation-defined characters
1011
1012 nondigit:
1013 _
1014 [a-zA-Z] /* regular expression */
1015
1016 digit:
1017 [0-9] /* regular expression */
1018
1019 1.4) Universal character names
1020
1021 universal-character-name:
1022 \u hex-quad
1023 \U hex-quad hex-quad
1024
1025 hex-quad:
1026 hexadecimal-digit hexadecimal-digit hexadecimal-digit hexadecimal-digit
1027
1028 1.5) Constants
1029
1030 constant:
1031 integer-constant
1032 enumeration-constant
1033 character-constant
1034
1035 integer-constant:
1036 decimal-constant integer-suffix-opt
1037 octal-constant integer-suffix-opt
1038 hexadecimal-constant integer-suffix-opt
1039
1040 decimal-constant:
1041 nonzero-digit
1042 decimal-constant digit
1043
1044 octal-constant:
1045 0
1046 octal-constant octal-digit
1047
1048 hexadecimal-constant:
1049 hexadecimal-prefix hexadecimal-digit
1050 hexadecimal-constant hexadecimal-digit
1051
1052 hexadecimal-prefix:
1053 0x
1054 0X
1055
1056 nonzero-digit:
1057 [1-9]
1058
1059 integer-suffix:
1060 unsigned-suffix long-suffix-opt
1061 unsigned-suffix long-long-suffix
1062 long-suffix unsigned-suffix-opt
1063 long-long-suffix unsigned-suffix-opt
1064
1065 unsigned-suffix:
1066 u
1067 U
1068
1069 long-suffix:
1070 l
1071 L
1072
1073 long-long-suffix:
1074 ll
1075 LL
1076
1077 digit-sequence:
1078 digit
1079 digit-sequence digit
1080
1081 hexadecimal-digit-sequence:
1082 hexadecimal-digit
1083 hexadecimal-digit-sequence hexadecimal-digit
1084
1085 enumeration-constant:
1086 identifier
1087 string-literal
1088
1089 character-constant:
1090 ' c-char-sequence '
1091 L' c-char-sequence '
1092
1093 c-char-sequence:
1094 c-char
1095 c-char-sequence c-char
1096
1097 c-char:
1098 any member of source charset except single-quote ('), backslash
1099 (\), or new-line character.
1100 escape-sequence
1101
1102 escape-sequence:
1103 simple-escape-sequence
1104 octal-escape-sequence
1105 hexadecimal-escape-sequence
1106 universal-character-name
1107
1108 simple-escape-sequence: one of
1109 \' \" \? \\ \a \b \f \n \r \t \v
1110
1111 octal-escape-sequence:
1112 \ octal-digit
1113 \ octal-digit octal-digit
1114 \ octal-digit octal-digit octal-digit
1115
1116 hexadecimal-escape-sequence:
1117 \x hexadecimal-digit
1118 hexadecimal-escape-sequence hexadecimal-digit
1119
1120 1.6) String literals
1121
1122 string-literal:
1123 " s-char-sequence-opt "
1124 L" s-char-sequence-opt "
1125
1126 s-char-sequence:
1127 s-char
1128 s-char-sequence s-char
1129
1130 s-char:
1131 any member of source charset except double-quote ("), backslash
1132 (\), or new-line character.
1133 escape-sequence
1134
1135 1.7) Punctuators
1136
1137 punctuator: one of
1138 [ ] ( ) { } . -> * + - < > : ; ... = ,
1139
1140
1141 2) Phrase structure grammar
1142
1143 primary-expression:
1144 identifier
1145 constant
1146 string-literal
1147 ( unary-expression )
1148
1149 postfix-expression:
1150 primary-expression
1151 postfix-expression [ unary-expression ]
1152 postfix-expression . identifier
1153 postfix-expressoin -> identifier
1154
1155 unary-expression:
1156 postfix-expression
1157 unary-operator postfix-expression
1158
1159 unary-operator: one of
1160 + -
1161
1162 assignment-operator:
1163 =
1164
1165 constant-expression:
1166 unary-expression
1167
1168 constant-expression-range:
1169 constant-expression ... constant-expression
1170
1171 2.2) Declarations:
1172
1173 declaration:
1174 declaration-specifiers ;
1175 declaration-specifiers storage-class-specifier declaration-specifiers declarator-list ;
1176 ctf-specifier ;
1177
1178 declaration-specifiers:
1179 type-specifier declaration-specifiers-opt
1180 type-qualifier declaration-specifiers-opt
1181
1182 declarator-list:
1183 declarator
1184 declarator-list , declarator
1185
1186 abstract-declarator-list:
1187 abstract-declarator
1188 abstract-declarator-list , abstract-declarator
1189
1190 storage-class-specifier:
1191 typedef
1192
1193 type-specifier:
1194 void
1195 char
1196 short
1197 int
1198 long
1199 float
1200 double
1201 signed
1202 unsigned
1203 _Bool
1204 _Complex
1205 struct-specifier
1206 variant-specifier
1207 enum-specifier
1208 typedef-name
1209 ctf-type-specifier
1210
1211 struct-specifier:
1212 struct identifier-opt { struct-or-variant-declaration-list-opt }
1213 struct identifier
1214
1215 struct-or-variant-declaration-list:
1216 struct-or-variant-declaration
1217 struct-or-variant-declaration-list struct-or-variant-declaration
1218
1219 struct-or-variant-declaration:
1220 specifier-qualifier-list struct-or-variant-declarator-list ;
1221 declaration-specifiers storage-class-specifier declaration-specifiers declarator-list ;
1222 typealias declaration-specifiers abstract-declarator-list : declaration-specifiers abstract-declarator-list ;
1223 typealias declaration-specifiers abstract-declarator-list : declarator-list ;
1224
1225 specifier-qualifier-list:
1226 type-specifier specifier-qualifier-list-opt
1227 type-qualifier specifier-qualifier-list-opt
1228
1229 struct-or-variant-declarator-list:
1230 struct-or-variant-declarator
1231 struct-or-variant-declarator-list , struct-or-variant-declarator
1232
1233 struct-or-variant-declarator:
1234 declarator
1235 declarator-opt : constant-expression
1236
1237 variant-specifier:
1238 variant identifier-opt variant-tag-opt { struct-or-variant-declaration-list }
1239 variant identifier variant-tag
1240
1241 variant-tag:
1242 < identifier >
1243
1244 enum-specifier:
1245 enum identifier-opt { enumerator-list }
1246 enum identifier-opt { enumerator-list , }
1247 enum identifier
1248 enum identifier-opt < type-specifier > { enumerator-list }
1249 enum identifier-opt < type-specifier > { enumerator-list , }
1250 enum identifier < type-specifier >
1251 enum identifier-opt < integer-constant > { enumerator-list }
1252 enum identifier-opt < integer-constant > { enumerator-list , }
1253 enum identifier < integer-constant >
1254
1255 enumerator-list:
1256 enumerator
1257 enumerator-list , enumerator
1258
1259 enumerator:
1260 enumeration-constant
1261 enumeration-constant = constant-expression
1262 enumeration-constant = constant-expression-range
1263
1264 type-qualifier:
1265 const
1266
1267 declarator:
1268 pointer-opt direct-declarator
1269
1270 direct-declarator:
1271 identifier
1272 ( declarator )
1273 direct-declarator [ type-specifier ]
1274 direct-declarator [ constant-expression ]
1275
1276 abstract-declarator:
1277 pointer-opt direct-abstract-declarator
1278
1279 direct-abstract-declarator:
1280 identifier-opt
1281 ( abstract-declarator )
1282 direct-abstract-declarator [ type-specifier ]
1283 direct-abstract-declarator [ constant-expression ]
1284 direct-abstract-declarator [ ]
1285
1286 pointer:
1287 * type-qualifier-list-opt
1288 * type-qualifier-list-opt pointer
1289
1290 type-qualifier-list:
1291 type-qualifier
1292 type-qualifier-list type-qualifier
1293
1294 typedef-name:
1295 identifier
1296
1297 2.3) CTF-specific declarations
1298
1299 ctf-specifier:
1300 event { ctf-assignment-expression-list-opt }
1301 stream { ctf-assignment-expression-list-opt }
1302 trace { ctf-assignment-expression-list-opt }
1303 typealias declaration-specifiers abstract-declarator-list : declaration-specifiers abstract-declarator-list ;
1304 typealias declaration-specifiers abstract-declarator-list : declarator-list ;
1305
1306 ctf-type-specifier:
1307 floating_point { ctf-assignment-expression-list-opt }
1308 integer { ctf-assignment-expression-list-opt }
1309 string { ctf-assignment-expression-list-opt }
1310
1311 ctf-assignment-expression-list:
1312 ctf-assignment-expression
1313 ctf-assignment-expression-list ; ctf-assignment-expression
1314
1315 ctf-assignment-expression:
1316 unary-expression assignment-operator unary-expression
1317 unary-expression type-assignment-operator type-specifier
1318 declaration-specifiers storage-class-specifier declaration-specifiers declarator-list
1319 typealias declaration-specifiers abstract-declarator-list : declaration-specifiers abstract-declarator-list
1320 typealias declaration-specifiers abstract-declarator-list : declarator-list
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