Remove enum < integer-constant > from grammar
[ctf.git] / common-trace-format-proposal.txt
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1
2RFC: Common Trace Format (CTF) Proposal (pre-v1.7)
3
4Mathieu Desnoyers, EfficiOS Inc.
5
6The goal of the present document is to propose a trace format that suits the
7needs of the embedded, telecom, high-performance and kernel communities. It is
8based on the Common Trace Format Requirements (v1.4) document. It is designed to
9allow traces to be natively generated by the Linux kernel, Linux user-space
10applications written in C/C++, and hardware components.
11
12The 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
17A reference implementation of a library to read and write this trace format is
18being implemented within the BabelTrace project, a converter between trace
19formats. 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
251. 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
432. High-level representation of a trace
44
45A trace is divided into multiple event streams. Each event stream contains a
46subset of the trace event types.
47
48The final output of the trace, after its generation and optional transport over
49the network, is expected to be either on permanent or temporary storage in a
50virtual file system. Because each event stream is appended to while a trace is
51being recorded, each is associated with a separate file for output. Therefore,
52a stored trace can be represented as a directory containing one file per stream.
53
54A 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
683. Event stream
69
70An event stream is divided in contiguous event packets of variable size. These
71subdivisions have a variable size. An event packet can contain a certain
72amount of padding at the end. The stream header is repeated at the
73beginning of each event packet. The rationale for the event stream
74design choices is explained in Appendix B. Stream Header Rationale.
75
76The event stream header will therefore be referred to as the "event packet
77header" throughout the rest of this document.
78
79
804. Types
81
82Types are organized as type classes. Each type class belong to either of two
83kind of types: basic types or compound types.
84
854.1 Basic types
86
87A basic type is a scalar type, as described in this section. It includes
88integers, GNU/C bitfields, enumerations, and floating point values.
89
904.1.1 Type inheritance
91
92Type specifications can be inherited to allow deriving types from a
93type class. For example, see the uint32_t named type derived from the "integer"
94type class below ("Integers" section). Types have a precise binary
95representation in the trace. A type class has methods to read and write these
96types, but must be derived into a type to be usable in an event field.
97
984.1.2 Alignment
99
100We define "byte-packed" types as aligned on the byte size, namely 8-bit.
101We define "bit-packed" types as following on the next bit, as defined by the
102"Integers" section.
103
104All basic types, except bitfields, are either aligned on an architecture-defined
105specific alignment or byte-packed, depending on the architecture preference.
106Architectures providing fast unaligned write byte-packed basic types to save
107space, aligning each type on byte boundaries (8-bit). Architectures with slow
108unaligned writes align types on specific alignment values. If no specific
109alignment is declared for a type, it is assumed to be bit-packed for
110integers with size not multiple of 8 bits and for gcc bitfields. All
111other types are byte-packed.
112
113Metadata attribute representation of a specific alignment:
114
115 align = value; /* value in bits */
116
1174.1.3 Byte order
118
119By default, the native endianness of the source architecture the trace is used.
120Byte order can be overridden for a basic type by specifying a "byte_order"
121attribute. Typical use-case is to specify the network byte order (big endian:
122"be") to save data captured from the network into the trace without conversion.
123If not specified, the byte order is native.
124
125Metadata representation:
126
127 byte_order = native OR network OR be OR le; /* network and be are aliases */
128
1294.1.4 Size
130
131Type size, in bits, for integers and floats is that returned by "sizeof()" in C
132multiplied by CHAR_BIT.
133We require the size of "char" and "unsigned char" types (CHAR_BIT) to be fixed
134to 8 bits for cross-endianness compatibility.
135
136Metadata representation:
137
138 size = value; (value is in bits)
139
1404.1.5 Integers
141
142Signed integers are represented in two-complement. Integer alignment, size,
143signedness and byte ordering are defined in the metadata. Integers aligned on
144byte size (8-bit) and with length multiple of byte size (8-bit) correspond to
145the C99 standard integers. In addition, integers with alignment and/or size that
146are _not_ a multiple of the byte size are permitted; these correspond to the C99
147standard bitfields, with the added specification that the CTF integer bitfields
148have a fixed binary representation. A MIT-licensed reference implementation of
149the CTF portable bitfields is available at:
150
151 http://git.efficios.com/?p=babeltrace.git;a=blob;f=include/babeltrace/bitfield.h
152
153Binary representation of integers:
154
155- On little and big endian:
156 - Within a byte, high bits correspond to an integer high bits, and low bits
157 correspond to low bits.
158- On little endian:
159 - Integer across multiple bytes are placed from the less significant to the
160 most significant.
161 - Consecutive integers are placed from lower bits to higher bits (even within
162 a byte).
163- On big endian:
164 - Integer across multiple bytes are placed from the most significant to the
165 less significant.
166 - Consecutive integers are placed from higher bits to lower bits (even within
167 a byte).
168
169This binary representation is derived from the bitfield implementation in GCC
170for little and big endian. However, contrary to what GCC does, integers can
171cross units boundaries (no padding is required). Padding can be explicitely
172added (see 4.1.6 GNU/C bitfields) to follow the GCC layout if needed.
173
174Metadata representation:
175
176 integer {
177 signed = true OR false; /* default false */
178 byte_order = native OR network OR be OR le; /* default native */
179 size = value; /* value in bits, no default */
180 align = value; /* value in bits */
181 }
182
183Example of type inheritance (creation of a uint32_t named type):
184
185typealias integer {
186 size = 32;
187 signed = false;
188 align = 32;
189} : uint32_t;
190
191Definition of a named 5-bit signed bitfield:
192
193typealias integer {
194 size = 5;
195 signed = true;
196 align = 1;
197} : int5_t;
198
1994.1.6 GNU/C bitfields
200
201The GNU/C bitfields follow closely the integer representation, with a
202particularity on alignment: if a bitfield cannot fit in the current unit, the
203unit is padded and the bitfield starts at the following unit. The unit size is
204defined by the size of the type "unit_type".
205
206Metadata representation:
207
208 unit_type name:size:
209
210As an example, the following structure declared in C compiled by GCC:
211
212struct example {
213 short a:12;
214 short b:5;
215};
216
217The example structure is aligned on the largest element (short). The second
218bitfield would be aligned on the next unit boundary, because it would not fit in
219the current unit.
220
2214.1.7 Floating point
222
223The floating point values byte ordering is defined in the metadata.
224
225Floating point values follow the IEEE 754-2008 standard interchange formats.
226Description of the floating point values include the exponent and mantissa size
227in bits. Some requirements are imposed on the floating point values:
228
229- FLT_RADIX must be 2.
230- mant_dig is the number of digits represented in the mantissa. It is specified
231 by the ISO C99 standard, section 5.2.4, as FLT_MANT_DIG, DBL_MANT_DIG and
232 LDBL_MANT_DIG as defined by <float.h>.
233- exp_dig is the number of digits represented in the exponent. Given that
234 mant_dig is one bit more than its actual size in bits (leading 1 is not
235 needed) and also given that the sign bit always takes one bit, exp_dig can be
236 specified as:
237
238 - sizeof(float) * CHAR_BIT - FLT_MANT_DIG
239 - sizeof(double) * CHAR_BIT - DBL_MANT_DIG
240 - sizeof(long double) * CHAR_BIT - LDBL_MANT_DIG
241
242Metadata representation:
243
244floating_point {
245 exp_dig = value;
246 mant_dig = value;
247 byte_order = native OR network OR be OR le;
248}
249
250Example of type inheritance:
251
252typealias floating_point {
253 exp_dig = 8; /* sizeof(float) * CHAR_BIT - FLT_MANT_DIG */
254 mant_dig = 24; /* FLT_MANT_DIG */
255 byte_order = native;
256} : float;
257
258TODO: define NaN, +inf, -inf behavior.
259
2604.1.8 Enumerations
261
262Enumerations are a mapping between an integer type and a table of strings. The
263numerical representation of the enumeration follows the integer type specified
264by the metadata. The enumeration mapping table is detailed in the enumeration
265description within the metadata. The mapping table maps inclusive value ranges
266(or single values) to strings. Instead of being limited to simple
267"value -> string" mappings, these enumerations map
268"[ start_value ... end_value ] -> string", which map inclusive ranges of
269values to strings. An enumeration from the C language can be represented in
270this format by having the same start_value and end_value for each element, which
271is in fact a range of size 1. This single-value range is supported without
272repeating the start and end values with the value = string declaration.
273
274enum name <integer_type> {
275 somestring = start_value1 ... end_value1,
276 "other string" = start_value2 ... end_value2,
277 yet_another_string, /* will be assigned to end_value2 + 1 */
278 "some other string" = value,
279 ...
280};
281
282If the values are omitted, the enumeration starts at 0 and increment of 1 for
283each entry:
284
285enum name <unsigned int> {
286 ZERO,
287 ONE,
288 TWO,
289 TEN = 10,
290 ELEVEN,
291};
292
293Overlapping ranges within a single enumeration are implementation defined.
294
295A nameless enumeration can be declared as a field type or as part of a typedef:
296
297enum <integer_type> {
298 ...
299}
300
301
3024.2 Compound types
303
304Compound are aggregation of type declarations. Compound types include
305structures, variant, arrays, sequences, and strings.
306
3074.2.1 Structures
308
309Structures are aligned on the largest alignment required by basic types
310contained within the structure. (This follows the ISO/C standard for structures)
311
312Metadata representation of a named structure:
313
314struct name {
315 field_type field_name;
316 field_type field_name;
317 ...
318};
319
320Example:
321
322struct example {
323 integer { /* Nameless type */
324 size = 16;
325 signed = true;
326 align = 16;
327 } first_field_name;
328 uint64_t second_field_name; /* Named type declared in the metadata */
329};
330
331The fields are placed in a sequence next to each other. They each possess a
332field name, which is a unique identifier within the structure.
333
334A nameless structure can be declared as a field type or as part of a typedef:
335
336struct {
337 ...
338}
339
3404.2.2 Variants (Discriminated/Tagged Unions)
341
342A CTF variant is a selection between different types. A CTF variant must
343always be defined within the scope of a structure or within fields
344contained within a structure (defined recursively). A "tag" enumeration
345field must appear in either the same lexical scope, prior to the variant
346field (in field declaration order), in an uppermost lexical scope (see
347Section 7.2.1), or in an uppermost dynamic scope (see Section 7.2.2).
348The type selection is indicated by the mapping from the enumeration
349value to the string used as variant type selector. The field to use as
350tag is specified by the "tag_field", specified between "< >" after the
351"variant" keyword for unnamed variants, and after "variant name" for
352named variants.
353
354The alignment of the variant is the alignment of the type as selected by the tag
355value for the specific instance of the variant. The alignment of the type
356containing the variant is independent of the variant alignment. The size of the
357variant is the size as selected by the tag value for the specific instance of
358the variant.
359
360A named variant declaration followed by its definition within a structure
361declaration:
362
363variant name {
364 field_type sel1;
365 field_type sel2;
366 field_type sel3;
367 ...
368};
369
370struct {
371 enum <integer_type> { sel1, sel2, sel3, ... } tag_field;
372 ...
373 variant name <tag_field> v;
374}
375
376An unnamed variant definition within a structure is expressed by the following
377metadata:
378
379struct {
380 enum <integer_type> { sel1, sel2, sel3, ... } tag_field;
381 ...
382 variant <tag_field> {
383 field_type sel1;
384 field_type sel2;
385 field_type sel3;
386 ...
387 } v;
388}
389
390Example of a named variant within a sequence that refers to a single tag field:
391
392variant example {
393 uint32_t a;
394 uint64_t b;
395 short c;
396};
397
398struct {
399 enum <uint2_t> { a, b, c } choice;
400 variant example <choice> v[unsigned int];
401}
402
403Example of an unnamed variant:
404
405struct {
406 enum <uint2_t> { a, b, c, d } choice;
407 /* Unrelated fields can be added between the variant and its tag */
408 int32_t somevalue;
409 variant <choice> {
410 uint32_t a;
411 uint64_t b;
412 short c;
413 struct {
414 unsigned int field1;
415 uint64_t field2;
416 } d;
417 } s;
418}
419
420Example of an unnamed variant within an array:
421
422struct {
423 enum <uint2_t> { a, b, c } choice;
424 variant <choice> {
425 uint32_t a;
426 uint64_t b;
427 short c;
428 } v[10];
429}
430
431Example of a variant type definition within a structure, where the defined type
432is then declared within an array of structures. This variant refers to a tag
433located in an upper lexical scope. This example clearly shows that a variant
434type definition referring to the tag "x" uses the closest preceding field from
435the lexical scope of the type definition.
436
437struct {
438 enum <uint2_t> { a, b, c, d } x;
439
440 typedef variant <x> { /*
441 * "x" refers to the preceding "x" enumeration in the
442 * lexical scope of the type definition.
443 */
444 uint32_t a;
445 uint64_t b;
446 short c;
447 } example_variant;
448
449 struct {
450 enum <int> { x, y, z } x; /* This enumeration is not used by "v". */
451 example_variant v; /*
452 * "v" uses the "enum <uint2_t> { a, b, c, d }"
453 * tag.
454 */
455 } a[10];
456}
457
4584.2.3 Arrays
459
460Arrays are fixed-length. Their length is declared in the type declaration within
461the metadata. They contain an array of "inner type" elements, which can refer to
462any type not containing the type of the array being declared (no circular
463dependency). The length is the number of elements in an array.
464
465Metadata representation of a named array:
466
467typedef elem_type name[length];
468
469A nameless array can be declared as a field type within a structure, e.g.:
470
471 uint8_t field_name[10];
472
473
4744.2.4 Sequences
475
476Sequences are dynamically-sized arrays. They start with an integer that specify
477the length of the sequence, followed by an array of "inner type" elements.
478The length is the number of elements in the sequence.
479
480Metadata representation for a named sequence:
481
482typedef elem_type name[length_type];
483
484A nameless sequence can be declared as a field type, e.g.:
485
486long field_name[int];
487
488The length type follows the integer types specifications, and the sequence
489elements follow the "array" specifications.
490
4914.2.5 Strings
492
493Strings are an array of bytes of variable size and are terminated by a '\0'
494"NULL" character. Their encoding is described in the metadata. In absence of
495encoding attribute information, the default encoding is UTF-8.
496
497Metadata representation of a named string type:
498
499typealias string {
500 encoding = UTF8 OR ASCII;
501} : name;
502
503A nameless string type can be declared as a field type:
504
505string field_name; /* Use default UTF8 encoding */
506
5075. Event Packet Header
508
509The event packet header consists of two part: one is mandatory and have a fixed
510layout. The second part, the "event packet context", has its layout described in
511the metadata.
512
513- Aligned on page size. Fixed size. Fields either aligned or packed (depending
514 on the architecture preference).
515 No padding at the end of the event packet header. Native architecture byte
516 ordering.
517
518Fixed layout (event packet header):
519
520- Magic number (CTF magic numbers: 0xC1FC1FC1 and its reverse endianness
521 representation: 0xC11FFCC1) It needs to have a non-symmetric bytewise
522 representation. Used to distinguish between big and little endian traces (this
523 information is determined by knowing the endianness of the architecture
524 reading the trace and comparing the magic number against its value and the
525 reverse, 0xC11FFCC1). This magic number specifies that we use the CTF metadata
526 description language described in this document. Different magic numbers
527 should be used for other metadata description languages.
528- Trace UUID, used to ensure the event packet match the metadata used.
529 (note: we cannot use a metadata checksum because metadata can be appended to
530 while tracing is active)
531- Stream ID, used as reference to stream description in metadata.
532
533Metadata-defined layout (event packet context):
534
535- Event packet content size (in bytes).
536- Event packet size (in bytes, includes padding).
537- Event packet content checksum (optional). Checksum excludes the event packet
538 header.
539- Per-stream event packet sequence count (to deal with UDP packet loss). The
540 number of significant sequence counter bits should also be present, so
541 wrap-arounds are deal with correctly.
542- Timestamp at the beginning and timestamp at the end of the event packet.
543 Both timestamps are written in the packet header, but sampled respectively
544 while (or before) writing the first event and while (or after) writing the
545 last event in the packet. The inclusive range between these timestamps should
546 include all event timestamps assigned to events contained within the packet.
547- Events discarded count
548 - Snapshot of a per-stream free-running counter, counting the number of
549 events discarded that were supposed to be written in the stream prior to
550 the first event in the event packet.
551 * Note: producer-consumer buffer full condition should fill the current
552 event packet with padding so we know exactly where events have been
553 discarded.
554- Lossless compression scheme used for the event packet content. Applied
555 directly to raw data. New types of compression can be added in following
556 versions of the format.
557 0: no compression scheme
558 1: bzip2
559 2: gzip
560 3: xz
561- Cypher used for the event packet content. Applied after compression.
562 0: no encryption
563 1: AES
564- Checksum scheme used for the event packet content. Applied after encryption.
565 0: no checksum
566 1: md5
567 2: sha1
568 3: crc32
569
5705.1 Event Packet Header Fixed Layout Description
571
572struct event_packet_header {
573 uint32_t magic;
574 uint8_t trace_uuid[16];
575 uint32_t stream_id;
576};
577
5785.2 Event Packet Context Description
579
580Event packet context example. These are declared within the stream declaration
581in the metadata. All these fields are optional except for "content_size" and
582"packet_size", which must be present in the context.
583
584An example event packet context type:
585
586struct event_packet_context {
587 uint64_t timestamp_begin;
588 uint64_t timestamp_end;
589 uint32_t checksum;
590 uint32_t stream_packet_count;
591 uint32_t events_discarded;
592 uint32_t cpu_id;
593 uint32_t/uint16_t content_size;
594 uint32_t/uint16_t packet_size;
595 uint8_t stream_packet_count_bits; /* Significant counter bits */
596 uint8_t compression_scheme;
597 uint8_t encryption_scheme;
598 uint8_t checksum_scheme;
599};
600
601
6026. Event Structure
603
604The overall structure of an event is:
605
6061 - Stream Packet Context (as specified by the stream metadata)
607 2 - Event Header (as specified by the stream metadata)
608 3 - Stream Event Context (as specified by the stream metadata)
609 4 - Event Context (as specified by the event metadata)
610 5 - Event Payload (as specified by the event metadata)
611
612This structure defines an implicit dynamic scoping, where variants
613located in inner structures (those with a higher number in the listing
614above) can refer to the fields of outer structures (with lower number in
615the listing above). See Section 7.2 Metadata Scopes for more detail.
616
6176.1 Event Header
618
619Event headers can be described within the metadata. We hereby propose, as an
620example, two types of events headers. Type 1 accommodates streams with less than
62131 event IDs. Type 2 accommodates streams with 31 or more event IDs.
622
623One major factor can vary between streams: the number of event IDs assigned to
624a stream. Luckily, this information tends to stay relatively constant (modulo
625event registration while trace is being recorded), so we can specify different
626representations for streams containing few event IDs and streams containing
627many event IDs, so we end up representing the event ID and timestamp as densely
628as possible in each case.
629
630The header is extended in the rare occasions where the information cannot be
631represented in the ranges available in the standard event header. They are also
632used in the rare occasions where the data required for a field could not be
633collected: the flag corresponding to the missing field within the missing_fields
634array is then set to 1.
635
636Types uintX_t represent an X-bit unsigned integer.
637
638
6396.1.1 Type 1 - Few event IDs
640
641 - Aligned on 32-bit (or 8-bit if byte-packed, depending on the architecture
642 preference).
643 - Native architecture byte ordering.
644 - For "compact" selection
645 - Fixed size: 32 bits.
646 - For "extended" selection
647 - Size depends on the architecture and variant alignment.
648
649struct event_header_1 {
650 /*
651 * id: range: 0 - 30.
652 * id 31 is reserved to indicate an extended header.
653 */
654 enum <uint5_t> { compact = 0 ... 30, extended = 31 } id;
655 variant <id> {
656 struct {
657 uint27_t timestamp;
658 } compact;
659 struct {
660 uint32_t id; /* 32-bit event IDs */
661 uint64_t timestamp; /* 64-bit timestamps */
662 } extended;
663 } v;
664};
665
666
6676.1.2 Type 2 - Many event IDs
668
669 - Aligned on 16-bit (or 8-bit if byte-packed, depending on the architecture
670 preference).
671 - Native architecture byte ordering.
672 - For "compact" selection
673 - Size depends on the architecture and variant alignment.
674 - For "extended" selection
675 - Size depends on the architecture and variant alignment.
676
677struct event_header_2 {
678 /*
679 * id: range: 0 - 65534.
680 * id 65535 is reserved to indicate an extended header.
681 */
682 enum <uint16_t> { compact = 0 ... 65534, extended = 65535 } id;
683 variant <id> {
684 struct {
685 uint32_t timestamp;
686 } compact;
687 struct {
688 uint32_t id; /* 32-bit event IDs */
689 uint64_t timestamp; /* 64-bit timestamps */
690 } extended;
691 } v;
692};
693
694
6956.2 Event Context
696
697The event context contains information relative to the current event. The choice
698and meaning of this information is specified by the metadata "stream" and
699"event" information. The "stream" context is applied to all events within the
700stream. The "stream" context structure follows the event header. The "event"
701context is applied to specific events. Its structure follows the "stream"
702context stucture.
703
704An example of stream-level event context is to save the event payload size with
705each event, or to save the current PID with each event. These are declared
706within the stream declaration within the metadata:
707
708 stream {
709 ...
710 event {
711 ...
712 context := struct {
713 uint pid;
714 uint16_t payload_size;
715 };
716 }
717 };
718
719An example of event-specific event context is to declare a bitmap of missing
720fields, only appended after the stream event context if the extended event
721header is selected. NR_FIELDS is the number of fields within the event (a
722numeric value).
723
724 event {
725 context = struct {
726 variant <id> {
727 struct { } compact;
728 struct {
729 uint1_t missing_fields[NR_FIELDS]; /* missing event fields bitmap */
730 } extended;
731 } v;
732 };
733 ...
734 }
735
7366.3 Event Payload
737
738An event payload contains fields specific to a given event type. The fields
739belonging to an event type are described in the event-specific metadata
740within a structure type.
741
7426.3.1 Padding
743
744No padding at the end of the event payload. This differs from the ISO/C standard
745for structures, but follows the CTF standard for structures. In a trace, even
746though it makes sense to align the beginning of a structure, it really makes no
747sense to add padding at the end of the structure, because structures are usually
748not followed by a structure of the same type.
749
750This trick can be done by adding a zero-length "end" field at the end of the C
751structures, and by using the offset of this field rather than using sizeof()
752when calculating the size of a structure (see Appendix "A. Helper macros").
753
7546.3.2 Alignment
755
756The event payload is aligned on the largest alignment required by types
757contained within the payload. (This follows the ISO/C standard for structures)
758
759
7607. Metadata
761
762The meta-data is located in a stream identified by its name: "metadata".
763It is made of "event packets", which each start with an event packet
764header. The event type within the metadata stream have no event header
765nor event context. Each event only contains a null-terminated "string"
766payload, which is a metadata description entry. The events are packed
767one next to another. Each event packet start with an event packet
768header, which contains, amongst other fields, the magic number and trace
769UUID. In the event packet header, the trace UUID is represented as an
770array of bytes. Within the string-based metadata description, the trace
771UUID is represented as a string of hexadecimal digits and dashes "-".
772
773The metadata can be parsed by reading through the metadata strings,
774skipping null-characters. Type names are made of a single identifier,
775and can be surrounded by prefix/postfix. Text contained within "/*" and
776"*/", as well as within "//" and end of line, are treated as comments.
777Boolean values can be represented as true, TRUE, or 1 for true, and
778false, FALSE, or 0 for false.
779
780
7817.1 Declaration vs Definition
782
783A declaration associates a layout to a type, without specifying where
784this type is located in the event structure hierarchy (see Section 6).
785This therefore includes typedef, typealias, as well as all type
786specifiers. In certain circumstances (typedef, structure field and
787variant field), a declaration is followed by a declarator, which specify
788the newly defined type name (for typedef), or the field name (for
789declarations located within structure and variants). Array and sequence,
790declared with square brackets ("[" "]"), are part of the declarator,
791similarly to C99. The enumeration type specifier and variant tag name
792(both specified with "<" ">") are part of the type specifier.
793
794A definition associates a type to a location in the event structure
795hierarchy (see Section 6). This association is denoted by ":=", as shown
796in Section 7.3.
797
798
7997.2 Metadata Scopes
800
801CTF metadata uses two different types of scoping: a lexical scope is
802used for declarations and type definitions, and a dynamic scope is used
803for variants references to tag fields.
804
8057.2.1 Lexical Scope
806
807Each of "trace", "stream", "event", "struct" and "variant" have their own
808nestable declaration scope, within which types can be declared using "typedef"
809and "typealias". A root declaration scope also contains all declarations
810located outside of any of the aforementioned declarations. An inner
811declaration scope can refer to type declared within its container
812lexical scope prior to the inner declaration scope. Redefinition of a
813typedef or typealias is not valid, although hiding an upper scope
814typedef or typealias is allowed within a sub-scope.
815
8167.2.2 Dynamic Scope
817
818A dynamic scope consists in the lexical scope augmented with the
819implicit event structure definition hierarchy presented at Section 6.
820The dynamic scope is only used for variant tag definitions. It is used
821at definition time to look up the location of the tag field associated
822with a variant.
823
824Therefore, variants in lower levels in the dynamic scope (e.g. event
825context) can refer to a tag field located in upper levels (e.g. in the
826event header) by specifying, in this case, the associated tag with
827<header.field_name>. This allows, for instance, the event context to
828define a variant referring to the "id" field of the event header as
829selector.
830
831The target dynamic scope must be specified explicitly when referring to
832a field outside of the local static scope. The dynamic scope prefixes
833are thus:
834
835 - Stream Packet Context: <stream.packet.context. >,
836 - Event Header: <stream.event.header. >,
837 - Stream Event Context: <stream.event.context. >,
838 - Event Context: <event.context. >,
839 - Event Payload: <event.fields. >.
840
841Multiple declarations of the same field name within a single scope is
842not valid. It is however valid to re-use the same field name in
843different scopes. There is no possible conflict, because the dynamic
844scope must be specified when a variant refers to a tag field located in
845a different dynamic scope.
846
847The information available in the dynamic scopes can be thought of as the
848current tracing context. At trace production, information about the
849current context is saved into the specified scope field levels. At trace
850consumption, for each event, the current trace context is therefore
851readable by accessing the upper dynamic scopes.
852
853
8547.3 Metadata Examples
855
856The grammar representing the CTF metadata is presented in
857Appendix C. CTF Metadata Grammar. This section presents a rather ligher
858reading that consists in examples of CTF metadata, with template values:
859
860trace {
861 major = value; /* Trace format version */
862 minor = value;
863 uuid = "aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaaa"; /* Trace UUID */
864 word_size = value;
865};
866
867stream {
868 id = stream_id;
869 /* Type 1 - Few event IDs; Type 2 - Many event IDs. See section 6.1. */
870 event.header := event_header_1 OR event_header_2;
871 event.context := struct {
872 ...
873 };
874 packet.context := struct {
875 ...
876 };
877};
878
879event {
880 name = event_name;
881 id = value; /* Numeric identifier within the stream */
882 stream = stream_id;
883 context := struct {
884 ...
885 };
886 fields := struct {
887 ...
888 };
889};
890
891/* More detail on types in section 4. Types */
892
893/*
894 * Named types:
895 *
896 * Type declarations behave similarly to the C standard.
897 */
898
899typedef aliased_type_prefix aliased_type new_type aliased_type_postfix;
900
901/* e.g.: typedef struct example new_type_name[10]; */
902
903/*
904 * typealias
905 *
906 * The "typealias" declaration can be used to give a name (including
907 * prefix/postfix) to a type. It should also be used to map basic C types
908 * (float, int, unsigned long, ...) to a CTF type. Typealias is a superset of
909 * "typedef": it also allows assignment of a simple variable identifier to a
910 * type.
911 */
912
913typealias type_class {
914 ...
915} : new_type_prefix new_type new_type_postfix;
916
917/*
918 * e.g.:
919 * typealias integer {
920 * size = 32;
921 * align = 32;
922 * signed = false;
923 * } : struct page *;
924 *
925 * typealias integer {
926 * size = 32;
927 * align = 32;
928 * signed = true;
929 * } : int;
930 */
931
932struct name {
933 ...
934};
935
936variant name {
937 ...
938};
939
940enum name <integer_type> {
941 ...
942};
943
944
945/*
946 * Unnamed types, contained within compound type fields, typedef or typealias.
947 */
948
949struct {
950 ...
951}
952
953variant {
954 ...
955}
956
957enum <integer_type> {
958 ...
959}
960
961typedef type new_type[length];
962
963struct {
964 type field_name[length];
965}
966
967typedef type new_type[length_type];
968
969struct {
970 type field_name[length_type];
971}
972
973integer {
974 ...
975}
976
977floating_point {
978 ...
979}
980
981struct {
982 integer_type field_name:size; /* GNU/C bitfield */
983}
984
985struct {
986 string field_name;
987}
988
989
990A. Helper macros
991
992The two following macros keep track of the size of a GNU/C structure without
993padding at the end by placing HEADER_END as the last field. A one byte end field
994is used for C90 compatibility (C99 flexible arrays could be used here). Note
995that this does not affect the effective structure size, which should always be
996calculated with the header_sizeof() helper.
997
998#define HEADER_END char end_field
999#define header_sizeof(type) offsetof(typeof(type), end_field)
1000
1001
1002B. Stream Header Rationale
1003
1004An event stream is divided in contiguous event packets of variable size. These
1005subdivisions allow the trace analyzer to perform a fast binary search by time
1006within the stream (typically requiring to index only the event packet headers)
1007without reading the whole stream. These subdivisions have a variable size to
1008eliminate the need to transfer the event packet padding when partially filled
1009event packets must be sent when streaming a trace for live viewing/analysis.
1010An event packet can contain a certain amount of padding at the end. Dividing
1011streams into event packets is also useful for network streaming over UDP and
1012flight recorder mode tracing (a whole event packet can be swapped out of the
1013buffer atomically for reading).
1014
1015The stream header is repeated at the beginning of each event packet to allow
1016flexibility in terms of:
1017
1018 - streaming support,
1019 - allowing arbitrary buffers to be discarded without making the trace
1020 unreadable,
1021 - allow UDP packet loss handling by either dealing with missing event packet
1022 or asking for re-transmission.
1023 - transparently support flight recorder mode,
1024 - transparently support crash dump.
1025
1026The event stream header will therefore be referred to as the "event packet
1027header" throughout the rest of this document.
1028
1029C. CTF Metadata Grammar
1030
1031/*
1032 * Common Trace Format (CTF) Metadata Grammar.
1033 *
1034 * Inspired from the C99 grammar:
1035 * http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1124.pdf (Annex A)
1036 *
1037 * Specialized for CTF needs by including only constant and declarations from
1038 * C99 (excluding function declarations), and by adding support for variants,
1039 * sequences and CTF-specific specifiers.
1040 */
1041
10421) Lexical grammar
1043
10441.1) Lexical elements
1045
1046token:
1047 keyword
1048 identifier
1049 constant
1050 string-literal
1051 punctuator
1052
10531.2) Keywords
1054
1055keyword: is one of
1056
1057const
1058char
1059double
1060enum
1061event
1062floating_point
1063float
1064integer
1065int
1066long
1067short
1068signed
1069stream
1070string
1071struct
1072trace
1073typealias
1074typedef
1075unsigned
1076variant
1077void
1078_Bool
1079_Complex
1080_Imaginary
1081
1082
10831.3) Identifiers
1084
1085identifier:
1086 identifier-nondigit
1087 identifier identifier-nondigit
1088 identifier digit
1089
1090identifier-nondigit:
1091 nondigit
1092 universal-character-name
1093 any other implementation-defined characters
1094
1095nondigit:
1096 _
1097 [a-zA-Z] /* regular expression */
1098
1099digit:
1100 [0-9] /* regular expression */
1101
11021.4) Universal character names
1103
1104universal-character-name:
1105 \u hex-quad
1106 \U hex-quad hex-quad
1107
1108hex-quad:
1109 hexadecimal-digit hexadecimal-digit hexadecimal-digit hexadecimal-digit
1110
11111.5) Constants
1112
1113constant:
1114 integer-constant
1115 enumeration-constant
1116 character-constant
1117
1118integer-constant:
1119 decimal-constant integer-suffix-opt
1120 octal-constant integer-suffix-opt
1121 hexadecimal-constant integer-suffix-opt
1122
1123decimal-constant:
1124 nonzero-digit
1125 decimal-constant digit
1126
1127octal-constant:
1128 0
1129 octal-constant octal-digit
1130
1131hexadecimal-constant:
1132 hexadecimal-prefix hexadecimal-digit
1133 hexadecimal-constant hexadecimal-digit
1134
1135hexadecimal-prefix:
1136 0x
1137 0X
1138
1139nonzero-digit:
1140 [1-9]
1141
1142integer-suffix:
1143 unsigned-suffix long-suffix-opt
1144 unsigned-suffix long-long-suffix
1145 long-suffix unsigned-suffix-opt
1146 long-long-suffix unsigned-suffix-opt
1147
1148unsigned-suffix:
1149 u
1150 U
1151
1152long-suffix:
1153 l
1154 L
1155
1156long-long-suffix:
1157 ll
1158 LL
1159
1160digit-sequence:
1161 digit
1162 digit-sequence digit
1163
1164hexadecimal-digit-sequence:
1165 hexadecimal-digit
1166 hexadecimal-digit-sequence hexadecimal-digit
1167
1168enumeration-constant:
1169 identifier
1170 string-literal
1171
1172character-constant:
1173 ' c-char-sequence '
1174 L' c-char-sequence '
1175
1176c-char-sequence:
1177 c-char
1178 c-char-sequence c-char
1179
1180c-char:
1181 any member of source charset except single-quote ('), backslash
1182 (\), or new-line character.
1183 escape-sequence
1184
1185escape-sequence:
1186 simple-escape-sequence
1187 octal-escape-sequence
1188 hexadecimal-escape-sequence
1189 universal-character-name
1190
1191simple-escape-sequence: one of
1192 \' \" \? \\ \a \b \f \n \r \t \v
1193
1194octal-escape-sequence:
1195 \ octal-digit
1196 \ octal-digit octal-digit
1197 \ octal-digit octal-digit octal-digit
1198
1199hexadecimal-escape-sequence:
1200 \x hexadecimal-digit
1201 hexadecimal-escape-sequence hexadecimal-digit
1202
12031.6) String literals
1204
1205string-literal:
1206 " s-char-sequence-opt "
1207 L" s-char-sequence-opt "
1208
1209s-char-sequence:
1210 s-char
1211 s-char-sequence s-char
1212
1213s-char:
1214 any member of source charset except double-quote ("), backslash
1215 (\), or new-line character.
1216 escape-sequence
1217
12181.7) Punctuators
1219
1220punctuator: one of
1221 [ ] ( ) { } . -> * + - < > : ; ... = ,
1222
1223
12242) Phrase structure grammar
1225
1226primary-expression:
1227 identifier
1228 constant
1229 string-literal
1230 ( unary-expression )
1231
1232postfix-expression:
1233 primary-expression
1234 postfix-expression [ unary-expression ]
1235 postfix-expression . identifier
1236 postfix-expressoin -> identifier
1237
1238unary-expression:
1239 postfix-expression
1240 unary-operator postfix-expression
1241
1242unary-operator: one of
1243 + -
1244
1245assignment-operator:
1246 =
1247
1248type-assignment-operator:
1249 :=
1250
1251constant-expression:
1252 unary-expression
1253
1254constant-expression-range:
1255 constant-expression ... constant-expression
1256
12572.2) Declarations:
1258
1259declaration:
1260 declaration-specifiers declarator-list-opt ;
1261 ctf-specifier ;
1262
1263declaration-specifiers:
1264 storage-class-specifier declaration-specifiers-opt
1265 type-specifier declaration-specifiers-opt
1266 type-qualifier declaration-specifiers-opt
1267
1268declarator-list:
1269 declarator
1270 declarator-list , declarator
1271
1272abstract-declarator-list:
1273 abstract-declarator
1274 abstract-declarator-list , abstract-declarator
1275
1276storage-class-specifier:
1277 typedef
1278
1279type-specifier:
1280 void
1281 char
1282 short
1283 int
1284 long
1285 float
1286 double
1287 signed
1288 unsigned
1289 _Bool
1290 _Complex
1291 _Imaginary
1292 struct-specifier
1293 variant-specifier
1294 enum-specifier
1295 typedef-name
1296 ctf-type-specifier
1297
1298struct-specifier:
1299 struct identifier-opt { struct-or-variant-declaration-list-opt }
1300 struct identifier
1301
1302struct-or-variant-declaration-list:
1303 struct-or-variant-declaration
1304 struct-or-variant-declaration-list struct-or-variant-declaration
1305
1306struct-or-variant-declaration:
1307 specifier-qualifier-list struct-or-variant-declarator-list ;
1308 declaration-specifiers storage-class-specifier declaration-specifiers declarator-list ;
1309 typealias declaration-specifiers abstract-declarator-list : declaration-specifiers abstract-declarator-list ;
1310 typealias declaration-specifiers abstract-declarator-list : declarator-list ;
1311
1312specifier-qualifier-list:
1313 type-specifier specifier-qualifier-list-opt
1314 type-qualifier specifier-qualifier-list-opt
1315
1316struct-or-variant-declarator-list:
1317 struct-or-variant-declarator
1318 struct-or-variant-declarator-list , struct-or-variant-declarator
1319
1320struct-or-variant-declarator:
1321 declarator
1322 declarator-opt : constant-expression
1323
1324variant-specifier:
1325 variant identifier-opt variant-tag-opt { struct-or-variant-declaration-list }
1326 variant identifier variant-tag
1327
1328variant-tag:
1329 < identifier >
1330
1331enum-specifier:
1332 enum identifier-opt { enumerator-list }
1333 enum identifier-opt { enumerator-list , }
1334 enum identifier
1335 enum identifier-opt < declaration-specifiers > { enumerator-list }
1336 enum identifier-opt < declaration-specifiers > { enumerator-list , }
1337 enum identifier < declaration-specifiers >
1338
1339enumerator-list:
1340 enumerator
1341 enumerator-list , enumerator
1342
1343enumerator:
1344 enumeration-constant
1345 enumeration-constant = constant-expression
1346 enumeration-constant = constant-expression-range
1347
1348type-qualifier:
1349 const
1350
1351declarator:
1352 pointer-opt direct-declarator
1353
1354direct-declarator:
1355 identifier
1356 ( declarator )
1357 direct-declarator [ type-specifier ]
1358 direct-declarator [ constant-expression ]
1359
1360abstract-declarator:
1361 pointer-opt direct-abstract-declarator
1362
1363direct-abstract-declarator:
1364 identifier-opt
1365 ( abstract-declarator )
1366 direct-abstract-declarator [ type-specifier ]
1367 direct-abstract-declarator [ constant-expression ]
1368 direct-abstract-declarator [ ]
1369
1370pointer:
1371 * type-qualifier-list-opt
1372 * type-qualifier-list-opt pointer
1373
1374type-qualifier-list:
1375 type-qualifier
1376 type-qualifier-list type-qualifier
1377
1378typedef-name:
1379 identifier
1380
13812.3) CTF-specific declarations
1382
1383ctf-specifier:
1384 event { ctf-assignment-expression-list-opt }
1385 stream { ctf-assignment-expression-list-opt }
1386 trace { ctf-assignment-expression-list-opt }
1387 typealias declaration-specifiers abstract-declarator-list : declaration-specifiers abstract-declarator-list ;
1388 typealias declaration-specifiers abstract-declarator-list : declarator-list ;
1389
1390ctf-type-specifier:
1391 floating_point { ctf-assignment-expression-list-opt }
1392 integer { ctf-assignment-expression-list-opt }
1393 string { ctf-assignment-expression-list-opt }
1394
1395ctf-assignment-expression-list:
1396 ctf-assignment-expression
1397 ctf-assignment-expression-list ; ctf-assignment-expression
1398
1399ctf-assignment-expression:
1400 unary-expression assignment-operator unary-expression
1401 unary-expression type-assignment-operator type-specifier
1402 declaration-specifiers storage-class-specifier declaration-specifiers declarator-list
1403 typealias declaration-specifiers abstract-declarator-list : declaration-specifiers abstract-declarator-list
1404 typealias declaration-specifiers abstract-declarator-list : declarator-list
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