Require trace byte_order field, remove use of magic number for autodetection
[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 number: 0xC1FC1FC1 This magic number specifies
534 that we use the CTF metadata description language described in this
535 document. Different magic numbers should be used for other metadata
536 description languages.
537 - Trace UUID, used to ensure the event packet match the metadata used.
538 (note: we cannot use a metadata checksum because metadata can be appended to
539 while tracing is active)
540 - Stream ID, used as reference to stream description in metadata.
541
542 Metadata-defined layout (event packet context):
543
544 - Event packet content size (in bytes).
545 - Event packet size (in bytes, includes padding).
546 - Event packet content checksum (optional). Checksum excludes the event packet
547 header.
548 - Per-stream event packet sequence count (to deal with UDP packet loss). The
549 number of significant sequence counter bits should also be present, so
550 wrap-arounds are deal with correctly.
551 - Timestamp at the beginning and timestamp at the end of the event packet.
552 Both timestamps are written in the packet header, but sampled respectively
553 while (or before) writing the first event and while (or after) writing the
554 last event in the packet. The inclusive range between these timestamps should
555 include all event timestamps assigned to events contained within the packet.
556 - Events discarded count
557 - Snapshot of a per-stream free-running counter, counting the number of
558 events discarded that were supposed to be written in the stream prior to
559 the first event in the event packet.
560 * Note: producer-consumer buffer full condition should fill the current
561 event packet with padding so we know exactly where events have been
562 discarded.
563 - Lossless compression scheme used for the event packet content. Applied
564 directly to raw data. New types of compression can be added in following
565 versions of the format.
566 0: no compression scheme
567 1: bzip2
568 2: gzip
569 3: xz
570 - Cypher used for the event packet content. Applied after compression.
571 0: no encryption
572 1: AES
573 - Checksum scheme used for the event packet content. Applied after encryption.
574 0: no checksum
575 1: md5
576 2: sha1
577 3: crc32
578
579 5.1 Event Packet Header Fixed Layout Description
580
581 The event packet header layout is indicated by the trace packet.header
582 field. Here is an example structure type for the packet header with the
583 fields typically expected:
584
585 struct event_packet_header {
586 uint32_t magic;
587 uint8_t trace_uuid[16];
588 uint32_t stream_id;
589 };
590
591 trace {
592 ...
593 packet.header := struct event_packet_header;
594 };
595
596 If the trace_uuid is not present, no validation that the metadata
597 actually corresponds to the stream is performed.
598
599 If the stream_id packet header field is missing, the trace can only
600 contain a single stream. Its "id" field can be left out, and its events
601 don't need to declare a "stream_id" field.
602
603
604 5.2 Event Packet Context Description
605
606 Event packet context example. These are declared within the stream declaration
607 in the metadata. All these fields are optional except for "content_size" and
608 "packet_size", which must be present in the context.
609
610 An example event packet context type:
611
612 struct event_packet_context {
613 uint64_t timestamp_begin;
614 uint64_t timestamp_end;
615 uint32_t checksum;
616 uint32_t stream_packet_count;
617 uint32_t events_discarded;
618 uint32_t cpu_id;
619 uint32_t/uint16_t content_size;
620 uint32_t/uint16_t packet_size;
621 uint8_t stream_packet_count_bits; /* Significant counter bits */
622 uint8_t compression_scheme;
623 uint8_t encryption_scheme;
624 uint8_t checksum_scheme;
625 };
626
627
628 6. Event Structure
629
630 The overall structure of an event is:
631
632 1 - Stream Packet Context (as specified by the stream metadata)
633 2 - Event Header (as specified by the stream metadata)
634 3 - Stream Event Context (as specified by the stream metadata)
635 4 - Event Context (as specified by the event metadata)
636 5 - Event Payload (as specified by the event metadata)
637
638 This structure defines an implicit dynamic scoping, where variants
639 located in inner structures (those with a higher number in the listing
640 above) can refer to the fields of outer structures (with lower number in
641 the listing above). See Section 7.3 TSDL Scopes for more detail.
642
643 6.1 Event Header
644
645 Event headers can be described within the metadata. We hereby propose, as an
646 example, two types of events headers. Type 1 accommodates streams with less than
647 31 event IDs. Type 2 accommodates streams with 31 or more event IDs.
648
649 One major factor can vary between streams: the number of event IDs assigned to
650 a stream. Luckily, this information tends to stay relatively constant (modulo
651 event registration while trace is being recorded), so we can specify different
652 representations for streams containing few event IDs and streams containing
653 many event IDs, so we end up representing the event ID and timestamp as densely
654 as possible in each case.
655
656 The header is extended in the rare occasions where the information cannot be
657 represented in the ranges available in the standard event header. They are also
658 used in the rare occasions where the data required for a field could not be
659 collected: the flag corresponding to the missing field within the missing_fields
660 array is then set to 1.
661
662 Types uintX_t represent an X-bit unsigned integer.
663
664
665 6.1.1 Type 1 - Few event IDs
666
667 - Aligned on 32-bit (or 8-bit if byte-packed, depending on the architecture
668 preference).
669 - Native architecture byte ordering.
670 - For "compact" selection
671 - Fixed size: 32 bits.
672 - For "extended" selection
673 - Size depends on the architecture and variant alignment.
674
675 struct event_header_1 {
676 /*
677 * id: range: 0 - 30.
678 * id 31 is reserved to indicate an extended header.
679 */
680 enum : uint5_t { compact = 0 ... 30, extended = 31 } id;
681 variant <id> {
682 struct {
683 uint27_t timestamp;
684 } compact;
685 struct {
686 uint32_t id; /* 32-bit event IDs */
687 uint64_t timestamp; /* 64-bit timestamps */
688 } extended;
689 } v;
690 };
691
692
693 6.1.2 Type 2 - Many event IDs
694
695 - Aligned on 16-bit (or 8-bit if byte-packed, depending on the architecture
696 preference).
697 - Native architecture byte ordering.
698 - For "compact" selection
699 - Size depends on the architecture and variant alignment.
700 - For "extended" selection
701 - Size depends on the architecture and variant alignment.
702
703 struct event_header_2 {
704 /*
705 * id: range: 0 - 65534.
706 * id 65535 is reserved to indicate an extended header.
707 */
708 enum : uint16_t { compact = 0 ... 65534, extended = 65535 } id;
709 variant <id> {
710 struct {
711 uint32_t timestamp;
712 } compact;
713 struct {
714 uint32_t id; /* 32-bit event IDs */
715 uint64_t timestamp; /* 64-bit timestamps */
716 } extended;
717 } v;
718 };
719
720
721 6.2 Event Context
722
723 The event context contains information relative to the current event. The choice
724 and meaning of this information is specified by the metadata "stream" and
725 "event" information. The "stream" context is applied to all events within the
726 stream. The "stream" context structure follows the event header. The "event"
727 context is applied to specific events. Its structure follows the "stream"
728 context stucture.
729
730 An example of stream-level event context is to save the event payload size with
731 each event, or to save the current PID with each event. These are declared
732 within the stream declaration within the metadata:
733
734 stream {
735 ...
736 event {
737 ...
738 context := struct {
739 uint pid;
740 uint16_t payload_size;
741 };
742 }
743 };
744
745 An example of event-specific event context is to declare a bitmap of missing
746 fields, only appended after the stream event context if the extended event
747 header is selected. NR_FIELDS is the number of fields within the event (a
748 numeric value).
749
750 event {
751 context = struct {
752 variant <id> {
753 struct { } compact;
754 struct {
755 uint1_t missing_fields[NR_FIELDS]; /* missing event fields bitmap */
756 } extended;
757 } v;
758 };
759 ...
760 }
761
762 6.3 Event Payload
763
764 An event payload contains fields specific to a given event type. The fields
765 belonging to an event type are described in the event-specific metadata
766 within a structure type.
767
768 6.3.1 Padding
769
770 No padding at the end of the event payload. This differs from the ISO/C standard
771 for structures, but follows the CTF standard for structures. In a trace, even
772 though it makes sense to align the beginning of a structure, it really makes no
773 sense to add padding at the end of the structure, because structures are usually
774 not followed by a structure of the same type.
775
776 This trick can be done by adding a zero-length "end" field at the end of the C
777 structures, and by using the offset of this field rather than using sizeof()
778 when calculating the size of a structure (see Appendix "A. Helper macros").
779
780 6.3.2 Alignment
781
782 The event payload is aligned on the largest alignment required by types
783 contained within the payload. (This follows the ISO/C standard for structures)
784
785
786 7. Trace Stream Description Language (TSDL)
787
788 The Trace Stream Description Language (TSDL) allows expression of the
789 binary trace streams layout in a C99-like Domain Specific Language
790 (DSL).
791
792
793 7.1 Metadata
794
795 The trace stream layout description is located in the trace meta-data.
796 The meta-data is itself located in a stream identified by its name:
797 "metadata".
798
799 It is made of "event packets", which each start with an event packet
800 header. The event type within the metadata stream have no event header
801 nor event context. Each event only contains a "string" payload without
802 any null-character. The events are packed one next to another. Each
803 event packet start with an event packet header, which contains, amongst
804 other fields, the magic number, trace UUID and packet length. In the
805 event packet header, the trace UUID is represented as an array of bytes.
806 Within the string-based metadata description, the trace UUID is
807 represented as a string of hexadecimal digits and dashes "-".
808
809 The metadata can be parsed by reading characters within the metadata
810 stream, for each packet starting after the packet header, for the length
811 of the packet payload specified in the header. Text contained within
812 "/*" and "*/", as well as within "//" and end of line, are treated as
813 comments. Boolean values can be represented as true, TRUE, or 1 for
814 true, and false, FALSE, or 0 for false.
815
816
817 7.2 Declaration vs Definition
818
819 A declaration associates a layout to a type, without specifying where
820 this type is located in the event structure hierarchy (see Section 6).
821 This therefore includes typedef, typealias, as well as all type
822 specifiers. In certain circumstances (typedef, structure field and
823 variant field), a declaration is followed by a declarator, which specify
824 the newly defined type name (for typedef), or the field name (for
825 declarations located within structure and variants). Array and sequence,
826 declared with square brackets ("[" "]"), are part of the declarator,
827 similarly to C99. The enumeration base type is specified by
828 ": enum_base", which is part of the type specifier. The variant tag
829 name, specified between "<" ">", is also part of the type specifier.
830
831 A definition associates a type to a location in the event structure
832 hierarchy (see Section 6). This association is denoted by ":=", as shown
833 in Section 7.3.
834
835
836 7.3 TSDL Scopes
837
838 TSDL uses two different types of scoping: a lexical scope is used for
839 declarations and type definitions, and a dynamic scope is used for
840 variants references to tag fields.
841
842 7.3.1 Lexical Scope
843
844 Each of "trace", "stream", "event", "struct" and "variant" have their own
845 nestable declaration scope, within which types can be declared using "typedef"
846 and "typealias". A root declaration scope also contains all declarations
847 located outside of any of the aforementioned declarations. An inner
848 declaration scope can refer to type declared within its container
849 lexical scope prior to the inner declaration scope. Redefinition of a
850 typedef or typealias is not valid, although hiding an upper scope
851 typedef or typealias is allowed within a sub-scope.
852
853 7.3.2 Dynamic Scope
854
855 A dynamic scope consists in the lexical scope augmented with the
856 implicit event structure definition hierarchy presented at Section 6.
857 The dynamic scope is only used for variant tag definitions. It is used
858 at definition time to look up the location of the tag field associated
859 with a variant.
860
861 Therefore, variants in lower levels in the dynamic scope (e.g. event
862 context) can refer to a tag field located in upper levels (e.g. in the
863 event header) by specifying, in this case, the associated tag with
864 <header.field_name>. This allows, for instance, the event context to
865 define a variant referring to the "id" field of the event header as
866 selector.
867
868 The target dynamic scope must be specified explicitly when referring to
869 a field outside of the local static scope. The dynamic scope prefixes
870 are thus:
871
872 - Trace Packet Header: <trace.packet.header. >,
873 - Stream Packet Context: <stream.packet.context. >,
874 - Event Header: <stream.event.header. >,
875 - Stream Event Context: <stream.event.context. >,
876 - Event Context: <event.context. >,
877 - Event Payload: <event.fields. >.
878
879 Multiple declarations of the same field name within a single scope is
880 not valid. It is however valid to re-use the same field name in
881 different scopes. There is no possible conflict, because the dynamic
882 scope must be specified when a variant refers to a tag field located in
883 a different dynamic scope.
884
885 The information available in the dynamic scopes can be thought of as the
886 current tracing context. At trace production, information about the
887 current context is saved into the specified scope field levels. At trace
888 consumption, for each event, the current trace context is therefore
889 readable by accessing the upper dynamic scopes.
890
891
892 7.4 TSDL Examples
893
894 The grammar representing the TSDL metadata is presented in Appendix C.
895 TSDL Grammar. This section presents a rather ligher reading that
896 consists in examples of TSDL metadata, with template values.
897
898 The stream "id" can be left out if there is only one stream in the
899 trace. The event "id" field can be left out if there is only one event
900 in a stream.
901
902 trace {
903 major = value; /* Trace format version */
904 minor = value;
905 uuid = "aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaaa"; /* Trace UUID */
906 byte_order = be OR le; /* Endianness (required) */
907 packet.header := struct {
908 uint32_t magic;
909 uint8_t trace_uuid[16];
910 uint32_t stream_id;
911 };
912 };
913
914 stream {
915 id = stream_id;
916 /* Type 1 - Few event IDs; Type 2 - Many event IDs. See section 6.1. */
917 event.header := event_header_1 OR event_header_2;
918 event.context := struct {
919 ...
920 };
921 packet.context := struct {
922 ...
923 };
924 };
925
926 event {
927 name = event_name;
928 id = value; /* Numeric identifier within the stream */
929 stream = stream_id;
930 context := struct {
931 ...
932 };
933 fields := struct {
934 ...
935 };
936 };
937
938 /* More detail on types in section 4. Types */
939
940 /*
941 * Named types:
942 *
943 * Type declarations behave similarly to the C standard.
944 */
945
946 typedef aliased_type_specifiers new_type_declarators;
947
948 /* e.g.: typedef struct example new_type_name[10]; */
949
950 /*
951 * typealias
952 *
953 * The "typealias" declaration can be used to give a name (including
954 * pointer declarator specifier) to a type. It should also be used to
955 * map basic C types (float, int, unsigned long, ...) to a CTF type.
956 * Typealias is a superset of "typedef": it also allows assignment of a
957 * simple variable identifier to a type.
958 */
959
960 typealias type_class {
961 ...
962 } := type_specifiers type_declarator;
963
964 /*
965 * e.g.:
966 * typealias integer {
967 * size = 32;
968 * align = 32;
969 * signed = false;
970 * } := struct page *;
971 *
972 * typealias integer {
973 * size = 32;
974 * align = 32;
975 * signed = true;
976 * } := int;
977 */
978
979 struct name {
980 ...
981 };
982
983 variant name {
984 ...
985 };
986
987 enum name : integer_type {
988 ...
989 };
990
991
992 /*
993 * Unnamed types, contained within compound type fields, typedef or typealias.
994 */
995
996 struct {
997 ...
998 }
999
1000 variant {
1001 ...
1002 }
1003
1004 enum : integer_type {
1005 ...
1006 }
1007
1008 typedef type new_type[length];
1009
1010 struct {
1011 type field_name[length];
1012 }
1013
1014 typedef type new_type[length_type];
1015
1016 struct {
1017 type field_name[length_type];
1018 }
1019
1020 integer {
1021 ...
1022 }
1023
1024 floating_point {
1025 ...
1026 }
1027
1028 struct {
1029 integer_type field_name:size; /* GNU/C bitfield */
1030 }
1031
1032 struct {
1033 string field_name;
1034 }
1035
1036
1037 A. Helper macros
1038
1039 The two following macros keep track of the size of a GNU/C structure without
1040 padding at the end by placing HEADER_END as the last field. A one byte end field
1041 is used for C90 compatibility (C99 flexible arrays could be used here). Note
1042 that this does not affect the effective structure size, which should always be
1043 calculated with the header_sizeof() helper.
1044
1045 #define HEADER_END char end_field
1046 #define header_sizeof(type) offsetof(typeof(type), end_field)
1047
1048
1049 B. Stream Header Rationale
1050
1051 An event stream is divided in contiguous event packets of variable size. These
1052 subdivisions allow the trace analyzer to perform a fast binary search by time
1053 within the stream (typically requiring to index only the event packet headers)
1054 without reading the whole stream. These subdivisions have a variable size to
1055 eliminate the need to transfer the event packet padding when partially filled
1056 event packets must be sent when streaming a trace for live viewing/analysis.
1057 An event packet can contain a certain amount of padding at the end. Dividing
1058 streams into event packets is also useful for network streaming over UDP and
1059 flight recorder mode tracing (a whole event packet can be swapped out of the
1060 buffer atomically for reading).
1061
1062 The stream header is repeated at the beginning of each event packet to allow
1063 flexibility in terms of:
1064
1065 - streaming support,
1066 - allowing arbitrary buffers to be discarded without making the trace
1067 unreadable,
1068 - allow UDP packet loss handling by either dealing with missing event packet
1069 or asking for re-transmission.
1070 - transparently support flight recorder mode,
1071 - transparently support crash dump.
1072
1073 The event stream header will therefore be referred to as the "event packet
1074 header" throughout the rest of this document.
1075
1076
1077 C. TSDL Grammar
1078
1079 /*
1080 * Common Trace Format (CTF) Trace Stream Description Language (TSDL) Grammar.
1081 *
1082 * Inspired from the C99 grammar:
1083 * http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1124.pdf (Annex A)
1084 * and c++1x grammar (draft)
1085 * http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2011/n3291.pdf (Annex A)
1086 *
1087 * Specialized for CTF needs by including only constant and declarations from
1088 * C99 (excluding function declarations), and by adding support for variants,
1089 * sequences and CTF-specific specifiers. Enumeration container types
1090 * semantic is inspired from c++1x enum-base.
1091 */
1092
1093 1) Lexical grammar
1094
1095 1.1) Lexical elements
1096
1097 token:
1098 keyword
1099 identifier
1100 constant
1101 string-literal
1102 punctuator
1103
1104 1.2) Keywords
1105
1106 keyword: is one of
1107
1108 const
1109 char
1110 double
1111 enum
1112 event
1113 floating_point
1114 float
1115 integer
1116 int
1117 long
1118 short
1119 signed
1120 stream
1121 string
1122 struct
1123 trace
1124 typealias
1125 typedef
1126 unsigned
1127 variant
1128 void
1129 _Bool
1130 _Complex
1131 _Imaginary
1132
1133
1134 1.3) Identifiers
1135
1136 identifier:
1137 identifier-nondigit
1138 identifier identifier-nondigit
1139 identifier digit
1140
1141 identifier-nondigit:
1142 nondigit
1143 universal-character-name
1144 any other implementation-defined characters
1145
1146 nondigit:
1147 _
1148 [a-zA-Z] /* regular expression */
1149
1150 digit:
1151 [0-9] /* regular expression */
1152
1153 1.4) Universal character names
1154
1155 universal-character-name:
1156 \u hex-quad
1157 \U hex-quad hex-quad
1158
1159 hex-quad:
1160 hexadecimal-digit hexadecimal-digit hexadecimal-digit hexadecimal-digit
1161
1162 1.5) Constants
1163
1164 constant:
1165 integer-constant
1166 enumeration-constant
1167 character-constant
1168
1169 integer-constant:
1170 decimal-constant integer-suffix-opt
1171 octal-constant integer-suffix-opt
1172 hexadecimal-constant integer-suffix-opt
1173
1174 decimal-constant:
1175 nonzero-digit
1176 decimal-constant digit
1177
1178 octal-constant:
1179 0
1180 octal-constant octal-digit
1181
1182 hexadecimal-constant:
1183 hexadecimal-prefix hexadecimal-digit
1184 hexadecimal-constant hexadecimal-digit
1185
1186 hexadecimal-prefix:
1187 0x
1188 0X
1189
1190 nonzero-digit:
1191 [1-9]
1192
1193 integer-suffix:
1194 unsigned-suffix long-suffix-opt
1195 unsigned-suffix long-long-suffix
1196 long-suffix unsigned-suffix-opt
1197 long-long-suffix unsigned-suffix-opt
1198
1199 unsigned-suffix:
1200 u
1201 U
1202
1203 long-suffix:
1204 l
1205 L
1206
1207 long-long-suffix:
1208 ll
1209 LL
1210
1211 digit-sequence:
1212 digit
1213 digit-sequence digit
1214
1215 hexadecimal-digit-sequence:
1216 hexadecimal-digit
1217 hexadecimal-digit-sequence hexadecimal-digit
1218
1219 enumeration-constant:
1220 identifier
1221 string-literal
1222
1223 character-constant:
1224 ' c-char-sequence '
1225 L' c-char-sequence '
1226
1227 c-char-sequence:
1228 c-char
1229 c-char-sequence c-char
1230
1231 c-char:
1232 any member of source charset except single-quote ('), backslash
1233 (\), or new-line character.
1234 escape-sequence
1235
1236 escape-sequence:
1237 simple-escape-sequence
1238 octal-escape-sequence
1239 hexadecimal-escape-sequence
1240 universal-character-name
1241
1242 simple-escape-sequence: one of
1243 \' \" \? \\ \a \b \f \n \r \t \v
1244
1245 octal-escape-sequence:
1246 \ octal-digit
1247 \ octal-digit octal-digit
1248 \ octal-digit octal-digit octal-digit
1249
1250 hexadecimal-escape-sequence:
1251 \x hexadecimal-digit
1252 hexadecimal-escape-sequence hexadecimal-digit
1253
1254 1.6) String literals
1255
1256 string-literal:
1257 " s-char-sequence-opt "
1258 L" s-char-sequence-opt "
1259
1260 s-char-sequence:
1261 s-char
1262 s-char-sequence s-char
1263
1264 s-char:
1265 any member of source charset except double-quote ("), backslash
1266 (\), or new-line character.
1267 escape-sequence
1268
1269 1.7) Punctuators
1270
1271 punctuator: one of
1272 [ ] ( ) { } . -> * + - < > : ; ... = ,
1273
1274
1275 2) Phrase structure grammar
1276
1277 primary-expression:
1278 identifier
1279 constant
1280 string-literal
1281 ( unary-expression )
1282
1283 postfix-expression:
1284 primary-expression
1285 postfix-expression [ unary-expression ]
1286 postfix-expression . identifier
1287 postfix-expressoin -> identifier
1288
1289 unary-expression:
1290 postfix-expression
1291 unary-operator postfix-expression
1292
1293 unary-operator: one of
1294 + -
1295
1296 assignment-operator:
1297 =
1298
1299 type-assignment-operator:
1300 :=
1301
1302 constant-expression:
1303 unary-expression
1304
1305 constant-expression-range:
1306 constant-expression ... constant-expression
1307
1308 2.2) Declarations:
1309
1310 declaration:
1311 declaration-specifiers declarator-list-opt ;
1312 ctf-specifier ;
1313
1314 declaration-specifiers:
1315 storage-class-specifier declaration-specifiers-opt
1316 type-specifier declaration-specifiers-opt
1317 type-qualifier declaration-specifiers-opt
1318
1319 declarator-list:
1320 declarator
1321 declarator-list , declarator
1322
1323 abstract-declarator-list:
1324 abstract-declarator
1325 abstract-declarator-list , abstract-declarator
1326
1327 storage-class-specifier:
1328 typedef
1329
1330 type-specifier:
1331 void
1332 char
1333 short
1334 int
1335 long
1336 float
1337 double
1338 signed
1339 unsigned
1340 _Bool
1341 _Complex
1342 _Imaginary
1343 struct-specifier
1344 variant-specifier
1345 enum-specifier
1346 typedef-name
1347 ctf-type-specifier
1348
1349 struct-specifier:
1350 struct identifier-opt { struct-or-variant-declaration-list-opt }
1351 struct identifier
1352
1353 struct-or-variant-declaration-list:
1354 struct-or-variant-declaration
1355 struct-or-variant-declaration-list struct-or-variant-declaration
1356
1357 struct-or-variant-declaration:
1358 specifier-qualifier-list struct-or-variant-declarator-list ;
1359 declaration-specifiers storage-class-specifier declaration-specifiers declarator-list ;
1360 typealias declaration-specifiers abstract-declarator-list := declaration-specifiers abstract-declarator-list ;
1361 typealias declaration-specifiers abstract-declarator-list := declarator-list ;
1362
1363 specifier-qualifier-list:
1364 type-specifier specifier-qualifier-list-opt
1365 type-qualifier specifier-qualifier-list-opt
1366
1367 struct-or-variant-declarator-list:
1368 struct-or-variant-declarator
1369 struct-or-variant-declarator-list , struct-or-variant-declarator
1370
1371 struct-or-variant-declarator:
1372 declarator
1373 declarator-opt : constant-expression
1374
1375 variant-specifier:
1376 variant identifier-opt variant-tag-opt { struct-or-variant-declaration-list }
1377 variant identifier variant-tag
1378
1379 variant-tag:
1380 < identifier >
1381
1382 enum-specifier:
1383 enum identifier-opt { enumerator-list }
1384 enum identifier-opt { enumerator-list , }
1385 enum identifier
1386 enum identifier-opt : declaration-specifiers { enumerator-list }
1387 enum identifier-opt : declaration-specifiers { enumerator-list , }
1388
1389 enumerator-list:
1390 enumerator
1391 enumerator-list , enumerator
1392
1393 enumerator:
1394 enumeration-constant
1395 enumeration-constant = constant-expression
1396 enumeration-constant = constant-expression-range
1397
1398 type-qualifier:
1399 const
1400
1401 declarator:
1402 pointer-opt direct-declarator
1403
1404 direct-declarator:
1405 identifier
1406 ( declarator )
1407 direct-declarator [ type-specifier ]
1408 direct-declarator [ constant-expression ]
1409
1410 abstract-declarator:
1411 pointer-opt direct-abstract-declarator
1412
1413 direct-abstract-declarator:
1414 identifier-opt
1415 ( abstract-declarator )
1416 direct-abstract-declarator [ type-specifier ]
1417 direct-abstract-declarator [ constant-expression ]
1418 direct-abstract-declarator [ ]
1419
1420 pointer:
1421 * type-qualifier-list-opt
1422 * type-qualifier-list-opt pointer
1423
1424 type-qualifier-list:
1425 type-qualifier
1426 type-qualifier-list type-qualifier
1427
1428 typedef-name:
1429 identifier
1430
1431 2.3) CTF-specific declarations
1432
1433 ctf-specifier:
1434 event { ctf-assignment-expression-list-opt }
1435 stream { ctf-assignment-expression-list-opt }
1436 trace { ctf-assignment-expression-list-opt }
1437 typealias declaration-specifiers abstract-declarator-list := declaration-specifiers abstract-declarator-list ;
1438 typealias declaration-specifiers abstract-declarator-list := declarator-list ;
1439
1440 ctf-type-specifier:
1441 floating_point { ctf-assignment-expression-list-opt }
1442 integer { ctf-assignment-expression-list-opt }
1443 string { ctf-assignment-expression-list-opt }
1444
1445 ctf-assignment-expression-list:
1446 ctf-assignment-expression
1447 ctf-assignment-expression-list ; ctf-assignment-expression
1448
1449 ctf-assignment-expression:
1450 unary-expression assignment-operator unary-expression
1451 unary-expression type-assignment-operator type-specifier
1452 declaration-specifiers storage-class-specifier declaration-specifiers declarator-list
1453 typealias declaration-specifiers abstract-declarator-list := declaration-specifiers abstract-declarator-list
1454 typealias declaration-specifiers abstract-declarator-list := declarator-list
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