Add trace { endian = big/little; } field
[ctf.git] / common-trace-format-proposal.txt
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5ba9f198 1
4767a9e7 2RFC: Common Trace Format (CTF) Proposal (pre-v1.7)
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3
4Mathieu Desnoyers, EfficiOS Inc.
5
6The goal of the present document is to propose a trace format that suits the
cc089c3a 7needs of the embedded, telecom, high-performance and kernel communities. It is
5ba9f198 8based on the Common Trace Format Requirements (v1.4) document. It is designed to
cc089c3a 9allow traces to be natively generated by the Linux kernel, Linux user-space
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10applications written in C/C++, and hardware components. One major element of
11CTF is the Trace Stream Description Language (TSDL) which flexibility
12enables description of various binary trace stream layouts.
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13
14The latest version of this document can be found at:
15
16 git tree: git://git.efficios.com/ctf.git
17 gitweb: http://git.efficios.com/?p=ctf.git
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18
19A reference implementation of a library to read and write this trace format is
20being implemented within the BabelTrace project, a converter between trace
21formats. The development tree is available at:
22
23 git tree: git://git.efficios.com/babeltrace.git
24 gitweb: http://git.efficios.com/?p=babeltrace.git
25
26
271. Preliminary definitions
28
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29 - Event Trace: An ordered sequence of events.
30 - Event Stream: An ordered sequence of events, containing a subset of the
31 trace event types.
32 - Event Packet: A sequence of physically contiguous events within an event
33 stream.
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34 - Event: This is the basic entry in a trace. (aka: a trace record).
35 - An event identifier (ID) relates to the class (a type) of event within
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36 an event stream.
37 e.g. event: irq_entry.
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38 - An event (or event record) relates to a specific instance of an event
39 class.
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40 e.g. event: irq_entry, at time X, on CPU Y
41 - Source Architecture: Architecture writing the trace.
42 - Reader Architecture: Architecture reading the trace.
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43
44
452. High-level representation of a trace
46
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47A trace is divided into multiple event streams. Each event stream contains a
48subset of the trace event types.
5ba9f198 49
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50The final output of the trace, after its generation and optional transport over
51the network, is expected to be either on permanent or temporary storage in a
52virtual file system. Because each event stream is appended to while a trace is
53being recorded, each is associated with a separate file for output. Therefore,
54a stored trace can be represented as a directory containing one file per stream.
5ba9f198 55
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56A metadata event stream contains information on trace event types
57expressed in the Trace Stream Description Language (TSDL). It describes:
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58
59- Trace version.
60- Types available.
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61- Per-stream event header description.
62- Per-stream event header selection.
63- Per-stream event context fields.
5ba9f198 64- Per-event
3bf79539 65 - Event type to stream mapping.
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66 - Event type to name mapping.
67 - Event type to ID mapping.
68 - Event fields description.
69
70
3bf79539 713. Event stream
5ba9f198 72
3bf79539 73An event stream is divided in contiguous event packets of variable size. These
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74subdivisions have a variable size. An event packet can contain a certain
75amount of padding at the end. The stream header is repeated at the
76beginning of each event packet. The rationale for the event stream
77design choices is explained in Appendix B. Stream Header Rationale.
5ba9f198 78
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79The event stream header will therefore be referred to as the "event packet
80header" throughout the rest of this document.
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81
82
834. Types
84
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85Types are organized as type classes. Each type class belong to either of two
86kind of types: basic types or compound types.
87
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884.1 Basic types
89
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90A basic type is a scalar type, as described in this section. It includes
91integers, GNU/C bitfields, enumerations, and floating point values.
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92
934.1.1 Type inheritance
94
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95Type specifications can be inherited to allow deriving types from a
96type class. For example, see the uint32_t named type derived from the "integer"
97type class below ("Integers" section). Types have a precise binary
98representation in the trace. A type class has methods to read and write these
99types, but must be derived into a type to be usable in an event field.
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100
1014.1.2 Alignment
102
103We define "byte-packed" types as aligned on the byte size, namely 8-bit.
104We define "bit-packed" types as following on the next bit, as defined by the
370eae99 105"Integers" section.
5ba9f198 106
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107All basic types, except bitfields, are either aligned on an architecture-defined
108specific alignment or byte-packed, depending on the architecture preference.
109Architectures providing fast unaligned write byte-packed basic types to save
5ba9f198 110space, aligning each type on byte boundaries (8-bit). Architectures with slow
3bf79539 111unaligned writes align types on specific alignment values. If no specific
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112alignment is declared for a type, it is assumed to be bit-packed for
113integers with size not multiple of 8 bits and for gcc bitfields. All
114other types are byte-packed.
5ba9f198 115
3bf79539 116Metadata attribute representation of a specific alignment:
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117
118 align = value; /* value in bits */
119
1204.1.3 Byte order
121
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122By default, the native endianness of the source architecture the trace is used.
123Byte order can be overridden for a basic type by specifying a "byte_order"
124attribute. Typical use-case is to specify the network byte order (big endian:
125"be") to save data captured from the network into the trace without conversion.
126If not specified, the byte order is native.
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127
128Metadata representation:
129
130 byte_order = native OR network OR be OR le; /* network and be are aliases */
131
1324.1.4 Size
133
134Type size, in bits, for integers and floats is that returned by "sizeof()" in C
135multiplied by CHAR_BIT.
136We require the size of "char" and "unsigned char" types (CHAR_BIT) to be fixed
137to 8 bits for cross-endianness compatibility.
138
139Metadata representation:
140
141 size = value; (value is in bits)
142
1434.1.5 Integers
144
145Signed integers are represented in two-complement. Integer alignment, size,
146signedness and byte ordering are defined in the metadata. Integers aligned on
147byte size (8-bit) and with length multiple of byte size (8-bit) correspond to
148the C99 standard integers. In addition, integers with alignment and/or size that
149are _not_ a multiple of the byte size are permitted; these correspond to the C99
150standard bitfields, with the added specification that the CTF integer bitfields
151have a fixed binary representation. A MIT-licensed reference implementation of
152the CTF portable bitfields is available at:
153
154 http://git.efficios.com/?p=babeltrace.git;a=blob;f=include/babeltrace/bitfield.h
155
156Binary representation of integers:
157
158- On little and big endian:
159 - Within a byte, high bits correspond to an integer high bits, and low bits
160 correspond to low bits.
161- On little endian:
162 - Integer across multiple bytes are placed from the less significant to the
163 most significant.
164 - Consecutive integers are placed from lower bits to higher bits (even within
165 a byte).
166- On big endian:
167 - Integer across multiple bytes are placed from the most significant to the
168 less significant.
169 - Consecutive integers are placed from higher bits to lower bits (even within
170 a byte).
171
172This binary representation is derived from the bitfield implementation in GCC
173for little and big endian. However, contrary to what GCC does, integers can
174cross units boundaries (no padding is required). Padding can be explicitely
175added (see 4.1.6 GNU/C bitfields) to follow the GCC layout if needed.
176
177Metadata representation:
178
80fd2569 179 integer {
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180 signed = true OR false; /* default false */
181 byte_order = native OR network OR be OR le; /* default native */
182 size = value; /* value in bits, no default */
183 align = value; /* value in bits */
2152348f 184 }
5ba9f198 185
80fd2569 186Example of type inheritance (creation of a uint32_t named type):
5ba9f198 187
359894ac 188typealias integer {
9e4e34e9 189 size = 32;
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190 signed = false;
191 align = 32;
38b8da21 192} := uint32_t;
5ba9f198 193
80fd2569 194Definition of a named 5-bit signed bitfield:
5ba9f198 195
359894ac 196typealias integer {
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197 size = 5;
198 signed = true;
199 align = 1;
38b8da21 200} := int5_t;
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201
2024.1.6 GNU/C bitfields
203
204The GNU/C bitfields follow closely the integer representation, with a
205particularity on alignment: if a bitfield cannot fit in the current unit, the
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206unit is padded and the bitfield starts at the following unit. The unit size is
207defined by the size of the type "unit_type".
5ba9f198 208
2152348f 209Metadata representation:
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210
211 unit_type name:size:
212
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213As an example, the following structure declared in C compiled by GCC:
214
215struct example {
216 short a:12;
217 short b:5;
218};
219
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220The example structure is aligned on the largest element (short). The second
221bitfield would be aligned on the next unit boundary, because it would not fit in
222the current unit.
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223
2244.1.7 Floating point
225
226The floating point values byte ordering is defined in the metadata.
227
228Floating point values follow the IEEE 754-2008 standard interchange formats.
229Description of the floating point values include the exponent and mantissa size
230in bits. Some requirements are imposed on the floating point values:
231
232- FLT_RADIX must be 2.
233- mant_dig is the number of digits represented in the mantissa. It is specified
234 by the ISO C99 standard, section 5.2.4, as FLT_MANT_DIG, DBL_MANT_DIG and
235 LDBL_MANT_DIG as defined by <float.h>.
236- exp_dig is the number of digits represented in the exponent. Given that
237 mant_dig is one bit more than its actual size in bits (leading 1 is not
238 needed) and also given that the sign bit always takes one bit, exp_dig can be
239 specified as:
240
241 - sizeof(float) * CHAR_BIT - FLT_MANT_DIG
242 - sizeof(double) * CHAR_BIT - DBL_MANT_DIG
243 - sizeof(long double) * CHAR_BIT - LDBL_MANT_DIG
244
245Metadata representation:
246
80fd2569 247floating_point {
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248 exp_dig = value;
249 mant_dig = value;
250 byte_order = native OR network OR be OR le;
2152348f 251}
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252
253Example of type inheritance:
254
359894ac 255typealias floating_point {
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256 exp_dig = 8; /* sizeof(float) * CHAR_BIT - FLT_MANT_DIG */
257 mant_dig = 24; /* FLT_MANT_DIG */
258 byte_order = native;
38b8da21 259} := float;
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260
261TODO: define NaN, +inf, -inf behavior.
262
2634.1.8 Enumerations
264
265Enumerations are a mapping between an integer type and a table of strings. The
266numerical representation of the enumeration follows the integer type specified
267by the metadata. The enumeration mapping table is detailed in the enumeration
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268description within the metadata. The mapping table maps inclusive value ranges
269(or single values) to strings. Instead of being limited to simple
270"value -> string" mappings, these enumerations map
80fd2569 271"[ start_value ... end_value ] -> string", which map inclusive ranges of
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272values to strings. An enumeration from the C language can be represented in
273this format by having the same start_value and end_value for each element, which
274is in fact a range of size 1. This single-value range is supported without
4767a9e7 275repeating the start and end values with the value = string declaration.
80fd2569 276
a9b83695 277enum name : integer_type {
359894ac 278 somestring = start_value1 ... end_value1,
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279 "other string" = start_value2 ... end_value2,
280 yet_another_string, /* will be assigned to end_value2 + 1 */
281 "some other string" = value,
282 ...
283};
284
285If the values are omitted, the enumeration starts at 0 and increment of 1 for
286each entry:
287
a9b83695 288enum name : unsigned int {
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289 ZERO,
290 ONE,
291 TWO,
292 TEN = 10,
293 ELEVEN,
3bf79539 294};
5ba9f198 295
80fd2569 296Overlapping ranges within a single enumeration are implementation defined.
5ba9f198 297
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298A nameless enumeration can be declared as a field type or as part of a typedef:
299
a9b83695 300enum : integer_type {
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301 ...
302}
303
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304Enumerations omitting the container type ": integer_type" use the "int"
305type (for compatibility with C99). The "int" type must be previously
306declared. E.g.:
307
308typealias integer { size = 32; align = 32; signed = true } := int;
309
310enum {
311 ...
312}
313
1fad7a85 314
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3154.2 Compound types
316
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317Compound are aggregation of type declarations. Compound types include
318structures, variant, arrays, sequences, and strings.
319
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3204.2.1 Structures
321
322Structures are aligned on the largest alignment required by basic types
323contained within the structure. (This follows the ISO/C standard for structures)
324
80fd2569 325Metadata representation of a named structure:
5ba9f198 326
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327struct name {
328 field_type field_name;
329 field_type field_name;
330 ...
331};
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332
333Example:
334
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335struct example {
336 integer { /* Nameless type */
337 size = 16;
338 signed = true;
339 align = 16;
340 } first_field_name;
341 uint64_t second_field_name; /* Named type declared in the metadata */
3bf79539 342};
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343
344The fields are placed in a sequence next to each other. They each possess a
345field name, which is a unique identifier within the structure.
346
2152348f 347A nameless structure can be declared as a field type or as part of a typedef:
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348
349struct {
350 ...
2152348f 351}
80fd2569 352
77a98c82 3534.2.2 Variants (Discriminated/Tagged Unions)
fcba70d4 354
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355A CTF variant is a selection between different types. A CTF variant must
356always be defined within the scope of a structure or within fields
357contained within a structure (defined recursively). A "tag" enumeration
358field must appear in either the same lexical scope, prior to the variant
359field (in field declaration order), in an uppermost lexical scope (see
6c7226e9 360Section 7.3.1), or in an uppermost dynamic scope (see Section 7.3.2).
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361The type selection is indicated by the mapping from the enumeration
362value to the string used as variant type selector. The field to use as
363tag is specified by the "tag_field", specified between "< >" after the
364"variant" keyword for unnamed variants, and after "variant name" for
365named variants.
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366
367The alignment of the variant is the alignment of the type as selected by the tag
368value for the specific instance of the variant. The alignment of the type
369containing the variant is independent of the variant alignment. The size of the
370variant is the size as selected by the tag value for the specific instance of
371the variant.
372
373A named variant declaration followed by its definition within a structure
374declaration:
375
376variant name {
377 field_type sel1;
378 field_type sel2;
379 field_type sel3;
380 ...
381};
382
383struct {
a9b83695 384 enum : integer_type { sel1, sel2, sel3, ... } tag_field;
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385 ...
386 variant name <tag_field> v;
387}
388
389An unnamed variant definition within a structure is expressed by the following
390metadata:
391
392struct {
a9b83695 393 enum : integer_type { sel1, sel2, sel3, ... } tag_field;
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394 ...
395 variant <tag_field> {
396 field_type sel1;
397 field_type sel2;
398 field_type sel3;
399 ...
400 } v;
401}
402
403Example of a named variant within a sequence that refers to a single tag field:
404
405variant example {
406 uint32_t a;
407 uint64_t b;
408 short c;
409};
410
411struct {
a9b83695 412 enum : uint2_t { a, b, c } choice;
15850440 413 variant example <choice> v[unsigned int];
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414}
415
416Example of an unnamed variant:
417
418struct {
a9b83695 419 enum : uint2_t { a, b, c, d } choice;
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420 /* Unrelated fields can be added between the variant and its tag */
421 int32_t somevalue;
422 variant <choice> {
423 uint32_t a;
424 uint64_t b;
425 short c;
426 struct {
427 unsigned int field1;
428 uint64_t field2;
429 } d;
430 } s;
431}
432
433Example of an unnamed variant within an array:
434
435struct {
a9b83695 436 enum : uint2_t { a, b, c } choice;
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437 variant <choice> {
438 uint32_t a;
439 uint64_t b;
440 short c;
15850440 441 } v[10];
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442}
443
444Example of a variant type definition within a structure, where the defined type
445is then declared within an array of structures. This variant refers to a tag
446located in an upper lexical scope. This example clearly shows that a variant
447type definition referring to the tag "x" uses the closest preceding field from
448the lexical scope of the type definition.
449
450struct {
a9b83695 451 enum : uint2_t { a, b, c, d } x;
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452
453 typedef variant <x> { /*
454 * "x" refers to the preceding "x" enumeration in the
455 * lexical scope of the type definition.
456 */
457 uint32_t a;
458 uint64_t b;
459 short c;
460 } example_variant;
461
462 struct {
a9b83695 463 enum : int { x, y, z } x; /* This enumeration is not used by "v". */
fcba70d4 464 example_variant v; /*
a9b83695 465 * "v" uses the "enum : uint2_t { a, b, c, d }"
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466 * tag.
467 */
468 } a[10];
469}
470
4714.2.3 Arrays
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472
473Arrays are fixed-length. Their length is declared in the type declaration within
474the metadata. They contain an array of "inner type" elements, which can refer to
475any type not containing the type of the array being declared (no circular
3bf79539 476dependency). The length is the number of elements in an array.
5ba9f198 477
2152348f 478Metadata representation of a named array:
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479
480typedef elem_type name[length];
5ba9f198 481
2152348f 482A nameless array can be declared as a field type within a structure, e.g.:
5ba9f198 483
2152348f 484 uint8_t field_name[10];
80fd2569 485
5ba9f198 486
fcba70d4 4874.2.4 Sequences
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488
489Sequences are dynamically-sized arrays. They start with an integer that specify
490the length of the sequence, followed by an array of "inner type" elements.
3bf79539 491The length is the number of elements in the sequence.
5ba9f198 492
2152348f 493Metadata representation for a named sequence:
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494
495typedef elem_type name[length_type];
496
497A nameless sequence can be declared as a field type, e.g.:
498
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499long field_name[int];
500
501The length type follows the integer types specifications, and the sequence
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502elements follow the "array" specifications.
503
fcba70d4 5044.2.5 Strings
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505
506Strings are an array of bytes of variable size and are terminated by a '\0'
507"NULL" character. Their encoding is described in the metadata. In absence of
508encoding attribute information, the default encoding is UTF-8.
509
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510Metadata representation of a named string type:
511
359894ac 512typealias string {
5ba9f198 513 encoding = UTF8 OR ASCII;
38b8da21 514} := name;
5ba9f198 515
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516A nameless string type can be declared as a field type:
517
518string field_name; /* Use default UTF8 encoding */
5ba9f198 519
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5205. Event Packet Header
521
522The event packet header consists of two part: one is mandatory and have a fixed
523layout. The second part, the "event packet context", has its layout described in
524the metadata.
5ba9f198 525
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526- Aligned on page size. Fixed size. Fields either aligned or packed (depending
527 on the architecture preference).
528 No padding at the end of the event packet header. Native architecture byte
5ba9f198 529 ordering.
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530
531Fixed layout (event packet header):
532
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533- Magic number (CTF magic numbers: 0xC1FC1FC1 and its reverse endianness
534 representation: 0xC11FFCC1) It needs to have a non-symmetric bytewise
535 representation. Used to distinguish between big and little endian traces (this
536 information is determined by knowing the endianness of the architecture
537 reading the trace and comparing the magic number against its value and the
538 reverse, 0xC11FFCC1). This magic number specifies that we use the CTF metadata
539 description language described in this document. Different magic numbers
540 should be used for other metadata description languages.
3bf79539 541- Trace UUID, used to ensure the event packet match the metadata used.
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542 (note: we cannot use a metadata checksum because metadata can be appended to
543 while tracing is active)
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544- Stream ID, used as reference to stream description in metadata.
545
546Metadata-defined layout (event packet context):
547
548- Event packet content size (in bytes).
549- Event packet size (in bytes, includes padding).
550- Event packet content checksum (optional). Checksum excludes the event packet
551 header.
552- Per-stream event packet sequence count (to deal with UDP packet loss). The
553 number of significant sequence counter bits should also be present, so
554 wrap-arounds are deal with correctly.
555- Timestamp at the beginning and timestamp at the end of the event packet.
556 Both timestamps are written in the packet header, but sampled respectively
557 while (or before) writing the first event and while (or after) writing the
558 last event in the packet. The inclusive range between these timestamps should
559 include all event timestamps assigned to events contained within the packet.
5ba9f198 560- Events discarded count
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561 - Snapshot of a per-stream free-running counter, counting the number of
562 events discarded that were supposed to be written in the stream prior to
563 the first event in the event packet.
5ba9f198 564 * Note: producer-consumer buffer full condition should fill the current
3bf79539 565 event packet with padding so we know exactly where events have been
5ba9f198 566 discarded.
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567- Lossless compression scheme used for the event packet content. Applied
568 directly to raw data. New types of compression can be added in following
569 versions of the format.
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570 0: no compression scheme
571 1: bzip2
572 2: gzip
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573 3: xz
574- Cypher used for the event packet content. Applied after compression.
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575 0: no encryption
576 1: AES
3bf79539 577- Checksum scheme used for the event packet content. Applied after encryption.
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578 0: no checksum
579 1: md5
580 2: sha1
581 3: crc32
582
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5835.1 Event Packet Header Fixed Layout Description
584
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585The event packet header layout is indicated by the trace packet.header
586field. Here is an example structure type for the packet header with the
587fields typically expected:
588
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589struct event_packet_header {
590 uint32_t magic;
591 uint8_t trace_uuid[16];
3bf79539 592 uint32_t stream_id;
80fd2569 593};
5ba9f198 594
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595trace {
596 ...
597 packet.header := struct event_packet_header;
598};
599
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6005.2 Event Packet Context Description
601
602Event packet context example. These are declared within the stream declaration
603in the metadata. All these fields are optional except for "content_size" and
604"packet_size", which must be present in the context.
605
606An example event packet context type:
607
80fd2569 608struct event_packet_context {
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609 uint64_t timestamp_begin;
610 uint64_t timestamp_end;
611 uint32_t checksum;
612 uint32_t stream_packet_count;
613 uint32_t events_discarded;
614 uint32_t cpu_id;
615 uint32_t/uint16_t content_size;
616 uint32_t/uint16_t packet_size;
617 uint8_t stream_packet_count_bits; /* Significant counter bits */
618 uint8_t compression_scheme;
619 uint8_t encryption_scheme;
3b0f8e4d 620 uint8_t checksum_scheme;
3bf79539 621};
5ba9f198 622
fcba70d4 623
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6246. Event Structure
625
626The overall structure of an event is:
627
fcba70d4 6281 - Stream Packet Context (as specified by the stream metadata)
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629 2 - Event Header (as specified by the stream metadata)
630 3 - Stream Event Context (as specified by the stream metadata)
631 4 - Event Context (as specified by the event metadata)
632 5 - Event Payload (as specified by the event metadata)
5ba9f198 633
fdf2bb05 634This structure defines an implicit dynamic scoping, where variants
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635located in inner structures (those with a higher number in the listing
636above) can refer to the fields of outer structures (with lower number in
6c7226e9 637the listing above). See Section 7.3 TSDL Scopes for more detail.
5ba9f198 638
fdf2bb05 6396.1 Event Header
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640
641Event headers can be described within the metadata. We hereby propose, as an
642example, two types of events headers. Type 1 accommodates streams with less than
64331 event IDs. Type 2 accommodates streams with 31 or more event IDs.
5ba9f198 644
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645One major factor can vary between streams: the number of event IDs assigned to
646a stream. Luckily, this information tends to stay relatively constant (modulo
5ba9f198 647event registration while trace is being recorded), so we can specify different
3bf79539 648representations for streams containing few event IDs and streams containing
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649many event IDs, so we end up representing the event ID and timestamp as densely
650as possible in each case.
651
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652The header is extended in the rare occasions where the information cannot be
653represented in the ranges available in the standard event header. They are also
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654used in the rare occasions where the data required for a field could not be
655collected: the flag corresponding to the missing field within the missing_fields
656array is then set to 1.
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657
658Types uintX_t represent an X-bit unsigned integer.
659
660
fdf2bb05 6616.1.1 Type 1 - Few event IDs
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662
663 - Aligned on 32-bit (or 8-bit if byte-packed, depending on the architecture
664 preference).
5ba9f198 665 - Native architecture byte ordering.
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666 - For "compact" selection
667 - Fixed size: 32 bits.
668 - For "extended" selection
669 - Size depends on the architecture and variant alignment.
5ba9f198 670
80fd2569 671struct event_header_1 {
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672 /*
673 * id: range: 0 - 30.
674 * id 31 is reserved to indicate an extended header.
675 */
a9b83695 676 enum : uint5_t { compact = 0 ... 30, extended = 31 } id;
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677 variant <id> {
678 struct {
679 uint27_t timestamp;
680 } compact;
681 struct {
682 uint32_t id; /* 32-bit event IDs */
683 uint64_t timestamp; /* 64-bit timestamps */
684 } extended;
685 } v;
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686};
687
5ba9f198 688
fdf2bb05 6896.1.2 Type 2 - Many event IDs
5ba9f198 690
fcba70d4 691 - Aligned on 16-bit (or 8-bit if byte-packed, depending on the architecture
5ba9f198 692 preference).
5ba9f198 693 - Native architecture byte ordering.
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694 - For "compact" selection
695 - Size depends on the architecture and variant alignment.
696 - For "extended" selection
697 - Size depends on the architecture and variant alignment.
5ba9f198 698
80fd2569 699struct event_header_2 {
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700 /*
701 * id: range: 0 - 65534.
702 * id 65535 is reserved to indicate an extended header.
703 */
a9b83695 704 enum : uint16_t { compact = 0 ... 65534, extended = 65535 } id;
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705 variant <id> {
706 struct {
707 uint32_t timestamp;
708 } compact;
709 struct {
710 uint32_t id; /* 32-bit event IDs */
711 uint64_t timestamp; /* 64-bit timestamps */
712 } extended;
713 } v;
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714};
715
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716
7176.2 Event Context
718
719The event context contains information relative to the current event. The choice
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720and meaning of this information is specified by the metadata "stream" and
721"event" information. The "stream" context is applied to all events within the
722stream. The "stream" context structure follows the event header. The "event"
723context is applied to specific events. Its structure follows the "stream"
724context stucture.
5ba9f198 725
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726An example of stream-level event context is to save the event payload size with
727each event, or to save the current PID with each event. These are declared
728within the stream declaration within the metadata:
5ba9f198 729
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730 stream {
731 ...
732 event {
733 ...
4fa992a5 734 context := struct {
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735 uint pid;
736 uint16_t payload_size;
3bf79539 737 };
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738 }
739 };
740
741An example of event-specific event context is to declare a bitmap of missing
742fields, only appended after the stream event context if the extended event
743header is selected. NR_FIELDS is the number of fields within the event (a
744numeric value).
5ba9f198 745
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746 event {
747 context = struct {
748 variant <id> {
749 struct { } compact;
750 struct {
751 uint1_t missing_fields[NR_FIELDS]; /* missing event fields bitmap */
752 } extended;
753 } v;
754 };
755 ...
756 }
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757
7586.3 Event Payload
759
760An event payload contains fields specific to a given event type. The fields
761belonging to an event type are described in the event-specific metadata
762within a structure type.
763
7646.3.1 Padding
765
766No padding at the end of the event payload. This differs from the ISO/C standard
767for structures, but follows the CTF standard for structures. In a trace, even
768though it makes sense to align the beginning of a structure, it really makes no
769sense to add padding at the end of the structure, because structures are usually
770not followed by a structure of the same type.
771
772This trick can be done by adding a zero-length "end" field at the end of the C
773structures, and by using the offset of this field rather than using sizeof()
3bf79539 774when calculating the size of a structure (see Appendix "A. Helper macros").
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775
7766.3.2 Alignment
777
778The event payload is aligned on the largest alignment required by types
779contained within the payload. (This follows the ISO/C standard for structures)
780
781
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7827. Trace Stream Description Language (TSDL)
783
784The Trace Stream Description Language (TSDL) allows expression of the
785binary trace streams layout in a C99-like Domain Specific Language
786(DSL).
787
788
7897.1 Metadata
790
791The trace stream layout description is located in the trace meta-data.
792The meta-data is itself located in a stream identified by its name:
793"metadata".
5ba9f198 794
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795It is made of "event packets", which each start with an event packet
796header. The event type within the metadata stream have no event header
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797nor event context. Each event only contains a "string" payload without
798any null-character. The events are packed one next to another. Each
799event packet start with an event packet header, which contains, amongst
800other fields, the magic number, trace UUID and packet length. In the
801event packet header, the trace UUID is represented as an array of bytes.
802Within the string-based metadata description, the trace UUID is
803represented as a string of hexadecimal digits and dashes "-".
4fafe1ad 804
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805The metadata can be parsed by reading characters within the metadata
806stream, for each packet starting after the packet header, for the length
807of the packet payload specified in the header. Text contained within
808"/*" and "*/", as well as within "//" and end of line, are treated as
809comments. Boolean values can be represented as true, TRUE, or 1 for
810true, and false, FALSE, or 0 for false.
fcba70d4 811
fdf2bb05 812
6c7226e9 8137.2 Declaration vs Definition
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814
815A declaration associates a layout to a type, without specifying where
816this type is located in the event structure hierarchy (see Section 6).
817This therefore includes typedef, typealias, as well as all type
818specifiers. In certain circumstances (typedef, structure field and
819variant field), a declaration is followed by a declarator, which specify
820the newly defined type name (for typedef), or the field name (for
821declarations located within structure and variants). Array and sequence,
822declared with square brackets ("[" "]"), are part of the declarator,
a9b83695 823similarly to C99. The enumeration base type is specified by
6c7226e9 824": enum_base", which is part of the type specifier. The variant tag
a9b83695 825name, specified between "<" ">", is also part of the type specifier.
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826
827A definition associates a type to a location in the event structure
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828hierarchy (see Section 6). This association is denoted by ":=", as shown
829in Section 7.3.
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830
831
6c7226e9 8327.3 TSDL Scopes
fdf2bb05 833
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834TSDL uses two different types of scoping: a lexical scope is used for
835declarations and type definitions, and a dynamic scope is used for
836variants references to tag fields.
fdf2bb05 837
6c7226e9 8387.3.1 Lexical Scope
fdf2bb05 839
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840Each of "trace", "stream", "event", "struct" and "variant" have their own
841nestable declaration scope, within which types can be declared using "typedef"
fdf2bb05 842and "typealias". A root declaration scope also contains all declarations
7d9d7e92 843located outside of any of the aforementioned declarations. An inner
fdf2bb05 844declaration scope can refer to type declared within its container
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845lexical scope prior to the inner declaration scope. Redefinition of a
846typedef or typealias is not valid, although hiding an upper scope
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847typedef or typealias is allowed within a sub-scope.
848
6c7226e9 8497.3.2 Dynamic Scope
fdf2bb05 850
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851A dynamic scope consists in the lexical scope augmented with the
852implicit event structure definition hierarchy presented at Section 6.
853The dynamic scope is only used for variant tag definitions. It is used
854at definition time to look up the location of the tag field associated
855with a variant.
856
857Therefore, variants in lower levels in the dynamic scope (e.g. event
858context) can refer to a tag field located in upper levels (e.g. in the
859event header) by specifying, in this case, the associated tag with
860<header.field_name>. This allows, for instance, the event context to
861define a variant referring to the "id" field of the event header as
862selector.
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863
864The target dynamic scope must be specified explicitly when referring to
865a field outside of the local static scope. The dynamic scope prefixes
866are thus:
867
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868 - Stream Packet Context: <stream.packet.context. >,
869 - Event Header: <stream.event.header. >,
870 - Stream Event Context: <stream.event.context. >,
871 - Event Context: <event.context. >,
872 - Event Payload: <event.fields. >.
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873
874Multiple declarations of the same field name within a single scope is
875not valid. It is however valid to re-use the same field name in
876different scopes. There is no possible conflict, because the dynamic
877scope must be specified when a variant refers to a tag field located in
878a different dynamic scope.
879
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880The information available in the dynamic scopes can be thought of as the
881current tracing context. At trace production, information about the
882current context is saved into the specified scope field levels. At trace
883consumption, for each event, the current trace context is therefore
884readable by accessing the upper dynamic scopes.
885
fdf2bb05 886
6c7226e9 8877.4 TSDL Examples
d285084f 888
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889The grammar representing the TSDL metadata is presented in Appendix C.
890TSDL Grammar. This section presents a rather ligher reading that
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891consists in examples of TSDL metadata, with template values.
892
893Note that the trace endianness is usually extracted from the packet
894header magic number. The "endian" field is only needed when the magic
895number packet header field is not present.
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896
897trace {
fdf2bb05 898 major = value; /* Trace format version */
5ba9f198 899 minor = value;
fdf2bb05 900 uuid = "aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaaa"; /* Trace UUID */
969f30c0 901 endian = big OR little; /* Endianness (optional) */
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902 packet.header := struct {
903 uint32_t magic;
904 uint8_t trace_uuid[16];
905 uint32_t stream_id;
906 };
3bf79539 907};
5ba9f198 908
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909stream {
910 id = stream_id;
fdf2bb05 911 /* Type 1 - Few event IDs; Type 2 - Many event IDs. See section 6.1. */
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912 event.header := event_header_1 OR event_header_2;
913 event.context := struct {
77a98c82 914 ...
3bf79539 915 };
4fa992a5 916 packet.context := struct {
77a98c82 917 ...
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918 };
919};
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920
921event {
3d13ef1a 922 name = event_name;
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923 id = value; /* Numeric identifier within the stream */
924 stream = stream_id;
4fa992a5 925 context := struct {
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926 ...
927 };
4fa992a5 928 fields := struct {
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929 ...
930 };
3bf79539 931};
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932
933/* More detail on types in section 4. Types */
934
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935/*
936 * Named types:
937 *
4fa992a5 938 * Type declarations behave similarly to the C standard.
3d13ef1a
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939 */
940
80af8ac6 941typedef aliased_type_specifiers new_type_declarators;
2152348f 942
3d13ef1a 943/* e.g.: typedef struct example new_type_name[10]; */
80fd2569 944
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945/*
946 * typealias
947 *
948 * The "typealias" declaration can be used to give a name (including
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949 * pointer declarator specifier) to a type. It should also be used to
950 * map basic C types (float, int, unsigned long, ...) to a CTF type.
951 * Typealias is a superset of "typedef": it also allows assignment of a
38b8da21 952 * simple variable identifier to a type.
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953 */
954
955typealias type_class {
80fd2569 956 ...
38b8da21 957} := type_specifiers type_declarator;
2152348f 958
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959/*
960 * e.g.:
4fa992a5 961 * typealias integer {
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MD
962 * size = 32;
963 * align = 32;
964 * signed = false;
38b8da21 965 * } := struct page *;
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966 *
967 * typealias integer {
968 * size = 32;
969 * align = 32;
970 * signed = true;
38b8da21 971 * } := int;
3d13ef1a 972 */
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973
974struct name {
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975 ...
976};
5ba9f198 977
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978variant name {
979 ...
980};
981
a9b83695 982enum name : integer_type {
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983 ...
984};
985
2152348f 986
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987/*
988 * Unnamed types, contained within compound type fields, typedef or typealias.
989 */
2152348f 990
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991struct {
992 ...
2152348f 993}
5ba9f198 994
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995variant {
996 ...
997}
998
a9b83695 999enum : integer_type {
80fd2569 1000 ...
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1001}
1002
1003typedef type new_type[length];
3bf79539 1004
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1005struct {
1006 type field_name[length];
1007}
1008
1009typedef type new_type[length_type];
1010
1011struct {
1012 type field_name[length_type];
1013}
1014
1015integer {
80fd2569 1016 ...
2152348f 1017}
3bf79539 1018
2152348f 1019floating_point {
80fd2569 1020 ...
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1021}
1022
1023struct {
1024 integer_type field_name:size; /* GNU/C bitfield */
1025}
1026
1027struct {
1028 string field_name;
1029}
3bf79539 1030
fcba70d4 1031
3bf79539 1032A. Helper macros
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1033
1034The two following macros keep track of the size of a GNU/C structure without
1035padding at the end by placing HEADER_END as the last field. A one byte end field
1036is used for C90 compatibility (C99 flexible arrays could be used here). Note
1037that this does not affect the effective structure size, which should always be
1038calculated with the header_sizeof() helper.
1039
1040#define HEADER_END char end_field
1041#define header_sizeof(type) offsetof(typeof(type), end_field)
3bf79539
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1042
1043
1044B. Stream Header Rationale
1045
1046An event stream is divided in contiguous event packets of variable size. These
1047subdivisions allow the trace analyzer to perform a fast binary search by time
1048within the stream (typically requiring to index only the event packet headers)
1049without reading the whole stream. These subdivisions have a variable size to
1050eliminate the need to transfer the event packet padding when partially filled
1051event packets must be sent when streaming a trace for live viewing/analysis.
1052An event packet can contain a certain amount of padding at the end. Dividing
1053streams into event packets is also useful for network streaming over UDP and
1054flight recorder mode tracing (a whole event packet can be swapped out of the
1055buffer atomically for reading).
1056
1057The stream header is repeated at the beginning of each event packet to allow
1058flexibility in terms of:
1059
1060 - streaming support,
1061 - allowing arbitrary buffers to be discarded without making the trace
1062 unreadable,
1063 - allow UDP packet loss handling by either dealing with missing event packet
1064 or asking for re-transmission.
1065 - transparently support flight recorder mode,
1066 - transparently support crash dump.
1067
1068The event stream header will therefore be referred to as the "event packet
1069header" throughout the rest of this document.
fcba70d4 1070
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1071
1072C. TSDL Grammar
fcba70d4 1073
4fa992a5 1074/*
6c7226e9 1075 * Common Trace Format (CTF) Trace Stream Description Language (TSDL) Grammar.
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1076 *
1077 * Inspired from the C99 grammar:
1078 * http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1124.pdf (Annex A)
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1079 * and c++1x grammar (draft)
1080 * http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2011/n3291.pdf (Annex A)
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1081 *
1082 * Specialized for CTF needs by including only constant and declarations from
1083 * C99 (excluding function declarations), and by adding support for variants,
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1084 * sequences and CTF-specific specifiers. Enumeration container types
1085 * semantic is inspired from c++1x enum-base.
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1086 */
1087
10881) Lexical grammar
1089
10901.1) Lexical elements
1091
1092token:
1093 keyword
1094 identifier
1095 constant
1096 string-literal
1097 punctuator
1098
10991.2) Keywords
1100
1101keyword: is one of
1102
1103const
1104char
1105double
1106enum
1107event
1108floating_point
1109float
1110integer
1111int
1112long
1113short
1114signed
1115stream
1116string
1117struct
1118trace
3e1e1a78 1119typealias
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1120typedef
1121unsigned
1122variant
1123void
1124_Bool
1125_Complex
1126_Imaginary
1127
1128
11291.3) Identifiers
1130
1131identifier:
1132 identifier-nondigit
1133 identifier identifier-nondigit
1134 identifier digit
1135
1136identifier-nondigit:
1137 nondigit
1138 universal-character-name
1139 any other implementation-defined characters
1140
1141nondigit:
1142 _
1143 [a-zA-Z] /* regular expression */
1144
1145digit:
1146 [0-9] /* regular expression */
1147
11481.4) Universal character names
1149
1150universal-character-name:
1151 \u hex-quad
1152 \U hex-quad hex-quad
1153
1154hex-quad:
1155 hexadecimal-digit hexadecimal-digit hexadecimal-digit hexadecimal-digit
1156
11571.5) Constants
1158
1159constant:
1160 integer-constant
1161 enumeration-constant
1162 character-constant
1163
1164integer-constant:
1165 decimal-constant integer-suffix-opt
1166 octal-constant integer-suffix-opt
1167 hexadecimal-constant integer-suffix-opt
1168
1169decimal-constant:
1170 nonzero-digit
1171 decimal-constant digit
1172
1173octal-constant:
1174 0
1175 octal-constant octal-digit
1176
1177hexadecimal-constant:
1178 hexadecimal-prefix hexadecimal-digit
1179 hexadecimal-constant hexadecimal-digit
1180
1181hexadecimal-prefix:
1182 0x
1183 0X
1184
1185nonzero-digit:
1186 [1-9]
1187
1188integer-suffix:
1189 unsigned-suffix long-suffix-opt
1190 unsigned-suffix long-long-suffix
1191 long-suffix unsigned-suffix-opt
1192 long-long-suffix unsigned-suffix-opt
1193
1194unsigned-suffix:
1195 u
1196 U
1197
1198long-suffix:
1199 l
1200 L
1201
1202long-long-suffix:
1203 ll
1204 LL
1205
1206digit-sequence:
1207 digit
1208 digit-sequence digit
1209
1210hexadecimal-digit-sequence:
1211 hexadecimal-digit
1212 hexadecimal-digit-sequence hexadecimal-digit
1213
1214enumeration-constant:
1215 identifier
1216 string-literal
1217
1218character-constant:
1219 ' c-char-sequence '
1220 L' c-char-sequence '
1221
1222c-char-sequence:
1223 c-char
1224 c-char-sequence c-char
1225
1226c-char:
1227 any member of source charset except single-quote ('), backslash
1228 (\), or new-line character.
1229 escape-sequence
1230
1231escape-sequence:
1232 simple-escape-sequence
1233 octal-escape-sequence
1234 hexadecimal-escape-sequence
1235 universal-character-name
1236
1237simple-escape-sequence: one of
1238 \' \" \? \\ \a \b \f \n \r \t \v
1239
1240octal-escape-sequence:
1241 \ octal-digit
1242 \ octal-digit octal-digit
1243 \ octal-digit octal-digit octal-digit
1244
1245hexadecimal-escape-sequence:
1246 \x hexadecimal-digit
1247 hexadecimal-escape-sequence hexadecimal-digit
1248
12491.6) String literals
1250
1251string-literal:
1252 " s-char-sequence-opt "
1253 L" s-char-sequence-opt "
1254
1255s-char-sequence:
1256 s-char
1257 s-char-sequence s-char
1258
1259s-char:
1260 any member of source charset except double-quote ("), backslash
1261 (\), or new-line character.
1262 escape-sequence
1263
12641.7) Punctuators
1265
1266punctuator: one of
1267 [ ] ( ) { } . -> * + - < > : ; ... = ,
1268
1269
12702) Phrase structure grammar
1271
1272primary-expression:
1273 identifier
1274 constant
1275 string-literal
1276 ( unary-expression )
1277
1278postfix-expression:
1279 primary-expression
1280 postfix-expression [ unary-expression ]
1281 postfix-expression . identifier
1282 postfix-expressoin -> identifier
1283
1284unary-expression:
1285 postfix-expression
1286 unary-operator postfix-expression
1287
1288unary-operator: one of
1289 + -
1290
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1291assignment-operator:
1292 =
1293
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1294type-assignment-operator:
1295 :=
1296
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1297constant-expression:
1298 unary-expression
1299
1300constant-expression-range:
1301 constant-expression ... constant-expression
1302
13032.2) Declarations:
1304
1305declaration:
689e04b4 1306 declaration-specifiers declarator-list-opt ;
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1307 ctf-specifier ;
1308
1309declaration-specifiers:
689e04b4 1310 storage-class-specifier declaration-specifiers-opt
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1311 type-specifier declaration-specifiers-opt
1312 type-qualifier declaration-specifiers-opt
1313
1314declarator-list:
1315 declarator
1316 declarator-list , declarator
1317
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1318abstract-declarator-list:
1319 abstract-declarator
1320 abstract-declarator-list , abstract-declarator
1321
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1322storage-class-specifier:
1323 typedef
1324
1325type-specifier:
1326 void
1327 char
1328 short
1329 int
1330 long
1331 float
1332 double
1333 signed
1334 unsigned
1335 _Bool
1336 _Complex
cfdd51ec 1337 _Imaginary
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1338 struct-specifier
1339 variant-specifier
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1340 enum-specifier
1341 typedef-name
1342 ctf-type-specifier
1343
1344struct-specifier:
3b0f8e4d 1345 struct identifier-opt { struct-or-variant-declaration-list-opt }
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1346 struct identifier
1347
1348struct-or-variant-declaration-list:
1349 struct-or-variant-declaration
1350 struct-or-variant-declaration-list struct-or-variant-declaration
1351
1352struct-or-variant-declaration:
1353 specifier-qualifier-list struct-or-variant-declarator-list ;
550aca33 1354 declaration-specifiers storage-class-specifier declaration-specifiers declarator-list ;
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1355 typealias declaration-specifiers abstract-declarator-list := declaration-specifiers abstract-declarator-list ;
1356 typealias declaration-specifiers abstract-declarator-list := declarator-list ;
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1357
1358specifier-qualifier-list:
1359 type-specifier specifier-qualifier-list-opt
1360 type-qualifier specifier-qualifier-list-opt
1361
1362struct-or-variant-declarator-list:
1363 struct-or-variant-declarator
1364 struct-or-variant-declarator-list , struct-or-variant-declarator
1365
1366struct-or-variant-declarator:
1367 declarator
1368 declarator-opt : constant-expression
1369
1370variant-specifier:
1371 variant identifier-opt variant-tag-opt { struct-or-variant-declaration-list }
1372 variant identifier variant-tag
1373
1374variant-tag:
1375 < identifier >
1376
1377enum-specifier:
1378 enum identifier-opt { enumerator-list }
1379 enum identifier-opt { enumerator-list , }
1380 enum identifier
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1381 enum identifier-opt : declaration-specifiers { enumerator-list }
1382 enum identifier-opt : declaration-specifiers { enumerator-list , }
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1383
1384enumerator-list:
1385 enumerator
1386 enumerator-list , enumerator
1387
1388enumerator:
1389 enumeration-constant
1390 enumeration-constant = constant-expression
1391 enumeration-constant = constant-expression-range
1392
1393type-qualifier:
1394 const
1395
1396declarator:
1397 pointer-opt direct-declarator
1398
1399direct-declarator:
1400 identifier
1401 ( declarator )
1402 direct-declarator [ type-specifier ]
1403 direct-declarator [ constant-expression ]
1404
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1405abstract-declarator:
1406 pointer-opt direct-abstract-declarator
1407
1408direct-abstract-declarator:
1409 identifier-opt
1410 ( abstract-declarator )
1411 direct-abstract-declarator [ type-specifier ]
1412 direct-abstract-declarator [ constant-expression ]
1413 direct-abstract-declarator [ ]
1414
4fa992a5 1415pointer:
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1416 * type-qualifier-list-opt
1417 * type-qualifier-list-opt pointer
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1418
1419type-qualifier-list:
1420 type-qualifier
1421 type-qualifier-list type-qualifier
1422
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1423typedef-name:
1424 identifier
1425
14262.3) CTF-specific declarations
1427
1428ctf-specifier:
1429 event { ctf-assignment-expression-list-opt }
1430 stream { ctf-assignment-expression-list-opt }
1431 trace { ctf-assignment-expression-list-opt }
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1432 typealias declaration-specifiers abstract-declarator-list := declaration-specifiers abstract-declarator-list ;
1433 typealias declaration-specifiers abstract-declarator-list := declarator-list ;
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1434
1435ctf-type-specifier:
1436 floating_point { ctf-assignment-expression-list-opt }
1437 integer { ctf-assignment-expression-list-opt }
1438 string { ctf-assignment-expression-list-opt }
1439
1440ctf-assignment-expression-list:
1441 ctf-assignment-expression
1442 ctf-assignment-expression-list ; ctf-assignment-expression
1443
1444ctf-assignment-expression:
1445 unary-expression assignment-operator unary-expression
1446 unary-expression type-assignment-operator type-specifier
550aca33 1447 declaration-specifiers storage-class-specifier declaration-specifiers declarator-list
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1448 typealias declaration-specifiers abstract-declarator-list := declaration-specifiers abstract-declarator-list
1449 typealias declaration-specifiers abstract-declarator-list := declarator-list
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