Explain limitations if packet header fields are not present
[ctf.git] / common-trace-format-proposal.txt
1
2 RFC: Common Trace Format (CTF) Proposal (pre-v1.7)
3
4 Mathieu Desnoyers, EfficiOS Inc.
5
6 The goal of the present document is to propose a trace format that suits the
7 needs of the embedded, telecom, high-performance and kernel communities. It is
8 based on the Common Trace Format Requirements (v1.4) document. It is designed to
9 allow traces to be natively generated by the Linux kernel, Linux user-space
10 applications written in C/C++, and hardware components. One major element of
11 CTF is the Trace Stream Description Language (TSDL) which flexibility
12 enables description of various binary trace stream layouts.
13
14 The latest version of this document can be found at:
15
16 git tree: git://git.efficios.com/ctf.git
17 gitweb: http://git.efficios.com/?p=ctf.git
18
19 A reference implementation of a library to read and write this trace format is
20 being implemented within the BabelTrace project, a converter between trace
21 formats. The development tree is available at:
22
23 git tree: git://git.efficios.com/babeltrace.git
24 gitweb: http://git.efficios.com/?p=babeltrace.git
25
26
27 1. Preliminary definitions
28
29 - Event Trace: An ordered sequence of events.
30 - Event Stream: An ordered sequence of events, containing a subset of the
31 trace event types.
32 - Event Packet: A sequence of physically contiguous events within an event
33 stream.
34 - Event: This is the basic entry in a trace. (aka: a trace record).
35 - An event identifier (ID) relates to the class (a type) of event within
36 an event stream.
37 e.g. event: irq_entry.
38 - An event (or event record) relates to a specific instance of an event
39 class.
40 e.g. event: irq_entry, at time X, on CPU Y
41 - Source Architecture: Architecture writing the trace.
42 - Reader Architecture: Architecture reading the trace.
43
44
45 2. High-level representation of a trace
46
47 A trace is divided into multiple event streams. Each event stream contains a
48 subset of the trace event types.
49
50 The final output of the trace, after its generation and optional transport over
51 the network, is expected to be either on permanent or temporary storage in a
52 virtual file system. Because each event stream is appended to while a trace is
53 being recorded, each is associated with a separate file for output. Therefore,
54 a stored trace can be represented as a directory containing one file per stream.
55
56 A metadata event stream contains information on trace event types
57 expressed in the Trace Stream Description Language (TSDL). It describes:
58
59 - Trace version.
60 - Types available.
61 - Per-stream event header description.
62 - Per-stream event header selection.
63 - Per-stream event context fields.
64 - Per-event
65 - Event type to stream mapping.
66 - Event type to name mapping.
67 - Event type to ID mapping.
68 - Event fields description.
69
70
71 3. Event stream
72
73 An event stream is divided in contiguous event packets of variable size. These
74 subdivisions have a variable size. An event packet can contain a certain
75 amount of padding at the end. The stream header is repeated at the
76 beginning of each event packet. The rationale for the event stream
77 design choices is explained in Appendix B. Stream Header Rationale.
78
79 The event stream header will therefore be referred to as the "event packet
80 header" throughout the rest of this document.
81
82
83 4. Types
84
85 Types are organized as type classes. Each type class belong to either of two
86 kind of types: basic types or compound types.
87
88 4.1 Basic types
89
90 A basic type is a scalar type, as described in this section. It includes
91 integers, GNU/C bitfields, enumerations, and floating point values.
92
93 4.1.1 Type inheritance
94
95 Type specifications can be inherited to allow deriving types from a
96 type class. For example, see the uint32_t named type derived from the "integer"
97 type class below ("Integers" section). Types have a precise binary
98 representation in the trace. A type class has methods to read and write these
99 types, but must be derived into a type to be usable in an event field.
100
101 4.1.2 Alignment
102
103 We define "byte-packed" types as aligned on the byte size, namely 8-bit.
104 We define "bit-packed" types as following on the next bit, as defined by the
105 "Integers" section.
106
107 All basic types, except bitfields, are either aligned on an architecture-defined
108 specific alignment or byte-packed, depending on the architecture preference.
109 Architectures providing fast unaligned write byte-packed basic types to save
110 space, aligning each type on byte boundaries (8-bit). Architectures with slow
111 unaligned writes align types on specific alignment values. If no specific
112 alignment is declared for a type, it is assumed to be bit-packed for
113 integers with size not multiple of 8 bits and for gcc bitfields. All
114 other types are byte-packed.
115
116 Metadata attribute representation of a specific alignment:
117
118 align = value; /* value in bits */
119
120 4.1.3 Byte order
121
122 By default, the native endianness of the source architecture the trace is used.
123 Byte order can be overridden for a basic type by specifying a "byte_order"
124 attribute. Typical use-case is to specify the network byte order (big endian:
125 "be") to save data captured from the network into the trace without conversion.
126 If not specified, the byte order is native.
127
128 Metadata representation:
129
130 byte_order = native OR network OR be OR le; /* network and be are aliases */
131
132 4.1.4 Size
133
134 Type size, in bits, for integers and floats is that returned by "sizeof()" in C
135 multiplied by CHAR_BIT.
136 We require the size of "char" and "unsigned char" types (CHAR_BIT) to be fixed
137 to 8 bits for cross-endianness compatibility.
138
139 Metadata representation:
140
141 size = value; (value is in bits)
142
143 4.1.5 Integers
144
145 Signed integers are represented in two-complement. Integer alignment, size,
146 signedness and byte ordering are defined in the metadata. Integers aligned on
147 byte size (8-bit) and with length multiple of byte size (8-bit) correspond to
148 the C99 standard integers. In addition, integers with alignment and/or size that
149 are _not_ a multiple of the byte size are permitted; these correspond to the C99
150 standard bitfields, with the added specification that the CTF integer bitfields
151 have a fixed binary representation. A MIT-licensed reference implementation of
152 the CTF portable bitfields is available at:
153
154 http://git.efficios.com/?p=babeltrace.git;a=blob;f=include/babeltrace/bitfield.h
155
156 Binary representation of integers:
157
158 - On little and big endian:
159 - Within a byte, high bits correspond to an integer high bits, and low bits
160 correspond to low bits.
161 - On little endian:
162 - Integer across multiple bytes are placed from the less significant to the
163 most significant.
164 - Consecutive integers are placed from lower bits to higher bits (even within
165 a byte).
166 - On big endian:
167 - Integer across multiple bytes are placed from the most significant to the
168 less significant.
169 - Consecutive integers are placed from higher bits to lower bits (even within
170 a byte).
171
172 This binary representation is derived from the bitfield implementation in GCC
173 for little and big endian. However, contrary to what GCC does, integers can
174 cross units boundaries (no padding is required). Padding can be explicitely
175 added (see 4.1.6 GNU/C bitfields) to follow the GCC layout if needed.
176
177 Metadata representation:
178
179 integer {
180 signed = true OR false; /* default false */
181 byte_order = native OR network OR be OR le; /* default native */
182 size = value; /* value in bits, no default */
183 align = value; /* value in bits */
184 }
185
186 Example of type inheritance (creation of a uint32_t named type):
187
188 typealias integer {
189 size = 32;
190 signed = false;
191 align = 32;
192 } := uint32_t;
193
194 Definition of a named 5-bit signed bitfield:
195
196 typealias integer {
197 size = 5;
198 signed = true;
199 align = 1;
200 } := int5_t;
201
202 4.1.6 GNU/C bitfields
203
204 The GNU/C bitfields follow closely the integer representation, with a
205 particularity on alignment: if a bitfield cannot fit in the current unit, the
206 unit is padded and the bitfield starts at the following unit. The unit size is
207 defined by the size of the type "unit_type".
208
209 Metadata representation:
210
211 unit_type name:size:
212
213 As an example, the following structure declared in C compiled by GCC:
214
215 struct example {
216 short a:12;
217 short b:5;
218 };
219
220 The example structure is aligned on the largest element (short). The second
221 bitfield would be aligned on the next unit boundary, because it would not fit in
222 the current unit.
223
224 4.1.7 Floating point
225
226 The floating point values byte ordering is defined in the metadata.
227
228 Floating point values follow the IEEE 754-2008 standard interchange formats.
229 Description of the floating point values include the exponent and mantissa size
230 in bits. Some requirements are imposed on the floating point values:
231
232 - FLT_RADIX must be 2.
233 - mant_dig is the number of digits represented in the mantissa. It is specified
234 by the ISO C99 standard, section 5.2.4, as FLT_MANT_DIG, DBL_MANT_DIG and
235 LDBL_MANT_DIG as defined by <float.h>.
236 - exp_dig is the number of digits represented in the exponent. Given that
237 mant_dig is one bit more than its actual size in bits (leading 1 is not
238 needed) and also given that the sign bit always takes one bit, exp_dig can be
239 specified as:
240
241 - sizeof(float) * CHAR_BIT - FLT_MANT_DIG
242 - sizeof(double) * CHAR_BIT - DBL_MANT_DIG
243 - sizeof(long double) * CHAR_BIT - LDBL_MANT_DIG
244
245 Metadata representation:
246
247 floating_point {
248 exp_dig = value;
249 mant_dig = value;
250 byte_order = native OR network OR be OR le;
251 }
252
253 Example of type inheritance:
254
255 typealias floating_point {
256 exp_dig = 8; /* sizeof(float) * CHAR_BIT - FLT_MANT_DIG */
257 mant_dig = 24; /* FLT_MANT_DIG */
258 byte_order = native;
259 } := float;
260
261 TODO: define NaN, +inf, -inf behavior.
262
263 4.1.8 Enumerations
264
265 Enumerations are a mapping between an integer type and a table of strings. The
266 numerical representation of the enumeration follows the integer type specified
267 by the metadata. The enumeration mapping table is detailed in the enumeration
268 description within the metadata. The mapping table maps inclusive value ranges
269 (or single values) to strings. Instead of being limited to simple
270 "value -> string" mappings, these enumerations map
271 "[ start_value ... end_value ] -> string", which map inclusive ranges of
272 values to strings. An enumeration from the C language can be represented in
273 this format by having the same start_value and end_value for each element, which
274 is in fact a range of size 1. This single-value range is supported without
275 repeating the start and end values with the value = string declaration.
276
277 enum name : integer_type {
278 somestring = start_value1 ... end_value1,
279 "other string" = start_value2 ... end_value2,
280 yet_another_string, /* will be assigned to end_value2 + 1 */
281 "some other string" = value,
282 ...
283 };
284
285 If the values are omitted, the enumeration starts at 0 and increment of 1 for
286 each entry:
287
288 enum name : unsigned int {
289 ZERO,
290 ONE,
291 TWO,
292 TEN = 10,
293 ELEVEN,
294 };
295
296 Overlapping ranges within a single enumeration are implementation defined.
297
298 A nameless enumeration can be declared as a field type or as part of a typedef:
299
300 enum : integer_type {
301 ...
302 }
303
304 Enumerations omitting the container type ": integer_type" use the "int"
305 type (for compatibility with C99). The "int" type must be previously
306 declared. E.g.:
307
308 typealias integer { size = 32; align = 32; signed = true } := int;
309
310 enum {
311 ...
312 }
313
314
315 4.2 Compound types
316
317 Compound are aggregation of type declarations. Compound types include
318 structures, variant, arrays, sequences, and strings.
319
320 4.2.1 Structures
321
322 Structures are aligned on the largest alignment required by basic types
323 contained within the structure. (This follows the ISO/C standard for structures)
324
325 Metadata representation of a named structure:
326
327 struct name {
328 field_type field_name;
329 field_type field_name;
330 ...
331 };
332
333 Example:
334
335 struct example {
336 integer { /* Nameless type */
337 size = 16;
338 signed = true;
339 align = 16;
340 } first_field_name;
341 uint64_t second_field_name; /* Named type declared in the metadata */
342 };
343
344 The fields are placed in a sequence next to each other. They each possess a
345 field name, which is a unique identifier within the structure.
346
347 A nameless structure can be declared as a field type or as part of a typedef:
348
349 struct {
350 ...
351 }
352
353 4.2.2 Variants (Discriminated/Tagged Unions)
354
355 A CTF variant is a selection between different types. A CTF variant must
356 always be defined within the scope of a structure or within fields
357 contained within a structure (defined recursively). A "tag" enumeration
358 field must appear in either the same lexical scope, prior to the variant
359 field (in field declaration order), in an uppermost lexical scope (see
360 Section 7.3.1), or in an uppermost dynamic scope (see Section 7.3.2).
361 The type selection is indicated by the mapping from the enumeration
362 value to the string used as variant type selector. The field to use as
363 tag is specified by the "tag_field", specified between "< >" after the
364 "variant" keyword for unnamed variants, and after "variant name" for
365 named variants.
366
367 The alignment of the variant is the alignment of the type as selected by the tag
368 value for the specific instance of the variant. The alignment of the type
369 containing the variant is independent of the variant alignment. The size of the
370 variant is the size as selected by the tag value for the specific instance of
371 the variant.
372
373 A named variant declaration followed by its definition within a structure
374 declaration:
375
376 variant name {
377 field_type sel1;
378 field_type sel2;
379 field_type sel3;
380 ...
381 };
382
383 struct {
384 enum : integer_type { sel1, sel2, sel3, ... } tag_field;
385 ...
386 variant name <tag_field> v;
387 }
388
389 An unnamed variant definition within a structure is expressed by the following
390 metadata:
391
392 struct {
393 enum : integer_type { sel1, sel2, sel3, ... } tag_field;
394 ...
395 variant <tag_field> {
396 field_type sel1;
397 field_type sel2;
398 field_type sel3;
399 ...
400 } v;
401 }
402
403 Example of a named variant within a sequence that refers to a single tag field:
404
405 variant example {
406 uint32_t a;
407 uint64_t b;
408 short c;
409 };
410
411 struct {
412 enum : uint2_t { a, b, c } choice;
413 variant example <choice> v[unsigned int];
414 }
415
416 Example of an unnamed variant:
417
418 struct {
419 enum : uint2_t { a, b, c, d } choice;
420 /* Unrelated fields can be added between the variant and its tag */
421 int32_t somevalue;
422 variant <choice> {
423 uint32_t a;
424 uint64_t b;
425 short c;
426 struct {
427 unsigned int field1;
428 uint64_t field2;
429 } d;
430 } s;
431 }
432
433 Example of an unnamed variant within an array:
434
435 struct {
436 enum : uint2_t { a, b, c } choice;
437 variant <choice> {
438 uint32_t a;
439 uint64_t b;
440 short c;
441 } v[10];
442 }
443
444 Example of a variant type definition within a structure, where the defined type
445 is then declared within an array of structures. This variant refers to a tag
446 located in an upper lexical scope. This example clearly shows that a variant
447 type definition referring to the tag "x" uses the closest preceding field from
448 the lexical scope of the type definition.
449
450 struct {
451 enum : uint2_t { a, b, c, d } x;
452
453 typedef variant <x> { /*
454 * "x" refers to the preceding "x" enumeration in the
455 * lexical scope of the type definition.
456 */
457 uint32_t a;
458 uint64_t b;
459 short c;
460 } example_variant;
461
462 struct {
463 enum : int { x, y, z } x; /* This enumeration is not used by "v". */
464 example_variant v; /*
465 * "v" uses the "enum : uint2_t { a, b, c, d }"
466 * tag.
467 */
468 } a[10];
469 }
470
471 4.2.3 Arrays
472
473 Arrays are fixed-length. Their length is declared in the type declaration within
474 the metadata. They contain an array of "inner type" elements, which can refer to
475 any type not containing the type of the array being declared (no circular
476 dependency). The length is the number of elements in an array.
477
478 Metadata representation of a named array:
479
480 typedef elem_type name[length];
481
482 A nameless array can be declared as a field type within a structure, e.g.:
483
484 uint8_t field_name[10];
485
486
487 4.2.4 Sequences
488
489 Sequences are dynamically-sized arrays. They start with an integer that specify
490 the length of the sequence, followed by an array of "inner type" elements.
491 The length is the number of elements in the sequence.
492
493 Metadata representation for a named sequence:
494
495 typedef elem_type name[length_type];
496
497 A nameless sequence can be declared as a field type, e.g.:
498
499 long field_name[int];
500
501 The length type follows the integer types specifications, and the sequence
502 elements follow the "array" specifications.
503
504 4.2.5 Strings
505
506 Strings are an array of bytes of variable size and are terminated by a '\0'
507 "NULL" character. Their encoding is described in the metadata. In absence of
508 encoding attribute information, the default encoding is UTF-8.
509
510 Metadata representation of a named string type:
511
512 typealias string {
513 encoding = UTF8 OR ASCII;
514 } := name;
515
516 A nameless string type can be declared as a field type:
517
518 string field_name; /* Use default UTF8 encoding */
519
520 5. Event Packet Header
521
522 The event packet header consists of two part: one is mandatory and have a fixed
523 layout. The second part, the "event packet context", has its layout described in
524 the metadata.
525
526 - Aligned on page size. Fixed size. Fields either aligned or packed (depending
527 on the architecture preference).
528 No padding at the end of the event packet header. Native architecture byte
529 ordering.
530
531 Fixed layout (event packet header):
532
533 - Magic number (CTF magic numbers: 0xC1FC1FC1 and its reverse endianness
534 representation: 0xC11FFCC1) It needs to have a non-symmetric bytewise
535 representation. Used to distinguish between big and little endian traces (this
536 information is determined by knowing the endianness of the architecture
537 reading the trace and comparing the magic number against its value and the
538 reverse, 0xC11FFCC1). This magic number specifies that we use the CTF metadata
539 description language described in this document. Different magic numbers
540 should be used for other metadata description languages.
541 - Trace UUID, used to ensure the event packet match the metadata used.
542 (note: we cannot use a metadata checksum because metadata can be appended to
543 while tracing is active)
544 - Stream ID, used as reference to stream description in metadata.
545
546 Metadata-defined layout (event packet context):
547
548 - Event packet content size (in bytes).
549 - Event packet size (in bytes, includes padding).
550 - Event packet content checksum (optional). Checksum excludes the event packet
551 header.
552 - Per-stream event packet sequence count (to deal with UDP packet loss). The
553 number of significant sequence counter bits should also be present, so
554 wrap-arounds are deal with correctly.
555 - Timestamp at the beginning and timestamp at the end of the event packet.
556 Both timestamps are written in the packet header, but sampled respectively
557 while (or before) writing the first event and while (or after) writing the
558 last event in the packet. The inclusive range between these timestamps should
559 include all event timestamps assigned to events contained within the packet.
560 - Events discarded count
561 - Snapshot of a per-stream free-running counter, counting the number of
562 events discarded that were supposed to be written in the stream prior to
563 the first event in the event packet.
564 * Note: producer-consumer buffer full condition should fill the current
565 event packet with padding so we know exactly where events have been
566 discarded.
567 - Lossless compression scheme used for the event packet content. Applied
568 directly to raw data. New types of compression can be added in following
569 versions of the format.
570 0: no compression scheme
571 1: bzip2
572 2: gzip
573 3: xz
574 - Cypher used for the event packet content. Applied after compression.
575 0: no encryption
576 1: AES
577 - Checksum scheme used for the event packet content. Applied after encryption.
578 0: no checksum
579 1: md5
580 2: sha1
581 3: crc32
582
583 5.1 Event Packet Header Fixed Layout Description
584
585 The event packet header layout is indicated by the trace packet.header
586 field. Here is an example structure type for the packet header with the
587 fields typically expected:
588
589 struct event_packet_header {
590 uint32_t magic;
591 uint8_t trace_uuid[16];
592 uint32_t stream_id;
593 };
594
595 trace {
596 ...
597 packet.header := struct event_packet_header;
598 };
599
600 If a packet header lacks the "magic" number field, the trace endianness
601 needs to be specified in the trace "endian" metadata attribute.
602
603 If the trace_uuid is not present, no validation that the metadata
604 actually corresponds to the stream is performed.
605
606 If the stream_id packet header field is missing, the trace can only
607 contain a single stream. Its "id" field can be left out, and its events
608 don't need to declare a "stream_id" field.
609
610
611 5.2 Event Packet Context Description
612
613 Event packet context example. These are declared within the stream declaration
614 in the metadata. All these fields are optional except for "content_size" and
615 "packet_size", which must be present in the context.
616
617 An example event packet context type:
618
619 struct event_packet_context {
620 uint64_t timestamp_begin;
621 uint64_t timestamp_end;
622 uint32_t checksum;
623 uint32_t stream_packet_count;
624 uint32_t events_discarded;
625 uint32_t cpu_id;
626 uint32_t/uint16_t content_size;
627 uint32_t/uint16_t packet_size;
628 uint8_t stream_packet_count_bits; /* Significant counter bits */
629 uint8_t compression_scheme;
630 uint8_t encryption_scheme;
631 uint8_t checksum_scheme;
632 };
633
634
635 6. Event Structure
636
637 The overall structure of an event is:
638
639 1 - Stream Packet Context (as specified by the stream metadata)
640 2 - Event Header (as specified by the stream metadata)
641 3 - Stream Event Context (as specified by the stream metadata)
642 4 - Event Context (as specified by the event metadata)
643 5 - Event Payload (as specified by the event metadata)
644
645 This structure defines an implicit dynamic scoping, where variants
646 located in inner structures (those with a higher number in the listing
647 above) can refer to the fields of outer structures (with lower number in
648 the listing above). See Section 7.3 TSDL Scopes for more detail.
649
650 6.1 Event Header
651
652 Event headers can be described within the metadata. We hereby propose, as an
653 example, two types of events headers. Type 1 accommodates streams with less than
654 31 event IDs. Type 2 accommodates streams with 31 or more event IDs.
655
656 One major factor can vary between streams: the number of event IDs assigned to
657 a stream. Luckily, this information tends to stay relatively constant (modulo
658 event registration while trace is being recorded), so we can specify different
659 representations for streams containing few event IDs and streams containing
660 many event IDs, so we end up representing the event ID and timestamp as densely
661 as possible in each case.
662
663 The header is extended in the rare occasions where the information cannot be
664 represented in the ranges available in the standard event header. They are also
665 used in the rare occasions where the data required for a field could not be
666 collected: the flag corresponding to the missing field within the missing_fields
667 array is then set to 1.
668
669 Types uintX_t represent an X-bit unsigned integer.
670
671
672 6.1.1 Type 1 - Few event IDs
673
674 - Aligned on 32-bit (or 8-bit if byte-packed, depending on the architecture
675 preference).
676 - Native architecture byte ordering.
677 - For "compact" selection
678 - Fixed size: 32 bits.
679 - For "extended" selection
680 - Size depends on the architecture and variant alignment.
681
682 struct event_header_1 {
683 /*
684 * id: range: 0 - 30.
685 * id 31 is reserved to indicate an extended header.
686 */
687 enum : uint5_t { compact = 0 ... 30, extended = 31 } id;
688 variant <id> {
689 struct {
690 uint27_t timestamp;
691 } compact;
692 struct {
693 uint32_t id; /* 32-bit event IDs */
694 uint64_t timestamp; /* 64-bit timestamps */
695 } extended;
696 } v;
697 };
698
699
700 6.1.2 Type 2 - Many event IDs
701
702 - Aligned on 16-bit (or 8-bit if byte-packed, depending on the architecture
703 preference).
704 - Native architecture byte ordering.
705 - For "compact" selection
706 - Size depends on the architecture and variant alignment.
707 - For "extended" selection
708 - Size depends on the architecture and variant alignment.
709
710 struct event_header_2 {
711 /*
712 * id: range: 0 - 65534.
713 * id 65535 is reserved to indicate an extended header.
714 */
715 enum : uint16_t { compact = 0 ... 65534, extended = 65535 } id;
716 variant <id> {
717 struct {
718 uint32_t timestamp;
719 } compact;
720 struct {
721 uint32_t id; /* 32-bit event IDs */
722 uint64_t timestamp; /* 64-bit timestamps */
723 } extended;
724 } v;
725 };
726
727
728 6.2 Event Context
729
730 The event context contains information relative to the current event. The choice
731 and meaning of this information is specified by the metadata "stream" and
732 "event" information. The "stream" context is applied to all events within the
733 stream. The "stream" context structure follows the event header. The "event"
734 context is applied to specific events. Its structure follows the "stream"
735 context stucture.
736
737 An example of stream-level event context is to save the event payload size with
738 each event, or to save the current PID with each event. These are declared
739 within the stream declaration within the metadata:
740
741 stream {
742 ...
743 event {
744 ...
745 context := struct {
746 uint pid;
747 uint16_t payload_size;
748 };
749 }
750 };
751
752 An example of event-specific event context is to declare a bitmap of missing
753 fields, only appended after the stream event context if the extended event
754 header is selected. NR_FIELDS is the number of fields within the event (a
755 numeric value).
756
757 event {
758 context = struct {
759 variant <id> {
760 struct { } compact;
761 struct {
762 uint1_t missing_fields[NR_FIELDS]; /* missing event fields bitmap */
763 } extended;
764 } v;
765 };
766 ...
767 }
768
769 6.3 Event Payload
770
771 An event payload contains fields specific to a given event type. The fields
772 belonging to an event type are described in the event-specific metadata
773 within a structure type.
774
775 6.3.1 Padding
776
777 No padding at the end of the event payload. This differs from the ISO/C standard
778 for structures, but follows the CTF standard for structures. In a trace, even
779 though it makes sense to align the beginning of a structure, it really makes no
780 sense to add padding at the end of the structure, because structures are usually
781 not followed by a structure of the same type.
782
783 This trick can be done by adding a zero-length "end" field at the end of the C
784 structures, and by using the offset of this field rather than using sizeof()
785 when calculating the size of a structure (see Appendix "A. Helper macros").
786
787 6.3.2 Alignment
788
789 The event payload is aligned on the largest alignment required by types
790 contained within the payload. (This follows the ISO/C standard for structures)
791
792
793 7. Trace Stream Description Language (TSDL)
794
795 The Trace Stream Description Language (TSDL) allows expression of the
796 binary trace streams layout in a C99-like Domain Specific Language
797 (DSL).
798
799
800 7.1 Metadata
801
802 The trace stream layout description is located in the trace meta-data.
803 The meta-data is itself located in a stream identified by its name:
804 "metadata".
805
806 It is made of "event packets", which each start with an event packet
807 header. The event type within the metadata stream have no event header
808 nor event context. Each event only contains a "string" payload without
809 any null-character. The events are packed one next to another. Each
810 event packet start with an event packet header, which contains, amongst
811 other fields, the magic number, trace UUID and packet length. In the
812 event packet header, the trace UUID is represented as an array of bytes.
813 Within the string-based metadata description, the trace UUID is
814 represented as a string of hexadecimal digits and dashes "-".
815
816 The metadata can be parsed by reading characters within the metadata
817 stream, for each packet starting after the packet header, for the length
818 of the packet payload specified in the header. Text contained within
819 "/*" and "*/", as well as within "//" and end of line, are treated as
820 comments. Boolean values can be represented as true, TRUE, or 1 for
821 true, and false, FALSE, or 0 for false.
822
823
824 7.2 Declaration vs Definition
825
826 A declaration associates a layout to a type, without specifying where
827 this type is located in the event structure hierarchy (see Section 6).
828 This therefore includes typedef, typealias, as well as all type
829 specifiers. In certain circumstances (typedef, structure field and
830 variant field), a declaration is followed by a declarator, which specify
831 the newly defined type name (for typedef), or the field name (for
832 declarations located within structure and variants). Array and sequence,
833 declared with square brackets ("[" "]"), are part of the declarator,
834 similarly to C99. The enumeration base type is specified by
835 ": enum_base", which is part of the type specifier. The variant tag
836 name, specified between "<" ">", is also part of the type specifier.
837
838 A definition associates a type to a location in the event structure
839 hierarchy (see Section 6). This association is denoted by ":=", as shown
840 in Section 7.3.
841
842
843 7.3 TSDL Scopes
844
845 TSDL uses two different types of scoping: a lexical scope is used for
846 declarations and type definitions, and a dynamic scope is used for
847 variants references to tag fields.
848
849 7.3.1 Lexical Scope
850
851 Each of "trace", "stream", "event", "struct" and "variant" have their own
852 nestable declaration scope, within which types can be declared using "typedef"
853 and "typealias". A root declaration scope also contains all declarations
854 located outside of any of the aforementioned declarations. An inner
855 declaration scope can refer to type declared within its container
856 lexical scope prior to the inner declaration scope. Redefinition of a
857 typedef or typealias is not valid, although hiding an upper scope
858 typedef or typealias is allowed within a sub-scope.
859
860 7.3.2 Dynamic Scope
861
862 A dynamic scope consists in the lexical scope augmented with the
863 implicit event structure definition hierarchy presented at Section 6.
864 The dynamic scope is only used for variant tag definitions. It is used
865 at definition time to look up the location of the tag field associated
866 with a variant.
867
868 Therefore, variants in lower levels in the dynamic scope (e.g. event
869 context) can refer to a tag field located in upper levels (e.g. in the
870 event header) by specifying, in this case, the associated tag with
871 <header.field_name>. This allows, for instance, the event context to
872 define a variant referring to the "id" field of the event header as
873 selector.
874
875 The target dynamic scope must be specified explicitly when referring to
876 a field outside of the local static scope. The dynamic scope prefixes
877 are thus:
878
879 - Stream Packet Context: <stream.packet.context. >,
880 - Event Header: <stream.event.header. >,
881 - Stream Event Context: <stream.event.context. >,
882 - Event Context: <event.context. >,
883 - Event Payload: <event.fields. >.
884
885 Multiple declarations of the same field name within a single scope is
886 not valid. It is however valid to re-use the same field name in
887 different scopes. There is no possible conflict, because the dynamic
888 scope must be specified when a variant refers to a tag field located in
889 a different dynamic scope.
890
891 The information available in the dynamic scopes can be thought of as the
892 current tracing context. At trace production, information about the
893 current context is saved into the specified scope field levels. At trace
894 consumption, for each event, the current trace context is therefore
895 readable by accessing the upper dynamic scopes.
896
897
898 7.4 TSDL Examples
899
900 The grammar representing the TSDL metadata is presented in Appendix C.
901 TSDL Grammar. This section presents a rather ligher reading that
902 consists in examples of TSDL metadata, with template values.
903
904 Note that the trace endianness is usually extracted from the packet
905 header magic number. The "endian" field is only needed when the magic
906 number packet header field is not present.
907
908 trace {
909 major = value; /* Trace format version */
910 minor = value;
911 uuid = "aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaaa"; /* Trace UUID */
912 endian = big OR little; /* Endianness (optional) */
913 packet.header := struct {
914 uint32_t magic;
915 uint8_t trace_uuid[16];
916 uint32_t stream_id;
917 };
918 };
919
920 stream {
921 id = stream_id;
922 /* Type 1 - Few event IDs; Type 2 - Many event IDs. See section 6.1. */
923 event.header := event_header_1 OR event_header_2;
924 event.context := struct {
925 ...
926 };
927 packet.context := struct {
928 ...
929 };
930 };
931
932 event {
933 name = event_name;
934 id = value; /* Numeric identifier within the stream */
935 stream = stream_id;
936 context := struct {
937 ...
938 };
939 fields := struct {
940 ...
941 };
942 };
943
944 /* More detail on types in section 4. Types */
945
946 /*
947 * Named types:
948 *
949 * Type declarations behave similarly to the C standard.
950 */
951
952 typedef aliased_type_specifiers new_type_declarators;
953
954 /* e.g.: typedef struct example new_type_name[10]; */
955
956 /*
957 * typealias
958 *
959 * The "typealias" declaration can be used to give a name (including
960 * pointer declarator specifier) to a type. It should also be used to
961 * map basic C types (float, int, unsigned long, ...) to a CTF type.
962 * Typealias is a superset of "typedef": it also allows assignment of a
963 * simple variable identifier to a type.
964 */
965
966 typealias type_class {
967 ...
968 } := type_specifiers type_declarator;
969
970 /*
971 * e.g.:
972 * typealias integer {
973 * size = 32;
974 * align = 32;
975 * signed = false;
976 * } := struct page *;
977 *
978 * typealias integer {
979 * size = 32;
980 * align = 32;
981 * signed = true;
982 * } := int;
983 */
984
985 struct name {
986 ...
987 };
988
989 variant name {
990 ...
991 };
992
993 enum name : integer_type {
994 ...
995 };
996
997
998 /*
999 * Unnamed types, contained within compound type fields, typedef or typealias.
1000 */
1001
1002 struct {
1003 ...
1004 }
1005
1006 variant {
1007 ...
1008 }
1009
1010 enum : integer_type {
1011 ...
1012 }
1013
1014 typedef type new_type[length];
1015
1016 struct {
1017 type field_name[length];
1018 }
1019
1020 typedef type new_type[length_type];
1021
1022 struct {
1023 type field_name[length_type];
1024 }
1025
1026 integer {
1027 ...
1028 }
1029
1030 floating_point {
1031 ...
1032 }
1033
1034 struct {
1035 integer_type field_name:size; /* GNU/C bitfield */
1036 }
1037
1038 struct {
1039 string field_name;
1040 }
1041
1042
1043 A. Helper macros
1044
1045 The two following macros keep track of the size of a GNU/C structure without
1046 padding at the end by placing HEADER_END as the last field. A one byte end field
1047 is used for C90 compatibility (C99 flexible arrays could be used here). Note
1048 that this does not affect the effective structure size, which should always be
1049 calculated with the header_sizeof() helper.
1050
1051 #define HEADER_END char end_field
1052 #define header_sizeof(type) offsetof(typeof(type), end_field)
1053
1054
1055 B. Stream Header Rationale
1056
1057 An event stream is divided in contiguous event packets of variable size. These
1058 subdivisions allow the trace analyzer to perform a fast binary search by time
1059 within the stream (typically requiring to index only the event packet headers)
1060 without reading the whole stream. These subdivisions have a variable size to
1061 eliminate the need to transfer the event packet padding when partially filled
1062 event packets must be sent when streaming a trace for live viewing/analysis.
1063 An event packet can contain a certain amount of padding at the end. Dividing
1064 streams into event packets is also useful for network streaming over UDP and
1065 flight recorder mode tracing (a whole event packet can be swapped out of the
1066 buffer atomically for reading).
1067
1068 The stream header is repeated at the beginning of each event packet to allow
1069 flexibility in terms of:
1070
1071 - streaming support,
1072 - allowing arbitrary buffers to be discarded without making the trace
1073 unreadable,
1074 - allow UDP packet loss handling by either dealing with missing event packet
1075 or asking for re-transmission.
1076 - transparently support flight recorder mode,
1077 - transparently support crash dump.
1078
1079 The event stream header will therefore be referred to as the "event packet
1080 header" throughout the rest of this document.
1081
1082
1083 C. TSDL Grammar
1084
1085 /*
1086 * Common Trace Format (CTF) Trace Stream Description Language (TSDL) Grammar.
1087 *
1088 * Inspired from the C99 grammar:
1089 * http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1124.pdf (Annex A)
1090 * and c++1x grammar (draft)
1091 * http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2011/n3291.pdf (Annex A)
1092 *
1093 * Specialized for CTF needs by including only constant and declarations from
1094 * C99 (excluding function declarations), and by adding support for variants,
1095 * sequences and CTF-specific specifiers. Enumeration container types
1096 * semantic is inspired from c++1x enum-base.
1097 */
1098
1099 1) Lexical grammar
1100
1101 1.1) Lexical elements
1102
1103 token:
1104 keyword
1105 identifier
1106 constant
1107 string-literal
1108 punctuator
1109
1110 1.2) Keywords
1111
1112 keyword: is one of
1113
1114 const
1115 char
1116 double
1117 enum
1118 event
1119 floating_point
1120 float
1121 integer
1122 int
1123 long
1124 short
1125 signed
1126 stream
1127 string
1128 struct
1129 trace
1130 typealias
1131 typedef
1132 unsigned
1133 variant
1134 void
1135 _Bool
1136 _Complex
1137 _Imaginary
1138
1139
1140 1.3) Identifiers
1141
1142 identifier:
1143 identifier-nondigit
1144 identifier identifier-nondigit
1145 identifier digit
1146
1147 identifier-nondigit:
1148 nondigit
1149 universal-character-name
1150 any other implementation-defined characters
1151
1152 nondigit:
1153 _
1154 [a-zA-Z] /* regular expression */
1155
1156 digit:
1157 [0-9] /* regular expression */
1158
1159 1.4) Universal character names
1160
1161 universal-character-name:
1162 \u hex-quad
1163 \U hex-quad hex-quad
1164
1165 hex-quad:
1166 hexadecimal-digit hexadecimal-digit hexadecimal-digit hexadecimal-digit
1167
1168 1.5) Constants
1169
1170 constant:
1171 integer-constant
1172 enumeration-constant
1173 character-constant
1174
1175 integer-constant:
1176 decimal-constant integer-suffix-opt
1177 octal-constant integer-suffix-opt
1178 hexadecimal-constant integer-suffix-opt
1179
1180 decimal-constant:
1181 nonzero-digit
1182 decimal-constant digit
1183
1184 octal-constant:
1185 0
1186 octal-constant octal-digit
1187
1188 hexadecimal-constant:
1189 hexadecimal-prefix hexadecimal-digit
1190 hexadecimal-constant hexadecimal-digit
1191
1192 hexadecimal-prefix:
1193 0x
1194 0X
1195
1196 nonzero-digit:
1197 [1-9]
1198
1199 integer-suffix:
1200 unsigned-suffix long-suffix-opt
1201 unsigned-suffix long-long-suffix
1202 long-suffix unsigned-suffix-opt
1203 long-long-suffix unsigned-suffix-opt
1204
1205 unsigned-suffix:
1206 u
1207 U
1208
1209 long-suffix:
1210 l
1211 L
1212
1213 long-long-suffix:
1214 ll
1215 LL
1216
1217 digit-sequence:
1218 digit
1219 digit-sequence digit
1220
1221 hexadecimal-digit-sequence:
1222 hexadecimal-digit
1223 hexadecimal-digit-sequence hexadecimal-digit
1224
1225 enumeration-constant:
1226 identifier
1227 string-literal
1228
1229 character-constant:
1230 ' c-char-sequence '
1231 L' c-char-sequence '
1232
1233 c-char-sequence:
1234 c-char
1235 c-char-sequence c-char
1236
1237 c-char:
1238 any member of source charset except single-quote ('), backslash
1239 (\), or new-line character.
1240 escape-sequence
1241
1242 escape-sequence:
1243 simple-escape-sequence
1244 octal-escape-sequence
1245 hexadecimal-escape-sequence
1246 universal-character-name
1247
1248 simple-escape-sequence: one of
1249 \' \" \? \\ \a \b \f \n \r \t \v
1250
1251 octal-escape-sequence:
1252 \ octal-digit
1253 \ octal-digit octal-digit
1254 \ octal-digit octal-digit octal-digit
1255
1256 hexadecimal-escape-sequence:
1257 \x hexadecimal-digit
1258 hexadecimal-escape-sequence hexadecimal-digit
1259
1260 1.6) String literals
1261
1262 string-literal:
1263 " s-char-sequence-opt "
1264 L" s-char-sequence-opt "
1265
1266 s-char-sequence:
1267 s-char
1268 s-char-sequence s-char
1269
1270 s-char:
1271 any member of source charset except double-quote ("), backslash
1272 (\), or new-line character.
1273 escape-sequence
1274
1275 1.7) Punctuators
1276
1277 punctuator: one of
1278 [ ] ( ) { } . -> * + - < > : ; ... = ,
1279
1280
1281 2) Phrase structure grammar
1282
1283 primary-expression:
1284 identifier
1285 constant
1286 string-literal
1287 ( unary-expression )
1288
1289 postfix-expression:
1290 primary-expression
1291 postfix-expression [ unary-expression ]
1292 postfix-expression . identifier
1293 postfix-expressoin -> identifier
1294
1295 unary-expression:
1296 postfix-expression
1297 unary-operator postfix-expression
1298
1299 unary-operator: one of
1300 + -
1301
1302 assignment-operator:
1303 =
1304
1305 type-assignment-operator:
1306 :=
1307
1308 constant-expression:
1309 unary-expression
1310
1311 constant-expression-range:
1312 constant-expression ... constant-expression
1313
1314 2.2) Declarations:
1315
1316 declaration:
1317 declaration-specifiers declarator-list-opt ;
1318 ctf-specifier ;
1319
1320 declaration-specifiers:
1321 storage-class-specifier declaration-specifiers-opt
1322 type-specifier declaration-specifiers-opt
1323 type-qualifier declaration-specifiers-opt
1324
1325 declarator-list:
1326 declarator
1327 declarator-list , declarator
1328
1329 abstract-declarator-list:
1330 abstract-declarator
1331 abstract-declarator-list , abstract-declarator
1332
1333 storage-class-specifier:
1334 typedef
1335
1336 type-specifier:
1337 void
1338 char
1339 short
1340 int
1341 long
1342 float
1343 double
1344 signed
1345 unsigned
1346 _Bool
1347 _Complex
1348 _Imaginary
1349 struct-specifier
1350 variant-specifier
1351 enum-specifier
1352 typedef-name
1353 ctf-type-specifier
1354
1355 struct-specifier:
1356 struct identifier-opt { struct-or-variant-declaration-list-opt }
1357 struct identifier
1358
1359 struct-or-variant-declaration-list:
1360 struct-or-variant-declaration
1361 struct-or-variant-declaration-list struct-or-variant-declaration
1362
1363 struct-or-variant-declaration:
1364 specifier-qualifier-list struct-or-variant-declarator-list ;
1365 declaration-specifiers storage-class-specifier declaration-specifiers declarator-list ;
1366 typealias declaration-specifiers abstract-declarator-list := declaration-specifiers abstract-declarator-list ;
1367 typealias declaration-specifiers abstract-declarator-list := declarator-list ;
1368
1369 specifier-qualifier-list:
1370 type-specifier specifier-qualifier-list-opt
1371 type-qualifier specifier-qualifier-list-opt
1372
1373 struct-or-variant-declarator-list:
1374 struct-or-variant-declarator
1375 struct-or-variant-declarator-list , struct-or-variant-declarator
1376
1377 struct-or-variant-declarator:
1378 declarator
1379 declarator-opt : constant-expression
1380
1381 variant-specifier:
1382 variant identifier-opt variant-tag-opt { struct-or-variant-declaration-list }
1383 variant identifier variant-tag
1384
1385 variant-tag:
1386 < identifier >
1387
1388 enum-specifier:
1389 enum identifier-opt { enumerator-list }
1390 enum identifier-opt { enumerator-list , }
1391 enum identifier
1392 enum identifier-opt : declaration-specifiers { enumerator-list }
1393 enum identifier-opt : declaration-specifiers { enumerator-list , }
1394
1395 enumerator-list:
1396 enumerator
1397 enumerator-list , enumerator
1398
1399 enumerator:
1400 enumeration-constant
1401 enumeration-constant = constant-expression
1402 enumeration-constant = constant-expression-range
1403
1404 type-qualifier:
1405 const
1406
1407 declarator:
1408 pointer-opt direct-declarator
1409
1410 direct-declarator:
1411 identifier
1412 ( declarator )
1413 direct-declarator [ type-specifier ]
1414 direct-declarator [ constant-expression ]
1415
1416 abstract-declarator:
1417 pointer-opt direct-abstract-declarator
1418
1419 direct-abstract-declarator:
1420 identifier-opt
1421 ( abstract-declarator )
1422 direct-abstract-declarator [ type-specifier ]
1423 direct-abstract-declarator [ constant-expression ]
1424 direct-abstract-declarator [ ]
1425
1426 pointer:
1427 * type-qualifier-list-opt
1428 * type-qualifier-list-opt pointer
1429
1430 type-qualifier-list:
1431 type-qualifier
1432 type-qualifier-list type-qualifier
1433
1434 typedef-name:
1435 identifier
1436
1437 2.3) CTF-specific declarations
1438
1439 ctf-specifier:
1440 event { ctf-assignment-expression-list-opt }
1441 stream { ctf-assignment-expression-list-opt }
1442 trace { ctf-assignment-expression-list-opt }
1443 typealias declaration-specifiers abstract-declarator-list := declaration-specifiers abstract-declarator-list ;
1444 typealias declaration-specifiers abstract-declarator-list := declarator-list ;
1445
1446 ctf-type-specifier:
1447 floating_point { ctf-assignment-expression-list-opt }
1448 integer { ctf-assignment-expression-list-opt }
1449 string { ctf-assignment-expression-list-opt }
1450
1451 ctf-assignment-expression-list:
1452 ctf-assignment-expression
1453 ctf-assignment-expression-list ; ctf-assignment-expression
1454
1455 ctf-assignment-expression:
1456 unary-expression assignment-operator unary-expression
1457 unary-expression type-assignment-operator type-specifier
1458 declaration-specifiers storage-class-specifier declaration-specifiers declarator-list
1459 typealias declaration-specifiers abstract-declarator-list := declaration-specifiers abstract-declarator-list
1460 typealias declaration-specifiers abstract-declarator-list := declarator-list
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