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