Explain that ids can be left out if single stream/event
[ctf.git] / common-trace-format-proposal.txt
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5ba9f198 1
4767a9e7 2RFC: Common Trace Format (CTF) Proposal (pre-v1.7)
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3
4Mathieu Desnoyers, EfficiOS Inc.
5
6The goal of the present document is to propose a trace format that suits the
cc089c3a 7needs of the embedded, telecom, high-performance and kernel communities. It is
5ba9f198 8based on the Common Trace Format Requirements (v1.4) document. It is designed to
cc089c3a 9allow traces to be natively generated by the Linux kernel, Linux user-space
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10applications written in C/C++, and hardware components. One major element of
11CTF is the Trace Stream Description Language (TSDL) which flexibility
12enables description of various binary trace stream layouts.
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13
14The 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
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18
19A reference implementation of a library to read and write this trace format is
20being implemented within the BabelTrace project, a converter between trace
21formats. 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
271. Preliminary definitions
28
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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.
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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
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36 an event stream.
37 e.g. event: irq_entry.
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38 - An event (or event record) relates to a specific instance of an event
39 class.
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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.
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43
44
452. High-level representation of a trace
46
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47A trace is divided into multiple event streams. Each event stream contains a
48subset of the trace event types.
5ba9f198 49
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50The final output of the trace, after its generation and optional transport over
51the network, is expected to be either on permanent or temporary storage in a
52virtual file system. Because each event stream is appended to while a trace is
53being recorded, each is associated with a separate file for output. Therefore,
54a stored trace can be represented as a directory containing one file per stream.
5ba9f198 55
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56A metadata event stream contains information on trace event types
57expressed in the Trace Stream Description Language (TSDL). It describes:
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58
59- Trace version.
60- Types available.
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61- Per-stream event header description.
62- Per-stream event header selection.
63- Per-stream event context fields.
5ba9f198 64- Per-event
3bf79539 65 - Event type to stream mapping.
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66 - Event type to name mapping.
67 - Event type to ID mapping.
68 - Event fields description.
69
70
3bf79539 713. Event stream
5ba9f198 72
3bf79539 73An event stream is divided in contiguous event packets of variable size. These
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74subdivisions have a variable size. An event packet can contain a certain
75amount of padding at the end. The stream header is repeated at the
76beginning of each event packet. The rationale for the event stream
77design choices is explained in Appendix B. Stream Header Rationale.
5ba9f198 78
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79The event stream header will therefore be referred to as the "event packet
80header" throughout the rest of this document.
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81
82
834. Types
84
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85Types are organized as type classes. Each type class belong to either of two
86kind of types: basic types or compound types.
87
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884.1 Basic types
89
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90A basic type is a scalar type, as described in this section. It includes
91integers, GNU/C bitfields, enumerations, and floating point values.
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92
934.1.1 Type inheritance
94
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95Type specifications can be inherited to allow deriving types from a
96type class. For example, see the uint32_t named type derived from the "integer"
97type class below ("Integers" section). Types have a precise binary
98representation in the trace. A type class has methods to read and write these
99types, but must be derived into a type to be usable in an event field.
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100
1014.1.2 Alignment
102
103We define "byte-packed" types as aligned on the byte size, namely 8-bit.
104We define "bit-packed" types as following on the next bit, as defined by the
370eae99 105"Integers" section.
5ba9f198 106
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107All basic types, except bitfields, are either aligned on an architecture-defined
108specific alignment or byte-packed, depending on the architecture preference.
109Architectures providing fast unaligned write byte-packed basic types to save
5ba9f198 110space, aligning each type on byte boundaries (8-bit). Architectures with slow
3bf79539 111unaligned writes align types on specific alignment values. If no specific
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112alignment is declared for a type, it is assumed to be bit-packed for
113integers with size not multiple of 8 bits and for gcc bitfields. All
114other types are byte-packed.
5ba9f198 115
3bf79539 116Metadata attribute representation of a specific alignment:
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117
118 align = value; /* value in bits */
119
1204.1.3 Byte order
121
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122By default, the native endianness of the source architecture the trace is used.
123Byte order can be overridden for a basic type by specifying a "byte_order"
124attribute. 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.
126If not specified, the byte order is native.
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127
128Metadata representation:
129
130 byte_order = native OR network OR be OR le; /* network and be are aliases */
131
1324.1.4 Size
133
134Type size, in bits, for integers and floats is that returned by "sizeof()" in C
135multiplied by CHAR_BIT.
136We require the size of "char" and "unsigned char" types (CHAR_BIT) to be fixed
137to 8 bits for cross-endianness compatibility.
138
139Metadata representation:
140
141 size = value; (value is in bits)
142
1434.1.5 Integers
144
145Signed integers are represented in two-complement. Integer alignment, size,
146signedness and byte ordering are defined in the metadata. Integers aligned on
147byte size (8-bit) and with length multiple of byte size (8-bit) correspond to
148the C99 standard integers. In addition, integers with alignment and/or size that
149are _not_ a multiple of the byte size are permitted; these correspond to the C99
150standard bitfields, with the added specification that the CTF integer bitfields
151have a fixed binary representation. A MIT-licensed reference implementation of
152the CTF portable bitfields is available at:
153
154 http://git.efficios.com/?p=babeltrace.git;a=blob;f=include/babeltrace/bitfield.h
155
156Binary 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
172This binary representation is derived from the bitfield implementation in GCC
173for little and big endian. However, contrary to what GCC does, integers can
174cross units boundaries (no padding is required). Padding can be explicitely
175added (see 4.1.6 GNU/C bitfields) to follow the GCC layout if needed.
176
177Metadata representation:
178
80fd2569 179 integer {
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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 */
2152348f 184 }
5ba9f198 185
80fd2569 186Example of type inheritance (creation of a uint32_t named type):
5ba9f198 187
359894ac 188typealias integer {
9e4e34e9 189 size = 32;
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190 signed = false;
191 align = 32;
38b8da21 192} := uint32_t;
5ba9f198 193
80fd2569 194Definition of a named 5-bit signed bitfield:
5ba9f198 195
359894ac 196typealias integer {
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197 size = 5;
198 signed = true;
199 align = 1;
38b8da21 200} := int5_t;
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201
2024.1.6 GNU/C bitfields
203
204The GNU/C bitfields follow closely the integer representation, with a
205particularity on alignment: if a bitfield cannot fit in the current unit, the
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206unit is padded and the bitfield starts at the following unit. The unit size is
207defined by the size of the type "unit_type".
5ba9f198 208
2152348f 209Metadata representation:
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210
211 unit_type name:size:
212
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213As an example, the following structure declared in C compiled by GCC:
214
215struct example {
216 short a:12;
217 short b:5;
218};
219
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220The example structure is aligned on the largest element (short). The second
221bitfield would be aligned on the next unit boundary, because it would not fit in
222the current unit.
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223
2244.1.7 Floating point
225
226The floating point values byte ordering is defined in the metadata.
227
228Floating point values follow the IEEE 754-2008 standard interchange formats.
229Description of the floating point values include the exponent and mantissa size
230in 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
245Metadata representation:
246
80fd2569 247floating_point {
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248 exp_dig = value;
249 mant_dig = value;
250 byte_order = native OR network OR be OR le;
2152348f 251}
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252
253Example of type inheritance:
254
359894ac 255typealias floating_point {
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256 exp_dig = 8; /* sizeof(float) * CHAR_BIT - FLT_MANT_DIG */
257 mant_dig = 24; /* FLT_MANT_DIG */
258 byte_order = native;
38b8da21 259} := float;
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260
261TODO: define NaN, +inf, -inf behavior.
262
2634.1.8 Enumerations
264
265Enumerations are a mapping between an integer type and a table of strings. The
266numerical representation of the enumeration follows the integer type specified
267by the metadata. The enumeration mapping table is detailed in the enumeration
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268description 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
80fd2569 271"[ start_value ... end_value ] -> string", which map inclusive ranges of
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272values to strings. An enumeration from the C language can be represented in
273this format by having the same start_value and end_value for each element, which
274is in fact a range of size 1. This single-value range is supported without
4767a9e7 275repeating the start and end values with the value = string declaration.
80fd2569 276
a9b83695 277enum name : integer_type {
359894ac 278 somestring = start_value1 ... end_value1,
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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
285If the values are omitted, the enumeration starts at 0 and increment of 1 for
286each entry:
287
a9b83695 288enum name : unsigned int {
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289 ZERO,
290 ONE,
291 TWO,
292 TEN = 10,
293 ELEVEN,
3bf79539 294};
5ba9f198 295
80fd2569 296Overlapping ranges within a single enumeration are implementation defined.
5ba9f198 297
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298A nameless enumeration can be declared as a field type or as part of a typedef:
299
a9b83695 300enum : integer_type {
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301 ...
302}
303
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304Enumerations omitting the container type ": integer_type" use the "int"
305type (for compatibility with C99). The "int" type must be previously
306declared. E.g.:
307
308typealias integer { size = 32; align = 32; signed = true } := int;
309
310enum {
311 ...
312}
313
1fad7a85 314
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3154.2 Compound types
316
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317Compound are aggregation of type declarations. Compound types include
318structures, variant, arrays, sequences, and strings.
319
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3204.2.1 Structures
321
322Structures are aligned on the largest alignment required by basic types
323contained within the structure. (This follows the ISO/C standard for structures)
324
80fd2569 325Metadata representation of a named structure:
5ba9f198 326
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327struct name {
328 field_type field_name;
329 field_type field_name;
330 ...
331};
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332
333Example:
334
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335struct 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 */
3bf79539 342};
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343
344The fields are placed in a sequence next to each other. They each possess a
345field name, which is a unique identifier within the structure.
346
2152348f 347A nameless structure can be declared as a field type or as part of a typedef:
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348
349struct {
350 ...
2152348f 351}
80fd2569 352
77a98c82 3534.2.2 Variants (Discriminated/Tagged Unions)
fcba70d4 354
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355A CTF variant is a selection between different types. A CTF variant must
356always be defined within the scope of a structure or within fields
357contained within a structure (defined recursively). A "tag" enumeration
358field must appear in either the same lexical scope, prior to the variant
359field (in field declaration order), in an uppermost lexical scope (see
6c7226e9 360Section 7.3.1), or in an uppermost dynamic scope (see Section 7.3.2).
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361The type selection is indicated by the mapping from the enumeration
362value to the string used as variant type selector. The field to use as
363tag is specified by the "tag_field", specified between "< >" after the
364"variant" keyword for unnamed variants, and after "variant name" for
365named variants.
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366
367The alignment of the variant is the alignment of the type as selected by the tag
368value for the specific instance of the variant. The alignment of the type
369containing the variant is independent of the variant alignment. The size of the
370variant is the size as selected by the tag value for the specific instance of
371the variant.
372
373A named variant declaration followed by its definition within a structure
374declaration:
375
376variant name {
377 field_type sel1;
378 field_type sel2;
379 field_type sel3;
380 ...
381};
382
383struct {
a9b83695 384 enum : integer_type { sel1, sel2, sel3, ... } tag_field;
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385 ...
386 variant name <tag_field> v;
387}
388
389An unnamed variant definition within a structure is expressed by the following
390metadata:
391
392struct {
a9b83695 393 enum : integer_type { sel1, sel2, sel3, ... } tag_field;
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394 ...
395 variant <tag_field> {
396 field_type sel1;
397 field_type sel2;
398 field_type sel3;
399 ...
400 } v;
401}
402
403Example of a named variant within a sequence that refers to a single tag field:
404
405variant example {
406 uint32_t a;
407 uint64_t b;
408 short c;
409};
410
411struct {
a9b83695 412 enum : uint2_t { a, b, c } choice;
15850440 413 variant example <choice> v[unsigned int];
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414}
415
416Example of an unnamed variant:
417
418struct {
a9b83695 419 enum : uint2_t { a, b, c, d } choice;
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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
433Example of an unnamed variant within an array:
434
435struct {
a9b83695 436 enum : uint2_t { a, b, c } choice;
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437 variant <choice> {
438 uint32_t a;
439 uint64_t b;
440 short c;
15850440 441 } v[10];
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442}
443
444Example of a variant type definition within a structure, where the defined type
445is then declared within an array of structures. This variant refers to a tag
446located in an upper lexical scope. This example clearly shows that a variant
447type definition referring to the tag "x" uses the closest preceding field from
448the lexical scope of the type definition.
449
450struct {
a9b83695 451 enum : uint2_t { a, b, c, d } x;
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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 {
a9b83695 463 enum : int { x, y, z } x; /* This enumeration is not used by "v". */
fcba70d4 464 example_variant v; /*
a9b83695 465 * "v" uses the "enum : uint2_t { a, b, c, d }"
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466 * tag.
467 */
468 } a[10];
469}
470
4714.2.3 Arrays
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472
473Arrays are fixed-length. Their length is declared in the type declaration within
474the metadata. They contain an array of "inner type" elements, which can refer to
475any type not containing the type of the array being declared (no circular
3bf79539 476dependency). The length is the number of elements in an array.
5ba9f198 477
2152348f 478Metadata representation of a named array:
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479
480typedef elem_type name[length];
5ba9f198 481
2152348f 482A nameless array can be declared as a field type within a structure, e.g.:
5ba9f198 483
2152348f 484 uint8_t field_name[10];
80fd2569 485
5ba9f198 486
fcba70d4 4874.2.4 Sequences
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488
489Sequences are dynamically-sized arrays. They start with an integer that specify
490the length of the sequence, followed by an array of "inner type" elements.
3bf79539 491The length is the number of elements in the sequence.
5ba9f198 492
2152348f 493Metadata representation for a named sequence:
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494
495typedef elem_type name[length_type];
496
497A nameless sequence can be declared as a field type, e.g.:
498
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499long field_name[int];
500
501The length type follows the integer types specifications, and the sequence
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502elements follow the "array" specifications.
503
fcba70d4 5044.2.5 Strings
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505
506Strings 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
508encoding attribute information, the default encoding is UTF-8.
509
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510Metadata representation of a named string type:
511
359894ac 512typealias string {
5ba9f198 513 encoding = UTF8 OR ASCII;
38b8da21 514} := name;
5ba9f198 515
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516A nameless string type can be declared as a field type:
517
518string field_name; /* Use default UTF8 encoding */
5ba9f198 519
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5205. Event Packet Header
521
522The event packet header consists of two part: one is mandatory and have a fixed
523layout. The second part, the "event packet context", has its layout described in
524the metadata.
5ba9f198 525
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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
5ba9f198 529 ordering.
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530
531Fixed layout (event packet header):
532
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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.
3bf79539 541- Trace UUID, used to ensure the event packet match the metadata used.
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542 (note: we cannot use a metadata checksum because metadata can be appended to
543 while tracing is active)
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544- Stream ID, used as reference to stream description in metadata.
545
546Metadata-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.
5ba9f198 560- Events discarded count
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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.
5ba9f198 564 * Note: producer-consumer buffer full condition should fill the current
3bf79539 565 event packet with padding so we know exactly where events have been
5ba9f198 566 discarded.
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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.
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570 0: no compression scheme
571 1: bzip2
572 2: gzip
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573 3: xz
574- Cypher used for the event packet content. Applied after compression.
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575 0: no encryption
576 1: AES
3bf79539 577- Checksum scheme used for the event packet content. Applied after encryption.
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578 0: no checksum
579 1: md5
580 2: sha1
581 3: crc32
582
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5835.1 Event Packet Header Fixed Layout Description
584
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585The event packet header layout is indicated by the trace packet.header
586field. Here is an example structure type for the packet header with the
587fields typically expected:
588
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589struct event_packet_header {
590 uint32_t magic;
591 uint8_t trace_uuid[16];
3bf79539 592 uint32_t stream_id;
80fd2569 593};
5ba9f198 594
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595trace {
596 ...
597 packet.header := struct event_packet_header;
598};
599
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600If a packet header lacks the "magic" number field, the trace endianness
601needs to be specified in the trace "endian" metadata attribute.
602
603If the trace_uuid is not present, no validation that the metadata
604actually corresponds to the stream is performed.
605
606If the stream_id packet header field is missing, the trace can only
607contain a single stream. Its "id" field can be left out, and its events
608don't need to declare a "stream_id" field.
609
610
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6115.2 Event Packet Context Description
612
613Event packet context example. These are declared within the stream declaration
614in the metadata. All these fields are optional except for "content_size" and
615"packet_size", which must be present in the context.
616
617An example event packet context type:
618
80fd2569 619struct event_packet_context {
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620 uint64_t timestamp_begin;
621 uint64_t timestamp_end;
622 uint32_t checksum;
623 uint32_t stream_packet_count;
624 uint32_t events_discarded;
625 uint32_t cpu_id;
626 uint32_t/uint16_t content_size;
627 uint32_t/uint16_t packet_size;
628 uint8_t stream_packet_count_bits; /* Significant counter bits */
629 uint8_t compression_scheme;
630 uint8_t encryption_scheme;
3b0f8e4d 631 uint8_t checksum_scheme;
3bf79539 632};
5ba9f198 633
fcba70d4 634
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6356. Event Structure
636
637The overall structure of an event is:
638
fcba70d4 6391 - Stream Packet Context (as specified by the stream metadata)
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640 2 - Event Header (as specified by the stream metadata)
641 3 - Stream Event Context (as specified by the stream metadata)
642 4 - Event Context (as specified by the event metadata)
643 5 - Event Payload (as specified by the event metadata)
5ba9f198 644
fdf2bb05 645This structure defines an implicit dynamic scoping, where variants
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646located in inner structures (those with a higher number in the listing
647above) can refer to the fields of outer structures (with lower number in
6c7226e9 648the listing above). See Section 7.3 TSDL Scopes for more detail.
5ba9f198 649
fdf2bb05 6506.1 Event Header
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651
652Event headers can be described within the metadata. We hereby propose, as an
653example, two types of events headers. Type 1 accommodates streams with less than
65431 event IDs. Type 2 accommodates streams with 31 or more event IDs.
5ba9f198 655
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656One major factor can vary between streams: the number of event IDs assigned to
657a stream. Luckily, this information tends to stay relatively constant (modulo
5ba9f198 658event registration while trace is being recorded), so we can specify different
3bf79539 659representations for streams containing few event IDs and streams containing
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660many event IDs, so we end up representing the event ID and timestamp as densely
661as possible in each case.
662
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663The header is extended in the rare occasions where the information cannot be
664represented in the ranges available in the standard event header. They are also
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665used in the rare occasions where the data required for a field could not be
666collected: the flag corresponding to the missing field within the missing_fields
667array is then set to 1.
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668
669Types uintX_t represent an X-bit unsigned integer.
670
671
fdf2bb05 6726.1.1 Type 1 - Few event IDs
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673
674 - Aligned on 32-bit (or 8-bit if byte-packed, depending on the architecture
675 preference).
5ba9f198 676 - Native architecture byte ordering.
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677 - For "compact" selection
678 - Fixed size: 32 bits.
679 - For "extended" selection
680 - Size depends on the architecture and variant alignment.
5ba9f198 681
80fd2569 682struct event_header_1 {
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683 /*
684 * id: range: 0 - 30.
685 * id 31 is reserved to indicate an extended header.
686 */
a9b83695 687 enum : uint5_t { compact = 0 ... 30, extended = 31 } id;
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688 variant <id> {
689 struct {
690 uint27_t timestamp;
691 } compact;
692 struct {
693 uint32_t id; /* 32-bit event IDs */
694 uint64_t timestamp; /* 64-bit timestamps */
695 } extended;
696 } v;
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697};
698
5ba9f198 699
fdf2bb05 7006.1.2 Type 2 - Many event IDs
5ba9f198 701
fcba70d4 702 - Aligned on 16-bit (or 8-bit if byte-packed, depending on the architecture
5ba9f198 703 preference).
5ba9f198 704 - Native architecture byte ordering.
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705 - For "compact" selection
706 - Size depends on the architecture and variant alignment.
707 - For "extended" selection
708 - Size depends on the architecture and variant alignment.
5ba9f198 709
80fd2569 710struct event_header_2 {
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711 /*
712 * id: range: 0 - 65534.
713 * id 65535 is reserved to indicate an extended header.
714 */
a9b83695 715 enum : uint16_t { compact = 0 ... 65534, extended = 65535 } id;
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716 variant <id> {
717 struct {
718 uint32_t timestamp;
719 } compact;
720 struct {
721 uint32_t id; /* 32-bit event IDs */
722 uint64_t timestamp; /* 64-bit timestamps */
723 } extended;
724 } v;
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725};
726
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727
7286.2 Event Context
729
730The event context contains information relative to the current event. The choice
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731and meaning of this information is specified by the metadata "stream" and
732"event" information. The "stream" context is applied to all events within the
733stream. The "stream" context structure follows the event header. The "event"
734context is applied to specific events. Its structure follows the "stream"
735context stucture.
5ba9f198 736
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737An example of stream-level event context is to save the event payload size with
738each event, or to save the current PID with each event. These are declared
739within the stream declaration within the metadata:
5ba9f198 740
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741 stream {
742 ...
743 event {
744 ...
4fa992a5 745 context := struct {
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746 uint pid;
747 uint16_t payload_size;
3bf79539 748 };
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749 }
750 };
751
752An example of event-specific event context is to declare a bitmap of missing
753fields, only appended after the stream event context if the extended event
754header is selected. NR_FIELDS is the number of fields within the event (a
755numeric value).
5ba9f198 756
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757 event {
758 context = struct {
759 variant <id> {
760 struct { } compact;
761 struct {
762 uint1_t missing_fields[NR_FIELDS]; /* missing event fields bitmap */
763 } extended;
764 } v;
765 };
766 ...
767 }
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768
7696.3 Event Payload
770
771An event payload contains fields specific to a given event type. The fields
772belonging to an event type are described in the event-specific metadata
773within a structure type.
774
7756.3.1 Padding
776
777No padding at the end of the event payload. This differs from the ISO/C standard
778for structures, but follows the CTF standard for structures. In a trace, even
779though it makes sense to align the beginning of a structure, it really makes no
780sense to add padding at the end of the structure, because structures are usually
781not followed by a structure of the same type.
782
783This trick can be done by adding a zero-length "end" field at the end of the C
784structures, and by using the offset of this field rather than using sizeof()
3bf79539 785when calculating the size of a structure (see Appendix "A. Helper macros").
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786
7876.3.2 Alignment
788
789The event payload is aligned on the largest alignment required by types
790contained within the payload. (This follows the ISO/C standard for structures)
791
792
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7937. Trace Stream Description Language (TSDL)
794
795The Trace Stream Description Language (TSDL) allows expression of the
796binary trace streams layout in a C99-like Domain Specific Language
797(DSL).
798
799
8007.1 Metadata
801
802The trace stream layout description is located in the trace meta-data.
803The meta-data is itself located in a stream identified by its name:
804"metadata".
5ba9f198 805
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806It is made of "event packets", which each start with an event packet
807header. The event type within the metadata stream have no event header
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808nor event context. Each event only contains a "string" payload without
809any null-character. The events are packed one next to another. Each
810event packet start with an event packet header, which contains, amongst
811other fields, the magic number, trace UUID and packet length. In the
812event packet header, the trace UUID is represented as an array of bytes.
813Within the string-based metadata description, the trace UUID is
814represented as a string of hexadecimal digits and dashes "-".
4fafe1ad 815
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816The metadata can be parsed by reading characters within the metadata
817stream, for each packet starting after the packet header, for the length
818of the packet payload specified in the header. Text contained within
819"/*" and "*/", as well as within "//" and end of line, are treated as
820comments. Boolean values can be represented as true, TRUE, or 1 for
821true, and false, FALSE, or 0 for false.
fcba70d4 822
fdf2bb05 823
6c7226e9 8247.2 Declaration vs Definition
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825
826A declaration associates a layout to a type, without specifying where
827this type is located in the event structure hierarchy (see Section 6).
828This therefore includes typedef, typealias, as well as all type
829specifiers. In certain circumstances (typedef, structure field and
830variant field), a declaration is followed by a declarator, which specify
831the newly defined type name (for typedef), or the field name (for
832declarations located within structure and variants). Array and sequence,
833declared with square brackets ("[" "]"), are part of the declarator,
a9b83695 834similarly to C99. The enumeration base type is specified by
6c7226e9 835": enum_base", which is part of the type specifier. The variant tag
a9b83695 836name, specified between "<" ">", is also part of the type specifier.
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837
838A definition associates a type to a location in the event structure
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839hierarchy (see Section 6). This association is denoted by ":=", as shown
840in Section 7.3.
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841
842
6c7226e9 8437.3 TSDL Scopes
fdf2bb05 844
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845TSDL uses two different types of scoping: a lexical scope is used for
846declarations and type definitions, and a dynamic scope is used for
847variants references to tag fields.
fdf2bb05 848
6c7226e9 8497.3.1 Lexical Scope
fdf2bb05 850
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851Each of "trace", "stream", "event", "struct" and "variant" have their own
852nestable declaration scope, within which types can be declared using "typedef"
fdf2bb05 853and "typealias". A root declaration scope also contains all declarations
7d9d7e92 854located outside of any of the aforementioned declarations. An inner
fdf2bb05 855declaration scope can refer to type declared within its container
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856lexical scope prior to the inner declaration scope. Redefinition of a
857typedef or typealias is not valid, although hiding an upper scope
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858typedef or typealias is allowed within a sub-scope.
859
6c7226e9 8607.3.2 Dynamic Scope
fdf2bb05 861
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862A dynamic scope consists in the lexical scope augmented with the
863implicit event structure definition hierarchy presented at Section 6.
864The dynamic scope is only used for variant tag definitions. It is used
865at definition time to look up the location of the tag field associated
866with a variant.
867
868Therefore, variants in lower levels in the dynamic scope (e.g. event
869context) can refer to a tag field located in upper levels (e.g. in the
870event header) by specifying, in this case, the associated tag with
871<header.field_name>. This allows, for instance, the event context to
872define a variant referring to the "id" field of the event header as
873selector.
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874
875The target dynamic scope must be specified explicitly when referring to
876a field outside of the local static scope. The dynamic scope prefixes
877are thus:
878
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879 - Stream Packet Context: <stream.packet.context. >,
880 - Event Header: <stream.event.header. >,
881 - Stream Event Context: <stream.event.context. >,
882 - Event Context: <event.context. >,
883 - Event Payload: <event.fields. >.
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884
885Multiple declarations of the same field name within a single scope is
886not valid. It is however valid to re-use the same field name in
887different scopes. There is no possible conflict, because the dynamic
888scope must be specified when a variant refers to a tag field located in
889a different dynamic scope.
890
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891The information available in the dynamic scopes can be thought of as the
892current tracing context. At trace production, information about the
893current context is saved into the specified scope field levels. At trace
894consumption, for each event, the current trace context is therefore
895readable by accessing the upper dynamic scopes.
896
fdf2bb05 897
6c7226e9 8987.4 TSDL Examples
d285084f 899
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900The grammar representing the TSDL metadata is presented in Appendix C.
901TSDL Grammar. This section presents a rather ligher reading that
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902consists in examples of TSDL metadata, with template values.
903
904Note that the trace endianness is usually extracted from the packet
905header magic number. The "endian" field is only needed when the magic
906number packet header field is not present.
5ba9f198 907
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908The stream "id" can be left out if there is only one stream in the
909trace. The event "id" field can be left out if there is only one event
910in a stream.
911
5ba9f198 912trace {
fdf2bb05 913 major = value; /* Trace format version */
5ba9f198 914 minor = value;
fdf2bb05 915 uuid = "aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaaa"; /* Trace UUID */
969f30c0 916 endian = big OR little; /* Endianness (optional) */
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917 packet.header := struct {
918 uint32_t magic;
919 uint8_t trace_uuid[16];
920 uint32_t stream_id;
921 };
3bf79539 922};
5ba9f198 923
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924stream {
925 id = stream_id;
fdf2bb05 926 /* Type 1 - Few event IDs; Type 2 - Many event IDs. See section 6.1. */
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927 event.header := event_header_1 OR event_header_2;
928 event.context := struct {
77a98c82 929 ...
3bf79539 930 };
4fa992a5 931 packet.context := struct {
77a98c82 932 ...
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933 };
934};
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935
936event {
3d13ef1a 937 name = event_name;
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938 id = value; /* Numeric identifier within the stream */
939 stream = stream_id;
4fa992a5 940 context := struct {
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941 ...
942 };
4fa992a5 943 fields := struct {
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944 ...
945 };
3bf79539 946};
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947
948/* More detail on types in section 4. Types */
949
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950/*
951 * Named types:
952 *
4fa992a5 953 * Type declarations behave similarly to the C standard.
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954 */
955
80af8ac6 956typedef aliased_type_specifiers new_type_declarators;
2152348f 957
3d13ef1a 958/* e.g.: typedef struct example new_type_name[10]; */
80fd2569 959
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960/*
961 * typealias
962 *
963 * The "typealias" declaration can be used to give a name (including
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964 * pointer declarator specifier) to a type. It should also be used to
965 * map basic C types (float, int, unsigned long, ...) to a CTF type.
966 * Typealias is a superset of "typedef": it also allows assignment of a
38b8da21 967 * simple variable identifier to a type.
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968 */
969
970typealias type_class {
80fd2569 971 ...
38b8da21 972} := type_specifiers type_declarator;
2152348f 973
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974/*
975 * e.g.:
4fa992a5 976 * typealias integer {
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977 * size = 32;
978 * align = 32;
979 * signed = false;
38b8da21 980 * } := struct page *;
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981 *
982 * typealias integer {
983 * size = 32;
984 * align = 32;
985 * signed = true;
38b8da21 986 * } := int;
3d13ef1a 987 */
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988
989struct name {
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990 ...
991};
5ba9f198 992
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993variant name {
994 ...
995};
996
a9b83695 997enum name : integer_type {
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998 ...
999};
1000
2152348f 1001
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1002/*
1003 * Unnamed types, contained within compound type fields, typedef or typealias.
1004 */
2152348f 1005
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1006struct {
1007 ...
2152348f 1008}
5ba9f198 1009
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1010variant {
1011 ...
1012}
1013
a9b83695 1014enum : integer_type {
80fd2569 1015 ...
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1016}
1017
1018typedef type new_type[length];
3bf79539 1019
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1020struct {
1021 type field_name[length];
1022}
1023
1024typedef type new_type[length_type];
1025
1026struct {
1027 type field_name[length_type];
1028}
1029
1030integer {
80fd2569 1031 ...
2152348f 1032}
3bf79539 1033
2152348f 1034floating_point {
80fd2569 1035 ...
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1036}
1037
1038struct {
1039 integer_type field_name:size; /* GNU/C bitfield */
1040}
1041
1042struct {
1043 string field_name;
1044}
3bf79539 1045
fcba70d4 1046
3bf79539 1047A. Helper macros
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1048
1049The two following macros keep track of the size of a GNU/C structure without
1050padding at the end by placing HEADER_END as the last field. A one byte end field
1051is used for C90 compatibility (C99 flexible arrays could be used here). Note
1052that this does not affect the effective structure size, which should always be
1053calculated with the header_sizeof() helper.
1054
1055#define HEADER_END char end_field
1056#define header_sizeof(type) offsetof(typeof(type), end_field)
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1057
1058
1059B. Stream Header Rationale
1060
1061An event stream is divided in contiguous event packets of variable size. These
1062subdivisions allow the trace analyzer to perform a fast binary search by time
1063within the stream (typically requiring to index only the event packet headers)
1064without reading the whole stream. These subdivisions have a variable size to
1065eliminate the need to transfer the event packet padding when partially filled
1066event packets must be sent when streaming a trace for live viewing/analysis.
1067An event packet can contain a certain amount of padding at the end. Dividing
1068streams into event packets is also useful for network streaming over UDP and
1069flight recorder mode tracing (a whole event packet can be swapped out of the
1070buffer atomically for reading).
1071
1072The stream header is repeated at the beginning of each event packet to allow
1073flexibility in terms of:
1074
1075 - streaming support,
1076 - allowing arbitrary buffers to be discarded without making the trace
1077 unreadable,
1078 - allow UDP packet loss handling by either dealing with missing event packet
1079 or asking for re-transmission.
1080 - transparently support flight recorder mode,
1081 - transparently support crash dump.
1082
1083The event stream header will therefore be referred to as the "event packet
1084header" throughout the rest of this document.
fcba70d4 1085
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1086
1087C. TSDL Grammar
fcba70d4 1088
4fa992a5 1089/*
6c7226e9 1090 * Common Trace Format (CTF) Trace Stream Description Language (TSDL) Grammar.
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1091 *
1092 * Inspired from the C99 grammar:
1093 * http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1124.pdf (Annex A)
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1094 * and c++1x grammar (draft)
1095 * http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2011/n3291.pdf (Annex A)
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1096 *
1097 * Specialized for CTF needs by including only constant and declarations from
1098 * C99 (excluding function declarations), and by adding support for variants,
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1099 * sequences and CTF-specific specifiers. Enumeration container types
1100 * semantic is inspired from c++1x enum-base.
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1101 */
1102
11031) Lexical grammar
1104
11051.1) Lexical elements
1106
1107token:
1108 keyword
1109 identifier
1110 constant
1111 string-literal
1112 punctuator
1113
11141.2) Keywords
1115
1116keyword: is one of
1117
1118const
1119char
1120double
1121enum
1122event
1123floating_point
1124float
1125integer
1126int
1127long
1128short
1129signed
1130stream
1131string
1132struct
1133trace
3e1e1a78 1134typealias
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1135typedef
1136unsigned
1137variant
1138void
1139_Bool
1140_Complex
1141_Imaginary
1142
1143
11441.3) Identifiers
1145
1146identifier:
1147 identifier-nondigit
1148 identifier identifier-nondigit
1149 identifier digit
1150
1151identifier-nondigit:
1152 nondigit
1153 universal-character-name
1154 any other implementation-defined characters
1155
1156nondigit:
1157 _
1158 [a-zA-Z] /* regular expression */
1159
1160digit:
1161 [0-9] /* regular expression */
1162
11631.4) Universal character names
1164
1165universal-character-name:
1166 \u hex-quad
1167 \U hex-quad hex-quad
1168
1169hex-quad:
1170 hexadecimal-digit hexadecimal-digit hexadecimal-digit hexadecimal-digit
1171
11721.5) Constants
1173
1174constant:
1175 integer-constant
1176 enumeration-constant
1177 character-constant
1178
1179integer-constant:
1180 decimal-constant integer-suffix-opt
1181 octal-constant integer-suffix-opt
1182 hexadecimal-constant integer-suffix-opt
1183
1184decimal-constant:
1185 nonzero-digit
1186 decimal-constant digit
1187
1188octal-constant:
1189 0
1190 octal-constant octal-digit
1191
1192hexadecimal-constant:
1193 hexadecimal-prefix hexadecimal-digit
1194 hexadecimal-constant hexadecimal-digit
1195
1196hexadecimal-prefix:
1197 0x
1198 0X
1199
1200nonzero-digit:
1201 [1-9]
1202
1203integer-suffix:
1204 unsigned-suffix long-suffix-opt
1205 unsigned-suffix long-long-suffix
1206 long-suffix unsigned-suffix-opt
1207 long-long-suffix unsigned-suffix-opt
1208
1209unsigned-suffix:
1210 u
1211 U
1212
1213long-suffix:
1214 l
1215 L
1216
1217long-long-suffix:
1218 ll
1219 LL
1220
1221digit-sequence:
1222 digit
1223 digit-sequence digit
1224
1225hexadecimal-digit-sequence:
1226 hexadecimal-digit
1227 hexadecimal-digit-sequence hexadecimal-digit
1228
1229enumeration-constant:
1230 identifier
1231 string-literal
1232
1233character-constant:
1234 ' c-char-sequence '
1235 L' c-char-sequence '
1236
1237c-char-sequence:
1238 c-char
1239 c-char-sequence c-char
1240
1241c-char:
1242 any member of source charset except single-quote ('), backslash
1243 (\), or new-line character.
1244 escape-sequence
1245
1246escape-sequence:
1247 simple-escape-sequence
1248 octal-escape-sequence
1249 hexadecimal-escape-sequence
1250 universal-character-name
1251
1252simple-escape-sequence: one of
1253 \' \" \? \\ \a \b \f \n \r \t \v
1254
1255octal-escape-sequence:
1256 \ octal-digit
1257 \ octal-digit octal-digit
1258 \ octal-digit octal-digit octal-digit
1259
1260hexadecimal-escape-sequence:
1261 \x hexadecimal-digit
1262 hexadecimal-escape-sequence hexadecimal-digit
1263
12641.6) String literals
1265
1266string-literal:
1267 " s-char-sequence-opt "
1268 L" s-char-sequence-opt "
1269
1270s-char-sequence:
1271 s-char
1272 s-char-sequence s-char
1273
1274s-char:
1275 any member of source charset except double-quote ("), backslash
1276 (\), or new-line character.
1277 escape-sequence
1278
12791.7) Punctuators
1280
1281punctuator: one of
1282 [ ] ( ) { } . -> * + - < > : ; ... = ,
1283
1284
12852) Phrase structure grammar
1286
1287primary-expression:
1288 identifier
1289 constant
1290 string-literal
1291 ( unary-expression )
1292
1293postfix-expression:
1294 primary-expression
1295 postfix-expression [ unary-expression ]
1296 postfix-expression . identifier
1297 postfix-expressoin -> identifier
1298
1299unary-expression:
1300 postfix-expression
1301 unary-operator postfix-expression
1302
1303unary-operator: one of
1304 + -
1305
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1306assignment-operator:
1307 =
1308
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1309type-assignment-operator:
1310 :=
1311
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1312constant-expression:
1313 unary-expression
1314
1315constant-expression-range:
1316 constant-expression ... constant-expression
1317
13182.2) Declarations:
1319
1320declaration:
689e04b4 1321 declaration-specifiers declarator-list-opt ;
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1322 ctf-specifier ;
1323
1324declaration-specifiers:
689e04b4 1325 storage-class-specifier declaration-specifiers-opt
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1326 type-specifier declaration-specifiers-opt
1327 type-qualifier declaration-specifiers-opt
1328
1329declarator-list:
1330 declarator
1331 declarator-list , declarator
1332
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1333abstract-declarator-list:
1334 abstract-declarator
1335 abstract-declarator-list , abstract-declarator
1336
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1337storage-class-specifier:
1338 typedef
1339
1340type-specifier:
1341 void
1342 char
1343 short
1344 int
1345 long
1346 float
1347 double
1348 signed
1349 unsigned
1350 _Bool
1351 _Complex
cfdd51ec 1352 _Imaginary
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1353 struct-specifier
1354 variant-specifier
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1355 enum-specifier
1356 typedef-name
1357 ctf-type-specifier
1358
1359struct-specifier:
3b0f8e4d 1360 struct identifier-opt { struct-or-variant-declaration-list-opt }
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1361 struct identifier
1362
1363struct-or-variant-declaration-list:
1364 struct-or-variant-declaration
1365 struct-or-variant-declaration-list struct-or-variant-declaration
1366
1367struct-or-variant-declaration:
1368 specifier-qualifier-list struct-or-variant-declarator-list ;
550aca33 1369 declaration-specifiers storage-class-specifier declaration-specifiers declarator-list ;
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1370 typealias declaration-specifiers abstract-declarator-list := declaration-specifiers abstract-declarator-list ;
1371 typealias declaration-specifiers abstract-declarator-list := declarator-list ;
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1372
1373specifier-qualifier-list:
1374 type-specifier specifier-qualifier-list-opt
1375 type-qualifier specifier-qualifier-list-opt
1376
1377struct-or-variant-declarator-list:
1378 struct-or-variant-declarator
1379 struct-or-variant-declarator-list , struct-or-variant-declarator
1380
1381struct-or-variant-declarator:
1382 declarator
1383 declarator-opt : constant-expression
1384
1385variant-specifier:
1386 variant identifier-opt variant-tag-opt { struct-or-variant-declaration-list }
1387 variant identifier variant-tag
1388
1389variant-tag:
1390 < identifier >
1391
1392enum-specifier:
1393 enum identifier-opt { enumerator-list }
1394 enum identifier-opt { enumerator-list , }
1395 enum identifier
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1396 enum identifier-opt : declaration-specifiers { enumerator-list }
1397 enum identifier-opt : declaration-specifiers { enumerator-list , }
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1398
1399enumerator-list:
1400 enumerator
1401 enumerator-list , enumerator
1402
1403enumerator:
1404 enumeration-constant
1405 enumeration-constant = constant-expression
1406 enumeration-constant = constant-expression-range
1407
1408type-qualifier:
1409 const
1410
1411declarator:
1412 pointer-opt direct-declarator
1413
1414direct-declarator:
1415 identifier
1416 ( declarator )
1417 direct-declarator [ type-specifier ]
1418 direct-declarator [ constant-expression ]
1419
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1420abstract-declarator:
1421 pointer-opt direct-abstract-declarator
1422
1423direct-abstract-declarator:
1424 identifier-opt
1425 ( abstract-declarator )
1426 direct-abstract-declarator [ type-specifier ]
1427 direct-abstract-declarator [ constant-expression ]
1428 direct-abstract-declarator [ ]
1429
4fa992a5 1430pointer:
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1431 * type-qualifier-list-opt
1432 * type-qualifier-list-opt pointer
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1433
1434type-qualifier-list:
1435 type-qualifier
1436 type-qualifier-list type-qualifier
1437
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1438typedef-name:
1439 identifier
1440
14412.3) CTF-specific declarations
1442
1443ctf-specifier:
1444 event { ctf-assignment-expression-list-opt }
1445 stream { ctf-assignment-expression-list-opt }
1446 trace { ctf-assignment-expression-list-opt }
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1447 typealias declaration-specifiers abstract-declarator-list := declaration-specifiers abstract-declarator-list ;
1448 typealias declaration-specifiers abstract-declarator-list := declarator-list ;
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1449
1450ctf-type-specifier:
1451 floating_point { ctf-assignment-expression-list-opt }
1452 integer { ctf-assignment-expression-list-opt }
1453 string { ctf-assignment-expression-list-opt }
1454
1455ctf-assignment-expression-list:
1456 ctf-assignment-expression
1457 ctf-assignment-expression-list ; ctf-assignment-expression
1458
1459ctf-assignment-expression:
1460 unary-expression assignment-operator unary-expression
1461 unary-expression type-assignment-operator type-specifier
550aca33 1462 declaration-specifiers storage-class-specifier declaration-specifiers declarator-list
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1463 typealias declaration-specifiers abstract-declarator-list := declaration-specifiers abstract-declarator-list
1464 typealias declaration-specifiers abstract-declarator-list := declarator-list
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