Explain that content size and packet size are opt.
[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
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607in the metadata. All these fields are optional. If the packet size field is
608missing, the whole stream only contains a single packet. If the content
609size field is missing, the packet is filled (no padding).
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610
611An example event packet context type:
612
80fd2569 613struct event_packet_context {
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614 uint64_t timestamp_begin;
615 uint64_t timestamp_end;
616 uint32_t checksum;
617 uint32_t stream_packet_count;
618 uint32_t events_discarded;
619 uint32_t cpu_id;
620 uint32_t/uint16_t content_size;
621 uint32_t/uint16_t packet_size;
622 uint8_t stream_packet_count_bits; /* Significant counter bits */
623 uint8_t compression_scheme;
624 uint8_t encryption_scheme;
3b0f8e4d 625 uint8_t checksum_scheme;
3bf79539 626};
5ba9f198 627
fcba70d4 628
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6296. Event Structure
630
631The overall structure of an event is:
632
fcba70d4 6331 - Stream Packet Context (as specified by the stream metadata)
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634 2 - Event Header (as specified by the stream metadata)
635 3 - Stream Event Context (as specified by the stream metadata)
636 4 - Event Context (as specified by the event metadata)
637 5 - Event Payload (as specified by the event metadata)
5ba9f198 638
fdf2bb05 639This structure defines an implicit dynamic scoping, where variants
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640located in inner structures (those with a higher number in the listing
641above) can refer to the fields of outer structures (with lower number in
6c7226e9 642the listing above). See Section 7.3 TSDL Scopes for more detail.
5ba9f198 643
fdf2bb05 6446.1 Event Header
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645
646Event headers can be described within the metadata. We hereby propose, as an
647example, two types of events headers. Type 1 accommodates streams with less than
64831 event IDs. Type 2 accommodates streams with 31 or more event IDs.
5ba9f198 649
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650One major factor can vary between streams: the number of event IDs assigned to
651a stream. Luckily, this information tends to stay relatively constant (modulo
5ba9f198 652event registration while trace is being recorded), so we can specify different
3bf79539 653representations for streams containing few event IDs and streams containing
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654many event IDs, so we end up representing the event ID and timestamp as densely
655as possible in each case.
656
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657The header is extended in the rare occasions where the information cannot be
658represented in the ranges available in the standard event header. They are also
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659used in the rare occasions where the data required for a field could not be
660collected: the flag corresponding to the missing field within the missing_fields
661array is then set to 1.
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662
663Types uintX_t represent an X-bit unsigned integer.
664
665
fdf2bb05 6666.1.1 Type 1 - Few event IDs
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667
668 - Aligned on 32-bit (or 8-bit if byte-packed, depending on the architecture
669 preference).
5ba9f198 670 - Native architecture byte ordering.
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671 - For "compact" selection
672 - Fixed size: 32 bits.
673 - For "extended" selection
674 - Size depends on the architecture and variant alignment.
5ba9f198 675
80fd2569 676struct event_header_1 {
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677 /*
678 * id: range: 0 - 30.
679 * id 31 is reserved to indicate an extended header.
680 */
a9b83695 681 enum : uint5_t { compact = 0 ... 30, extended = 31 } id;
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682 variant <id> {
683 struct {
684 uint27_t timestamp;
685 } compact;
686 struct {
687 uint32_t id; /* 32-bit event IDs */
688 uint64_t timestamp; /* 64-bit timestamps */
689 } extended;
690 } v;
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691};
692
5ba9f198 693
fdf2bb05 6946.1.2 Type 2 - Many event IDs
5ba9f198 695
fcba70d4 696 - Aligned on 16-bit (or 8-bit if byte-packed, depending on the architecture
5ba9f198 697 preference).
5ba9f198 698 - Native architecture byte ordering.
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699 - For "compact" selection
700 - Size depends on the architecture and variant alignment.
701 - For "extended" selection
702 - Size depends on the architecture and variant alignment.
5ba9f198 703
80fd2569 704struct event_header_2 {
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705 /*
706 * id: range: 0 - 65534.
707 * id 65535 is reserved to indicate an extended header.
708 */
a9b83695 709 enum : uint16_t { compact = 0 ... 65534, extended = 65535 } id;
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710 variant <id> {
711 struct {
712 uint32_t timestamp;
713 } compact;
714 struct {
715 uint32_t id; /* 32-bit event IDs */
716 uint64_t timestamp; /* 64-bit timestamps */
717 } extended;
718 } v;
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719};
720
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721
7226.2 Event Context
723
724The event context contains information relative to the current event. The choice
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725and meaning of this information is specified by the metadata "stream" and
726"event" information. The "stream" context is applied to all events within the
727stream. The "stream" context structure follows the event header. The "event"
728context is applied to specific events. Its structure follows the "stream"
729context stucture.
5ba9f198 730
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731An example of stream-level event context is to save the event payload size with
732each event, or to save the current PID with each event. These are declared
733within the stream declaration within the metadata:
5ba9f198 734
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735 stream {
736 ...
737 event {
738 ...
4fa992a5 739 context := struct {
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740 uint pid;
741 uint16_t payload_size;
3bf79539 742 };
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743 }
744 };
745
746An example of event-specific event context is to declare a bitmap of missing
747fields, only appended after the stream event context if the extended event
748header is selected. NR_FIELDS is the number of fields within the event (a
749numeric value).
5ba9f198 750
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751 event {
752 context = struct {
753 variant <id> {
754 struct { } compact;
755 struct {
756 uint1_t missing_fields[NR_FIELDS]; /* missing event fields bitmap */
757 } extended;
758 } v;
759 };
760 ...
761 }
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762
7636.3 Event Payload
764
765An event payload contains fields specific to a given event type. The fields
766belonging to an event type are described in the event-specific metadata
767within a structure type.
768
7696.3.1 Padding
770
771No padding at the end of the event payload. This differs from the ISO/C standard
772for structures, but follows the CTF standard for structures. In a trace, even
773though it makes sense to align the beginning of a structure, it really makes no
774sense to add padding at the end of the structure, because structures are usually
775not followed by a structure of the same type.
776
777This trick can be done by adding a zero-length "end" field at the end of the C
778structures, and by using the offset of this field rather than using sizeof()
3bf79539 779when calculating the size of a structure (see Appendix "A. Helper macros").
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780
7816.3.2 Alignment
782
783The event payload is aligned on the largest alignment required by types
784contained within the payload. (This follows the ISO/C standard for structures)
785
786
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7877. Trace Stream Description Language (TSDL)
788
789The Trace Stream Description Language (TSDL) allows expression of the
790binary trace streams layout in a C99-like Domain Specific Language
791(DSL).
792
793
7947.1 Metadata
795
796The trace stream layout description is located in the trace meta-data.
797The meta-data is itself located in a stream identified by its name:
798"metadata".
5ba9f198 799
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800It is made of "event packets", which each start with an event packet
801header. The event type within the metadata stream have no event header
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802nor event context. Each event only contains a "string" payload without
803any null-character. The events are packed one next to another. Each
804event packet start with an event packet header, which contains, amongst
805other fields, the magic number, trace UUID and packet length. In the
806event packet header, the trace UUID is represented as an array of bytes.
807Within the string-based metadata description, the trace UUID is
808represented as a string of hexadecimal digits and dashes "-".
4fafe1ad 809
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810The metadata can be parsed by reading characters within the metadata
811stream, for each packet starting after the packet header, for the length
812of the packet payload specified in the header. Text contained within
813"/*" and "*/", as well as within "//" and end of line, are treated as
814comments. Boolean values can be represented as true, TRUE, or 1 for
815true, and false, FALSE, or 0 for false.
fcba70d4 816
fdf2bb05 817
6c7226e9 8187.2 Declaration vs Definition
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819
820A declaration associates a layout to a type, without specifying where
821this type is located in the event structure hierarchy (see Section 6).
822This therefore includes typedef, typealias, as well as all type
823specifiers. In certain circumstances (typedef, structure field and
824variant field), a declaration is followed by a declarator, which specify
825the newly defined type name (for typedef), or the field name (for
826declarations located within structure and variants). Array and sequence,
827declared with square brackets ("[" "]"), are part of the declarator,
a9b83695 828similarly to C99. The enumeration base type is specified by
6c7226e9 829": enum_base", which is part of the type specifier. The variant tag
a9b83695 830name, specified between "<" ">", is also part of the type specifier.
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831
832A definition associates a type to a location in the event structure
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833hierarchy (see Section 6). This association is denoted by ":=", as shown
834in Section 7.3.
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835
836
6c7226e9 8377.3 TSDL Scopes
fdf2bb05 838
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839TSDL uses two different types of scoping: a lexical scope is used for
840declarations and type definitions, and a dynamic scope is used for
841variants references to tag fields.
fdf2bb05 842
6c7226e9 8437.3.1 Lexical Scope
fdf2bb05 844
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845Each of "trace", "stream", "event", "struct" and "variant" have their own
846nestable declaration scope, within which types can be declared using "typedef"
fdf2bb05 847and "typealias". A root declaration scope also contains all declarations
7d9d7e92 848located outside of any of the aforementioned declarations. An inner
fdf2bb05 849declaration scope can refer to type declared within its container
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850lexical scope prior to the inner declaration scope. Redefinition of a
851typedef or typealias is not valid, although hiding an upper scope
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852typedef or typealias is allowed within a sub-scope.
853
6c7226e9 8547.3.2 Dynamic Scope
fdf2bb05 855
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856A dynamic scope consists in the lexical scope augmented with the
857implicit event structure definition hierarchy presented at Section 6.
858The dynamic scope is only used for variant tag definitions. It is used
859at definition time to look up the location of the tag field associated
860with a variant.
861
862Therefore, variants in lower levels in the dynamic scope (e.g. event
863context) can refer to a tag field located in upper levels (e.g. in the
864event header) by specifying, in this case, the associated tag with
865<header.field_name>. This allows, for instance, the event context to
866define a variant referring to the "id" field of the event header as
867selector.
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868
869The target dynamic scope must be specified explicitly when referring to
870a field outside of the local static scope. The dynamic scope prefixes
871are thus:
872
e0d9e2c7 873 - Trace Packet Header: <trace.packet.header. >,
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874 - Stream Packet Context: <stream.packet.context. >,
875 - Event Header: <stream.event.header. >,
876 - Stream Event Context: <stream.event.context. >,
877 - Event Context: <event.context. >,
878 - Event Payload: <event.fields. >.
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879
880Multiple declarations of the same field name within a single scope is
881not valid. It is however valid to re-use the same field name in
882different scopes. There is no possible conflict, because the dynamic
883scope must be specified when a variant refers to a tag field located in
884a different dynamic scope.
885
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886The information available in the dynamic scopes can be thought of as the
887current tracing context. At trace production, information about the
888current context is saved into the specified scope field levels. At trace
889consumption, for each event, the current trace context is therefore
890readable by accessing the upper dynamic scopes.
891
fdf2bb05 892
6c7226e9 8937.4 TSDL Examples
d285084f 894
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895The grammar representing the TSDL metadata is presented in Appendix C.
896TSDL Grammar. This section presents a rather ligher reading that
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897consists in examples of TSDL metadata, with template values.
898
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899The stream "id" can be left out if there is only one stream in the
900trace. The event "id" field can be left out if there is only one event
901in a stream.
902
5ba9f198 903trace {
fdf2bb05 904 major = value; /* Trace format version */
5ba9f198 905 minor = value;
fdf2bb05 906 uuid = "aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaaa"; /* Trace UUID */
58997e9e 907 byte_order = be OR le; /* Endianness (required) */
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908 packet.header := struct {
909 uint32_t magic;
910 uint8_t trace_uuid[16];
911 uint32_t stream_id;
912 };
3bf79539 913};
5ba9f198 914
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915stream {
916 id = stream_id;
fdf2bb05 917 /* Type 1 - Few event IDs; Type 2 - Many event IDs. See section 6.1. */
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918 event.header := event_header_1 OR event_header_2;
919 event.context := struct {
77a98c82 920 ...
3bf79539 921 };
4fa992a5 922 packet.context := struct {
77a98c82 923 ...
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924 };
925};
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926
927event {
3d13ef1a 928 name = event_name;
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929 id = value; /* Numeric identifier within the stream */
930 stream = stream_id;
4fa992a5 931 context := struct {
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932 ...
933 };
4fa992a5 934 fields := struct {
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935 ...
936 };
3bf79539 937};
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938
939/* More detail on types in section 4. Types */
940
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941/*
942 * Named types:
943 *
4fa992a5 944 * Type declarations behave similarly to the C standard.
3d13ef1a
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945 */
946
80af8ac6 947typedef aliased_type_specifiers new_type_declarators;
2152348f 948
3d13ef1a 949/* e.g.: typedef struct example new_type_name[10]; */
80fd2569 950
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951/*
952 * typealias
953 *
954 * The "typealias" declaration can be used to give a name (including
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955 * pointer declarator specifier) to a type. It should also be used to
956 * map basic C types (float, int, unsigned long, ...) to a CTF type.
957 * Typealias is a superset of "typedef": it also allows assignment of a
38b8da21 958 * simple variable identifier to a type.
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959 */
960
961typealias type_class {
80fd2569 962 ...
38b8da21 963} := type_specifiers type_declarator;
2152348f 964
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965/*
966 * e.g.:
4fa992a5 967 * typealias integer {
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968 * size = 32;
969 * align = 32;
970 * signed = false;
38b8da21 971 * } := struct page *;
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972 *
973 * typealias integer {
974 * size = 32;
975 * align = 32;
976 * signed = true;
38b8da21 977 * } := int;
3d13ef1a 978 */
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979
980struct name {
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981 ...
982};
5ba9f198 983
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984variant name {
985 ...
986};
987
a9b83695 988enum name : integer_type {
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989 ...
990};
991
2152348f 992
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993/*
994 * Unnamed types, contained within compound type fields, typedef or typealias.
995 */
2152348f 996
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997struct {
998 ...
2152348f 999}
5ba9f198 1000
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1001variant {
1002 ...
1003}
1004
a9b83695 1005enum : integer_type {
80fd2569 1006 ...
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1007}
1008
1009typedef type new_type[length];
3bf79539 1010
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1011struct {
1012 type field_name[length];
1013}
1014
1015typedef type new_type[length_type];
1016
1017struct {
1018 type field_name[length_type];
1019}
1020
1021integer {
80fd2569 1022 ...
2152348f 1023}
3bf79539 1024
2152348f 1025floating_point {
80fd2569 1026 ...
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MD
1027}
1028
1029struct {
1030 integer_type field_name:size; /* GNU/C bitfield */
1031}
1032
1033struct {
1034 string field_name;
1035}
3bf79539 1036
fcba70d4 1037
3bf79539 1038A. Helper macros
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1039
1040The two following macros keep track of the size of a GNU/C structure without
1041padding at the end by placing HEADER_END as the last field. A one byte end field
1042is used for C90 compatibility (C99 flexible arrays could be used here). Note
1043that this does not affect the effective structure size, which should always be
1044calculated with the header_sizeof() helper.
1045
1046#define HEADER_END char end_field
1047#define header_sizeof(type) offsetof(typeof(type), end_field)
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1048
1049
1050B. Stream Header Rationale
1051
1052An event stream is divided in contiguous event packets of variable size. These
1053subdivisions allow the trace analyzer to perform a fast binary search by time
1054within the stream (typically requiring to index only the event packet headers)
1055without reading the whole stream. These subdivisions have a variable size to
1056eliminate the need to transfer the event packet padding when partially filled
1057event packets must be sent when streaming a trace for live viewing/analysis.
1058An event packet can contain a certain amount of padding at the end. Dividing
1059streams into event packets is also useful for network streaming over UDP and
1060flight recorder mode tracing (a whole event packet can be swapped out of the
1061buffer atomically for reading).
1062
1063The stream header is repeated at the beginning of each event packet to allow
1064flexibility in terms of:
1065
1066 - streaming support,
1067 - allowing arbitrary buffers to be discarded without making the trace
1068 unreadable,
1069 - allow UDP packet loss handling by either dealing with missing event packet
1070 or asking for re-transmission.
1071 - transparently support flight recorder mode,
1072 - transparently support crash dump.
1073
1074The event stream header will therefore be referred to as the "event packet
1075header" throughout the rest of this document.
fcba70d4 1076
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1077
1078C. TSDL Grammar
fcba70d4 1079
4fa992a5 1080/*
6c7226e9 1081 * Common Trace Format (CTF) Trace Stream Description Language (TSDL) Grammar.
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1082 *
1083 * Inspired from the C99 grammar:
1084 * http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1124.pdf (Annex A)
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1085 * and c++1x grammar (draft)
1086 * http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2011/n3291.pdf (Annex A)
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1087 *
1088 * Specialized for CTF needs by including only constant and declarations from
1089 * C99 (excluding function declarations), and by adding support for variants,
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1090 * sequences and CTF-specific specifiers. Enumeration container types
1091 * semantic is inspired from c++1x enum-base.
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1092 */
1093
10941) Lexical grammar
1095
10961.1) Lexical elements
1097
1098token:
1099 keyword
1100 identifier
1101 constant
1102 string-literal
1103 punctuator
1104
11051.2) Keywords
1106
1107keyword: is one of
1108
1109const
1110char
1111double
1112enum
1113event
1114floating_point
1115float
1116integer
1117int
1118long
1119short
1120signed
1121stream
1122string
1123struct
1124trace
3e1e1a78 1125typealias
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1126typedef
1127unsigned
1128variant
1129void
1130_Bool
1131_Complex
1132_Imaginary
1133
1134
11351.3) Identifiers
1136
1137identifier:
1138 identifier-nondigit
1139 identifier identifier-nondigit
1140 identifier digit
1141
1142identifier-nondigit:
1143 nondigit
1144 universal-character-name
1145 any other implementation-defined characters
1146
1147nondigit:
1148 _
1149 [a-zA-Z] /* regular expression */
1150
1151digit:
1152 [0-9] /* regular expression */
1153
11541.4) Universal character names
1155
1156universal-character-name:
1157 \u hex-quad
1158 \U hex-quad hex-quad
1159
1160hex-quad:
1161 hexadecimal-digit hexadecimal-digit hexadecimal-digit hexadecimal-digit
1162
11631.5) Constants
1164
1165constant:
1166 integer-constant
1167 enumeration-constant
1168 character-constant
1169
1170integer-constant:
1171 decimal-constant integer-suffix-opt
1172 octal-constant integer-suffix-opt
1173 hexadecimal-constant integer-suffix-opt
1174
1175decimal-constant:
1176 nonzero-digit
1177 decimal-constant digit
1178
1179octal-constant:
1180 0
1181 octal-constant octal-digit
1182
1183hexadecimal-constant:
1184 hexadecimal-prefix hexadecimal-digit
1185 hexadecimal-constant hexadecimal-digit
1186
1187hexadecimal-prefix:
1188 0x
1189 0X
1190
1191nonzero-digit:
1192 [1-9]
1193
1194integer-suffix:
1195 unsigned-suffix long-suffix-opt
1196 unsigned-suffix long-long-suffix
1197 long-suffix unsigned-suffix-opt
1198 long-long-suffix unsigned-suffix-opt
1199
1200unsigned-suffix:
1201 u
1202 U
1203
1204long-suffix:
1205 l
1206 L
1207
1208long-long-suffix:
1209 ll
1210 LL
1211
1212digit-sequence:
1213 digit
1214 digit-sequence digit
1215
1216hexadecimal-digit-sequence:
1217 hexadecimal-digit
1218 hexadecimal-digit-sequence hexadecimal-digit
1219
1220enumeration-constant:
1221 identifier
1222 string-literal
1223
1224character-constant:
1225 ' c-char-sequence '
1226 L' c-char-sequence '
1227
1228c-char-sequence:
1229 c-char
1230 c-char-sequence c-char
1231
1232c-char:
1233 any member of source charset except single-quote ('), backslash
1234 (\), or new-line character.
1235 escape-sequence
1236
1237escape-sequence:
1238 simple-escape-sequence
1239 octal-escape-sequence
1240 hexadecimal-escape-sequence
1241 universal-character-name
1242
1243simple-escape-sequence: one of
1244 \' \" \? \\ \a \b \f \n \r \t \v
1245
1246octal-escape-sequence:
1247 \ octal-digit
1248 \ octal-digit octal-digit
1249 \ octal-digit octal-digit octal-digit
1250
1251hexadecimal-escape-sequence:
1252 \x hexadecimal-digit
1253 hexadecimal-escape-sequence hexadecimal-digit
1254
12551.6) String literals
1256
1257string-literal:
1258 " s-char-sequence-opt "
1259 L" s-char-sequence-opt "
1260
1261s-char-sequence:
1262 s-char
1263 s-char-sequence s-char
1264
1265s-char:
1266 any member of source charset except double-quote ("), backslash
1267 (\), or new-line character.
1268 escape-sequence
1269
12701.7) Punctuators
1271
1272punctuator: one of
1273 [ ] ( ) { } . -> * + - < > : ; ... = ,
1274
1275
12762) Phrase structure grammar
1277
1278primary-expression:
1279 identifier
1280 constant
1281 string-literal
1282 ( unary-expression )
1283
1284postfix-expression:
1285 primary-expression
1286 postfix-expression [ unary-expression ]
1287 postfix-expression . identifier
1288 postfix-expressoin -> identifier
1289
1290unary-expression:
1291 postfix-expression
1292 unary-operator postfix-expression
1293
1294unary-operator: one of
1295 + -
1296
4fa992a5
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1297assignment-operator:
1298 =
1299
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1300type-assignment-operator:
1301 :=
1302
4fa992a5
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1303constant-expression:
1304 unary-expression
1305
1306constant-expression-range:
1307 constant-expression ... constant-expression
1308
13092.2) Declarations:
1310
1311declaration:
689e04b4 1312 declaration-specifiers declarator-list-opt ;
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1313 ctf-specifier ;
1314
1315declaration-specifiers:
689e04b4 1316 storage-class-specifier declaration-specifiers-opt
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1317 type-specifier declaration-specifiers-opt
1318 type-qualifier declaration-specifiers-opt
1319
1320declarator-list:
1321 declarator
1322 declarator-list , declarator
1323
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1324abstract-declarator-list:
1325 abstract-declarator
1326 abstract-declarator-list , abstract-declarator
1327
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1328storage-class-specifier:
1329 typedef
1330
1331type-specifier:
1332 void
1333 char
1334 short
1335 int
1336 long
1337 float
1338 double
1339 signed
1340 unsigned
1341 _Bool
1342 _Complex
cfdd51ec 1343 _Imaginary
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1344 struct-specifier
1345 variant-specifier
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1346 enum-specifier
1347 typedef-name
1348 ctf-type-specifier
1349
1350struct-specifier:
3b0f8e4d 1351 struct identifier-opt { struct-or-variant-declaration-list-opt }
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1352 struct identifier
1353
1354struct-or-variant-declaration-list:
1355 struct-or-variant-declaration
1356 struct-or-variant-declaration-list struct-or-variant-declaration
1357
1358struct-or-variant-declaration:
1359 specifier-qualifier-list struct-or-variant-declarator-list ;
550aca33 1360 declaration-specifiers storage-class-specifier declaration-specifiers declarator-list ;
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1361 typealias declaration-specifiers abstract-declarator-list := declaration-specifiers abstract-declarator-list ;
1362 typealias declaration-specifiers abstract-declarator-list := declarator-list ;
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1363
1364specifier-qualifier-list:
1365 type-specifier specifier-qualifier-list-opt
1366 type-qualifier specifier-qualifier-list-opt
1367
1368struct-or-variant-declarator-list:
1369 struct-or-variant-declarator
1370 struct-or-variant-declarator-list , struct-or-variant-declarator
1371
1372struct-or-variant-declarator:
1373 declarator
1374 declarator-opt : constant-expression
1375
1376variant-specifier:
1377 variant identifier-opt variant-tag-opt { struct-or-variant-declaration-list }
1378 variant identifier variant-tag
1379
1380variant-tag:
1381 < identifier >
1382
1383enum-specifier:
1384 enum identifier-opt { enumerator-list }
1385 enum identifier-opt { enumerator-list , }
1386 enum identifier
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1387 enum identifier-opt : declaration-specifiers { enumerator-list }
1388 enum identifier-opt : declaration-specifiers { enumerator-list , }
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1389
1390enumerator-list:
1391 enumerator
1392 enumerator-list , enumerator
1393
1394enumerator:
1395 enumeration-constant
1396 enumeration-constant = constant-expression
1397 enumeration-constant = constant-expression-range
1398
1399type-qualifier:
1400 const
1401
1402declarator:
1403 pointer-opt direct-declarator
1404
1405direct-declarator:
1406 identifier
1407 ( declarator )
1408 direct-declarator [ type-specifier ]
1409 direct-declarator [ constant-expression ]
1410
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1411abstract-declarator:
1412 pointer-opt direct-abstract-declarator
1413
1414direct-abstract-declarator:
1415 identifier-opt
1416 ( abstract-declarator )
1417 direct-abstract-declarator [ type-specifier ]
1418 direct-abstract-declarator [ constant-expression ]
1419 direct-abstract-declarator [ ]
1420
4fa992a5 1421pointer:
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1422 * type-qualifier-list-opt
1423 * type-qualifier-list-opt pointer
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1424
1425type-qualifier-list:
1426 type-qualifier
1427 type-qualifier-list type-qualifier
1428
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1429typedef-name:
1430 identifier
1431
14322.3) CTF-specific declarations
1433
1434ctf-specifier:
1435 event { ctf-assignment-expression-list-opt }
1436 stream { ctf-assignment-expression-list-opt }
1437 trace { ctf-assignment-expression-list-opt }
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1438 typealias declaration-specifiers abstract-declarator-list := declaration-specifiers abstract-declarator-list ;
1439 typealias declaration-specifiers abstract-declarator-list := declarator-list ;
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1440
1441ctf-type-specifier:
1442 floating_point { ctf-assignment-expression-list-opt }
1443 integer { ctf-assignment-expression-list-opt }
1444 string { ctf-assignment-expression-list-opt }
1445
1446ctf-assignment-expression-list:
1447 ctf-assignment-expression
1448 ctf-assignment-expression-list ; ctf-assignment-expression
1449
1450ctf-assignment-expression:
1451 unary-expression assignment-operator unary-expression
1452 unary-expression type-assignment-operator type-specifier
550aca33 1453 declaration-specifiers storage-class-specifier declaration-specifiers declarator-list
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1454 typealias declaration-specifiers abstract-declarator-list := declaration-specifiers abstract-declarator-list
1455 typealias declaration-specifiers abstract-declarator-list := declarator-list
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