Add trace { endian = big/little; } field
[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 Note that the trace endianness is usually extracted from the packet
894 header magic number. The "endian" field is only needed when the magic
895 number packet header field is not present.
896
897 trace {
898 major = value; /* Trace format version */
899 minor = value;
900 uuid = "aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaaa"; /* Trace UUID */
901 endian = big OR little; /* Endianness (optional) */
902 packet.header := struct {
903 uint32_t magic;
904 uint8_t trace_uuid[16];
905 uint32_t stream_id;
906 };
907 };
908
909 stream {
910 id = stream_id;
911 /* Type 1 - Few event IDs; Type 2 - Many event IDs. See section 6.1. */
912 event.header := event_header_1 OR event_header_2;
913 event.context := struct {
914 ...
915 };
916 packet.context := struct {
917 ...
918 };
919 };
920
921 event {
922 name = event_name;
923 id = value; /* Numeric identifier within the stream */
924 stream = stream_id;
925 context := struct {
926 ...
927 };
928 fields := struct {
929 ...
930 };
931 };
932
933 /* More detail on types in section 4. Types */
934
935 /*
936 * Named types:
937 *
938 * Type declarations behave similarly to the C standard.
939 */
940
941 typedef aliased_type_specifiers new_type_declarators;
942
943 /* e.g.: typedef struct example new_type_name[10]; */
944
945 /*
946 * typealias
947 *
948 * The "typealias" declaration can be used to give a name (including
949 * pointer declarator specifier) to a type. It should also be used to
950 * map basic C types (float, int, unsigned long, ...) to a CTF type.
951 * Typealias is a superset of "typedef": it also allows assignment of a
952 * simple variable identifier to a type.
953 */
954
955 typealias type_class {
956 ...
957 } := type_specifiers type_declarator;
958
959 /*
960 * e.g.:
961 * typealias integer {
962 * size = 32;
963 * align = 32;
964 * signed = false;
965 * } := struct page *;
966 *
967 * typealias integer {
968 * size = 32;
969 * align = 32;
970 * signed = true;
971 * } := int;
972 */
973
974 struct name {
975 ...
976 };
977
978 variant name {
979 ...
980 };
981
982 enum name : integer_type {
983 ...
984 };
985
986
987 /*
988 * Unnamed types, contained within compound type fields, typedef or typealias.
989 */
990
991 struct {
992 ...
993 }
994
995 variant {
996 ...
997 }
998
999 enum : integer_type {
1000 ...
1001 }
1002
1003 typedef type new_type[length];
1004
1005 struct {
1006 type field_name[length];
1007 }
1008
1009 typedef type new_type[length_type];
1010
1011 struct {
1012 type field_name[length_type];
1013 }
1014
1015 integer {
1016 ...
1017 }
1018
1019 floating_point {
1020 ...
1021 }
1022
1023 struct {
1024 integer_type field_name:size; /* GNU/C bitfield */
1025 }
1026
1027 struct {
1028 string field_name;
1029 }
1030
1031
1032 A. Helper macros
1033
1034 The two following macros keep track of the size of a GNU/C structure without
1035 padding at the end by placing HEADER_END as the last field. A one byte end field
1036 is used for C90 compatibility (C99 flexible arrays could be used here). Note
1037 that this does not affect the effective structure size, which should always be
1038 calculated with the header_sizeof() helper.
1039
1040 #define HEADER_END char end_field
1041 #define header_sizeof(type) offsetof(typeof(type), end_field)
1042
1043
1044 B. Stream Header Rationale
1045
1046 An event stream is divided in contiguous event packets of variable size. These
1047 subdivisions allow the trace analyzer to perform a fast binary search by time
1048 within the stream (typically requiring to index only the event packet headers)
1049 without reading the whole stream. These subdivisions have a variable size to
1050 eliminate the need to transfer the event packet padding when partially filled
1051 event packets must be sent when streaming a trace for live viewing/analysis.
1052 An event packet can contain a certain amount of padding at the end. Dividing
1053 streams into event packets is also useful for network streaming over UDP and
1054 flight recorder mode tracing (a whole event packet can be swapped out of the
1055 buffer atomically for reading).
1056
1057 The stream header is repeated at the beginning of each event packet to allow
1058 flexibility in terms of:
1059
1060 - streaming support,
1061 - allowing arbitrary buffers to be discarded without making the trace
1062 unreadable,
1063 - allow UDP packet loss handling by either dealing with missing event packet
1064 or asking for re-transmission.
1065 - transparently support flight recorder mode,
1066 - transparently support crash dump.
1067
1068 The event stream header will therefore be referred to as the "event packet
1069 header" throughout the rest of this document.
1070
1071
1072 C. TSDL Grammar
1073
1074 /*
1075 * Common Trace Format (CTF) Trace Stream Description Language (TSDL) Grammar.
1076 *
1077 * Inspired from the C99 grammar:
1078 * http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1124.pdf (Annex A)
1079 * and c++1x grammar (draft)
1080 * http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2011/n3291.pdf (Annex A)
1081 *
1082 * Specialized for CTF needs by including only constant and declarations from
1083 * C99 (excluding function declarations), and by adding support for variants,
1084 * sequences and CTF-specific specifiers. Enumeration container types
1085 * semantic is inspired from c++1x enum-base.
1086 */
1087
1088 1) Lexical grammar
1089
1090 1.1) Lexical elements
1091
1092 token:
1093 keyword
1094 identifier
1095 constant
1096 string-literal
1097 punctuator
1098
1099 1.2) Keywords
1100
1101 keyword: is one of
1102
1103 const
1104 char
1105 double
1106 enum
1107 event
1108 floating_point
1109 float
1110 integer
1111 int
1112 long
1113 short
1114 signed
1115 stream
1116 string
1117 struct
1118 trace
1119 typealias
1120 typedef
1121 unsigned
1122 variant
1123 void
1124 _Bool
1125 _Complex
1126 _Imaginary
1127
1128
1129 1.3) Identifiers
1130
1131 identifier:
1132 identifier-nondigit
1133 identifier identifier-nondigit
1134 identifier digit
1135
1136 identifier-nondigit:
1137 nondigit
1138 universal-character-name
1139 any other implementation-defined characters
1140
1141 nondigit:
1142 _
1143 [a-zA-Z] /* regular expression */
1144
1145 digit:
1146 [0-9] /* regular expression */
1147
1148 1.4) Universal character names
1149
1150 universal-character-name:
1151 \u hex-quad
1152 \U hex-quad hex-quad
1153
1154 hex-quad:
1155 hexadecimal-digit hexadecimal-digit hexadecimal-digit hexadecimal-digit
1156
1157 1.5) Constants
1158
1159 constant:
1160 integer-constant
1161 enumeration-constant
1162 character-constant
1163
1164 integer-constant:
1165 decimal-constant integer-suffix-opt
1166 octal-constant integer-suffix-opt
1167 hexadecimal-constant integer-suffix-opt
1168
1169 decimal-constant:
1170 nonzero-digit
1171 decimal-constant digit
1172
1173 octal-constant:
1174 0
1175 octal-constant octal-digit
1176
1177 hexadecimal-constant:
1178 hexadecimal-prefix hexadecimal-digit
1179 hexadecimal-constant hexadecimal-digit
1180
1181 hexadecimal-prefix:
1182 0x
1183 0X
1184
1185 nonzero-digit:
1186 [1-9]
1187
1188 integer-suffix:
1189 unsigned-suffix long-suffix-opt
1190 unsigned-suffix long-long-suffix
1191 long-suffix unsigned-suffix-opt
1192 long-long-suffix unsigned-suffix-opt
1193
1194 unsigned-suffix:
1195 u
1196 U
1197
1198 long-suffix:
1199 l
1200 L
1201
1202 long-long-suffix:
1203 ll
1204 LL
1205
1206 digit-sequence:
1207 digit
1208 digit-sequence digit
1209
1210 hexadecimal-digit-sequence:
1211 hexadecimal-digit
1212 hexadecimal-digit-sequence hexadecimal-digit
1213
1214 enumeration-constant:
1215 identifier
1216 string-literal
1217
1218 character-constant:
1219 ' c-char-sequence '
1220 L' c-char-sequence '
1221
1222 c-char-sequence:
1223 c-char
1224 c-char-sequence c-char
1225
1226 c-char:
1227 any member of source charset except single-quote ('), backslash
1228 (\), or new-line character.
1229 escape-sequence
1230
1231 escape-sequence:
1232 simple-escape-sequence
1233 octal-escape-sequence
1234 hexadecimal-escape-sequence
1235 universal-character-name
1236
1237 simple-escape-sequence: one of
1238 \' \" \? \\ \a \b \f \n \r \t \v
1239
1240 octal-escape-sequence:
1241 \ octal-digit
1242 \ octal-digit octal-digit
1243 \ octal-digit octal-digit octal-digit
1244
1245 hexadecimal-escape-sequence:
1246 \x hexadecimal-digit
1247 hexadecimal-escape-sequence hexadecimal-digit
1248
1249 1.6) String literals
1250
1251 string-literal:
1252 " s-char-sequence-opt "
1253 L" s-char-sequence-opt "
1254
1255 s-char-sequence:
1256 s-char
1257 s-char-sequence s-char
1258
1259 s-char:
1260 any member of source charset except double-quote ("), backslash
1261 (\), or new-line character.
1262 escape-sequence
1263
1264 1.7) Punctuators
1265
1266 punctuator: one of
1267 [ ] ( ) { } . -> * + - < > : ; ... = ,
1268
1269
1270 2) Phrase structure grammar
1271
1272 primary-expression:
1273 identifier
1274 constant
1275 string-literal
1276 ( unary-expression )
1277
1278 postfix-expression:
1279 primary-expression
1280 postfix-expression [ unary-expression ]
1281 postfix-expression . identifier
1282 postfix-expressoin -> identifier
1283
1284 unary-expression:
1285 postfix-expression
1286 unary-operator postfix-expression
1287
1288 unary-operator: one of
1289 + -
1290
1291 assignment-operator:
1292 =
1293
1294 type-assignment-operator:
1295 :=
1296
1297 constant-expression:
1298 unary-expression
1299
1300 constant-expression-range:
1301 constant-expression ... constant-expression
1302
1303 2.2) Declarations:
1304
1305 declaration:
1306 declaration-specifiers declarator-list-opt ;
1307 ctf-specifier ;
1308
1309 declaration-specifiers:
1310 storage-class-specifier declaration-specifiers-opt
1311 type-specifier declaration-specifiers-opt
1312 type-qualifier declaration-specifiers-opt
1313
1314 declarator-list:
1315 declarator
1316 declarator-list , declarator
1317
1318 abstract-declarator-list:
1319 abstract-declarator
1320 abstract-declarator-list , abstract-declarator
1321
1322 storage-class-specifier:
1323 typedef
1324
1325 type-specifier:
1326 void
1327 char
1328 short
1329 int
1330 long
1331 float
1332 double
1333 signed
1334 unsigned
1335 _Bool
1336 _Complex
1337 _Imaginary
1338 struct-specifier
1339 variant-specifier
1340 enum-specifier
1341 typedef-name
1342 ctf-type-specifier
1343
1344 struct-specifier:
1345 struct identifier-opt { struct-or-variant-declaration-list-opt }
1346 struct identifier
1347
1348 struct-or-variant-declaration-list:
1349 struct-or-variant-declaration
1350 struct-or-variant-declaration-list struct-or-variant-declaration
1351
1352 struct-or-variant-declaration:
1353 specifier-qualifier-list struct-or-variant-declarator-list ;
1354 declaration-specifiers storage-class-specifier declaration-specifiers declarator-list ;
1355 typealias declaration-specifiers abstract-declarator-list := declaration-specifiers abstract-declarator-list ;
1356 typealias declaration-specifiers abstract-declarator-list := declarator-list ;
1357
1358 specifier-qualifier-list:
1359 type-specifier specifier-qualifier-list-opt
1360 type-qualifier specifier-qualifier-list-opt
1361
1362 struct-or-variant-declarator-list:
1363 struct-or-variant-declarator
1364 struct-or-variant-declarator-list , struct-or-variant-declarator
1365
1366 struct-or-variant-declarator:
1367 declarator
1368 declarator-opt : constant-expression
1369
1370 variant-specifier:
1371 variant identifier-opt variant-tag-opt { struct-or-variant-declaration-list }
1372 variant identifier variant-tag
1373
1374 variant-tag:
1375 < identifier >
1376
1377 enum-specifier:
1378 enum identifier-opt { enumerator-list }
1379 enum identifier-opt { enumerator-list , }
1380 enum identifier
1381 enum identifier-opt : declaration-specifiers { enumerator-list }
1382 enum identifier-opt : declaration-specifiers { enumerator-list , }
1383
1384 enumerator-list:
1385 enumerator
1386 enumerator-list , enumerator
1387
1388 enumerator:
1389 enumeration-constant
1390 enumeration-constant = constant-expression
1391 enumeration-constant = constant-expression-range
1392
1393 type-qualifier:
1394 const
1395
1396 declarator:
1397 pointer-opt direct-declarator
1398
1399 direct-declarator:
1400 identifier
1401 ( declarator )
1402 direct-declarator [ type-specifier ]
1403 direct-declarator [ constant-expression ]
1404
1405 abstract-declarator:
1406 pointer-opt direct-abstract-declarator
1407
1408 direct-abstract-declarator:
1409 identifier-opt
1410 ( abstract-declarator )
1411 direct-abstract-declarator [ type-specifier ]
1412 direct-abstract-declarator [ constant-expression ]
1413 direct-abstract-declarator [ ]
1414
1415 pointer:
1416 * type-qualifier-list-opt
1417 * type-qualifier-list-opt pointer
1418
1419 type-qualifier-list:
1420 type-qualifier
1421 type-qualifier-list type-qualifier
1422
1423 typedef-name:
1424 identifier
1425
1426 2.3) CTF-specific declarations
1427
1428 ctf-specifier:
1429 event { ctf-assignment-expression-list-opt }
1430 stream { ctf-assignment-expression-list-opt }
1431 trace { ctf-assignment-expression-list-opt }
1432 typealias declaration-specifiers abstract-declarator-list := declaration-specifiers abstract-declarator-list ;
1433 typealias declaration-specifiers abstract-declarator-list := declarator-list ;
1434
1435 ctf-type-specifier:
1436 floating_point { ctf-assignment-expression-list-opt }
1437 integer { ctf-assignment-expression-list-opt }
1438 string { ctf-assignment-expression-list-opt }
1439
1440 ctf-assignment-expression-list:
1441 ctf-assignment-expression
1442 ctf-assignment-expression-list ; ctf-assignment-expression
1443
1444 ctf-assignment-expression:
1445 unary-expression assignment-operator unary-expression
1446 unary-expression type-assignment-operator type-specifier
1447 declaration-specifiers storage-class-specifier declaration-specifiers declarator-list
1448 typealias declaration-specifiers abstract-declarator-list := declaration-specifiers abstract-declarator-list
1449 typealias declaration-specifiers abstract-declarator-list := declarator-list
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