Remove "word_size" from trace description
[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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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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5915.2 Event Packet Context Description
592
593Event packet context example. These are declared within the stream declaration
594in the metadata. All these fields are optional except for "content_size" and
595"packet_size", which must be present in the context.
596
597An example event packet context type:
598
80fd2569 599struct event_packet_context {
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600 uint64_t timestamp_begin;
601 uint64_t timestamp_end;
602 uint32_t checksum;
603 uint32_t stream_packet_count;
604 uint32_t events_discarded;
605 uint32_t cpu_id;
606 uint32_t/uint16_t content_size;
607 uint32_t/uint16_t packet_size;
608 uint8_t stream_packet_count_bits; /* Significant counter bits */
609 uint8_t compression_scheme;
610 uint8_t encryption_scheme;
3b0f8e4d 611 uint8_t checksum_scheme;
3bf79539 612};
5ba9f198 613
fcba70d4 614
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6156. Event Structure
616
617The overall structure of an event is:
618
fcba70d4 6191 - Stream Packet Context (as specified by the stream metadata)
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620 2 - Event Header (as specified by the stream metadata)
621 3 - Stream Event Context (as specified by the stream metadata)
622 4 - Event Context (as specified by the event metadata)
623 5 - Event Payload (as specified by the event metadata)
5ba9f198 624
fdf2bb05 625This structure defines an implicit dynamic scoping, where variants
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626located in inner structures (those with a higher number in the listing
627above) can refer to the fields of outer structures (with lower number in
6c7226e9 628the listing above). See Section 7.3 TSDL Scopes for more detail.
5ba9f198 629
fdf2bb05 6306.1 Event Header
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631
632Event headers can be described within the metadata. We hereby propose, as an
633example, two types of events headers. Type 1 accommodates streams with less than
63431 event IDs. Type 2 accommodates streams with 31 or more event IDs.
5ba9f198 635
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636One major factor can vary between streams: the number of event IDs assigned to
637a stream. Luckily, this information tends to stay relatively constant (modulo
5ba9f198 638event registration while trace is being recorded), so we can specify different
3bf79539 639representations for streams containing few event IDs and streams containing
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640many event IDs, so we end up representing the event ID and timestamp as densely
641as possible in each case.
642
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643The header is extended in the rare occasions where the information cannot be
644represented in the ranges available in the standard event header. They are also
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645used in the rare occasions where the data required for a field could not be
646collected: the flag corresponding to the missing field within the missing_fields
647array is then set to 1.
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648
649Types uintX_t represent an X-bit unsigned integer.
650
651
fdf2bb05 6526.1.1 Type 1 - Few event IDs
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653
654 - Aligned on 32-bit (or 8-bit if byte-packed, depending on the architecture
655 preference).
5ba9f198 656 - Native architecture byte ordering.
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657 - For "compact" selection
658 - Fixed size: 32 bits.
659 - For "extended" selection
660 - Size depends on the architecture and variant alignment.
5ba9f198 661
80fd2569 662struct event_header_1 {
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663 /*
664 * id: range: 0 - 30.
665 * id 31 is reserved to indicate an extended header.
666 */
a9b83695 667 enum : uint5_t { compact = 0 ... 30, extended = 31 } id;
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668 variant <id> {
669 struct {
670 uint27_t timestamp;
671 } compact;
672 struct {
673 uint32_t id; /* 32-bit event IDs */
674 uint64_t timestamp; /* 64-bit timestamps */
675 } extended;
676 } v;
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677};
678
5ba9f198 679
fdf2bb05 6806.1.2 Type 2 - Many event IDs
5ba9f198 681
fcba70d4 682 - Aligned on 16-bit (or 8-bit if byte-packed, depending on the architecture
5ba9f198 683 preference).
5ba9f198 684 - Native architecture byte ordering.
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685 - For "compact" selection
686 - Size depends on the architecture and variant alignment.
687 - For "extended" selection
688 - Size depends on the architecture and variant alignment.
5ba9f198 689
80fd2569 690struct event_header_2 {
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691 /*
692 * id: range: 0 - 65534.
693 * id 65535 is reserved to indicate an extended header.
694 */
a9b83695 695 enum : uint16_t { compact = 0 ... 65534, extended = 65535 } id;
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696 variant <id> {
697 struct {
698 uint32_t timestamp;
699 } compact;
700 struct {
701 uint32_t id; /* 32-bit event IDs */
702 uint64_t timestamp; /* 64-bit timestamps */
703 } extended;
704 } v;
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705};
706
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707
7086.2 Event Context
709
710The event context contains information relative to the current event. The choice
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711and meaning of this information is specified by the metadata "stream" and
712"event" information. The "stream" context is applied to all events within the
713stream. The "stream" context structure follows the event header. The "event"
714context is applied to specific events. Its structure follows the "stream"
715context stucture.
5ba9f198 716
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717An example of stream-level event context is to save the event payload size with
718each event, or to save the current PID with each event. These are declared
719within the stream declaration within the metadata:
5ba9f198 720
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721 stream {
722 ...
723 event {
724 ...
4fa992a5 725 context := struct {
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726 uint pid;
727 uint16_t payload_size;
3bf79539 728 };
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729 }
730 };
731
732An example of event-specific event context is to declare a bitmap of missing
733fields, only appended after the stream event context if the extended event
734header is selected. NR_FIELDS is the number of fields within the event (a
735numeric value).
5ba9f198 736
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737 event {
738 context = struct {
739 variant <id> {
740 struct { } compact;
741 struct {
742 uint1_t missing_fields[NR_FIELDS]; /* missing event fields bitmap */
743 } extended;
744 } v;
745 };
746 ...
747 }
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748
7496.3 Event Payload
750
751An event payload contains fields specific to a given event type. The fields
752belonging to an event type are described in the event-specific metadata
753within a structure type.
754
7556.3.1 Padding
756
757No padding at the end of the event payload. This differs from the ISO/C standard
758for structures, but follows the CTF standard for structures. In a trace, even
759though it makes sense to align the beginning of a structure, it really makes no
760sense to add padding at the end of the structure, because structures are usually
761not followed by a structure of the same type.
762
763This trick can be done by adding a zero-length "end" field at the end of the C
764structures, and by using the offset of this field rather than using sizeof()
3bf79539 765when calculating the size of a structure (see Appendix "A. Helper macros").
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766
7676.3.2 Alignment
768
769The event payload is aligned on the largest alignment required by types
770contained within the payload. (This follows the ISO/C standard for structures)
771
772
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7737. Trace Stream Description Language (TSDL)
774
775The Trace Stream Description Language (TSDL) allows expression of the
776binary trace streams layout in a C99-like Domain Specific Language
777(DSL).
778
779
7807.1 Metadata
781
782The trace stream layout description is located in the trace meta-data.
783The meta-data is itself located in a stream identified by its name:
784"metadata".
5ba9f198 785
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786It is made of "event packets", which each start with an event packet
787header. The event type within the metadata stream have no event header
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788nor event context. Each event only contains a "string" payload without
789any null-character. The events are packed one next to another. Each
790event packet start with an event packet header, which contains, amongst
791other fields, the magic number, trace UUID and packet length. In the
792event packet header, the trace UUID is represented as an array of bytes.
793Within the string-based metadata description, the trace UUID is
794represented as a string of hexadecimal digits and dashes "-".
4fafe1ad 795
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796The metadata can be parsed by reading characters within the metadata
797stream, for each packet starting after the packet header, for the length
798of the packet payload specified in the header. Text contained within
799"/*" and "*/", as well as within "//" and end of line, are treated as
800comments. Boolean values can be represented as true, TRUE, or 1 for
801true, and false, FALSE, or 0 for false.
fcba70d4 802
fdf2bb05 803
6c7226e9 8047.2 Declaration vs Definition
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805
806A declaration associates a layout to a type, without specifying where
807this type is located in the event structure hierarchy (see Section 6).
808This therefore includes typedef, typealias, as well as all type
809specifiers. In certain circumstances (typedef, structure field and
810variant field), a declaration is followed by a declarator, which specify
811the newly defined type name (for typedef), or the field name (for
812declarations located within structure and variants). Array and sequence,
813declared with square brackets ("[" "]"), are part of the declarator,
a9b83695 814similarly to C99. The enumeration base type is specified by
6c7226e9 815": enum_base", which is part of the type specifier. The variant tag
a9b83695 816name, specified between "<" ">", is also part of the type specifier.
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817
818A definition associates a type to a location in the event structure
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819hierarchy (see Section 6). This association is denoted by ":=", as shown
820in Section 7.3.
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821
822
6c7226e9 8237.3 TSDL Scopes
fdf2bb05 824
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825TSDL uses two different types of scoping: a lexical scope is used for
826declarations and type definitions, and a dynamic scope is used for
827variants references to tag fields.
fdf2bb05 828
6c7226e9 8297.3.1 Lexical Scope
fdf2bb05 830
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831Each of "trace", "stream", "event", "struct" and "variant" have their own
832nestable declaration scope, within which types can be declared using "typedef"
fdf2bb05 833and "typealias". A root declaration scope also contains all declarations
7d9d7e92 834located outside of any of the aforementioned declarations. An inner
fdf2bb05 835declaration scope can refer to type declared within its container
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836lexical scope prior to the inner declaration scope. Redefinition of a
837typedef or typealias is not valid, although hiding an upper scope
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838typedef or typealias is allowed within a sub-scope.
839
6c7226e9 8407.3.2 Dynamic Scope
fdf2bb05 841
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842A dynamic scope consists in the lexical scope augmented with the
843implicit event structure definition hierarchy presented at Section 6.
844The dynamic scope is only used for variant tag definitions. It is used
845at definition time to look up the location of the tag field associated
846with a variant.
847
848Therefore, variants in lower levels in the dynamic scope (e.g. event
849context) can refer to a tag field located in upper levels (e.g. in the
850event header) by specifying, in this case, the associated tag with
851<header.field_name>. This allows, for instance, the event context to
852define a variant referring to the "id" field of the event header as
853selector.
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854
855The target dynamic scope must be specified explicitly when referring to
856a field outside of the local static scope. The dynamic scope prefixes
857are thus:
858
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859 - Stream Packet Context: <stream.packet.context. >,
860 - Event Header: <stream.event.header. >,
861 - Stream Event Context: <stream.event.context. >,
862 - Event Context: <event.context. >,
863 - Event Payload: <event.fields. >.
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864
865Multiple declarations of the same field name within a single scope is
866not valid. It is however valid to re-use the same field name in
867different scopes. There is no possible conflict, because the dynamic
868scope must be specified when a variant refers to a tag field located in
869a different dynamic scope.
870
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871The information available in the dynamic scopes can be thought of as the
872current tracing context. At trace production, information about the
873current context is saved into the specified scope field levels. At trace
874consumption, for each event, the current trace context is therefore
875readable by accessing the upper dynamic scopes.
876
fdf2bb05 877
6c7226e9 8787.4 TSDL Examples
d285084f 879
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880The grammar representing the TSDL metadata is presented in Appendix C.
881TSDL Grammar. This section presents a rather ligher reading that
882consists in examples of TSDL metadata, with template values:
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883
884trace {
fdf2bb05 885 major = value; /* Trace format version */
5ba9f198 886 minor = value;
fdf2bb05 887 uuid = "aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaaa"; /* Trace UUID */
3bf79539 888};
5ba9f198 889
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890stream {
891 id = stream_id;
fdf2bb05 892 /* Type 1 - Few event IDs; Type 2 - Many event IDs. See section 6.1. */
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893 event.header := event_header_1 OR event_header_2;
894 event.context := struct {
77a98c82 895 ...
3bf79539 896 };
4fa992a5 897 packet.context := struct {
77a98c82 898 ...
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899 };
900};
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901
902event {
3d13ef1a 903 name = event_name;
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904 id = value; /* Numeric identifier within the stream */
905 stream = stream_id;
4fa992a5 906 context := struct {
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907 ...
908 };
4fa992a5 909 fields := struct {
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910 ...
911 };
3bf79539 912};
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913
914/* More detail on types in section 4. Types */
915
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916/*
917 * Named types:
918 *
4fa992a5 919 * Type declarations behave similarly to the C standard.
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920 */
921
80af8ac6 922typedef aliased_type_specifiers new_type_declarators;
2152348f 923
3d13ef1a 924/* e.g.: typedef struct example new_type_name[10]; */
80fd2569 925
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926/*
927 * typealias
928 *
929 * The "typealias" declaration can be used to give a name (including
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930 * pointer declarator specifier) to a type. It should also be used to
931 * map basic C types (float, int, unsigned long, ...) to a CTF type.
932 * Typealias is a superset of "typedef": it also allows assignment of a
38b8da21 933 * simple variable identifier to a type.
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MD
934 */
935
936typealias type_class {
80fd2569 937 ...
38b8da21 938} := type_specifiers type_declarator;
2152348f 939
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940/*
941 * e.g.:
4fa992a5 942 * typealias integer {
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MD
943 * size = 32;
944 * align = 32;
945 * signed = false;
38b8da21 946 * } := struct page *;
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947 *
948 * typealias integer {
949 * size = 32;
950 * align = 32;
951 * signed = true;
38b8da21 952 * } := int;
3d13ef1a 953 */
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954
955struct name {
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956 ...
957};
5ba9f198 958
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959variant name {
960 ...
961};
962
a9b83695 963enum name : integer_type {
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964 ...
965};
966
2152348f 967
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968/*
969 * Unnamed types, contained within compound type fields, typedef or typealias.
970 */
2152348f 971
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972struct {
973 ...
2152348f 974}
5ba9f198 975
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976variant {
977 ...
978}
979
a9b83695 980enum : integer_type {
80fd2569 981 ...
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MD
982}
983
984typedef type new_type[length];
3bf79539 985
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986struct {
987 type field_name[length];
988}
989
990typedef type new_type[length_type];
991
992struct {
993 type field_name[length_type];
994}
995
996integer {
80fd2569 997 ...
2152348f 998}
3bf79539 999
2152348f 1000floating_point {
80fd2569 1001 ...
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1002}
1003
1004struct {
1005 integer_type field_name:size; /* GNU/C bitfield */
1006}
1007
1008struct {
1009 string field_name;
1010}
3bf79539 1011
fcba70d4 1012
3bf79539 1013A. Helper macros
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1014
1015The two following macros keep track of the size of a GNU/C structure without
1016padding at the end by placing HEADER_END as the last field. A one byte end field
1017is used for C90 compatibility (C99 flexible arrays could be used here). Note
1018that this does not affect the effective structure size, which should always be
1019calculated with the header_sizeof() helper.
1020
1021#define HEADER_END char end_field
1022#define header_sizeof(type) offsetof(typeof(type), end_field)
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1023
1024
1025B. Stream Header Rationale
1026
1027An event stream is divided in contiguous event packets of variable size. These
1028subdivisions allow the trace analyzer to perform a fast binary search by time
1029within the stream (typically requiring to index only the event packet headers)
1030without reading the whole stream. These subdivisions have a variable size to
1031eliminate the need to transfer the event packet padding when partially filled
1032event packets must be sent when streaming a trace for live viewing/analysis.
1033An event packet can contain a certain amount of padding at the end. Dividing
1034streams into event packets is also useful for network streaming over UDP and
1035flight recorder mode tracing (a whole event packet can be swapped out of the
1036buffer atomically for reading).
1037
1038The stream header is repeated at the beginning of each event packet to allow
1039flexibility in terms of:
1040
1041 - streaming support,
1042 - allowing arbitrary buffers to be discarded without making the trace
1043 unreadable,
1044 - allow UDP packet loss handling by either dealing with missing event packet
1045 or asking for re-transmission.
1046 - transparently support flight recorder mode,
1047 - transparently support crash dump.
1048
1049The event stream header will therefore be referred to as the "event packet
1050header" throughout the rest of this document.
fcba70d4 1051
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1052
1053C. TSDL Grammar
fcba70d4 1054
4fa992a5 1055/*
6c7226e9 1056 * Common Trace Format (CTF) Trace Stream Description Language (TSDL) Grammar.
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1057 *
1058 * Inspired from the C99 grammar:
1059 * http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1124.pdf (Annex A)
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1060 * and c++1x grammar (draft)
1061 * http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2011/n3291.pdf (Annex A)
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1062 *
1063 * Specialized for CTF needs by including only constant and declarations from
1064 * C99 (excluding function declarations), and by adding support for variants,
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1065 * sequences and CTF-specific specifiers. Enumeration container types
1066 * semantic is inspired from c++1x enum-base.
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1067 */
1068
10691) Lexical grammar
1070
10711.1) Lexical elements
1072
1073token:
1074 keyword
1075 identifier
1076 constant
1077 string-literal
1078 punctuator
1079
10801.2) Keywords
1081
1082keyword: is one of
1083
1084const
1085char
1086double
1087enum
1088event
1089floating_point
1090float
1091integer
1092int
1093long
1094short
1095signed
1096stream
1097string
1098struct
1099trace
3e1e1a78 1100typealias
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1101typedef
1102unsigned
1103variant
1104void
1105_Bool
1106_Complex
1107_Imaginary
1108
1109
11101.3) Identifiers
1111
1112identifier:
1113 identifier-nondigit
1114 identifier identifier-nondigit
1115 identifier digit
1116
1117identifier-nondigit:
1118 nondigit
1119 universal-character-name
1120 any other implementation-defined characters
1121
1122nondigit:
1123 _
1124 [a-zA-Z] /* regular expression */
1125
1126digit:
1127 [0-9] /* regular expression */
1128
11291.4) Universal character names
1130
1131universal-character-name:
1132 \u hex-quad
1133 \U hex-quad hex-quad
1134
1135hex-quad:
1136 hexadecimal-digit hexadecimal-digit hexadecimal-digit hexadecimal-digit
1137
11381.5) Constants
1139
1140constant:
1141 integer-constant
1142 enumeration-constant
1143 character-constant
1144
1145integer-constant:
1146 decimal-constant integer-suffix-opt
1147 octal-constant integer-suffix-opt
1148 hexadecimal-constant integer-suffix-opt
1149
1150decimal-constant:
1151 nonzero-digit
1152 decimal-constant digit
1153
1154octal-constant:
1155 0
1156 octal-constant octal-digit
1157
1158hexadecimal-constant:
1159 hexadecimal-prefix hexadecimal-digit
1160 hexadecimal-constant hexadecimal-digit
1161
1162hexadecimal-prefix:
1163 0x
1164 0X
1165
1166nonzero-digit:
1167 [1-9]
1168
1169integer-suffix:
1170 unsigned-suffix long-suffix-opt
1171 unsigned-suffix long-long-suffix
1172 long-suffix unsigned-suffix-opt
1173 long-long-suffix unsigned-suffix-opt
1174
1175unsigned-suffix:
1176 u
1177 U
1178
1179long-suffix:
1180 l
1181 L
1182
1183long-long-suffix:
1184 ll
1185 LL
1186
1187digit-sequence:
1188 digit
1189 digit-sequence digit
1190
1191hexadecimal-digit-sequence:
1192 hexadecimal-digit
1193 hexadecimal-digit-sequence hexadecimal-digit
1194
1195enumeration-constant:
1196 identifier
1197 string-literal
1198
1199character-constant:
1200 ' c-char-sequence '
1201 L' c-char-sequence '
1202
1203c-char-sequence:
1204 c-char
1205 c-char-sequence c-char
1206
1207c-char:
1208 any member of source charset except single-quote ('), backslash
1209 (\), or new-line character.
1210 escape-sequence
1211
1212escape-sequence:
1213 simple-escape-sequence
1214 octal-escape-sequence
1215 hexadecimal-escape-sequence
1216 universal-character-name
1217
1218simple-escape-sequence: one of
1219 \' \" \? \\ \a \b \f \n \r \t \v
1220
1221octal-escape-sequence:
1222 \ octal-digit
1223 \ octal-digit octal-digit
1224 \ octal-digit octal-digit octal-digit
1225
1226hexadecimal-escape-sequence:
1227 \x hexadecimal-digit
1228 hexadecimal-escape-sequence hexadecimal-digit
1229
12301.6) String literals
1231
1232string-literal:
1233 " s-char-sequence-opt "
1234 L" s-char-sequence-opt "
1235
1236s-char-sequence:
1237 s-char
1238 s-char-sequence s-char
1239
1240s-char:
1241 any member of source charset except double-quote ("), backslash
1242 (\), or new-line character.
1243 escape-sequence
1244
12451.7) Punctuators
1246
1247punctuator: one of
1248 [ ] ( ) { } . -> * + - < > : ; ... = ,
1249
1250
12512) Phrase structure grammar
1252
1253primary-expression:
1254 identifier
1255 constant
1256 string-literal
1257 ( unary-expression )
1258
1259postfix-expression:
1260 primary-expression
1261 postfix-expression [ unary-expression ]
1262 postfix-expression . identifier
1263 postfix-expressoin -> identifier
1264
1265unary-expression:
1266 postfix-expression
1267 unary-operator postfix-expression
1268
1269unary-operator: one of
1270 + -
1271
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1272assignment-operator:
1273 =
1274
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1275type-assignment-operator:
1276 :=
1277
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1278constant-expression:
1279 unary-expression
1280
1281constant-expression-range:
1282 constant-expression ... constant-expression
1283
12842.2) Declarations:
1285
1286declaration:
689e04b4 1287 declaration-specifiers declarator-list-opt ;
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1288 ctf-specifier ;
1289
1290declaration-specifiers:
689e04b4 1291 storage-class-specifier declaration-specifiers-opt
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1292 type-specifier declaration-specifiers-opt
1293 type-qualifier declaration-specifiers-opt
1294
1295declarator-list:
1296 declarator
1297 declarator-list , declarator
1298
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1299abstract-declarator-list:
1300 abstract-declarator
1301 abstract-declarator-list , abstract-declarator
1302
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1303storage-class-specifier:
1304 typedef
1305
1306type-specifier:
1307 void
1308 char
1309 short
1310 int
1311 long
1312 float
1313 double
1314 signed
1315 unsigned
1316 _Bool
1317 _Complex
cfdd51ec 1318 _Imaginary
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1319 struct-specifier
1320 variant-specifier
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1321 enum-specifier
1322 typedef-name
1323 ctf-type-specifier
1324
1325struct-specifier:
3b0f8e4d 1326 struct identifier-opt { struct-or-variant-declaration-list-opt }
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1327 struct identifier
1328
1329struct-or-variant-declaration-list:
1330 struct-or-variant-declaration
1331 struct-or-variant-declaration-list struct-or-variant-declaration
1332
1333struct-or-variant-declaration:
1334 specifier-qualifier-list struct-or-variant-declarator-list ;
550aca33 1335 declaration-specifiers storage-class-specifier declaration-specifiers declarator-list ;
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1336 typealias declaration-specifiers abstract-declarator-list := declaration-specifiers abstract-declarator-list ;
1337 typealias declaration-specifiers abstract-declarator-list := declarator-list ;
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1338
1339specifier-qualifier-list:
1340 type-specifier specifier-qualifier-list-opt
1341 type-qualifier specifier-qualifier-list-opt
1342
1343struct-or-variant-declarator-list:
1344 struct-or-variant-declarator
1345 struct-or-variant-declarator-list , struct-or-variant-declarator
1346
1347struct-or-variant-declarator:
1348 declarator
1349 declarator-opt : constant-expression
1350
1351variant-specifier:
1352 variant identifier-opt variant-tag-opt { struct-or-variant-declaration-list }
1353 variant identifier variant-tag
1354
1355variant-tag:
1356 < identifier >
1357
1358enum-specifier:
1359 enum identifier-opt { enumerator-list }
1360 enum identifier-opt { enumerator-list , }
1361 enum identifier
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1362 enum identifier-opt : declaration-specifiers { enumerator-list }
1363 enum identifier-opt : declaration-specifiers { enumerator-list , }
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1364
1365enumerator-list:
1366 enumerator
1367 enumerator-list , enumerator
1368
1369enumerator:
1370 enumeration-constant
1371 enumeration-constant = constant-expression
1372 enumeration-constant = constant-expression-range
1373
1374type-qualifier:
1375 const
1376
1377declarator:
1378 pointer-opt direct-declarator
1379
1380direct-declarator:
1381 identifier
1382 ( declarator )
1383 direct-declarator [ type-specifier ]
1384 direct-declarator [ constant-expression ]
1385
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1386abstract-declarator:
1387 pointer-opt direct-abstract-declarator
1388
1389direct-abstract-declarator:
1390 identifier-opt
1391 ( abstract-declarator )
1392 direct-abstract-declarator [ type-specifier ]
1393 direct-abstract-declarator [ constant-expression ]
1394 direct-abstract-declarator [ ]
1395
4fa992a5 1396pointer:
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1397 * type-qualifier-list-opt
1398 * type-qualifier-list-opt pointer
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1399
1400type-qualifier-list:
1401 type-qualifier
1402 type-qualifier-list type-qualifier
1403
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1404typedef-name:
1405 identifier
1406
14072.3) CTF-specific declarations
1408
1409ctf-specifier:
1410 event { ctf-assignment-expression-list-opt }
1411 stream { ctf-assignment-expression-list-opt }
1412 trace { ctf-assignment-expression-list-opt }
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1413 typealias declaration-specifiers abstract-declarator-list := declaration-specifiers abstract-declarator-list ;
1414 typealias declaration-specifiers abstract-declarator-list := declarator-list ;
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1415
1416ctf-type-specifier:
1417 floating_point { ctf-assignment-expression-list-opt }
1418 integer { ctf-assignment-expression-list-opt }
1419 string { ctf-assignment-expression-list-opt }
1420
1421ctf-assignment-expression-list:
1422 ctf-assignment-expression
1423 ctf-assignment-expression-list ; ctf-assignment-expression
1424
1425ctf-assignment-expression:
1426 unary-expression assignment-operator unary-expression
1427 unary-expression type-assignment-operator type-specifier
550aca33 1428 declaration-specifiers storage-class-specifier declaration-specifiers declarator-list
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1429 typealias declaration-specifiers abstract-declarator-list := declaration-specifiers abstract-declarator-list
1430 typealias declaration-specifiers abstract-declarator-list := declarator-list
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