fix typo
[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 number: 0xC1FC1FC1 This magic number specifies
534 that we use the CTF metadata description language described in this
535 document. Different magic numbers should be used for other metadata
536 description languages.
3bf79539 537- Trace UUID, used to ensure the event packet match the metadata used.
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538 (note: we cannot use a metadata checksum because metadata can be appended to
539 while tracing is active)
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540- Stream ID, used as reference to stream description in metadata.
541
542Metadata-defined layout (event packet context):
543
544- Event packet content size (in bytes).
545- Event packet size (in bytes, includes padding).
546- Event packet content checksum (optional). Checksum excludes the event packet
547 header.
548- Per-stream event packet sequence count (to deal with UDP packet loss). The
549 number of significant sequence counter bits should also be present, so
b11853af 550 wrap-arounds are dealt with correctly.
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551- Timestamp at the beginning and timestamp at the end of the event packet.
552 Both timestamps are written in the packet header, but sampled respectively
553 while (or before) writing the first event and while (or after) writing the
554 last event in the packet. The inclusive range between these timestamps should
555 include all event timestamps assigned to events contained within the packet.
5ba9f198 556- Events discarded count
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557 - Snapshot of a per-stream free-running counter, counting the number of
558 events discarded that were supposed to be written in the stream prior to
559 the first event in the event packet.
5ba9f198 560 * Note: producer-consumer buffer full condition should fill the current
3bf79539 561 event packet with padding so we know exactly where events have been
5ba9f198 562 discarded.
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563- Lossless compression scheme used for the event packet content. Applied
564 directly to raw data. New types of compression can be added in following
565 versions of the format.
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566 0: no compression scheme
567 1: bzip2
568 2: gzip
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569 3: xz
570- Cypher used for the event packet content. Applied after compression.
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571 0: no encryption
572 1: AES
3bf79539 573- Checksum scheme used for the event packet content. Applied after encryption.
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574 0: no checksum
575 1: md5
576 2: sha1
577 3: crc32
578
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5795.1 Event Packet Header Fixed Layout Description
580
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581The event packet header layout is indicated by the trace packet.header
582field. Here is an example structure type for the packet header with the
583fields typically expected:
584
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585struct event_packet_header {
586 uint32_t magic;
587 uint8_t trace_uuid[16];
3bf79539 588 uint32_t stream_id;
80fd2569 589};
5ba9f198 590
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591trace {
592 ...
593 packet.header := struct event_packet_header;
594};
595
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596If the trace_uuid is not present, no validation that the metadata
597actually corresponds to the stream is performed.
598
599If the stream_id packet header field is missing, the trace can only
600contain a single stream. Its "id" field can be left out, and its events
601don't need to declare a "stream_id" field.
602
603
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6045.2 Event Packet Context Description
605
606Event packet context example. These are declared within the stream declaration
607in the metadata. All these fields are optional except for "content_size" and
608"packet_size", which must be present in the context.
609
610An example event packet context type:
611
80fd2569 612struct event_packet_context {
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613 uint64_t timestamp_begin;
614 uint64_t timestamp_end;
615 uint32_t checksum;
616 uint32_t stream_packet_count;
617 uint32_t events_discarded;
618 uint32_t cpu_id;
619 uint32_t/uint16_t content_size;
620 uint32_t/uint16_t packet_size;
621 uint8_t stream_packet_count_bits; /* Significant counter bits */
622 uint8_t compression_scheme;
623 uint8_t encryption_scheme;
3b0f8e4d 624 uint8_t checksum_scheme;
3bf79539 625};
5ba9f198 626
fcba70d4 627
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6286. Event Structure
629
630The overall structure of an event is:
631
fcba70d4 6321 - Stream Packet Context (as specified by the stream metadata)
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633 2 - Event Header (as specified by the stream metadata)
634 3 - Stream Event Context (as specified by the stream metadata)
635 4 - Event Context (as specified by the event metadata)
636 5 - Event Payload (as specified by the event metadata)
5ba9f198 637
fdf2bb05 638This structure defines an implicit dynamic scoping, where variants
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639located in inner structures (those with a higher number in the listing
640above) can refer to the fields of outer structures (with lower number in
6c7226e9 641the listing above). See Section 7.3 TSDL Scopes for more detail.
5ba9f198 642
fdf2bb05 6436.1 Event Header
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644
645Event headers can be described within the metadata. We hereby propose, as an
646example, two types of events headers. Type 1 accommodates streams with less than
64731 event IDs. Type 2 accommodates streams with 31 or more event IDs.
5ba9f198 648
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649One major factor can vary between streams: the number of event IDs assigned to
650a stream. Luckily, this information tends to stay relatively constant (modulo
5ba9f198 651event registration while trace is being recorded), so we can specify different
3bf79539 652representations for streams containing few event IDs and streams containing
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653many event IDs, so we end up representing the event ID and timestamp as densely
654as possible in each case.
655
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656The header is extended in the rare occasions where the information cannot be
657represented in the ranges available in the standard event header. They are also
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658used in the rare occasions where the data required for a field could not be
659collected: the flag corresponding to the missing field within the missing_fields
660array is then set to 1.
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661
662Types uintX_t represent an X-bit unsigned integer.
663
664
fdf2bb05 6656.1.1 Type 1 - Few event IDs
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666
667 - Aligned on 32-bit (or 8-bit if byte-packed, depending on the architecture
668 preference).
5ba9f198 669 - Native architecture byte ordering.
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670 - For "compact" selection
671 - Fixed size: 32 bits.
672 - For "extended" selection
673 - Size depends on the architecture and variant alignment.
5ba9f198 674
80fd2569 675struct event_header_1 {
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676 /*
677 * id: range: 0 - 30.
678 * id 31 is reserved to indicate an extended header.
679 */
a9b83695 680 enum : uint5_t { compact = 0 ... 30, extended = 31 } id;
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681 variant <id> {
682 struct {
683 uint27_t timestamp;
684 } compact;
685 struct {
686 uint32_t id; /* 32-bit event IDs */
687 uint64_t timestamp; /* 64-bit timestamps */
688 } extended;
689 } v;
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690};
691
5ba9f198 692
fdf2bb05 6936.1.2 Type 2 - Many event IDs
5ba9f198 694
fcba70d4 695 - Aligned on 16-bit (or 8-bit if byte-packed, depending on the architecture
5ba9f198 696 preference).
5ba9f198 697 - Native architecture byte ordering.
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698 - For "compact" selection
699 - Size depends on the architecture and variant alignment.
700 - For "extended" selection
701 - Size depends on the architecture and variant alignment.
5ba9f198 702
80fd2569 703struct event_header_2 {
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704 /*
705 * id: range: 0 - 65534.
706 * id 65535 is reserved to indicate an extended header.
707 */
a9b83695 708 enum : uint16_t { compact = 0 ... 65534, extended = 65535 } id;
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709 variant <id> {
710 struct {
711 uint32_t timestamp;
712 } compact;
713 struct {
714 uint32_t id; /* 32-bit event IDs */
715 uint64_t timestamp; /* 64-bit timestamps */
716 } extended;
717 } v;
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718};
719
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720
7216.2 Event Context
722
723The event context contains information relative to the current event. The choice
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724and meaning of this information is specified by the metadata "stream" and
725"event" information. The "stream" context is applied to all events within the
726stream. The "stream" context structure follows the event header. The "event"
727context is applied to specific events. Its structure follows the "stream"
728context stucture.
5ba9f198 729
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730An example of stream-level event context is to save the event payload size with
731each event, or to save the current PID with each event. These are declared
732within the stream declaration within the metadata:
5ba9f198 733
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734 stream {
735 ...
736 event {
737 ...
4fa992a5 738 context := struct {
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739 uint pid;
740 uint16_t payload_size;
3bf79539 741 };
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742 }
743 };
744
745An example of event-specific event context is to declare a bitmap of missing
746fields, only appended after the stream event context if the extended event
747header is selected. NR_FIELDS is the number of fields within the event (a
748numeric value).
5ba9f198 749
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750 event {
751 context = struct {
752 variant <id> {
753 struct { } compact;
754 struct {
755 uint1_t missing_fields[NR_FIELDS]; /* missing event fields bitmap */
756 } extended;
757 } v;
758 };
759 ...
760 }
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761
7626.3 Event Payload
763
764An event payload contains fields specific to a given event type. The fields
765belonging to an event type are described in the event-specific metadata
766within a structure type.
767
7686.3.1 Padding
769
770No padding at the end of the event payload. This differs from the ISO/C standard
771for structures, but follows the CTF standard for structures. In a trace, even
772though it makes sense to align the beginning of a structure, it really makes no
773sense to add padding at the end of the structure, because structures are usually
774not followed by a structure of the same type.
775
776This trick can be done by adding a zero-length "end" field at the end of the C
777structures, and by using the offset of this field rather than using sizeof()
3bf79539 778when calculating the size of a structure (see Appendix "A. Helper macros").
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779
7806.3.2 Alignment
781
782The event payload is aligned on the largest alignment required by types
783contained within the payload. (This follows the ISO/C standard for structures)
784
785
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7867. Trace Stream Description Language (TSDL)
787
788The Trace Stream Description Language (TSDL) allows expression of the
789binary trace streams layout in a C99-like Domain Specific Language
790(DSL).
791
792
7937.1 Metadata
794
795The trace stream layout description is located in the trace meta-data.
796The meta-data is itself located in a stream identified by its name:
797"metadata".
5ba9f198 798
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799It is made of "event packets", which each start with an event packet
800header. The event type within the metadata stream have no event header
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801nor event context. Each event only contains a "string" payload without
802any null-character. The events are packed one next to another. Each
803event packet start with an event packet header, which contains, amongst
804other fields, the magic number, trace UUID and packet length. In the
805event packet header, the trace UUID is represented as an array of bytes.
806Within the string-based metadata description, the trace UUID is
807represented as a string of hexadecimal digits and dashes "-".
4fafe1ad 808
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809The metadata can be parsed by reading characters within the metadata
810stream, for each packet starting after the packet header, for the length
811of the packet payload specified in the header. Text contained within
812"/*" and "*/", as well as within "//" and end of line, are treated as
813comments. Boolean values can be represented as true, TRUE, or 1 for
814true, and false, FALSE, or 0 for false.
fcba70d4 815
fdf2bb05 816
6c7226e9 8177.2 Declaration vs Definition
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818
819A declaration associates a layout to a type, without specifying where
820this type is located in the event structure hierarchy (see Section 6).
821This therefore includes typedef, typealias, as well as all type
822specifiers. In certain circumstances (typedef, structure field and
823variant field), a declaration is followed by a declarator, which specify
824the newly defined type name (for typedef), or the field name (for
825declarations located within structure and variants). Array and sequence,
826declared with square brackets ("[" "]"), are part of the declarator,
a9b83695 827similarly to C99. The enumeration base type is specified by
6c7226e9 828": enum_base", which is part of the type specifier. The variant tag
a9b83695 829name, specified between "<" ">", is also part of the type specifier.
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830
831A definition associates a type to a location in the event structure
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832hierarchy (see Section 6). This association is denoted by ":=", as shown
833in Section 7.3.
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834
835
6c7226e9 8367.3 TSDL Scopes
fdf2bb05 837
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838TSDL uses two different types of scoping: a lexical scope is used for
839declarations and type definitions, and a dynamic scope is used for
840variants references to tag fields.
fdf2bb05 841
6c7226e9 8427.3.1 Lexical Scope
fdf2bb05 843
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844Each of "trace", "stream", "event", "struct" and "variant" have their own
845nestable declaration scope, within which types can be declared using "typedef"
fdf2bb05 846and "typealias". A root declaration scope also contains all declarations
7d9d7e92 847located outside of any of the aforementioned declarations. An inner
fdf2bb05 848declaration scope can refer to type declared within its container
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849lexical scope prior to the inner declaration scope. Redefinition of a
850typedef or typealias is not valid, although hiding an upper scope
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851typedef or typealias is allowed within a sub-scope.
852
6c7226e9 8537.3.2 Dynamic Scope
fdf2bb05 854
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855A dynamic scope consists in the lexical scope augmented with the
856implicit event structure definition hierarchy presented at Section 6.
857The dynamic scope is only used for variant tag definitions. It is used
858at definition time to look up the location of the tag field associated
859with a variant.
860
861Therefore, variants in lower levels in the dynamic scope (e.g. event
862context) can refer to a tag field located in upper levels (e.g. in the
863event header) by specifying, in this case, the associated tag with
864<header.field_name>. This allows, for instance, the event context to
865define a variant referring to the "id" field of the event header as
866selector.
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867
868The target dynamic scope must be specified explicitly when referring to
869a field outside of the local static scope. The dynamic scope prefixes
870are thus:
871
e0d9e2c7 872 - Trace Packet Header: <trace.packet.header. >,
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873 - Stream Packet Context: <stream.packet.context. >,
874 - Event Header: <stream.event.header. >,
875 - Stream Event Context: <stream.event.context. >,
876 - Event Context: <event.context. >,
877 - Event Payload: <event.fields. >.
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878
879Multiple declarations of the same field name within a single scope is
880not valid. It is however valid to re-use the same field name in
881different scopes. There is no possible conflict, because the dynamic
882scope must be specified when a variant refers to a tag field located in
883a different dynamic scope.
884
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885The information available in the dynamic scopes can be thought of as the
886current tracing context. At trace production, information about the
887current context is saved into the specified scope field levels. At trace
888consumption, for each event, the current trace context is therefore
889readable by accessing the upper dynamic scopes.
890
fdf2bb05 891
6c7226e9 8927.4 TSDL Examples
d285084f 893
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894The grammar representing the TSDL metadata is presented in Appendix C.
895TSDL Grammar. This section presents a rather ligher reading that
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896consists in examples of TSDL metadata, with template values.
897
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898The stream "id" can be left out if there is only one stream in the
899trace. The event "id" field can be left out if there is only one event
900in a stream.
901
5ba9f198 902trace {
fdf2bb05 903 major = value; /* Trace format version */
5ba9f198 904 minor = value;
fdf2bb05 905 uuid = "aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaaa"; /* Trace UUID */
58997e9e 906 byte_order = be OR le; /* Endianness (required) */
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907 packet.header := struct {
908 uint32_t magic;
909 uint8_t trace_uuid[16];
910 uint32_t stream_id;
911 };
3bf79539 912};
5ba9f198 913
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914stream {
915 id = stream_id;
fdf2bb05 916 /* Type 1 - Few event IDs; Type 2 - Many event IDs. See section 6.1. */
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917 event.header := event_header_1 OR event_header_2;
918 event.context := struct {
77a98c82 919 ...
3bf79539 920 };
4fa992a5 921 packet.context := struct {
77a98c82 922 ...
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923 };
924};
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925
926event {
3d13ef1a 927 name = event_name;
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928 id = value; /* Numeric identifier within the stream */
929 stream = stream_id;
4fa992a5 930 context := struct {
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931 ...
932 };
4fa992a5 933 fields := struct {
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934 ...
935 };
3bf79539 936};
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937
938/* More detail on types in section 4. Types */
939
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940/*
941 * Named types:
942 *
4fa992a5 943 * Type declarations behave similarly to the C standard.
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944 */
945
80af8ac6 946typedef aliased_type_specifiers new_type_declarators;
2152348f 947
3d13ef1a 948/* e.g.: typedef struct example new_type_name[10]; */
80fd2569 949
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950/*
951 * typealias
952 *
953 * The "typealias" declaration can be used to give a name (including
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954 * pointer declarator specifier) to a type. It should also be used to
955 * map basic C types (float, int, unsigned long, ...) to a CTF type.
956 * Typealias is a superset of "typedef": it also allows assignment of a
38b8da21 957 * simple variable identifier to a type.
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958 */
959
960typealias type_class {
80fd2569 961 ...
38b8da21 962} := type_specifiers type_declarator;
2152348f 963
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964/*
965 * e.g.:
4fa992a5 966 * typealias integer {
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967 * size = 32;
968 * align = 32;
969 * signed = false;
38b8da21 970 * } := struct page *;
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971 *
972 * typealias integer {
973 * size = 32;
974 * align = 32;
975 * signed = true;
38b8da21 976 * } := int;
3d13ef1a 977 */
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978
979struct name {
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980 ...
981};
5ba9f198 982
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983variant name {
984 ...
985};
986
a9b83695 987enum name : integer_type {
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988 ...
989};
990
2152348f 991
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992/*
993 * Unnamed types, contained within compound type fields, typedef or typealias.
994 */
2152348f 995
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996struct {
997 ...
2152348f 998}
5ba9f198 999
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1000variant {
1001 ...
1002}
1003
a9b83695 1004enum : integer_type {
80fd2569 1005 ...
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1006}
1007
1008typedef type new_type[length];
3bf79539 1009
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1010struct {
1011 type field_name[length];
1012}
1013
1014typedef type new_type[length_type];
1015
1016struct {
1017 type field_name[length_type];
1018}
1019
1020integer {
80fd2569 1021 ...
2152348f 1022}
3bf79539 1023
2152348f 1024floating_point {
80fd2569 1025 ...
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1026}
1027
1028struct {
1029 integer_type field_name:size; /* GNU/C bitfield */
1030}
1031
1032struct {
1033 string field_name;
1034}
3bf79539 1035
fcba70d4 1036
3bf79539 1037A. Helper macros
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1038
1039The two following macros keep track of the size of a GNU/C structure without
1040padding at the end by placing HEADER_END as the last field. A one byte end field
1041is used for C90 compatibility (C99 flexible arrays could be used here). Note
1042that this does not affect the effective structure size, which should always be
1043calculated with the header_sizeof() helper.
1044
1045#define HEADER_END char end_field
1046#define header_sizeof(type) offsetof(typeof(type), end_field)
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1047
1048
1049B. Stream Header Rationale
1050
1051An event stream is divided in contiguous event packets of variable size. These
1052subdivisions allow the trace analyzer to perform a fast binary search by time
1053within the stream (typically requiring to index only the event packet headers)
1054without reading the whole stream. These subdivisions have a variable size to
1055eliminate the need to transfer the event packet padding when partially filled
1056event packets must be sent when streaming a trace for live viewing/analysis.
1057An event packet can contain a certain amount of padding at the end. Dividing
1058streams into event packets is also useful for network streaming over UDP and
1059flight recorder mode tracing (a whole event packet can be swapped out of the
1060buffer atomically for reading).
1061
1062The stream header is repeated at the beginning of each event packet to allow
1063flexibility in terms of:
1064
1065 - streaming support,
1066 - allowing arbitrary buffers to be discarded without making the trace
1067 unreadable,
1068 - allow UDP packet loss handling by either dealing with missing event packet
1069 or asking for re-transmission.
1070 - transparently support flight recorder mode,
1071 - transparently support crash dump.
1072
1073The event stream header will therefore be referred to as the "event packet
1074header" throughout the rest of this document.
fcba70d4 1075
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1076
1077C. TSDL Grammar
fcba70d4 1078
4fa992a5 1079/*
6c7226e9 1080 * Common Trace Format (CTF) Trace Stream Description Language (TSDL) Grammar.
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1081 *
1082 * Inspired from the C99 grammar:
1083 * http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1124.pdf (Annex A)
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1084 * and c++1x grammar (draft)
1085 * http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2011/n3291.pdf (Annex A)
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1086 *
1087 * Specialized for CTF needs by including only constant and declarations from
1088 * C99 (excluding function declarations), and by adding support for variants,
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1089 * sequences and CTF-specific specifiers. Enumeration container types
1090 * semantic is inspired from c++1x enum-base.
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1091 */
1092
10931) Lexical grammar
1094
10951.1) Lexical elements
1096
1097token:
1098 keyword
1099 identifier
1100 constant
1101 string-literal
1102 punctuator
1103
11041.2) Keywords
1105
1106keyword: is one of
1107
1108const
1109char
1110double
1111enum
1112event
1113floating_point
1114float
1115integer
1116int
1117long
1118short
1119signed
1120stream
1121string
1122struct
1123trace
3e1e1a78 1124typealias
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1125typedef
1126unsigned
1127variant
1128void
1129_Bool
1130_Complex
1131_Imaginary
1132
1133
11341.3) Identifiers
1135
1136identifier:
1137 identifier-nondigit
1138 identifier identifier-nondigit
1139 identifier digit
1140
1141identifier-nondigit:
1142 nondigit
1143 universal-character-name
1144 any other implementation-defined characters
1145
1146nondigit:
1147 _
1148 [a-zA-Z] /* regular expression */
1149
1150digit:
1151 [0-9] /* regular expression */
1152
11531.4) Universal character names
1154
1155universal-character-name:
1156 \u hex-quad
1157 \U hex-quad hex-quad
1158
1159hex-quad:
1160 hexadecimal-digit hexadecimal-digit hexadecimal-digit hexadecimal-digit
1161
11621.5) Constants
1163
1164constant:
1165 integer-constant
1166 enumeration-constant
1167 character-constant
1168
1169integer-constant:
1170 decimal-constant integer-suffix-opt
1171 octal-constant integer-suffix-opt
1172 hexadecimal-constant integer-suffix-opt
1173
1174decimal-constant:
1175 nonzero-digit
1176 decimal-constant digit
1177
1178octal-constant:
1179 0
1180 octal-constant octal-digit
1181
1182hexadecimal-constant:
1183 hexadecimal-prefix hexadecimal-digit
1184 hexadecimal-constant hexadecimal-digit
1185
1186hexadecimal-prefix:
1187 0x
1188 0X
1189
1190nonzero-digit:
1191 [1-9]
1192
1193integer-suffix:
1194 unsigned-suffix long-suffix-opt
1195 unsigned-suffix long-long-suffix
1196 long-suffix unsigned-suffix-opt
1197 long-long-suffix unsigned-suffix-opt
1198
1199unsigned-suffix:
1200 u
1201 U
1202
1203long-suffix:
1204 l
1205 L
1206
1207long-long-suffix:
1208 ll
1209 LL
1210
1211digit-sequence:
1212 digit
1213 digit-sequence digit
1214
1215hexadecimal-digit-sequence:
1216 hexadecimal-digit
1217 hexadecimal-digit-sequence hexadecimal-digit
1218
1219enumeration-constant:
1220 identifier
1221 string-literal
1222
1223character-constant:
1224 ' c-char-sequence '
1225 L' c-char-sequence '
1226
1227c-char-sequence:
1228 c-char
1229 c-char-sequence c-char
1230
1231c-char:
1232 any member of source charset except single-quote ('), backslash
1233 (\), or new-line character.
1234 escape-sequence
1235
1236escape-sequence:
1237 simple-escape-sequence
1238 octal-escape-sequence
1239 hexadecimal-escape-sequence
1240 universal-character-name
1241
1242simple-escape-sequence: one of
1243 \' \" \? \\ \a \b \f \n \r \t \v
1244
1245octal-escape-sequence:
1246 \ octal-digit
1247 \ octal-digit octal-digit
1248 \ octal-digit octal-digit octal-digit
1249
1250hexadecimal-escape-sequence:
1251 \x hexadecimal-digit
1252 hexadecimal-escape-sequence hexadecimal-digit
1253
12541.6) String literals
1255
1256string-literal:
1257 " s-char-sequence-opt "
1258 L" s-char-sequence-opt "
1259
1260s-char-sequence:
1261 s-char
1262 s-char-sequence s-char
1263
1264s-char:
1265 any member of source charset except double-quote ("), backslash
1266 (\), or new-line character.
1267 escape-sequence
1268
12691.7) Punctuators
1270
1271punctuator: one of
1272 [ ] ( ) { } . -> * + - < > : ; ... = ,
1273
1274
12752) Phrase structure grammar
1276
1277primary-expression:
1278 identifier
1279 constant
1280 string-literal
1281 ( unary-expression )
1282
1283postfix-expression:
1284 primary-expression
1285 postfix-expression [ unary-expression ]
1286 postfix-expression . identifier
1287 postfix-expressoin -> identifier
1288
1289unary-expression:
1290 postfix-expression
1291 unary-operator postfix-expression
1292
1293unary-operator: one of
1294 + -
1295
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1296assignment-operator:
1297 =
1298
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1299type-assignment-operator:
1300 :=
1301
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1302constant-expression:
1303 unary-expression
1304
1305constant-expression-range:
1306 constant-expression ... constant-expression
1307
13082.2) Declarations:
1309
1310declaration:
689e04b4 1311 declaration-specifiers declarator-list-opt ;
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1312 ctf-specifier ;
1313
1314declaration-specifiers:
689e04b4 1315 storage-class-specifier declaration-specifiers-opt
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1316 type-specifier declaration-specifiers-opt
1317 type-qualifier declaration-specifiers-opt
1318
1319declarator-list:
1320 declarator
1321 declarator-list , declarator
1322
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1323abstract-declarator-list:
1324 abstract-declarator
1325 abstract-declarator-list , abstract-declarator
1326
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1327storage-class-specifier:
1328 typedef
1329
1330type-specifier:
1331 void
1332 char
1333 short
1334 int
1335 long
1336 float
1337 double
1338 signed
1339 unsigned
1340 _Bool
1341 _Complex
cfdd51ec 1342 _Imaginary
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1343 struct-specifier
1344 variant-specifier
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1345 enum-specifier
1346 typedef-name
1347 ctf-type-specifier
1348
1349struct-specifier:
3b0f8e4d 1350 struct identifier-opt { struct-or-variant-declaration-list-opt }
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1351 struct identifier
1352
1353struct-or-variant-declaration-list:
1354 struct-or-variant-declaration
1355 struct-or-variant-declaration-list struct-or-variant-declaration
1356
1357struct-or-variant-declaration:
1358 specifier-qualifier-list struct-or-variant-declarator-list ;
550aca33 1359 declaration-specifiers storage-class-specifier declaration-specifiers declarator-list ;
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1360 typealias declaration-specifiers abstract-declarator-list := declaration-specifiers abstract-declarator-list ;
1361 typealias declaration-specifiers abstract-declarator-list := declarator-list ;
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1362
1363specifier-qualifier-list:
1364 type-specifier specifier-qualifier-list-opt
1365 type-qualifier specifier-qualifier-list-opt
1366
1367struct-or-variant-declarator-list:
1368 struct-or-variant-declarator
1369 struct-or-variant-declarator-list , struct-or-variant-declarator
1370
1371struct-or-variant-declarator:
1372 declarator
1373 declarator-opt : constant-expression
1374
1375variant-specifier:
1376 variant identifier-opt variant-tag-opt { struct-or-variant-declaration-list }
1377 variant identifier variant-tag
1378
1379variant-tag:
1380 < identifier >
1381
1382enum-specifier:
1383 enum identifier-opt { enumerator-list }
1384 enum identifier-opt { enumerator-list , }
1385 enum identifier
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1386 enum identifier-opt : declaration-specifiers { enumerator-list }
1387 enum identifier-opt : declaration-specifiers { enumerator-list , }
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1388
1389enumerator-list:
1390 enumerator
1391 enumerator-list , enumerator
1392
1393enumerator:
1394 enumeration-constant
1395 enumeration-constant = constant-expression
1396 enumeration-constant = constant-expression-range
1397
1398type-qualifier:
1399 const
1400
1401declarator:
1402 pointer-opt direct-declarator
1403
1404direct-declarator:
1405 identifier
1406 ( declarator )
1407 direct-declarator [ type-specifier ]
1408 direct-declarator [ constant-expression ]
1409
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1410abstract-declarator:
1411 pointer-opt direct-abstract-declarator
1412
1413direct-abstract-declarator:
1414 identifier-opt
1415 ( abstract-declarator )
1416 direct-abstract-declarator [ type-specifier ]
1417 direct-abstract-declarator [ constant-expression ]
1418 direct-abstract-declarator [ ]
1419
4fa992a5 1420pointer:
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1421 * type-qualifier-list-opt
1422 * type-qualifier-list-opt pointer
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1423
1424type-qualifier-list:
1425 type-qualifier
1426 type-qualifier-list type-qualifier
1427
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1428typedef-name:
1429 identifier
1430
14312.3) CTF-specific declarations
1432
1433ctf-specifier:
1434 event { ctf-assignment-expression-list-opt }
1435 stream { ctf-assignment-expression-list-opt }
1436 trace { ctf-assignment-expression-list-opt }
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1437 typealias declaration-specifiers abstract-declarator-list := declaration-specifiers abstract-declarator-list ;
1438 typealias declaration-specifiers abstract-declarator-list := declarator-list ;
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1439
1440ctf-type-specifier:
1441 floating_point { ctf-assignment-expression-list-opt }
1442 integer { ctf-assignment-expression-list-opt }
1443 string { ctf-assignment-expression-list-opt }
1444
1445ctf-assignment-expression-list:
1446 ctf-assignment-expression
1447 ctf-assignment-expression-list ; ctf-assignment-expression
1448
1449ctf-assignment-expression:
1450 unary-expression assignment-operator unary-expression
1451 unary-expression type-assignment-operator type-specifier
550aca33 1452 declaration-specifiers storage-class-specifier declaration-specifiers declarator-list
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1453 typealias declaration-specifiers abstract-declarator-list := declaration-specifiers abstract-declarator-list
1454 typealias declaration-specifiers abstract-declarator-list := declarator-list
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