Clarify declaration/definition and scope
[ctf.git] / common-trace-format-proposal.txt
1
2 RFC: Common Trace Format (CTF) Proposal (pre-v1.7)
3
4 Mathieu Desnoyers, EfficiOS Inc.
5
6 The goal of the present document is to propose a trace format that suits the
7 needs of the embedded, telecom, high-performance and kernel communities. It is
8 based on the Common Trace Format Requirements (v1.4) document. It is designed to
9 allow traces to be natively generated by the Linux kernel, Linux user-space
10 applications written in C/C++, and hardware components.
11
12 The latest version of this document can be found at:
13
14 git tree: git://git.efficios.com/ctf.git
15 gitweb: http://git.efficios.com/?p=ctf.git
16
17 A reference implementation of a library to read and write this trace format is
18 being implemented within the BabelTrace project, a converter between trace
19 formats. The development tree is available at:
20
21 git tree: git://git.efficios.com/babeltrace.git
22 gitweb: http://git.efficios.com/?p=babeltrace.git
23
24
25 1. Preliminary definitions
26
27 - Event Trace: An ordered sequence of events.
28 - Event Stream: An ordered sequence of events, containing a subset of the
29 trace event types.
30 - Event Packet: A sequence of physically contiguous events within an event
31 stream.
32 - Event: This is the basic entry in a trace. (aka: a trace record).
33 - An event identifier (ID) relates to the class (a type) of event within
34 an event stream.
35 e.g. event: irq_entry.
36 - An event (or event record) relates to a specific instance of an event
37 class.
38 e.g. event: irq_entry, at time X, on CPU Y
39 - Source Architecture: Architecture writing the trace.
40 - Reader Architecture: Architecture reading the trace.
41
42
43 2. High-level representation of a trace
44
45 A trace is divided into multiple event streams. Each event stream contains a
46 subset of the trace event types.
47
48 The final output of the trace, after its generation and optional transport over
49 the network, is expected to be either on permanent or temporary storage in a
50 virtual file system. Because each event stream is appended to while a trace is
51 being recorded, each is associated with a separate file for output. Therefore,
52 a stored trace can be represented as a directory containing one file per stream.
53
54 A metadata event stream contains information on trace event types. It describes:
55
56 - Trace version.
57 - Types available.
58 - Per-stream event header description.
59 - Per-stream event header selection.
60 - Per-stream event context fields.
61 - Per-event
62 - Event type to stream mapping.
63 - Event type to name mapping.
64 - Event type to ID mapping.
65 - Event fields description.
66
67
68 3. Event stream
69
70 An event stream is divided in contiguous event packets of variable size. These
71 subdivisions have a variable size. An event packet can contain a certain amount
72 of padding at the end. The rationale for the event stream design choices is
73 explained in Appendix B. Stream Header Rationale.
74
75 An event stream is divided in contiguous event packets of variable size. These
76 subdivisions have a variable size. An event packet can contain a certain amount
77 of padding at the end. The stream header is repeated at the beginning of each
78 event packet.
79
80 The event stream header will therefore be referred to as the "event packet
81 header" throughout the rest of this document.
82
83
84 4. Types
85
86 Types are organized as type classes. Each type class belong to either of two
87 kind of types: basic types or compound types.
88
89 4.1 Basic types
90
91 A basic type is a scalar type, as described in this section. It includes
92 integers, GNU/C bitfields, enumerations, and floating point values.
93
94 4.1.1 Type inheritance
95
96 Type specifications can be inherited to allow deriving types from a
97 type class. For example, see the uint32_t named type derived from the "integer"
98 type class below ("Integers" section). Types have a precise binary
99 representation in the trace. A type class has methods to read and write these
100 types, but must be derived into a type to be usable in an event field.
101
102 4.1.2 Alignment
103
104 We define "byte-packed" types as aligned on the byte size, namely 8-bit.
105 We define "bit-packed" types as following on the next bit, as defined by the
106 "bitfields" section.
107
108 All basic types, except bitfields, are either aligned on an architecture-defined
109 specific alignment or byte-packed, depending on the architecture preference.
110 Architectures providing fast unaligned write byte-packed basic types to save
111 space, aligning each type on byte boundaries (8-bit). Architectures with slow
112 unaligned writes align types on specific alignment values. If no specific
113 alignment is declared for a type nor its parents, it is assumed to be bit-packed
114 for bitfields and byte-packed for other types.
115
116 Metadata attribute representation of a specific alignment:
117
118 align = value; /* value in bits */
119
120 4.1.3 Byte order
121
122 By default, the native endianness of the source architecture the trace is used.
123 Byte order can be overridden for a basic type by specifying a "byte_order"
124 attribute. Typical use-case is to specify the network byte order (big endian:
125 "be") to save data captured from the network into the trace without conversion.
126 If not specified, the byte order is native.
127
128 Metadata representation:
129
130 byte_order = native OR network OR be OR le; /* network and be are aliases */
131
132 4.1.4 Size
133
134 Type size, in bits, for integers and floats is that returned by "sizeof()" in C
135 multiplied by CHAR_BIT.
136 We require the size of "char" and "unsigned char" types (CHAR_BIT) to be fixed
137 to 8 bits for cross-endianness compatibility.
138
139 Metadata representation:
140
141 size = value; (value is in bits)
142
143 4.1.5 Integers
144
145 Signed integers are represented in two-complement. Integer alignment, size,
146 signedness and byte ordering are defined in the metadata. Integers aligned on
147 byte size (8-bit) and with length multiple of byte size (8-bit) correspond to
148 the C99 standard integers. In addition, integers with alignment and/or size that
149 are _not_ a multiple of the byte size are permitted; these correspond to the C99
150 standard bitfields, with the added specification that the CTF integer bitfields
151 have a fixed binary representation. A MIT-licensed reference implementation of
152 the CTF portable bitfields is available at:
153
154 http://git.efficios.com/?p=babeltrace.git;a=blob;f=include/babeltrace/bitfield.h
155
156 Binary representation of integers:
157
158 - On little and big endian:
159 - Within a byte, high bits correspond to an integer high bits, and low bits
160 correspond to low bits.
161 - On little endian:
162 - Integer across multiple bytes are placed from the less significant to the
163 most significant.
164 - Consecutive integers are placed from lower bits to higher bits (even within
165 a byte).
166 - On big endian:
167 - Integer across multiple bytes are placed from the most significant to the
168 less significant.
169 - Consecutive integers are placed from higher bits to lower bits (even within
170 a byte).
171
172 This binary representation is derived from the bitfield implementation in GCC
173 for little and big endian. However, contrary to what GCC does, integers can
174 cross units boundaries (no padding is required). Padding can be explicitely
175 added (see 4.1.6 GNU/C bitfields) to follow the GCC layout if needed.
176
177 Metadata representation:
178
179 integer {
180 signed = true OR false; /* default false */
181 byte_order = native OR network OR be OR le; /* default native */
182 size = value; /* value in bits, no default */
183 align = value; /* value in bits */
184 }
185
186 Example of type inheritance (creation of a uint32_t named type):
187
188 typealias integer {
189 size = 32;
190 signed = false;
191 align = 32;
192 } : uint32_t;
193
194 Definition of a named 5-bit signed bitfield:
195
196 typealias integer {
197 size = 5;
198 signed = true;
199 align = 1;
200 } : int5_t;
201
202 4.1.6 GNU/C bitfields
203
204 The GNU/C bitfields follow closely the integer representation, with a
205 particularity on alignment: if a bitfield cannot fit in the current unit, the
206 unit is padded and the bitfield starts at the following unit. The unit size is
207 defined by the size of the type "unit_type".
208
209 Metadata representation:
210
211 unit_type name:size:
212
213 As an example, the following structure declared in C compiled by GCC:
214
215 struct example {
216 short a:12;
217 short b:5;
218 };
219
220 The example structure is aligned on the largest element (short). The second
221 bitfield would be aligned on the next unit boundary, because it would not fit in
222 the current unit.
223
224 4.1.7 Floating point
225
226 The floating point values byte ordering is defined in the metadata.
227
228 Floating point values follow the IEEE 754-2008 standard interchange formats.
229 Description of the floating point values include the exponent and mantissa size
230 in bits. Some requirements are imposed on the floating point values:
231
232 - FLT_RADIX must be 2.
233 - mant_dig is the number of digits represented in the mantissa. It is specified
234 by the ISO C99 standard, section 5.2.4, as FLT_MANT_DIG, DBL_MANT_DIG and
235 LDBL_MANT_DIG as defined by <float.h>.
236 - exp_dig is the number of digits represented in the exponent. Given that
237 mant_dig is one bit more than its actual size in bits (leading 1 is not
238 needed) and also given that the sign bit always takes one bit, exp_dig can be
239 specified as:
240
241 - sizeof(float) * CHAR_BIT - FLT_MANT_DIG
242 - sizeof(double) * CHAR_BIT - DBL_MANT_DIG
243 - sizeof(long double) * CHAR_BIT - LDBL_MANT_DIG
244
245 Metadata representation:
246
247 floating_point {
248 exp_dig = value;
249 mant_dig = value;
250 byte_order = native OR network OR be OR le;
251 }
252
253 Example of type inheritance:
254
255 typealias floating_point {
256 exp_dig = 8; /* sizeof(float) * CHAR_BIT - FLT_MANT_DIG */
257 mant_dig = 24; /* FLT_MANT_DIG */
258 byte_order = native;
259 } : float;
260
261 TODO: define NaN, +inf, -inf behavior.
262
263 4.1.8 Enumerations
264
265 Enumerations are a mapping between an integer type and a table of strings. The
266 numerical representation of the enumeration follows the integer type specified
267 by the metadata. The enumeration mapping table is detailed in the enumeration
268 description within the metadata. The mapping table maps inclusive value ranges
269 (or single values) to strings. Instead of being limited to simple
270 "value -> string" mappings, these enumerations map
271 "[ start_value ... end_value ] -> string", which map inclusive ranges of
272 values to strings. An enumeration from the C language can be represented in
273 this format by having the same start_value and end_value for each element, which
274 is in fact a range of size 1. This single-value range is supported without
275 repeating the start and end values with the value = string declaration.
276
277 If a numeric value is encountered between < >, it represents the integer type
278 size used to hold the enumeration, in bits.
279
280 enum name <integer_type OR size> {
281 somestring = start_value1 ... end_value1,
282 "other string" = start_value2 ... end_value2,
283 yet_another_string, /* will be assigned to end_value2 + 1 */
284 "some other string" = value,
285 ...
286 };
287
288 If the values are omitted, the enumeration starts at 0 and increment of 1 for
289 each entry:
290
291 enum name <32> {
292 ZERO,
293 ONE,
294 TWO,
295 TEN = 10,
296 ELEVEN,
297 };
298
299 Overlapping ranges within a single enumeration are implementation defined.
300
301 A nameless enumeration can be declared as a field type or as part of a typedef:
302
303 enum <integer_type> {
304 ...
305 }
306
307
308 4.2 Compound types
309
310 Compound are aggregation of type declarations. Compound types include
311 structures, variant, arrays, sequences, and strings.
312
313 4.2.1 Structures
314
315 Structures are aligned on the largest alignment required by basic types
316 contained within the structure. (This follows the ISO/C standard for structures)
317
318 Metadata representation of a named structure:
319
320 struct name {
321 field_type field_name;
322 field_type field_name;
323 ...
324 };
325
326 Example:
327
328 struct example {
329 integer { /* Nameless type */
330 size = 16;
331 signed = true;
332 align = 16;
333 } first_field_name;
334 uint64_t second_field_name; /* Named type declared in the metadata */
335 };
336
337 The fields are placed in a sequence next to each other. They each possess a
338 field name, which is a unique identifier within the structure.
339
340 A nameless structure can be declared as a field type or as part of a typedef:
341
342 struct {
343 ...
344 }
345
346 4.2.2 Variants (Discriminated/Tagged Unions)
347
348 A CTF variant is a selection between different types. A CTF variant must
349 always be defined within the scope of a structure or within fields
350 contained within a structure (defined recursively). A "tag" enumeration
351 field must appear in either the same lexical scope, prior to the variant
352 field (in field declaration order), in an uppermost lexical scope (see
353 Section 7.2.1), or in an uppermost dynamic scope (see Section 7.2.2).
354 The type selection is indicated by the mapping from the enumeration
355 value to the string used as variant type selector. The field to use as
356 tag is specified by the "tag_field", specified between "< >" after the
357 "variant" keyword for unnamed variants, and after "variant name" for
358 named variants.
359
360 The alignment of the variant is the alignment of the type as selected by the tag
361 value for the specific instance of the variant. The alignment of the type
362 containing the variant is independent of the variant alignment. The size of the
363 variant is the size as selected by the tag value for the specific instance of
364 the variant.
365
366 A named variant declaration followed by its definition within a structure
367 declaration:
368
369 variant name {
370 field_type sel1;
371 field_type sel2;
372 field_type sel3;
373 ...
374 };
375
376 struct {
377 enum <integer_type or size> { sel1, sel2, sel3, ... } tag_field;
378 ...
379 variant name <tag_field> v;
380 }
381
382 An unnamed variant definition within a structure is expressed by the following
383 metadata:
384
385 struct {
386 enum <integer_type or size> { sel1, sel2, sel3, ... } tag_field;
387 ...
388 variant <tag_field> {
389 field_type sel1;
390 field_type sel2;
391 field_type sel3;
392 ...
393 } v;
394 }
395
396 Example of a named variant within a sequence that refers to a single tag field:
397
398 variant example {
399 uint32_t a;
400 uint64_t b;
401 short c;
402 };
403
404 struct {
405 enum <uint2_t> { a, b, c } choice;
406 variant example <choice> v[unsigned int];
407 }
408
409 Example of an unnamed variant:
410
411 struct {
412 enum <uint2_t> { a, b, c, d } choice;
413 /* Unrelated fields can be added between the variant and its tag */
414 int32_t somevalue;
415 variant <choice> {
416 uint32_t a;
417 uint64_t b;
418 short c;
419 struct {
420 unsigned int field1;
421 uint64_t field2;
422 } d;
423 } s;
424 }
425
426 Example of an unnamed variant within an array:
427
428 struct {
429 enum <uint2_t> { a, b, c } choice;
430 variant <choice> {
431 uint32_t a;
432 uint64_t b;
433 short c;
434 } v[10];
435 }
436
437 Example of a variant type definition within a structure, where the defined type
438 is then declared within an array of structures. This variant refers to a tag
439 located in an upper lexical scope. This example clearly shows that a variant
440 type definition referring to the tag "x" uses the closest preceding field from
441 the lexical scope of the type definition.
442
443 struct {
444 enum <uint2_t> { a, b, c, d } x;
445
446 typedef variant <x> { /*
447 * "x" refers to the preceding "x" enumeration in the
448 * lexical scope of the type definition.
449 */
450 uint32_t a;
451 uint64_t b;
452 short c;
453 } example_variant;
454
455 struct {
456 enum <int> { x, y, z } x; /* This enumeration is not used by "v". */
457 example_variant v; /*
458 * "v" uses the "enum <uint2_t> { a, b, c, d }"
459 * tag.
460 */
461 } a[10];
462 }
463
464 4.2.3 Arrays
465
466 Arrays are fixed-length. Their length is declared in the type declaration within
467 the metadata. They contain an array of "inner type" elements, which can refer to
468 any type not containing the type of the array being declared (no circular
469 dependency). The length is the number of elements in an array.
470
471 Metadata representation of a named array:
472
473 typedef elem_type name[length];
474
475 A nameless array can be declared as a field type within a structure, e.g.:
476
477 uint8_t field_name[10];
478
479
480 4.2.4 Sequences
481
482 Sequences are dynamically-sized arrays. They start with an integer that specify
483 the length of the sequence, followed by an array of "inner type" elements.
484 The length is the number of elements in the sequence.
485
486 Metadata representation for a named sequence:
487
488 typedef elem_type name[length_type];
489
490 A nameless sequence can be declared as a field type, e.g.:
491
492 long field_name[int];
493
494 The length type follows the integer types specifications, and the sequence
495 elements follow the "array" specifications.
496
497 4.2.5 Strings
498
499 Strings are an array of bytes of variable size and are terminated by a '\0'
500 "NULL" character. Their encoding is described in the metadata. In absence of
501 encoding attribute information, the default encoding is UTF-8.
502
503 Metadata representation of a named string type:
504
505 typealias string {
506 encoding = UTF8 OR ASCII;
507 } : name;
508
509 A nameless string type can be declared as a field type:
510
511 string field_name; /* Use default UTF8 encoding */
512
513 5. Event Packet Header
514
515 The event packet header consists of two part: one is mandatory and have a fixed
516 layout. The second part, the "event packet context", has its layout described in
517 the metadata.
518
519 - Aligned on page size. Fixed size. Fields either aligned or packed (depending
520 on the architecture preference).
521 No padding at the end of the event packet header. Native architecture byte
522 ordering.
523
524 Fixed layout (event packet header):
525
526 - Magic number (CTF magic numbers: 0xC1FC1FC1 and its reverse endianness
527 representation: 0xC11FFCC1) It needs to have a non-symmetric bytewise
528 representation. Used to distinguish between big and little endian traces (this
529 information is determined by knowing the endianness of the architecture
530 reading the trace and comparing the magic number against its value and the
531 reverse, 0xC11FFCC1). This magic number specifies that we use the CTF metadata
532 description language described in this document. Different magic numbers
533 should be used for other metadata description languages.
534 - Trace UUID, used to ensure the event packet match the metadata used.
535 (note: we cannot use a metadata checksum because metadata can be appended to
536 while tracing is active)
537 - Stream ID, used as reference to stream description in metadata.
538
539 Metadata-defined layout (event packet context):
540
541 - Event packet content size (in bytes).
542 - Event packet size (in bytes, includes padding).
543 - Event packet content checksum (optional). Checksum excludes the event packet
544 header.
545 - Per-stream event packet sequence count (to deal with UDP packet loss). The
546 number of significant sequence counter bits should also be present, so
547 wrap-arounds are deal with correctly.
548 - Timestamp at the beginning and timestamp at the end of the event packet.
549 Both timestamps are written in the packet header, but sampled respectively
550 while (or before) writing the first event and while (or after) writing the
551 last event in the packet. The inclusive range between these timestamps should
552 include all event timestamps assigned to events contained within the packet.
553 - Events discarded count
554 - Snapshot of a per-stream free-running counter, counting the number of
555 events discarded that were supposed to be written in the stream prior to
556 the first event in the event packet.
557 * Note: producer-consumer buffer full condition should fill the current
558 event packet with padding so we know exactly where events have been
559 discarded.
560 - Lossless compression scheme used for the event packet content. Applied
561 directly to raw data. New types of compression can be added in following
562 versions of the format.
563 0: no compression scheme
564 1: bzip2
565 2: gzip
566 3: xz
567 - Cypher used for the event packet content. Applied after compression.
568 0: no encryption
569 1: AES
570 - Checksum scheme used for the event packet content. Applied after encryption.
571 0: no checksum
572 1: md5
573 2: sha1
574 3: crc32
575
576 5.1 Event Packet Header Fixed Layout Description
577
578 struct event_packet_header {
579 uint32_t magic;
580 uint8_t trace_uuid[16];
581 uint32_t stream_id;
582 };
583
584 5.2 Event Packet Context Description
585
586 Event packet context example. These are declared within the stream declaration
587 in the metadata. All these fields are optional except for "content_size" and
588 "packet_size", which must be present in the context.
589
590 An example event packet context type:
591
592 struct event_packet_context {
593 uint64_t timestamp_begin;
594 uint64_t timestamp_end;
595 uint32_t checksum;
596 uint32_t stream_packet_count;
597 uint32_t events_discarded;
598 uint32_t cpu_id;
599 uint32_t/uint16_t content_size;
600 uint32_t/uint16_t packet_size;
601 uint8_t stream_packet_count_bits; /* Significant counter bits */
602 uint8_t compression_scheme;
603 uint8_t encryption_scheme;
604 uint8_t checksum_scheme;
605 };
606
607
608 6. Event Structure
609
610 The overall structure of an event is:
611
612 1 - Stream Packet Context (as specified by the stream metadata)
613 2 - Event Header (as specified by the stream metadata)
614 3 - Stream Event Context (as specified by the stream metadata)
615 4 - Event Context (as specified by the event metadata)
616 5 - Event Payload (as specified by the event metadata)
617
618 This structure defines an implicit dynamic scoping, where variants
619 located in structures with higher number can refer to the fields of
620 structures with lower number. See Section 7.2 Metadata Scopes for more
621 detail.
622
623 6.1 Event Header
624
625 Event headers can be described within the metadata. We hereby propose, as an
626 example, two types of events headers. Type 1 accommodates streams with less than
627 31 event IDs. Type 2 accommodates streams with 31 or more event IDs.
628
629 One major factor can vary between streams: the number of event IDs assigned to
630 a stream. Luckily, this information tends to stay relatively constant (modulo
631 event registration while trace is being recorded), so we can specify different
632 representations for streams containing few event IDs and streams containing
633 many event IDs, so we end up representing the event ID and timestamp as densely
634 as possible in each case.
635
636 The header is extended in the rare occasions where the information cannot be
637 represented in the ranges available in the standard event header. They are also
638 used in the rare occasions where the data required for a field could not be
639 collected: the flag corresponding to the missing field within the missing_fields
640 array is then set to 1.
641
642 Types uintX_t represent an X-bit unsigned integer.
643
644
645 6.1.1 Type 1 - Few event IDs
646
647 - Aligned on 32-bit (or 8-bit if byte-packed, depending on the architecture
648 preference).
649 - Native architecture byte ordering.
650 - For "compact" selection
651 - Fixed size: 32 bits.
652 - For "extended" selection
653 - Size depends on the architecture and variant alignment.
654
655 struct event_header_1 {
656 /*
657 * id: range: 0 - 30.
658 * id 31 is reserved to indicate an extended header.
659 */
660 enum <uint5_t> { compact = 0 ... 30, extended = 31 } id;
661 variant <id> {
662 struct {
663 uint27_t timestamp;
664 } compact;
665 struct {
666 uint32_t id; /* 32-bit event IDs */
667 uint64_t timestamp; /* 64-bit timestamps */
668 } extended;
669 } v;
670 };
671
672
673 6.1.2 Type 2 - Many event IDs
674
675 - Aligned on 16-bit (or 8-bit if byte-packed, depending on the architecture
676 preference).
677 - Native architecture byte ordering.
678 - For "compact" selection
679 - Size depends on the architecture and variant alignment.
680 - For "extended" selection
681 - Size depends on the architecture and variant alignment.
682
683 struct event_header_2 {
684 /*
685 * id: range: 0 - 65534.
686 * id 65535 is reserved to indicate an extended header.
687 */
688 enum <uint16_t> { compact = 0 ... 65534, extended = 65535 } id;
689 variant <id> {
690 struct {
691 uint32_t timestamp;
692 } compact;
693 struct {
694 uint32_t id; /* 32-bit event IDs */
695 uint64_t timestamp; /* 64-bit timestamps */
696 } extended;
697 } v;
698 };
699
700
701 6.2 Event Context
702
703 The event context contains information relative to the current event. The choice
704 and meaning of this information is specified by the metadata "stream" and
705 "event" information. The "stream" context is applied to all events within the
706 stream. The "stream" context structure follows the event header. The "event"
707 context is applied to specific events. Its structure follows the "stream"
708 context stucture.
709
710 An example of stream-level event context is to save the event payload size with
711 each event, or to save the current PID with each event. These are declared
712 within the stream declaration within the metadata:
713
714 stream {
715 ...
716 event {
717 ...
718 context := struct {
719 uint pid;
720 uint16_t payload_size;
721 };
722 }
723 };
724
725 An example of event-specific event context is to declare a bitmap of missing
726 fields, only appended after the stream event context if the extended event
727 header is selected. NR_FIELDS is the number of fields within the event (a
728 numeric value).
729
730 event {
731 context = struct {
732 variant <id> {
733 struct { } compact;
734 struct {
735 uint1_t missing_fields[NR_FIELDS]; /* missing event fields bitmap */
736 } extended;
737 } v;
738 };
739 ...
740 }
741
742 6.3 Event Payload
743
744 An event payload contains fields specific to a given event type. The fields
745 belonging to an event type are described in the event-specific metadata
746 within a structure type.
747
748 6.3.1 Padding
749
750 No padding at the end of the event payload. This differs from the ISO/C standard
751 for structures, but follows the CTF standard for structures. In a trace, even
752 though it makes sense to align the beginning of a structure, it really makes no
753 sense to add padding at the end of the structure, because structures are usually
754 not followed by a structure of the same type.
755
756 This trick can be done by adding a zero-length "end" field at the end of the C
757 structures, and by using the offset of this field rather than using sizeof()
758 when calculating the size of a structure (see Appendix "A. Helper macros").
759
760 6.3.2 Alignment
761
762 The event payload is aligned on the largest alignment required by types
763 contained within the payload. (This follows the ISO/C standard for structures)
764
765
766 7. Metadata
767
768 The meta-data is located in a stream named "metadata". It is made of "event
769 packets", which each start with an event packet header. The event type within
770 the metadata stream have no event header nor event context. Each event only
771 contains a null-terminated "string" payload, which is a metadata description
772 entry. The events are packed one next to another. Each event packet start with
773 an event packet header, which contains, amongst other fields, the magic number
774 and trace UUID. The trace UUID is represented as a string of hexadecimal digits
775 and dashes "-".
776
777 The metadata can be parsed by reading through the metadata strings, skipping
778 newlines and null-characters. Type names are made of a single identifier, and
779 can be surrounded by prefix/postfix. Text contained within "/*" and "*/", as
780 well as within "//" and end of line, are treated as comments. Boolean values can
781 be represented as true, TRUE, or 1 for true, and false, FALSE, or 0 for false.
782
783
784 7.1 Declaration vs Definition
785
786 A declaration associates a layout to a type, without specifying where
787 this type is located in the event structure hierarchy (see Section 6).
788 This therefore includes typedef, typealias, as well as all type
789 specifiers. In certain circumstances (typedef, structure field and
790 variant field), a declaration is followed by a declarator, which specify
791 the newly defined type name (for typedef), or the field name (for
792 declarations located within structure and variants). Array and sequence,
793 declared with square brackets ("[" "]"), are part of the declarator,
794 similarly to C99.
795
796 A definition associates a type to a location in the event structure
797 hierarchy (see Section 6).
798
799
800 7.2 Metadata Scopes
801
802 CTF metadata uses two different types of scoping: a lexical scope is
803 used for declarations and type definitions, and a dynamic scope is used
804 for variants references to tag fields.
805
806 7.2.1 Lexical Scope
807
808 Each of "trace", "stream", "event", "struct" and "variant" have their own
809 nestable declaration scope, within which types can be declared using "typedef"
810 and "typealias". A root declaration scope also contains all declarations
811 located outside of any of the aforementioned declarations. An innermost
812 declaration scope can refer to type declared within its container
813 lexical scope prior to the innermost declaration scope. Redefinition of
814 a typedef or typealias is not valid, although hiding an uppermost scope
815 typedef or typealias is allowed within a sub-scope.
816
817 7.2.2 Dynamic Scope
818
819 For variant tag definition only, the dynamic scope used to look up the
820 location of the associated tag field consists in the lexical scope of
821 the structures where the variant is declared, extended with the implicit
822 dynamic scope specified by the event structure hierarchy presented at
823 the beginning of Section 6. Therefore, lower levels in the dynamic scope
824 (e.g. event context) can refer to a tag field located in upper levels
825 (e.g. in the event header) by specifying, in this case,
826 "header.field_name" as tag identifier. This allows, for instance, the
827 event context to define a variant referring to the "id" field of the
828 event header as 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
847 7.2 Metadata Examples
848
849 The grammar representing the CTF metadata is presented in
850 Appendix C. CTF Metadata Grammar. This section presents a rather ligher
851 reading that consists in examples of CTF metadata, with template values:
852
853 trace {
854 major = value; /* Trace format version */
855 minor = value;
856 uuid = "aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaaa"; /* Trace UUID */
857 word_size = value;
858 };
859
860 stream {
861 id = stream_id;
862 /* Type 1 - Few event IDs; Type 2 - Many event IDs. See section 6.1. */
863 event.header := event_header_1 OR event_header_2;
864 event.context := struct {
865 ...
866 };
867 packet.context := struct {
868 ...
869 };
870 };
871
872 event {
873 name = event_name;
874 id = value; /* Numeric identifier within the stream */
875 stream = stream_id;
876 context := struct {
877 ...
878 };
879 fields := struct {
880 ...
881 };
882 };
883
884 /* More detail on types in section 4. Types */
885
886 /*
887 * Named types:
888 *
889 * Type declarations behave similarly to the C standard.
890 */
891
892 typedef aliased_type_prefix aliased_type new_type aliased_type_postfix;
893
894 /* e.g.: typedef struct example new_type_name[10]; */
895
896 /*
897 * typealias
898 *
899 * The "typealias" declaration can be used to give a name (including
900 * prefix/postfix) to a type. It should also be used to map basic C types
901 * (float, int, unsigned long, ...) to a CTF type. Typealias is a superset of
902 * "typedef": it also allows assignment of a simple variable identifier to a
903 * type.
904 */
905
906 typealias type_class {
907 ...
908 } : new_type_prefix new_type new_type_postfix;
909
910 /*
911 * e.g.:
912 * typealias integer {
913 * size = 32;
914 * align = 32;
915 * signed = false;
916 * } : struct page *;
917 *
918 * typealias integer {
919 * size = 32;
920 * align = 32;
921 * signed = true;
922 * } : int;
923 */
924
925 struct name {
926 ...
927 };
928
929 variant name {
930 ...
931 };
932
933 enum name <integer_type or size> {
934 ...
935 };
936
937
938 /*
939 * Unnamed types, contained within compound type fields, typedef or typealias.
940 */
941
942 struct {
943 ...
944 }
945
946 variant {
947 ...
948 }
949
950 enum <integer_type or size> {
951 ...
952 }
953
954 typedef type new_type[length];
955
956 struct {
957 type field_name[length];
958 }
959
960 typedef type new_type[length_type];
961
962 struct {
963 type field_name[length_type];
964 }
965
966 integer {
967 ...
968 }
969
970 floating_point {
971 ...
972 }
973
974 struct {
975 integer_type field_name:size; /* GNU/C bitfield */
976 }
977
978 struct {
979 string field_name;
980 }
981
982
983 A. Helper macros
984
985 The two following macros keep track of the size of a GNU/C structure without
986 padding at the end by placing HEADER_END as the last field. A one byte end field
987 is used for C90 compatibility (C99 flexible arrays could be used here). Note
988 that this does not affect the effective structure size, which should always be
989 calculated with the header_sizeof() helper.
990
991 #define HEADER_END char end_field
992 #define header_sizeof(type) offsetof(typeof(type), end_field)
993
994
995 B. Stream Header Rationale
996
997 An event stream is divided in contiguous event packets of variable size. These
998 subdivisions allow the trace analyzer to perform a fast binary search by time
999 within the stream (typically requiring to index only the event packet headers)
1000 without reading the whole stream. These subdivisions have a variable size to
1001 eliminate the need to transfer the event packet padding when partially filled
1002 event packets must be sent when streaming a trace for live viewing/analysis.
1003 An event packet can contain a certain amount of padding at the end. Dividing
1004 streams into event packets is also useful for network streaming over UDP and
1005 flight recorder mode tracing (a whole event packet can be swapped out of the
1006 buffer atomically for reading).
1007
1008 The stream header is repeated at the beginning of each event packet to allow
1009 flexibility in terms of:
1010
1011 - streaming support,
1012 - allowing arbitrary buffers to be discarded without making the trace
1013 unreadable,
1014 - allow UDP packet loss handling by either dealing with missing event packet
1015 or asking for re-transmission.
1016 - transparently support flight recorder mode,
1017 - transparently support crash dump.
1018
1019 The event stream header will therefore be referred to as the "event packet
1020 header" throughout the rest of this document.
1021
1022 C. CTF Metadata Grammar
1023
1024 /*
1025 * Common Trace Format (CTF) Metadata Grammar.
1026 *
1027 * Inspired from the C99 grammar:
1028 * http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1124.pdf (Annex A)
1029 *
1030 * Specialized for CTF needs by including only constant and declarations from
1031 * C99 (excluding function declarations), and by adding support for variants,
1032 * sequences and CTF-specific specifiers.
1033 */
1034
1035 1) Lexical grammar
1036
1037 1.1) Lexical elements
1038
1039 token:
1040 keyword
1041 identifier
1042 constant
1043 string-literal
1044 punctuator
1045
1046 1.2) Keywords
1047
1048 keyword: is one of
1049
1050 const
1051 char
1052 double
1053 enum
1054 event
1055 floating_point
1056 float
1057 integer
1058 int
1059 long
1060 short
1061 signed
1062 stream
1063 string
1064 struct
1065 trace
1066 typealias
1067 typedef
1068 unsigned
1069 variant
1070 void
1071 _Bool
1072 _Complex
1073 _Imaginary
1074
1075
1076 1.3) Identifiers
1077
1078 identifier:
1079 identifier-nondigit
1080 identifier identifier-nondigit
1081 identifier digit
1082
1083 identifier-nondigit:
1084 nondigit
1085 universal-character-name
1086 any other implementation-defined characters
1087
1088 nondigit:
1089 _
1090 [a-zA-Z] /* regular expression */
1091
1092 digit:
1093 [0-9] /* regular expression */
1094
1095 1.4) Universal character names
1096
1097 universal-character-name:
1098 \u hex-quad
1099 \U hex-quad hex-quad
1100
1101 hex-quad:
1102 hexadecimal-digit hexadecimal-digit hexadecimal-digit hexadecimal-digit
1103
1104 1.5) Constants
1105
1106 constant:
1107 integer-constant
1108 enumeration-constant
1109 character-constant
1110
1111 integer-constant:
1112 decimal-constant integer-suffix-opt
1113 octal-constant integer-suffix-opt
1114 hexadecimal-constant integer-suffix-opt
1115
1116 decimal-constant:
1117 nonzero-digit
1118 decimal-constant digit
1119
1120 octal-constant:
1121 0
1122 octal-constant octal-digit
1123
1124 hexadecimal-constant:
1125 hexadecimal-prefix hexadecimal-digit
1126 hexadecimal-constant hexadecimal-digit
1127
1128 hexadecimal-prefix:
1129 0x
1130 0X
1131
1132 nonzero-digit:
1133 [1-9]
1134
1135 integer-suffix:
1136 unsigned-suffix long-suffix-opt
1137 unsigned-suffix long-long-suffix
1138 long-suffix unsigned-suffix-opt
1139 long-long-suffix unsigned-suffix-opt
1140
1141 unsigned-suffix:
1142 u
1143 U
1144
1145 long-suffix:
1146 l
1147 L
1148
1149 long-long-suffix:
1150 ll
1151 LL
1152
1153 digit-sequence:
1154 digit
1155 digit-sequence digit
1156
1157 hexadecimal-digit-sequence:
1158 hexadecimal-digit
1159 hexadecimal-digit-sequence hexadecimal-digit
1160
1161 enumeration-constant:
1162 identifier
1163 string-literal
1164
1165 character-constant:
1166 ' c-char-sequence '
1167 L' c-char-sequence '
1168
1169 c-char-sequence:
1170 c-char
1171 c-char-sequence c-char
1172
1173 c-char:
1174 any member of source charset except single-quote ('), backslash
1175 (\), or new-line character.
1176 escape-sequence
1177
1178 escape-sequence:
1179 simple-escape-sequence
1180 octal-escape-sequence
1181 hexadecimal-escape-sequence
1182 universal-character-name
1183
1184 simple-escape-sequence: one of
1185 \' \" \? \\ \a \b \f \n \r \t \v
1186
1187 octal-escape-sequence:
1188 \ octal-digit
1189 \ octal-digit octal-digit
1190 \ octal-digit octal-digit octal-digit
1191
1192 hexadecimal-escape-sequence:
1193 \x hexadecimal-digit
1194 hexadecimal-escape-sequence hexadecimal-digit
1195
1196 1.6) String literals
1197
1198 string-literal:
1199 " s-char-sequence-opt "
1200 L" s-char-sequence-opt "
1201
1202 s-char-sequence:
1203 s-char
1204 s-char-sequence s-char
1205
1206 s-char:
1207 any member of source charset except double-quote ("), backslash
1208 (\), or new-line character.
1209 escape-sequence
1210
1211 1.7) Punctuators
1212
1213 punctuator: one of
1214 [ ] ( ) { } . -> * + - < > : ; ... = ,
1215
1216
1217 2) Phrase structure grammar
1218
1219 primary-expression:
1220 identifier
1221 constant
1222 string-literal
1223 ( unary-expression )
1224
1225 postfix-expression:
1226 primary-expression
1227 postfix-expression [ unary-expression ]
1228 postfix-expression . identifier
1229 postfix-expressoin -> identifier
1230
1231 unary-expression:
1232 postfix-expression
1233 unary-operator postfix-expression
1234
1235 unary-operator: one of
1236 + -
1237
1238 assignment-operator:
1239 =
1240
1241 constant-expression:
1242 unary-expression
1243
1244 constant-expression-range:
1245 constant-expression ... constant-expression
1246
1247 2.2) Declarations:
1248
1249 declaration:
1250 declaration-specifiers ;
1251 declaration-specifiers storage-class-specifier declaration-specifiers declarator-list ;
1252 ctf-specifier ;
1253
1254 declaration-specifiers:
1255 type-specifier declaration-specifiers-opt
1256 type-qualifier declaration-specifiers-opt
1257
1258 declarator-list:
1259 declarator
1260 declarator-list , declarator
1261
1262 abstract-declarator-list:
1263 abstract-declarator
1264 abstract-declarator-list , abstract-declarator
1265
1266 storage-class-specifier:
1267 typedef
1268
1269 type-specifier:
1270 void
1271 char
1272 short
1273 int
1274 long
1275 float
1276 double
1277 signed
1278 unsigned
1279 _Bool
1280 _Complex
1281 struct-specifier
1282 variant-specifier
1283 enum-specifier
1284 typedef-name
1285 ctf-type-specifier
1286
1287 struct-specifier:
1288 struct identifier-opt { struct-or-variant-declaration-list-opt }
1289 struct identifier
1290
1291 struct-or-variant-declaration-list:
1292 struct-or-variant-declaration
1293 struct-or-variant-declaration-list struct-or-variant-declaration
1294
1295 struct-or-variant-declaration:
1296 specifier-qualifier-list struct-or-variant-declarator-list ;
1297 declaration-specifiers storage-class-specifier declaration-specifiers declarator-list ;
1298 typealias declaration-specifiers abstract-declarator-list : declaration-specifiers abstract-declarator-list ;
1299 typealias declaration-specifiers abstract-declarator-list : declarator-list ;
1300
1301 specifier-qualifier-list:
1302 type-specifier specifier-qualifier-list-opt
1303 type-qualifier specifier-qualifier-list-opt
1304
1305 struct-or-variant-declarator-list:
1306 struct-or-variant-declarator
1307 struct-or-variant-declarator-list , struct-or-variant-declarator
1308
1309 struct-or-variant-declarator:
1310 declarator
1311 declarator-opt : constant-expression
1312
1313 variant-specifier:
1314 variant identifier-opt variant-tag-opt { struct-or-variant-declaration-list }
1315 variant identifier variant-tag
1316
1317 variant-tag:
1318 < identifier >
1319
1320 enum-specifier:
1321 enum identifier-opt { enumerator-list }
1322 enum identifier-opt { enumerator-list , }
1323 enum identifier
1324 enum identifier-opt < declaration-specifiers > { enumerator-list }
1325 enum identifier-opt < declaration-specifiers > { enumerator-list , }
1326 enum identifier < declaration-specifiers >
1327 enum identifier-opt < integer-constant > { enumerator-list }
1328 enum identifier-opt < integer-constant > { enumerator-list , }
1329 enum identifier < integer-constant >
1330
1331 enumerator-list:
1332 enumerator
1333 enumerator-list , enumerator
1334
1335 enumerator:
1336 enumeration-constant
1337 enumeration-constant = constant-expression
1338 enumeration-constant = constant-expression-range
1339
1340 type-qualifier:
1341 const
1342
1343 declarator:
1344 pointer-opt direct-declarator
1345
1346 direct-declarator:
1347 identifier
1348 ( declarator )
1349 direct-declarator [ type-specifier ]
1350 direct-declarator [ constant-expression ]
1351
1352 abstract-declarator:
1353 pointer-opt direct-abstract-declarator
1354
1355 direct-abstract-declarator:
1356 identifier-opt
1357 ( abstract-declarator )
1358 direct-abstract-declarator [ type-specifier ]
1359 direct-abstract-declarator [ constant-expression ]
1360 direct-abstract-declarator [ ]
1361
1362 pointer:
1363 * type-qualifier-list-opt
1364 * type-qualifier-list-opt pointer
1365
1366 type-qualifier-list:
1367 type-qualifier
1368 type-qualifier-list type-qualifier
1369
1370 typedef-name:
1371 identifier
1372
1373 2.3) CTF-specific declarations
1374
1375 ctf-specifier:
1376 event { ctf-assignment-expression-list-opt }
1377 stream { ctf-assignment-expression-list-opt }
1378 trace { ctf-assignment-expression-list-opt }
1379 typealias declaration-specifiers abstract-declarator-list : declaration-specifiers abstract-declarator-list ;
1380 typealias declaration-specifiers abstract-declarator-list : declarator-list ;
1381
1382 ctf-type-specifier:
1383 floating_point { ctf-assignment-expression-list-opt }
1384 integer { ctf-assignment-expression-list-opt }
1385 string { ctf-assignment-expression-list-opt }
1386
1387 ctf-assignment-expression-list:
1388 ctf-assignment-expression
1389 ctf-assignment-expression-list ; ctf-assignment-expression
1390
1391 ctf-assignment-expression:
1392 unary-expression assignment-operator unary-expression
1393 unary-expression type-assignment-operator type-specifier
1394 declaration-specifiers storage-class-specifier declaration-specifiers declarator-list
1395 typealias declaration-specifiers abstract-declarator-list : declaration-specifiers abstract-declarator-list
1396 typealias declaration-specifiers abstract-declarator-list : declarator-list
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