Make struct event_packet_header explicitly declared
[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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6005.2 Event Packet Context Description
601
602Event packet context example. These are declared within the stream declaration
603in the metadata. All these fields are optional except for "content_size" and
604"packet_size", which must be present in the context.
605
606An example event packet context type:
607
80fd2569 608struct event_packet_context {
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609 uint64_t timestamp_begin;
610 uint64_t timestamp_end;
611 uint32_t checksum;
612 uint32_t stream_packet_count;
613 uint32_t events_discarded;
614 uint32_t cpu_id;
615 uint32_t/uint16_t content_size;
616 uint32_t/uint16_t packet_size;
617 uint8_t stream_packet_count_bits; /* Significant counter bits */
618 uint8_t compression_scheme;
619 uint8_t encryption_scheme;
3b0f8e4d 620 uint8_t checksum_scheme;
3bf79539 621};
5ba9f198 622
fcba70d4 623
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6246. Event Structure
625
626The overall structure of an event is:
627
fcba70d4 6281 - Stream Packet Context (as specified by the stream metadata)
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629 2 - Event Header (as specified by the stream metadata)
630 3 - Stream Event Context (as specified by the stream metadata)
631 4 - Event Context (as specified by the event metadata)
632 5 - Event Payload (as specified by the event metadata)
5ba9f198 633
fdf2bb05 634This structure defines an implicit dynamic scoping, where variants
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635located in inner structures (those with a higher number in the listing
636above) can refer to the fields of outer structures (with lower number in
6c7226e9 637the listing above). See Section 7.3 TSDL Scopes for more detail.
5ba9f198 638
fdf2bb05 6396.1 Event Header
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640
641Event headers can be described within the metadata. We hereby propose, as an
642example, two types of events headers. Type 1 accommodates streams with less than
64331 event IDs. Type 2 accommodates streams with 31 or more event IDs.
5ba9f198 644
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645One major factor can vary between streams: the number of event IDs assigned to
646a stream. Luckily, this information tends to stay relatively constant (modulo
5ba9f198 647event registration while trace is being recorded), so we can specify different
3bf79539 648representations for streams containing few event IDs and streams containing
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649many event IDs, so we end up representing the event ID and timestamp as densely
650as possible in each case.
651
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652The header is extended in the rare occasions where the information cannot be
653represented in the ranges available in the standard event header. They are also
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654used in the rare occasions where the data required for a field could not be
655collected: the flag corresponding to the missing field within the missing_fields
656array is then set to 1.
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657
658Types uintX_t represent an X-bit unsigned integer.
659
660
fdf2bb05 6616.1.1 Type 1 - Few event IDs
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662
663 - Aligned on 32-bit (or 8-bit if byte-packed, depending on the architecture
664 preference).
5ba9f198 665 - Native architecture byte ordering.
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666 - For "compact" selection
667 - Fixed size: 32 bits.
668 - For "extended" selection
669 - Size depends on the architecture and variant alignment.
5ba9f198 670
80fd2569 671struct event_header_1 {
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672 /*
673 * id: range: 0 - 30.
674 * id 31 is reserved to indicate an extended header.
675 */
a9b83695 676 enum : uint5_t { compact = 0 ... 30, extended = 31 } id;
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677 variant <id> {
678 struct {
679 uint27_t timestamp;
680 } compact;
681 struct {
682 uint32_t id; /* 32-bit event IDs */
683 uint64_t timestamp; /* 64-bit timestamps */
684 } extended;
685 } v;
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686};
687
5ba9f198 688
fdf2bb05 6896.1.2 Type 2 - Many event IDs
5ba9f198 690
fcba70d4 691 - Aligned on 16-bit (or 8-bit if byte-packed, depending on the architecture
5ba9f198 692 preference).
5ba9f198 693 - Native architecture byte ordering.
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694 - For "compact" selection
695 - Size depends on the architecture and variant alignment.
696 - For "extended" selection
697 - Size depends on the architecture and variant alignment.
5ba9f198 698
80fd2569 699struct event_header_2 {
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700 /*
701 * id: range: 0 - 65534.
702 * id 65535 is reserved to indicate an extended header.
703 */
a9b83695 704 enum : uint16_t { compact = 0 ... 65534, extended = 65535 } id;
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705 variant <id> {
706 struct {
707 uint32_t timestamp;
708 } compact;
709 struct {
710 uint32_t id; /* 32-bit event IDs */
711 uint64_t timestamp; /* 64-bit timestamps */
712 } extended;
713 } v;
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714};
715
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716
7176.2 Event Context
718
719The event context contains information relative to the current event. The choice
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720and meaning of this information is specified by the metadata "stream" and
721"event" information. The "stream" context is applied to all events within the
722stream. The "stream" context structure follows the event header. The "event"
723context is applied to specific events. Its structure follows the "stream"
724context stucture.
5ba9f198 725
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726An example of stream-level event context is to save the event payload size with
727each event, or to save the current PID with each event. These are declared
728within the stream declaration within the metadata:
5ba9f198 729
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730 stream {
731 ...
732 event {
733 ...
4fa992a5 734 context := struct {
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735 uint pid;
736 uint16_t payload_size;
3bf79539 737 };
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738 }
739 };
740
741An example of event-specific event context is to declare a bitmap of missing
742fields, only appended after the stream event context if the extended event
743header is selected. NR_FIELDS is the number of fields within the event (a
744numeric value).
5ba9f198 745
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746 event {
747 context = struct {
748 variant <id> {
749 struct { } compact;
750 struct {
751 uint1_t missing_fields[NR_FIELDS]; /* missing event fields bitmap */
752 } extended;
753 } v;
754 };
755 ...
756 }
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757
7586.3 Event Payload
759
760An event payload contains fields specific to a given event type. The fields
761belonging to an event type are described in the event-specific metadata
762within a structure type.
763
7646.3.1 Padding
765
766No padding at the end of the event payload. This differs from the ISO/C standard
767for structures, but follows the CTF standard for structures. In a trace, even
768though it makes sense to align the beginning of a structure, it really makes no
769sense to add padding at the end of the structure, because structures are usually
770not followed by a structure of the same type.
771
772This trick can be done by adding a zero-length "end" field at the end of the C
773structures, and by using the offset of this field rather than using sizeof()
3bf79539 774when calculating the size of a structure (see Appendix "A. Helper macros").
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775
7766.3.2 Alignment
777
778The event payload is aligned on the largest alignment required by types
779contained within the payload. (This follows the ISO/C standard for structures)
780
781
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7827. Trace Stream Description Language (TSDL)
783
784The Trace Stream Description Language (TSDL) allows expression of the
785binary trace streams layout in a C99-like Domain Specific Language
786(DSL).
787
788
7897.1 Metadata
790
791The trace stream layout description is located in the trace meta-data.
792The meta-data is itself located in a stream identified by its name:
793"metadata".
5ba9f198 794
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795It is made of "event packets", which each start with an event packet
796header. The event type within the metadata stream have no event header
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797nor event context. Each event only contains a "string" payload without
798any null-character. The events are packed one next to another. Each
799event packet start with an event packet header, which contains, amongst
800other fields, the magic number, trace UUID and packet length. In the
801event packet header, the trace UUID is represented as an array of bytes.
802Within the string-based metadata description, the trace UUID is
803represented as a string of hexadecimal digits and dashes "-".
4fafe1ad 804
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805The metadata can be parsed by reading characters within the metadata
806stream, for each packet starting after the packet header, for the length
807of the packet payload specified in the header. Text contained within
808"/*" and "*/", as well as within "//" and end of line, are treated as
809comments. Boolean values can be represented as true, TRUE, or 1 for
810true, and false, FALSE, or 0 for false.
fcba70d4 811
fdf2bb05 812
6c7226e9 8137.2 Declaration vs Definition
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814
815A declaration associates a layout to a type, without specifying where
816this type is located in the event structure hierarchy (see Section 6).
817This therefore includes typedef, typealias, as well as all type
818specifiers. In certain circumstances (typedef, structure field and
819variant field), a declaration is followed by a declarator, which specify
820the newly defined type name (for typedef), or the field name (for
821declarations located within structure and variants). Array and sequence,
822declared with square brackets ("[" "]"), are part of the declarator,
a9b83695 823similarly to C99. The enumeration base type is specified by
6c7226e9 824": enum_base", which is part of the type specifier. The variant tag
a9b83695 825name, specified between "<" ">", is also part of the type specifier.
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826
827A definition associates a type to a location in the event structure
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828hierarchy (see Section 6). This association is denoted by ":=", as shown
829in Section 7.3.
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830
831
6c7226e9 8327.3 TSDL Scopes
fdf2bb05 833
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834TSDL uses two different types of scoping: a lexical scope is used for
835declarations and type definitions, and a dynamic scope is used for
836variants references to tag fields.
fdf2bb05 837
6c7226e9 8387.3.1 Lexical Scope
fdf2bb05 839
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840Each of "trace", "stream", "event", "struct" and "variant" have their own
841nestable declaration scope, within which types can be declared using "typedef"
fdf2bb05 842and "typealias". A root declaration scope also contains all declarations
7d9d7e92 843located outside of any of the aforementioned declarations. An inner
fdf2bb05 844declaration scope can refer to type declared within its container
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845lexical scope prior to the inner declaration scope. Redefinition of a
846typedef or typealias is not valid, although hiding an upper scope
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847typedef or typealias is allowed within a sub-scope.
848
6c7226e9 8497.3.2 Dynamic Scope
fdf2bb05 850
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851A dynamic scope consists in the lexical scope augmented with the
852implicit event structure definition hierarchy presented at Section 6.
853The dynamic scope is only used for variant tag definitions. It is used
854at definition time to look up the location of the tag field associated
855with a variant.
856
857Therefore, variants in lower levels in the dynamic scope (e.g. event
858context) can refer to a tag field located in upper levels (e.g. in the
859event header) by specifying, in this case, the associated tag with
860<header.field_name>. This allows, for instance, the event context to
861define a variant referring to the "id" field of the event header as
862selector.
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863
864The target dynamic scope must be specified explicitly when referring to
865a field outside of the local static scope. The dynamic scope prefixes
866are thus:
867
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868 - Stream Packet Context: <stream.packet.context. >,
869 - Event Header: <stream.event.header. >,
870 - Stream Event Context: <stream.event.context. >,
871 - Event Context: <event.context. >,
872 - Event Payload: <event.fields. >.
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873
874Multiple declarations of the same field name within a single scope is
875not valid. It is however valid to re-use the same field name in
876different scopes. There is no possible conflict, because the dynamic
877scope must be specified when a variant refers to a tag field located in
878a different dynamic scope.
879
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880The information available in the dynamic scopes can be thought of as the
881current tracing context. At trace production, information about the
882current context is saved into the specified scope field levels. At trace
883consumption, for each event, the current trace context is therefore
884readable by accessing the upper dynamic scopes.
885
fdf2bb05 886
6c7226e9 8877.4 TSDL Examples
d285084f 888
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889The grammar representing the TSDL metadata is presented in Appendix C.
890TSDL Grammar. This section presents a rather ligher reading that
891consists in examples of TSDL metadata, with template values:
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892
893trace {
fdf2bb05 894 major = value; /* Trace format version */
5ba9f198 895 minor = value;
fdf2bb05 896 uuid = "aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaaa"; /* Trace UUID */
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897 packet.header := struct {
898 uint32_t magic;
899 uint8_t trace_uuid[16];
900 uint32_t stream_id;
901 };
3bf79539 902};
5ba9f198 903
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904stream {
905 id = stream_id;
fdf2bb05 906 /* Type 1 - Few event IDs; Type 2 - Many event IDs. See section 6.1. */
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907 event.header := event_header_1 OR event_header_2;
908 event.context := struct {
77a98c82 909 ...
3bf79539 910 };
4fa992a5 911 packet.context := struct {
77a98c82 912 ...
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913 };
914};
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915
916event {
3d13ef1a 917 name = event_name;
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918 id = value; /* Numeric identifier within the stream */
919 stream = stream_id;
4fa992a5 920 context := struct {
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921 ...
922 };
4fa992a5 923 fields := struct {
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924 ...
925 };
3bf79539 926};
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927
928/* More detail on types in section 4. Types */
929
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930/*
931 * Named types:
932 *
4fa992a5 933 * Type declarations behave similarly to the C standard.
3d13ef1a
MD
934 */
935
80af8ac6 936typedef aliased_type_specifiers new_type_declarators;
2152348f 937
3d13ef1a 938/* e.g.: typedef struct example new_type_name[10]; */
80fd2569 939
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940/*
941 * typealias
942 *
943 * The "typealias" declaration can be used to give a name (including
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944 * pointer declarator specifier) to a type. It should also be used to
945 * map basic C types (float, int, unsigned long, ...) to a CTF type.
946 * Typealias is a superset of "typedef": it also allows assignment of a
38b8da21 947 * simple variable identifier to a type.
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948 */
949
950typealias type_class {
80fd2569 951 ...
38b8da21 952} := type_specifiers type_declarator;
2152348f 953
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954/*
955 * e.g.:
4fa992a5 956 * typealias integer {
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MD
957 * size = 32;
958 * align = 32;
959 * signed = false;
38b8da21 960 * } := struct page *;
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961 *
962 * typealias integer {
963 * size = 32;
964 * align = 32;
965 * signed = true;
38b8da21 966 * } := int;
3d13ef1a 967 */
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968
969struct name {
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970 ...
971};
5ba9f198 972
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973variant name {
974 ...
975};
976
a9b83695 977enum name : integer_type {
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978 ...
979};
980
2152348f 981
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982/*
983 * Unnamed types, contained within compound type fields, typedef or typealias.
984 */
2152348f 985
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986struct {
987 ...
2152348f 988}
5ba9f198 989
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990variant {
991 ...
992}
993
a9b83695 994enum : integer_type {
80fd2569 995 ...
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MD
996}
997
998typedef type new_type[length];
3bf79539 999
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1000struct {
1001 type field_name[length];
1002}
1003
1004typedef type new_type[length_type];
1005
1006struct {
1007 type field_name[length_type];
1008}
1009
1010integer {
80fd2569 1011 ...
2152348f 1012}
3bf79539 1013
2152348f 1014floating_point {
80fd2569 1015 ...
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1016}
1017
1018struct {
1019 integer_type field_name:size; /* GNU/C bitfield */
1020}
1021
1022struct {
1023 string field_name;
1024}
3bf79539 1025
fcba70d4 1026
3bf79539 1027A. Helper macros
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1028
1029The two following macros keep track of the size of a GNU/C structure without
1030padding at the end by placing HEADER_END as the last field. A one byte end field
1031is used for C90 compatibility (C99 flexible arrays could be used here). Note
1032that this does not affect the effective structure size, which should always be
1033calculated with the header_sizeof() helper.
1034
1035#define HEADER_END char end_field
1036#define header_sizeof(type) offsetof(typeof(type), end_field)
3bf79539
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1037
1038
1039B. Stream Header Rationale
1040
1041An event stream is divided in contiguous event packets of variable size. These
1042subdivisions allow the trace analyzer to perform a fast binary search by time
1043within the stream (typically requiring to index only the event packet headers)
1044without reading the whole stream. These subdivisions have a variable size to
1045eliminate the need to transfer the event packet padding when partially filled
1046event packets must be sent when streaming a trace for live viewing/analysis.
1047An event packet can contain a certain amount of padding at the end. Dividing
1048streams into event packets is also useful for network streaming over UDP and
1049flight recorder mode tracing (a whole event packet can be swapped out of the
1050buffer atomically for reading).
1051
1052The stream header is repeated at the beginning of each event packet to allow
1053flexibility in terms of:
1054
1055 - streaming support,
1056 - allowing arbitrary buffers to be discarded without making the trace
1057 unreadable,
1058 - allow UDP packet loss handling by either dealing with missing event packet
1059 or asking for re-transmission.
1060 - transparently support flight recorder mode,
1061 - transparently support crash dump.
1062
1063The event stream header will therefore be referred to as the "event packet
1064header" throughout the rest of this document.
fcba70d4 1065
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1066
1067C. TSDL Grammar
fcba70d4 1068
4fa992a5 1069/*
6c7226e9 1070 * Common Trace Format (CTF) Trace Stream Description Language (TSDL) Grammar.
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1071 *
1072 * Inspired from the C99 grammar:
1073 * http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1124.pdf (Annex A)
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1074 * and c++1x grammar (draft)
1075 * http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2011/n3291.pdf (Annex A)
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1076 *
1077 * Specialized for CTF needs by including only constant and declarations from
1078 * C99 (excluding function declarations), and by adding support for variants,
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1079 * sequences and CTF-specific specifiers. Enumeration container types
1080 * semantic is inspired from c++1x enum-base.
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1081 */
1082
10831) Lexical grammar
1084
10851.1) Lexical elements
1086
1087token:
1088 keyword
1089 identifier
1090 constant
1091 string-literal
1092 punctuator
1093
10941.2) Keywords
1095
1096keyword: is one of
1097
1098const
1099char
1100double
1101enum
1102event
1103floating_point
1104float
1105integer
1106int
1107long
1108short
1109signed
1110stream
1111string
1112struct
1113trace
3e1e1a78 1114typealias
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1115typedef
1116unsigned
1117variant
1118void
1119_Bool
1120_Complex
1121_Imaginary
1122
1123
11241.3) Identifiers
1125
1126identifier:
1127 identifier-nondigit
1128 identifier identifier-nondigit
1129 identifier digit
1130
1131identifier-nondigit:
1132 nondigit
1133 universal-character-name
1134 any other implementation-defined characters
1135
1136nondigit:
1137 _
1138 [a-zA-Z] /* regular expression */
1139
1140digit:
1141 [0-9] /* regular expression */
1142
11431.4) Universal character names
1144
1145universal-character-name:
1146 \u hex-quad
1147 \U hex-quad hex-quad
1148
1149hex-quad:
1150 hexadecimal-digit hexadecimal-digit hexadecimal-digit hexadecimal-digit
1151
11521.5) Constants
1153
1154constant:
1155 integer-constant
1156 enumeration-constant
1157 character-constant
1158
1159integer-constant:
1160 decimal-constant integer-suffix-opt
1161 octal-constant integer-suffix-opt
1162 hexadecimal-constant integer-suffix-opt
1163
1164decimal-constant:
1165 nonzero-digit
1166 decimal-constant digit
1167
1168octal-constant:
1169 0
1170 octal-constant octal-digit
1171
1172hexadecimal-constant:
1173 hexadecimal-prefix hexadecimal-digit
1174 hexadecimal-constant hexadecimal-digit
1175
1176hexadecimal-prefix:
1177 0x
1178 0X
1179
1180nonzero-digit:
1181 [1-9]
1182
1183integer-suffix:
1184 unsigned-suffix long-suffix-opt
1185 unsigned-suffix long-long-suffix
1186 long-suffix unsigned-suffix-opt
1187 long-long-suffix unsigned-suffix-opt
1188
1189unsigned-suffix:
1190 u
1191 U
1192
1193long-suffix:
1194 l
1195 L
1196
1197long-long-suffix:
1198 ll
1199 LL
1200
1201digit-sequence:
1202 digit
1203 digit-sequence digit
1204
1205hexadecimal-digit-sequence:
1206 hexadecimal-digit
1207 hexadecimal-digit-sequence hexadecimal-digit
1208
1209enumeration-constant:
1210 identifier
1211 string-literal
1212
1213character-constant:
1214 ' c-char-sequence '
1215 L' c-char-sequence '
1216
1217c-char-sequence:
1218 c-char
1219 c-char-sequence c-char
1220
1221c-char:
1222 any member of source charset except single-quote ('), backslash
1223 (\), or new-line character.
1224 escape-sequence
1225
1226escape-sequence:
1227 simple-escape-sequence
1228 octal-escape-sequence
1229 hexadecimal-escape-sequence
1230 universal-character-name
1231
1232simple-escape-sequence: one of
1233 \' \" \? \\ \a \b \f \n \r \t \v
1234
1235octal-escape-sequence:
1236 \ octal-digit
1237 \ octal-digit octal-digit
1238 \ octal-digit octal-digit octal-digit
1239
1240hexadecimal-escape-sequence:
1241 \x hexadecimal-digit
1242 hexadecimal-escape-sequence hexadecimal-digit
1243
12441.6) String literals
1245
1246string-literal:
1247 " s-char-sequence-opt "
1248 L" s-char-sequence-opt "
1249
1250s-char-sequence:
1251 s-char
1252 s-char-sequence s-char
1253
1254s-char:
1255 any member of source charset except double-quote ("), backslash
1256 (\), or new-line character.
1257 escape-sequence
1258
12591.7) Punctuators
1260
1261punctuator: one of
1262 [ ] ( ) { } . -> * + - < > : ; ... = ,
1263
1264
12652) Phrase structure grammar
1266
1267primary-expression:
1268 identifier
1269 constant
1270 string-literal
1271 ( unary-expression )
1272
1273postfix-expression:
1274 primary-expression
1275 postfix-expression [ unary-expression ]
1276 postfix-expression . identifier
1277 postfix-expressoin -> identifier
1278
1279unary-expression:
1280 postfix-expression
1281 unary-operator postfix-expression
1282
1283unary-operator: one of
1284 + -
1285
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1286assignment-operator:
1287 =
1288
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1289type-assignment-operator:
1290 :=
1291
4fa992a5
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1292constant-expression:
1293 unary-expression
1294
1295constant-expression-range:
1296 constant-expression ... constant-expression
1297
12982.2) Declarations:
1299
1300declaration:
689e04b4 1301 declaration-specifiers declarator-list-opt ;
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1302 ctf-specifier ;
1303
1304declaration-specifiers:
689e04b4 1305 storage-class-specifier declaration-specifiers-opt
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1306 type-specifier declaration-specifiers-opt
1307 type-qualifier declaration-specifiers-opt
1308
1309declarator-list:
1310 declarator
1311 declarator-list , declarator
1312
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1313abstract-declarator-list:
1314 abstract-declarator
1315 abstract-declarator-list , abstract-declarator
1316
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1317storage-class-specifier:
1318 typedef
1319
1320type-specifier:
1321 void
1322 char
1323 short
1324 int
1325 long
1326 float
1327 double
1328 signed
1329 unsigned
1330 _Bool
1331 _Complex
cfdd51ec 1332 _Imaginary
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1333 struct-specifier
1334 variant-specifier
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1335 enum-specifier
1336 typedef-name
1337 ctf-type-specifier
1338
1339struct-specifier:
3b0f8e4d 1340 struct identifier-opt { struct-or-variant-declaration-list-opt }
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1341 struct identifier
1342
1343struct-or-variant-declaration-list:
1344 struct-or-variant-declaration
1345 struct-or-variant-declaration-list struct-or-variant-declaration
1346
1347struct-or-variant-declaration:
1348 specifier-qualifier-list struct-or-variant-declarator-list ;
550aca33 1349 declaration-specifiers storage-class-specifier declaration-specifiers declarator-list ;
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1350 typealias declaration-specifiers abstract-declarator-list := declaration-specifiers abstract-declarator-list ;
1351 typealias declaration-specifiers abstract-declarator-list := declarator-list ;
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1352
1353specifier-qualifier-list:
1354 type-specifier specifier-qualifier-list-opt
1355 type-qualifier specifier-qualifier-list-opt
1356
1357struct-or-variant-declarator-list:
1358 struct-or-variant-declarator
1359 struct-or-variant-declarator-list , struct-or-variant-declarator
1360
1361struct-or-variant-declarator:
1362 declarator
1363 declarator-opt : constant-expression
1364
1365variant-specifier:
1366 variant identifier-opt variant-tag-opt { struct-or-variant-declaration-list }
1367 variant identifier variant-tag
1368
1369variant-tag:
1370 < identifier >
1371
1372enum-specifier:
1373 enum identifier-opt { enumerator-list }
1374 enum identifier-opt { enumerator-list , }
1375 enum identifier
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1376 enum identifier-opt : declaration-specifiers { enumerator-list }
1377 enum identifier-opt : declaration-specifiers { enumerator-list , }
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1378
1379enumerator-list:
1380 enumerator
1381 enumerator-list , enumerator
1382
1383enumerator:
1384 enumeration-constant
1385 enumeration-constant = constant-expression
1386 enumeration-constant = constant-expression-range
1387
1388type-qualifier:
1389 const
1390
1391declarator:
1392 pointer-opt direct-declarator
1393
1394direct-declarator:
1395 identifier
1396 ( declarator )
1397 direct-declarator [ type-specifier ]
1398 direct-declarator [ constant-expression ]
1399
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1400abstract-declarator:
1401 pointer-opt direct-abstract-declarator
1402
1403direct-abstract-declarator:
1404 identifier-opt
1405 ( abstract-declarator )
1406 direct-abstract-declarator [ type-specifier ]
1407 direct-abstract-declarator [ constant-expression ]
1408 direct-abstract-declarator [ ]
1409
4fa992a5 1410pointer:
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1411 * type-qualifier-list-opt
1412 * type-qualifier-list-opt pointer
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1413
1414type-qualifier-list:
1415 type-qualifier
1416 type-qualifier-list type-qualifier
1417
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1418typedef-name:
1419 identifier
1420
14212.3) CTF-specific declarations
1422
1423ctf-specifier:
1424 event { ctf-assignment-expression-list-opt }
1425 stream { ctf-assignment-expression-list-opt }
1426 trace { ctf-assignment-expression-list-opt }
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1427 typealias declaration-specifiers abstract-declarator-list := declaration-specifiers abstract-declarator-list ;
1428 typealias declaration-specifiers abstract-declarator-list := declarator-list ;
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1429
1430ctf-type-specifier:
1431 floating_point { ctf-assignment-expression-list-opt }
1432 integer { ctf-assignment-expression-list-opt }
1433 string { ctf-assignment-expression-list-opt }
1434
1435ctf-assignment-expression-list:
1436 ctf-assignment-expression
1437 ctf-assignment-expression-list ; ctf-assignment-expression
1438
1439ctf-assignment-expression:
1440 unary-expression assignment-operator unary-expression
1441 unary-expression type-assignment-operator type-specifier
550aca33 1442 declaration-specifiers storage-class-specifier declaration-specifiers declarator-list
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1443 typealias declaration-specifiers abstract-declarator-list := declaration-specifiers abstract-declarator-list
1444 typealias declaration-specifiers abstract-declarator-list := declarator-list
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