Add enum {} default mapping to integer type
[ctf.git] / common-trace-format-proposal.txt
CommitLineData
5ba9f198 1
4767a9e7 2RFC: Common Trace Format (CTF) Proposal (pre-v1.7)
5ba9f198
MD
3
4Mathieu Desnoyers, EfficiOS Inc.
5
6The goal of the present document is to propose a trace format that suits the
cc089c3a 7needs of the embedded, telecom, high-performance and kernel communities. It is
5ba9f198 8based on the Common Trace Format Requirements (v1.4) document. It is designed to
cc089c3a
MD
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
5ba9f198
MD
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
3bf79539
MD
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.
5ba9f198
MD
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
3bf79539
MD
34 an event stream.
35 e.g. event: irq_entry.
5ba9f198
MD
36 - An event (or event record) relates to a specific instance of an event
37 class.
3bf79539
MD
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.
5ba9f198
MD
41
42
432. High-level representation of a trace
44
3bf79539
MD
45A trace is divided into multiple event streams. Each event stream contains a
46subset of the trace event types.
5ba9f198 47
3bf79539
MD
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.
5ba9f198 53
3bf79539 54A metadata event stream contains information on trace event types. It describes:
5ba9f198
MD
55
56- Trace version.
57- Types available.
3bf79539
MD
58- Per-stream event header description.
59- Per-stream event header selection.
60- Per-stream event context fields.
5ba9f198 61- Per-event
3bf79539 62 - Event type to stream mapping.
5ba9f198
MD
63 - Event type to name mapping.
64 - Event type to ID mapping.
65 - Event fields description.
66
67
3bf79539 683. Event stream
5ba9f198 69
3bf79539 70An event stream is divided in contiguous event packets of variable size. These
ae8c075a
MD
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.
5ba9f198 75
3bf79539
MD
76The event stream header will therefore be referred to as the "event packet
77header" throughout the rest of this document.
5ba9f198
MD
78
79
804. Types
81
1fad7a85
MD
82Types are organized as type classes. Each type class belong to either of two
83kind of types: basic types or compound types.
84
5ba9f198
MD
854.1 Basic types
86
1fad7a85
MD
87A basic type is a scalar type, as described in this section. It includes
88integers, GNU/C bitfields, enumerations, and floating point values.
5ba9f198
MD
89
904.1.1 Type inheritance
91
80fd2569
MD
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.
5ba9f198
MD
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
370eae99 102"Integers" section.
5ba9f198 103
3bf79539
MD
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
5ba9f198 107space, aligning each type on byte boundaries (8-bit). Architectures with slow
3bf79539 108unaligned writes align types on specific alignment values. If no specific
370eae99
MD
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.
5ba9f198 112
3bf79539 113Metadata attribute representation of a specific alignment:
5ba9f198
MD
114
115 align = value; /* value in bits */
116
1174.1.3 Byte order
118
3bf79539
MD
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.
5ba9f198
MD
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
80fd2569 176 integer {
5ba9f198
MD
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 */
2152348f 181 }
5ba9f198 182
80fd2569 183Example of type inheritance (creation of a uint32_t named type):
5ba9f198 184
359894ac 185typealias integer {
9e4e34e9 186 size = 32;
5ba9f198
MD
187 signed = false;
188 align = 32;
38b8da21 189} := uint32_t;
5ba9f198 190
80fd2569 191Definition of a named 5-bit signed bitfield:
5ba9f198 192
359894ac 193typealias integer {
5ba9f198
MD
194 size = 5;
195 signed = true;
196 align = 1;
38b8da21 197} := int5_t;
5ba9f198
MD
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
80fd2569
MD
203unit is padded and the bitfield starts at the following unit. The unit size is
204defined by the size of the type "unit_type".
5ba9f198 205
2152348f 206Metadata representation:
80fd2569
MD
207
208 unit_type name:size:
209
5ba9f198
MD
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
2152348f
MD
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.
5ba9f198
MD
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
80fd2569 244floating_point {
5ba9f198
MD
245 exp_dig = value;
246 mant_dig = value;
247 byte_order = native OR network OR be OR le;
2152348f 248}
5ba9f198
MD
249
250Example of type inheritance:
251
359894ac 252typealias floating_point {
5ba9f198
MD
253 exp_dig = 8; /* sizeof(float) * CHAR_BIT - FLT_MANT_DIG */
254 mant_dig = 24; /* FLT_MANT_DIG */
255 byte_order = native;
38b8da21 256} := float;
5ba9f198
MD
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
3bf79539
MD
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
80fd2569 268"[ start_value ... end_value ] -> string", which map inclusive ranges of
3bf79539
MD
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
4767a9e7 272repeating the start and end values with the value = string declaration.
80fd2569 273
a9b83695 274enum name : integer_type {
359894ac 275 somestring = start_value1 ... end_value1,
80fd2569
MD
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
a9b83695 285enum name : unsigned int {
80fd2569
MD
286 ZERO,
287 ONE,
288 TWO,
289 TEN = 10,
290 ELEVEN,
3bf79539 291};
5ba9f198 292
80fd2569 293Overlapping ranges within a single enumeration are implementation defined.
5ba9f198 294
2152348f
MD
295A nameless enumeration can be declared as a field type or as part of a typedef:
296
a9b83695 297enum : integer_type {
2152348f
MD
298 ...
299}
300
c2742c56
MD
301Enumerations omitting the container type ": integer_type" use the "int"
302type (for compatibility with C99). The "int" type must be previously
303declared. E.g.:
304
305typealias integer { size = 32; align = 32; signed = true } := int;
306
307enum {
308 ...
309}
310
1fad7a85 311
5ba9f198
MD
3124.2 Compound types
313
1fad7a85
MD
314Compound are aggregation of type declarations. Compound types include
315structures, variant, arrays, sequences, and strings.
316
5ba9f198
MD
3174.2.1 Structures
318
319Structures are aligned on the largest alignment required by basic types
320contained within the structure. (This follows the ISO/C standard for structures)
321
80fd2569 322Metadata representation of a named structure:
5ba9f198 323
80fd2569
MD
324struct name {
325 field_type field_name;
326 field_type field_name;
327 ...
328};
5ba9f198
MD
329
330Example:
331
80fd2569
MD
332struct example {
333 integer { /* Nameless type */
334 size = 16;
335 signed = true;
336 align = 16;
337 } first_field_name;
338 uint64_t second_field_name; /* Named type declared in the metadata */
3bf79539 339};
5ba9f198
MD
340
341The fields are placed in a sequence next to each other. They each possess a
342field name, which is a unique identifier within the structure.
343
2152348f 344A nameless structure can be declared as a field type or as part of a typedef:
80fd2569
MD
345
346struct {
347 ...
2152348f 348}
80fd2569 349
77a98c82 3504.2.2 Variants (Discriminated/Tagged Unions)
fcba70d4 351
fdf2bb05
MD
352A CTF variant is a selection between different types. A CTF variant must
353always be defined within the scope of a structure or within fields
354contained within a structure (defined recursively). A "tag" enumeration
355field must appear in either the same lexical scope, prior to the variant
356field (in field declaration order), in an uppermost lexical scope (see
357Section 7.2.1), or in an uppermost dynamic scope (see Section 7.2.2).
358The type selection is indicated by the mapping from the enumeration
359value to the string used as variant type selector. The field to use as
360tag is specified by the "tag_field", specified between "< >" after the
361"variant" keyword for unnamed variants, and after "variant name" for
362named variants.
fcba70d4
MD
363
364The alignment of the variant is the alignment of the type as selected by the tag
365value for the specific instance of the variant. The alignment of the type
366containing the variant is independent of the variant alignment. The size of the
367variant is the size as selected by the tag value for the specific instance of
368the variant.
369
370A named variant declaration followed by its definition within a structure
371declaration:
372
373variant name {
374 field_type sel1;
375 field_type sel2;
376 field_type sel3;
377 ...
378};
379
380struct {
a9b83695 381 enum : integer_type { sel1, sel2, sel3, ... } tag_field;
fcba70d4
MD
382 ...
383 variant name <tag_field> v;
384}
385
386An unnamed variant definition within a structure is expressed by the following
387metadata:
388
389struct {
a9b83695 390 enum : integer_type { sel1, sel2, sel3, ... } tag_field;
fcba70d4
MD
391 ...
392 variant <tag_field> {
393 field_type sel1;
394 field_type sel2;
395 field_type sel3;
396 ...
397 } v;
398}
399
400Example of a named variant within a sequence that refers to a single tag field:
401
402variant example {
403 uint32_t a;
404 uint64_t b;
405 short c;
406};
407
408struct {
a9b83695 409 enum : uint2_t { a, b, c } choice;
15850440 410 variant example <choice> v[unsigned int];
fcba70d4
MD
411}
412
413Example of an unnamed variant:
414
415struct {
a9b83695 416 enum : uint2_t { a, b, c, d } choice;
fcba70d4
MD
417 /* Unrelated fields can be added between the variant and its tag */
418 int32_t somevalue;
419 variant <choice> {
420 uint32_t a;
421 uint64_t b;
422 short c;
423 struct {
424 unsigned int field1;
425 uint64_t field2;
426 } d;
427 } s;
428}
429
430Example of an unnamed variant within an array:
431
432struct {
a9b83695 433 enum : uint2_t { a, b, c } choice;
fcba70d4
MD
434 variant <choice> {
435 uint32_t a;
436 uint64_t b;
437 short c;
15850440 438 } v[10];
fcba70d4
MD
439}
440
441Example of a variant type definition within a structure, where the defined type
442is then declared within an array of structures. This variant refers to a tag
443located in an upper lexical scope. This example clearly shows that a variant
444type definition referring to the tag "x" uses the closest preceding field from
445the lexical scope of the type definition.
446
447struct {
a9b83695 448 enum : uint2_t { a, b, c, d } x;
fcba70d4
MD
449
450 typedef variant <x> { /*
451 * "x" refers to the preceding "x" enumeration in the
452 * lexical scope of the type definition.
453 */
454 uint32_t a;
455 uint64_t b;
456 short c;
457 } example_variant;
458
459 struct {
a9b83695 460 enum : int { x, y, z } x; /* This enumeration is not used by "v". */
fcba70d4 461 example_variant v; /*
a9b83695 462 * "v" uses the "enum : uint2_t { a, b, c, d }"
fcba70d4
MD
463 * tag.
464 */
465 } a[10];
466}
467
4684.2.3 Arrays
5ba9f198
MD
469
470Arrays are fixed-length. Their length is declared in the type declaration within
471the metadata. They contain an array of "inner type" elements, which can refer to
472any type not containing the type of the array being declared (no circular
3bf79539 473dependency). The length is the number of elements in an array.
5ba9f198 474
2152348f 475Metadata representation of a named array:
80fd2569
MD
476
477typedef elem_type name[length];
5ba9f198 478
2152348f 479A nameless array can be declared as a field type within a structure, e.g.:
5ba9f198 480
2152348f 481 uint8_t field_name[10];
80fd2569 482
5ba9f198 483
fcba70d4 4844.2.4 Sequences
5ba9f198
MD
485
486Sequences are dynamically-sized arrays. They start with an integer that specify
487the length of the sequence, followed by an array of "inner type" elements.
3bf79539 488The length is the number of elements in the sequence.
5ba9f198 489
2152348f 490Metadata representation for a named sequence:
80fd2569
MD
491
492typedef elem_type name[length_type];
493
494A nameless sequence can be declared as a field type, e.g.:
495
80fd2569
MD
496long field_name[int];
497
498The length type follows the integer types specifications, and the sequence
5ba9f198
MD
499elements follow the "array" specifications.
500
fcba70d4 5014.2.5 Strings
5ba9f198
MD
502
503Strings are an array of bytes of variable size and are terminated by a '\0'
504"NULL" character. Their encoding is described in the metadata. In absence of
505encoding attribute information, the default encoding is UTF-8.
506
80fd2569
MD
507Metadata representation of a named string type:
508
359894ac 509typealias string {
5ba9f198 510 encoding = UTF8 OR ASCII;
38b8da21 511} := name;
5ba9f198 512
80fd2569
MD
513A nameless string type can be declared as a field type:
514
515string field_name; /* Use default UTF8 encoding */
5ba9f198 516
3bf79539
MD
5175. Event Packet Header
518
519The event packet header consists of two part: one is mandatory and have a fixed
520layout. The second part, the "event packet context", has its layout described in
521the metadata.
5ba9f198 522
3bf79539
MD
523- Aligned on page size. Fixed size. Fields either aligned or packed (depending
524 on the architecture preference).
525 No padding at the end of the event packet header. Native architecture byte
5ba9f198 526 ordering.
3bf79539
MD
527
528Fixed layout (event packet header):
529
5ba9f198
MD
530- Magic number (CTF magic numbers: 0xC1FC1FC1 and its reverse endianness
531 representation: 0xC11FFCC1) It needs to have a non-symmetric bytewise
532 representation. Used to distinguish between big and little endian traces (this
533 information is determined by knowing the endianness of the architecture
534 reading the trace and comparing the magic number against its value and the
535 reverse, 0xC11FFCC1). This magic number specifies that we use the CTF metadata
536 description language described in this document. Different magic numbers
537 should be used for other metadata description languages.
3bf79539 538- Trace UUID, used to ensure the event packet match the metadata used.
5ba9f198
MD
539 (note: we cannot use a metadata checksum because metadata can be appended to
540 while tracing is active)
3bf79539
MD
541- Stream ID, used as reference to stream description in metadata.
542
543Metadata-defined layout (event packet context):
544
545- Event packet content size (in bytes).
546- Event packet size (in bytes, includes padding).
547- Event packet content checksum (optional). Checksum excludes the event packet
548 header.
549- Per-stream event packet sequence count (to deal with UDP packet loss). The
550 number of significant sequence counter bits should also be present, so
551 wrap-arounds are deal with correctly.
552- Timestamp at the beginning and timestamp at the end of the event packet.
553 Both timestamps are written in the packet header, but sampled respectively
554 while (or before) writing the first event and while (or after) writing the
555 last event in the packet. The inclusive range between these timestamps should
556 include all event timestamps assigned to events contained within the packet.
5ba9f198 557- Events discarded count
3bf79539
MD
558 - Snapshot of a per-stream free-running counter, counting the number of
559 events discarded that were supposed to be written in the stream prior to
560 the first event in the event packet.
5ba9f198 561 * Note: producer-consumer buffer full condition should fill the current
3bf79539 562 event packet with padding so we know exactly where events have been
5ba9f198 563 discarded.
3bf79539
MD
564- Lossless compression scheme used for the event packet content. Applied
565 directly to raw data. New types of compression can be added in following
566 versions of the format.
5ba9f198
MD
567 0: no compression scheme
568 1: bzip2
569 2: gzip
3bf79539
MD
570 3: xz
571- Cypher used for the event packet content. Applied after compression.
5ba9f198
MD
572 0: no encryption
573 1: AES
3bf79539 574- Checksum scheme used for the event packet content. Applied after encryption.
5ba9f198
MD
575 0: no checksum
576 1: md5
577 2: sha1
578 3: crc32
579
3bf79539
MD
5805.1 Event Packet Header Fixed Layout Description
581
80fd2569
MD
582struct event_packet_header {
583 uint32_t magic;
584 uint8_t trace_uuid[16];
3bf79539 585 uint32_t stream_id;
80fd2569 586};
5ba9f198 587
3bf79539
MD
5885.2 Event Packet Context Description
589
590Event packet context example. These are declared within the stream declaration
591in the metadata. All these fields are optional except for "content_size" and
592"packet_size", which must be present in the context.
593
594An example event packet context type:
595
80fd2569 596struct event_packet_context {
3bf79539
MD
597 uint64_t timestamp_begin;
598 uint64_t timestamp_end;
599 uint32_t checksum;
600 uint32_t stream_packet_count;
601 uint32_t events_discarded;
602 uint32_t cpu_id;
603 uint32_t/uint16_t content_size;
604 uint32_t/uint16_t packet_size;
605 uint8_t stream_packet_count_bits; /* Significant counter bits */
606 uint8_t compression_scheme;
607 uint8_t encryption_scheme;
3b0f8e4d 608 uint8_t checksum_scheme;
3bf79539 609};
5ba9f198 610
fcba70d4 611
5ba9f198
MD
6126. Event Structure
613
614The overall structure of an event is:
615
fcba70d4 6161 - Stream Packet Context (as specified by the stream metadata)
fdf2bb05
MD
617 2 - Event Header (as specified by the stream metadata)
618 3 - Stream Event Context (as specified by the stream metadata)
619 4 - Event Context (as specified by the event metadata)
620 5 - Event Payload (as specified by the event metadata)
5ba9f198 621
fdf2bb05 622This structure defines an implicit dynamic scoping, where variants
7d9d7e92
MD
623located in inner structures (those with a higher number in the listing
624above) can refer to the fields of outer structures (with lower number in
625the listing above). See Section 7.2 Metadata Scopes for more detail.
5ba9f198 626
fdf2bb05 6276.1 Event Header
fcba70d4
MD
628
629Event headers can be described within the metadata. We hereby propose, as an
630example, two types of events headers. Type 1 accommodates streams with less than
63131 event IDs. Type 2 accommodates streams with 31 or more event IDs.
5ba9f198 632
3bf79539
MD
633One major factor can vary between streams: the number of event IDs assigned to
634a stream. Luckily, this information tends to stay relatively constant (modulo
5ba9f198 635event registration while trace is being recorded), so we can specify different
3bf79539 636representations for streams containing few event IDs and streams containing
5ba9f198
MD
637many event IDs, so we end up representing the event ID and timestamp as densely
638as possible in each case.
639
fcba70d4
MD
640The header is extended in the rare occasions where the information cannot be
641represented in the ranges available in the standard event header. They are also
3bf79539
MD
642used in the rare occasions where the data required for a field could not be
643collected: the flag corresponding to the missing field within the missing_fields
644array is then set to 1.
5ba9f198
MD
645
646Types uintX_t represent an X-bit unsigned integer.
647
648
fdf2bb05 6496.1.1 Type 1 - Few event IDs
5ba9f198
MD
650
651 - Aligned on 32-bit (or 8-bit if byte-packed, depending on the architecture
652 preference).
5ba9f198 653 - Native architecture byte ordering.
fcba70d4
MD
654 - For "compact" selection
655 - Fixed size: 32 bits.
656 - For "extended" selection
657 - Size depends on the architecture and variant alignment.
5ba9f198 658
80fd2569 659struct event_header_1 {
fcba70d4
MD
660 /*
661 * id: range: 0 - 30.
662 * id 31 is reserved to indicate an extended header.
663 */
a9b83695 664 enum : uint5_t { compact = 0 ... 30, extended = 31 } id;
fcba70d4
MD
665 variant <id> {
666 struct {
667 uint27_t timestamp;
668 } compact;
669 struct {
670 uint32_t id; /* 32-bit event IDs */
671 uint64_t timestamp; /* 64-bit timestamps */
672 } extended;
673 } v;
5ba9f198
MD
674};
675
5ba9f198 676
fdf2bb05 6776.1.2 Type 2 - Many event IDs
5ba9f198 678
fcba70d4 679 - Aligned on 16-bit (or 8-bit if byte-packed, depending on the architecture
5ba9f198 680 preference).
5ba9f198 681 - Native architecture byte ordering.
fcba70d4
MD
682 - For "compact" selection
683 - Size depends on the architecture and variant alignment.
684 - For "extended" selection
685 - Size depends on the architecture and variant alignment.
5ba9f198 686
80fd2569 687struct event_header_2 {
fcba70d4
MD
688 /*
689 * id: range: 0 - 65534.
690 * id 65535 is reserved to indicate an extended header.
691 */
a9b83695 692 enum : uint16_t { compact = 0 ... 65534, extended = 65535 } id;
fcba70d4
MD
693 variant <id> {
694 struct {
695 uint32_t timestamp;
696 } compact;
697 struct {
698 uint32_t id; /* 32-bit event IDs */
699 uint64_t timestamp; /* 64-bit timestamps */
700 } extended;
701 } v;
5ba9f198
MD
702};
703
5ba9f198
MD
704
7056.2 Event Context
706
707The event context contains information relative to the current event. The choice
fcba70d4
MD
708and meaning of this information is specified by the metadata "stream" and
709"event" information. The "stream" context is applied to all events within the
710stream. The "stream" context structure follows the event header. The "event"
711context is applied to specific events. Its structure follows the "stream"
712context stucture.
5ba9f198 713
fcba70d4
MD
714An example of stream-level event context is to save the event payload size with
715each event, or to save the current PID with each event. These are declared
716within the stream declaration within the metadata:
5ba9f198 717
fcba70d4
MD
718 stream {
719 ...
720 event {
721 ...
4fa992a5 722 context := struct {
80fd2569
MD
723 uint pid;
724 uint16_t payload_size;
3bf79539 725 };
fcba70d4
MD
726 }
727 };
728
729An example of event-specific event context is to declare a bitmap of missing
730fields, only appended after the stream event context if the extended event
731header is selected. NR_FIELDS is the number of fields within the event (a
732numeric value).
5ba9f198 733
fcba70d4
MD
734 event {
735 context = struct {
736 variant <id> {
737 struct { } compact;
738 struct {
739 uint1_t missing_fields[NR_FIELDS]; /* missing event fields bitmap */
740 } extended;
741 } v;
742 };
743 ...
744 }
5ba9f198
MD
745
7466.3 Event Payload
747
748An event payload contains fields specific to a given event type. The fields
749belonging to an event type are described in the event-specific metadata
750within a structure type.
751
7526.3.1 Padding
753
754No padding at the end of the event payload. This differs from the ISO/C standard
755for structures, but follows the CTF standard for structures. In a trace, even
756though it makes sense to align the beginning of a structure, it really makes no
757sense to add padding at the end of the structure, because structures are usually
758not followed by a structure of the same type.
759
760This trick can be done by adding a zero-length "end" field at the end of the C
761structures, and by using the offset of this field rather than using sizeof()
3bf79539 762when calculating the size of a structure (see Appendix "A. Helper macros").
5ba9f198
MD
763
7646.3.2 Alignment
765
766The event payload is aligned on the largest alignment required by types
767contained within the payload. (This follows the ISO/C standard for structures)
768
769
5ba9f198
MD
7707. Metadata
771
4fafe1ad
MD
772The meta-data is located in a stream identified by its name: "metadata".
773It is made of "event packets", which each start with an event packet
774header. The event type within the metadata stream have no event header
775nor event context. Each event only contains a null-terminated "string"
776payload, which is a metadata description entry. The events are packed
777one next to another. Each event packet start with an event packet
778header, which contains, amongst other fields, the magic number and trace
779UUID. In the event packet header, the trace UUID is represented as an
780array of bytes. Within the string-based metadata description, the trace
781UUID is represented as a string of hexadecimal digits and dashes "-".
782
783The metadata can be parsed by reading through the metadata strings,
784skipping null-characters. Type names are made of a single identifier,
785and can be surrounded by prefix/postfix. Text contained within "/*" and
786"*/", as well as within "//" and end of line, are treated as comments.
787Boolean values can be represented as true, TRUE, or 1 for true, and
788false, FALSE, or 0 for false.
fcba70d4 789
fdf2bb05
MD
790
7917.1 Declaration vs Definition
792
793A declaration associates a layout to a type, without specifying where
794this type is located in the event structure hierarchy (see Section 6).
795This therefore includes typedef, typealias, as well as all type
796specifiers. In certain circumstances (typedef, structure field and
797variant field), a declaration is followed by a declarator, which specify
798the newly defined type name (for typedef), or the field name (for
799declarations located within structure and variants). Array and sequence,
800declared with square brackets ("[" "]"), are part of the declarator,
a9b83695
MD
801similarly to C99. The enumeration base type is specified by
802": base_type", which is part of the type specifier. The variant tag
803name, specified between "<" ">", is also part of the type specifier.
fdf2bb05
MD
804
805A definition associates a type to a location in the event structure
b9606a77
MD
806hierarchy (see Section 6). This association is denoted by ":=", as shown
807in Section 7.3.
fdf2bb05
MD
808
809
8107.2 Metadata Scopes
811
812CTF metadata uses two different types of scoping: a lexical scope is
813used for declarations and type definitions, and a dynamic scope is used
814for variants references to tag fields.
815
8167.2.1 Lexical Scope
817
d285084f
MD
818Each of "trace", "stream", "event", "struct" and "variant" have their own
819nestable declaration scope, within which types can be declared using "typedef"
fdf2bb05 820and "typealias". A root declaration scope also contains all declarations
7d9d7e92 821located outside of any of the aforementioned declarations. An inner
fdf2bb05 822declaration scope can refer to type declared within its container
7d9d7e92
MD
823lexical scope prior to the inner declaration scope. Redefinition of a
824typedef or typealias is not valid, although hiding an upper scope
fdf2bb05
MD
825typedef or typealias is allowed within a sub-scope.
826
8277.2.2 Dynamic Scope
828
7d9d7e92
MD
829A dynamic scope consists in the lexical scope augmented with the
830implicit event structure definition hierarchy presented at Section 6.
831The dynamic scope is only used for variant tag definitions. It is used
832at definition time to look up the location of the tag field associated
833with a variant.
834
835Therefore, variants in lower levels in the dynamic scope (e.g. event
836context) can refer to a tag field located in upper levels (e.g. in the
837event header) by specifying, in this case, the associated tag with
838<header.field_name>. This allows, for instance, the event context to
839define a variant referring to the "id" field of the event header as
840selector.
fdf2bb05
MD
841
842The target dynamic scope must be specified explicitly when referring to
843a field outside of the local static scope. The dynamic scope prefixes
844are thus:
845
7d9d7e92
MD
846 - Stream Packet Context: <stream.packet.context. >,
847 - Event Header: <stream.event.header. >,
848 - Stream Event Context: <stream.event.context. >,
849 - Event Context: <event.context. >,
850 - Event Payload: <event.fields. >.
fdf2bb05
MD
851
852Multiple declarations of the same field name within a single scope is
853not valid. It is however valid to re-use the same field name in
854different scopes. There is no possible conflict, because the dynamic
855scope must be specified when a variant refers to a tag field located in
856a different dynamic scope.
857
457d8b0a
MD
858The information available in the dynamic scopes can be thought of as the
859current tracing context. At trace production, information about the
860current context is saved into the specified scope field levels. At trace
861consumption, for each event, the current trace context is therefore
862readable by accessing the upper dynamic scopes.
863
fdf2bb05 864
b9606a77 8657.3 Metadata Examples
d285084f 866
fcba70d4 867The grammar representing the CTF metadata is presented in
fdf2bb05
MD
868Appendix C. CTF Metadata Grammar. This section presents a rather ligher
869reading that consists in examples of CTF metadata, with template values:
5ba9f198
MD
870
871trace {
fdf2bb05 872 major = value; /* Trace format version */
5ba9f198 873 minor = value;
fdf2bb05 874 uuid = "aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaaa"; /* Trace UUID */
3bf79539
MD
875 word_size = value;
876};
5ba9f198 877
3bf79539
MD
878stream {
879 id = stream_id;
fdf2bb05 880 /* Type 1 - Few event IDs; Type 2 - Many event IDs. See section 6.1. */
4fa992a5
MD
881 event.header := event_header_1 OR event_header_2;
882 event.context := struct {
77a98c82 883 ...
3bf79539 884 };
4fa992a5 885 packet.context := struct {
77a98c82 886 ...
3bf79539
MD
887 };
888};
5ba9f198
MD
889
890event {
3d13ef1a 891 name = event_name;
3bf79539
MD
892 id = value; /* Numeric identifier within the stream */
893 stream = stream_id;
4fa992a5 894 context := struct {
fcba70d4
MD
895 ...
896 };
4fa992a5 897 fields := struct {
80fd2569
MD
898 ...
899 };
3bf79539 900};
5ba9f198
MD
901
902/* More detail on types in section 4. Types */
903
3d13ef1a
MD
904/*
905 * Named types:
906 *
4fa992a5 907 * Type declarations behave similarly to the C standard.
3d13ef1a
MD
908 */
909
80af8ac6 910typedef aliased_type_specifiers new_type_declarators;
2152348f 911
3d13ef1a 912/* e.g.: typedef struct example new_type_name[10]; */
80fd2569 913
4fa992a5
MD
914/*
915 * typealias
916 *
917 * The "typealias" declaration can be used to give a name (including
80af8ac6
MD
918 * pointer declarator specifier) to a type. It should also be used to
919 * map basic C types (float, int, unsigned long, ...) to a CTF type.
920 * Typealias is a superset of "typedef": it also allows assignment of a
38b8da21 921 * simple variable identifier to a type.
4fa992a5
MD
922 */
923
924typealias type_class {
80fd2569 925 ...
38b8da21 926} := type_specifiers type_declarator;
2152348f 927
3d13ef1a
MD
928/*
929 * e.g.:
4fa992a5 930 * typealias integer {
3d13ef1a
MD
931 * size = 32;
932 * align = 32;
933 * signed = false;
38b8da21 934 * } := struct page *;
359894ac
MD
935 *
936 * typealias integer {
937 * size = 32;
938 * align = 32;
939 * signed = true;
38b8da21 940 * } := int;
3d13ef1a 941 */
80fd2569
MD
942
943struct name {
3bf79539
MD
944 ...
945};
5ba9f198 946
fcba70d4
MD
947variant name {
948 ...
949};
950
a9b83695 951enum name : integer_type {
3bf79539
MD
952 ...
953};
954
2152348f 955
4fa992a5
MD
956/*
957 * Unnamed types, contained within compound type fields, typedef or typealias.
958 */
2152348f 959
80fd2569
MD
960struct {
961 ...
2152348f 962}
5ba9f198 963
fcba70d4
MD
964variant {
965 ...
966}
967
a9b83695 968enum : integer_type {
80fd2569 969 ...
2152348f
MD
970}
971
972typedef type new_type[length];
3bf79539 973
2152348f
MD
974struct {
975 type field_name[length];
976}
977
978typedef type new_type[length_type];
979
980struct {
981 type field_name[length_type];
982}
983
984integer {
80fd2569 985 ...
2152348f 986}
3bf79539 987
2152348f 988floating_point {
80fd2569 989 ...
2152348f
MD
990}
991
992struct {
993 integer_type field_name:size; /* GNU/C bitfield */
994}
995
996struct {
997 string field_name;
998}
3bf79539 999
fcba70d4 1000
3bf79539 1001A. Helper macros
5ba9f198
MD
1002
1003The two following macros keep track of the size of a GNU/C structure without
1004padding at the end by placing HEADER_END as the last field. A one byte end field
1005is used for C90 compatibility (C99 flexible arrays could be used here). Note
1006that this does not affect the effective structure size, which should always be
1007calculated with the header_sizeof() helper.
1008
1009#define HEADER_END char end_field
1010#define header_sizeof(type) offsetof(typeof(type), end_field)
3bf79539
MD
1011
1012
1013B. Stream Header Rationale
1014
1015An event stream is divided in contiguous event packets of variable size. These
1016subdivisions allow the trace analyzer to perform a fast binary search by time
1017within the stream (typically requiring to index only the event packet headers)
1018without reading the whole stream. These subdivisions have a variable size to
1019eliminate the need to transfer the event packet padding when partially filled
1020event packets must be sent when streaming a trace for live viewing/analysis.
1021An event packet can contain a certain amount of padding at the end. Dividing
1022streams into event packets is also useful for network streaming over UDP and
1023flight recorder mode tracing (a whole event packet can be swapped out of the
1024buffer atomically for reading).
1025
1026The stream header is repeated at the beginning of each event packet to allow
1027flexibility in terms of:
1028
1029 - streaming support,
1030 - allowing arbitrary buffers to be discarded without making the trace
1031 unreadable,
1032 - allow UDP packet loss handling by either dealing with missing event packet
1033 or asking for re-transmission.
1034 - transparently support flight recorder mode,
1035 - transparently support crash dump.
1036
1037The event stream header will therefore be referred to as the "event packet
1038header" throughout the rest of this document.
fcba70d4
MD
1039
1040C. CTF Metadata Grammar
1041
4fa992a5
MD
1042/*
1043 * Common Trace Format (CTF) Metadata Grammar.
1044 *
1045 * Inspired from the C99 grammar:
1046 * http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1124.pdf (Annex A)
1047 *
1048 * Specialized for CTF needs by including only constant and declarations from
1049 * C99 (excluding function declarations), and by adding support for variants,
1050 * sequences and CTF-specific specifiers.
1051 */
1052
10531) Lexical grammar
1054
10551.1) Lexical elements
1056
1057token:
1058 keyword
1059 identifier
1060 constant
1061 string-literal
1062 punctuator
1063
10641.2) Keywords
1065
1066keyword: is one of
1067
1068const
1069char
1070double
1071enum
1072event
1073floating_point
1074float
1075integer
1076int
1077long
1078short
1079signed
1080stream
1081string
1082struct
1083trace
3e1e1a78 1084typealias
4fa992a5
MD
1085typedef
1086unsigned
1087variant
1088void
1089_Bool
1090_Complex
1091_Imaginary
1092
1093
10941.3) Identifiers
1095
1096identifier:
1097 identifier-nondigit
1098 identifier identifier-nondigit
1099 identifier digit
1100
1101identifier-nondigit:
1102 nondigit
1103 universal-character-name
1104 any other implementation-defined characters
1105
1106nondigit:
1107 _
1108 [a-zA-Z] /* regular expression */
1109
1110digit:
1111 [0-9] /* regular expression */
1112
11131.4) Universal character names
1114
1115universal-character-name:
1116 \u hex-quad
1117 \U hex-quad hex-quad
1118
1119hex-quad:
1120 hexadecimal-digit hexadecimal-digit hexadecimal-digit hexadecimal-digit
1121
11221.5) Constants
1123
1124constant:
1125 integer-constant
1126 enumeration-constant
1127 character-constant
1128
1129integer-constant:
1130 decimal-constant integer-suffix-opt
1131 octal-constant integer-suffix-opt
1132 hexadecimal-constant integer-suffix-opt
1133
1134decimal-constant:
1135 nonzero-digit
1136 decimal-constant digit
1137
1138octal-constant:
1139 0
1140 octal-constant octal-digit
1141
1142hexadecimal-constant:
1143 hexadecimal-prefix hexadecimal-digit
1144 hexadecimal-constant hexadecimal-digit
1145
1146hexadecimal-prefix:
1147 0x
1148 0X
1149
1150nonzero-digit:
1151 [1-9]
1152
1153integer-suffix:
1154 unsigned-suffix long-suffix-opt
1155 unsigned-suffix long-long-suffix
1156 long-suffix unsigned-suffix-opt
1157 long-long-suffix unsigned-suffix-opt
1158
1159unsigned-suffix:
1160 u
1161 U
1162
1163long-suffix:
1164 l
1165 L
1166
1167long-long-suffix:
1168 ll
1169 LL
1170
1171digit-sequence:
1172 digit
1173 digit-sequence digit
1174
1175hexadecimal-digit-sequence:
1176 hexadecimal-digit
1177 hexadecimal-digit-sequence hexadecimal-digit
1178
1179enumeration-constant:
1180 identifier
1181 string-literal
1182
1183character-constant:
1184 ' c-char-sequence '
1185 L' c-char-sequence '
1186
1187c-char-sequence:
1188 c-char
1189 c-char-sequence c-char
1190
1191c-char:
1192 any member of source charset except single-quote ('), backslash
1193 (\), or new-line character.
1194 escape-sequence
1195
1196escape-sequence:
1197 simple-escape-sequence
1198 octal-escape-sequence
1199 hexadecimal-escape-sequence
1200 universal-character-name
1201
1202simple-escape-sequence: one of
1203 \' \" \? \\ \a \b \f \n \r \t \v
1204
1205octal-escape-sequence:
1206 \ octal-digit
1207 \ octal-digit octal-digit
1208 \ octal-digit octal-digit octal-digit
1209
1210hexadecimal-escape-sequence:
1211 \x hexadecimal-digit
1212 hexadecimal-escape-sequence hexadecimal-digit
1213
12141.6) String literals
1215
1216string-literal:
1217 " s-char-sequence-opt "
1218 L" s-char-sequence-opt "
1219
1220s-char-sequence:
1221 s-char
1222 s-char-sequence s-char
1223
1224s-char:
1225 any member of source charset except double-quote ("), backslash
1226 (\), or new-line character.
1227 escape-sequence
1228
12291.7) Punctuators
1230
1231punctuator: one of
1232 [ ] ( ) { } . -> * + - < > : ; ... = ,
1233
1234
12352) Phrase structure grammar
1236
1237primary-expression:
1238 identifier
1239 constant
1240 string-literal
1241 ( unary-expression )
1242
1243postfix-expression:
1244 primary-expression
1245 postfix-expression [ unary-expression ]
1246 postfix-expression . identifier
1247 postfix-expressoin -> identifier
1248
1249unary-expression:
1250 postfix-expression
1251 unary-operator postfix-expression
1252
1253unary-operator: one of
1254 + -
1255
4fa992a5
MD
1256assignment-operator:
1257 =
1258
b9606a77
MD
1259type-assignment-operator:
1260 :=
1261
4fa992a5
MD
1262constant-expression:
1263 unary-expression
1264
1265constant-expression-range:
1266 constant-expression ... constant-expression
1267
12682.2) Declarations:
1269
1270declaration:
689e04b4 1271 declaration-specifiers declarator-list-opt ;
4fa992a5
MD
1272 ctf-specifier ;
1273
1274declaration-specifiers:
689e04b4 1275 storage-class-specifier declaration-specifiers-opt
4fa992a5
MD
1276 type-specifier declaration-specifiers-opt
1277 type-qualifier declaration-specifiers-opt
1278
1279declarator-list:
1280 declarator
1281 declarator-list , declarator
1282
d285084f
MD
1283abstract-declarator-list:
1284 abstract-declarator
1285 abstract-declarator-list , abstract-declarator
1286
4fa992a5
MD
1287storage-class-specifier:
1288 typedef
1289
1290type-specifier:
1291 void
1292 char
1293 short
1294 int
1295 long
1296 float
1297 double
1298 signed
1299 unsigned
1300 _Bool
1301 _Complex
cfdd51ec 1302 _Imaginary
9dfcfc0f
MD
1303 struct-specifier
1304 variant-specifier
4fa992a5
MD
1305 enum-specifier
1306 typedef-name
1307 ctf-type-specifier
1308
1309struct-specifier:
3b0f8e4d 1310 struct identifier-opt { struct-or-variant-declaration-list-opt }
4fa992a5
MD
1311 struct identifier
1312
1313struct-or-variant-declaration-list:
1314 struct-or-variant-declaration
1315 struct-or-variant-declaration-list struct-or-variant-declaration
1316
1317struct-or-variant-declaration:
1318 specifier-qualifier-list struct-or-variant-declarator-list ;
550aca33 1319 declaration-specifiers storage-class-specifier declaration-specifiers declarator-list ;
38b8da21
MD
1320 typealias declaration-specifiers abstract-declarator-list := declaration-specifiers abstract-declarator-list ;
1321 typealias declaration-specifiers abstract-declarator-list := declarator-list ;
4fa992a5
MD
1322
1323specifier-qualifier-list:
1324 type-specifier specifier-qualifier-list-opt
1325 type-qualifier specifier-qualifier-list-opt
1326
1327struct-or-variant-declarator-list:
1328 struct-or-variant-declarator
1329 struct-or-variant-declarator-list , struct-or-variant-declarator
1330
1331struct-or-variant-declarator:
1332 declarator
1333 declarator-opt : constant-expression
1334
1335variant-specifier:
1336 variant identifier-opt variant-tag-opt { struct-or-variant-declaration-list }
1337 variant identifier variant-tag
1338
1339variant-tag:
1340 < identifier >
1341
1342enum-specifier:
1343 enum identifier-opt { enumerator-list }
1344 enum identifier-opt { enumerator-list , }
1345 enum identifier
a9b83695
MD
1346 enum identifier-opt : declaration-specifiers { enumerator-list }
1347 enum identifier-opt : declaration-specifiers { enumerator-list , }
4fa992a5
MD
1348
1349enumerator-list:
1350 enumerator
1351 enumerator-list , enumerator
1352
1353enumerator:
1354 enumeration-constant
1355 enumeration-constant = constant-expression
1356 enumeration-constant = constant-expression-range
1357
1358type-qualifier:
1359 const
1360
1361declarator:
1362 pointer-opt direct-declarator
1363
1364direct-declarator:
1365 identifier
1366 ( declarator )
1367 direct-declarator [ type-specifier ]
1368 direct-declarator [ constant-expression ]
1369
d285084f
MD
1370abstract-declarator:
1371 pointer-opt direct-abstract-declarator
1372
1373direct-abstract-declarator:
1374 identifier-opt
1375 ( abstract-declarator )
1376 direct-abstract-declarator [ type-specifier ]
1377 direct-abstract-declarator [ constant-expression ]
1378 direct-abstract-declarator [ ]
1379
4fa992a5 1380pointer:
3b0f8e4d
MD
1381 * type-qualifier-list-opt
1382 * type-qualifier-list-opt pointer
4fa992a5
MD
1383
1384type-qualifier-list:
1385 type-qualifier
1386 type-qualifier-list type-qualifier
1387
4fa992a5
MD
1388typedef-name:
1389 identifier
1390
13912.3) CTF-specific declarations
1392
1393ctf-specifier:
1394 event { ctf-assignment-expression-list-opt }
1395 stream { ctf-assignment-expression-list-opt }
1396 trace { ctf-assignment-expression-list-opt }
38b8da21
MD
1397 typealias declaration-specifiers abstract-declarator-list := declaration-specifiers abstract-declarator-list ;
1398 typealias declaration-specifiers abstract-declarator-list := declarator-list ;
4fa992a5
MD
1399
1400ctf-type-specifier:
1401 floating_point { ctf-assignment-expression-list-opt }
1402 integer { ctf-assignment-expression-list-opt }
1403 string { ctf-assignment-expression-list-opt }
1404
1405ctf-assignment-expression-list:
1406 ctf-assignment-expression
1407 ctf-assignment-expression-list ; ctf-assignment-expression
1408
1409ctf-assignment-expression:
1410 unary-expression assignment-operator unary-expression
1411 unary-expression type-assignment-operator type-specifier
550aca33 1412 declaration-specifiers storage-class-specifier declaration-specifiers declarator-list
38b8da21
MD
1413 typealias declaration-specifiers abstract-declarator-list := declaration-specifiers abstract-declarator-list
1414 typealias declaration-specifiers abstract-declarator-list := declarator-list
This page took 0.173453 seconds and 4 git commands to generate.