Add missing type assignment operator
[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
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9allow traces to be natively generated by the Linux kernel, Linux user-space
10applications written in C/C++, and hardware components.
11
12The latest version of this document can be found at:
13
14 git tree: git://git.efficios.com/ctf.git
15 gitweb: http://git.efficios.com/?p=ctf.git
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16
17A reference implementation of a library to read and write this trace format is
18being implemented within the BabelTrace project, a converter between trace
19formats. The development tree is available at:
20
21 git tree: git://git.efficios.com/babeltrace.git
22 gitweb: http://git.efficios.com/?p=babeltrace.git
23
24
251. Preliminary definitions
26
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27 - Event Trace: An ordered sequence of events.
28 - Event Stream: An ordered sequence of events, containing a subset of the
29 trace event types.
30 - Event Packet: A sequence of physically contiguous events within an event
31 stream.
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32 - Event: This is the basic entry in a trace. (aka: a trace record).
33 - An event identifier (ID) relates to the class (a type) of event within
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34 an event stream.
35 e.g. event: irq_entry.
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36 - An event (or event record) relates to a specific instance of an event
37 class.
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38 e.g. event: irq_entry, at time X, on CPU Y
39 - Source Architecture: Architecture writing the trace.
40 - Reader Architecture: Architecture reading the trace.
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41
42
432. High-level representation of a trace
44
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45A trace is divided into multiple event streams. Each event stream contains a
46subset of the trace event types.
5ba9f198 47
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48The final output of the trace, after its generation and optional transport over
49the network, is expected to be either on permanent or temporary storage in a
50virtual file system. Because each event stream is appended to while a trace is
51being recorded, each is associated with a separate file for output. Therefore,
52a stored trace can be represented as a directory containing one file per stream.
5ba9f198 53
3bf79539 54A metadata event stream contains information on trace event types. It describes:
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55
56- Trace version.
57- Types available.
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58- Per-stream event header description.
59- Per-stream event header selection.
60- Per-stream event context fields.
5ba9f198 61- Per-event
3bf79539 62 - Event type to stream mapping.
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63 - Event type to name mapping.
64 - Event type to ID mapping.
65 - Event fields description.
66
67
3bf79539 683. Event stream
5ba9f198 69
3bf79539 70An event stream is divided in contiguous event packets of variable size. These
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71subdivisions have a variable size. An event packet can contain a certain
72amount of padding at the end. The stream header is repeated at the
73beginning of each event packet. The rationale for the event stream
74design choices is explained in Appendix B. Stream Header Rationale.
5ba9f198 75
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76The event stream header will therefore be referred to as the "event packet
77header" throughout the rest of this document.
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78
79
804. Types
81
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82Types are organized as type classes. Each type class belong to either of two
83kind of types: basic types or compound types.
84
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854.1 Basic types
86
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87A basic type is a scalar type, as described in this section. It includes
88integers, GNU/C bitfields, enumerations, and floating point values.
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89
904.1.1 Type inheritance
91
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92Type specifications can be inherited to allow deriving types from a
93type class. For example, see the uint32_t named type derived from the "integer"
94type class below ("Integers" section). Types have a precise binary
95representation in the trace. A type class has methods to read and write these
96types, but must be derived into a type to be usable in an event field.
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97
984.1.2 Alignment
99
100We define "byte-packed" types as aligned on the byte size, namely 8-bit.
101We define "bit-packed" types as following on the next bit, as defined by the
102"bitfields" section.
5ba9f198 103
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104All basic types, except bitfields, are either aligned on an architecture-defined
105specific alignment or byte-packed, depending on the architecture preference.
106Architectures providing fast unaligned write byte-packed basic types to save
5ba9f198 107space, aligning each type on byte boundaries (8-bit). Architectures with slow
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108unaligned writes align types on specific alignment values. If no specific
109alignment is declared for a type nor its parents, it is assumed to be bit-packed
110for bitfields and byte-packed for other types.
5ba9f198 111
3bf79539 112Metadata attribute representation of a specific alignment:
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113
114 align = value; /* value in bits */
115
1164.1.3 Byte order
117
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118By default, the native endianness of the source architecture the trace is used.
119Byte order can be overridden for a basic type by specifying a "byte_order"
120attribute. Typical use-case is to specify the network byte order (big endian:
121"be") to save data captured from the network into the trace without conversion.
122If not specified, the byte order is native.
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123
124Metadata representation:
125
126 byte_order = native OR network OR be OR le; /* network and be are aliases */
127
1284.1.4 Size
129
130Type size, in bits, for integers and floats is that returned by "sizeof()" in C
131multiplied by CHAR_BIT.
132We require the size of "char" and "unsigned char" types (CHAR_BIT) to be fixed
133to 8 bits for cross-endianness compatibility.
134
135Metadata representation:
136
137 size = value; (value is in bits)
138
1394.1.5 Integers
140
141Signed integers are represented in two-complement. Integer alignment, size,
142signedness and byte ordering are defined in the metadata. Integers aligned on
143byte size (8-bit) and with length multiple of byte size (8-bit) correspond to
144the C99 standard integers. In addition, integers with alignment and/or size that
145are _not_ a multiple of the byte size are permitted; these correspond to the C99
146standard bitfields, with the added specification that the CTF integer bitfields
147have a fixed binary representation. A MIT-licensed reference implementation of
148the CTF portable bitfields is available at:
149
150 http://git.efficios.com/?p=babeltrace.git;a=blob;f=include/babeltrace/bitfield.h
151
152Binary representation of integers:
153
154- On little and big endian:
155 - Within a byte, high bits correspond to an integer high bits, and low bits
156 correspond to low bits.
157- On little endian:
158 - Integer across multiple bytes are placed from the less significant to the
159 most significant.
160 - Consecutive integers are placed from lower bits to higher bits (even within
161 a byte).
162- On big endian:
163 - Integer across multiple bytes are placed from the most significant to the
164 less significant.
165 - Consecutive integers are placed from higher bits to lower bits (even within
166 a byte).
167
168This binary representation is derived from the bitfield implementation in GCC
169for little and big endian. However, contrary to what GCC does, integers can
170cross units boundaries (no padding is required). Padding can be explicitely
171added (see 4.1.6 GNU/C bitfields) to follow the GCC layout if needed.
172
173Metadata representation:
174
80fd2569 175 integer {
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176 signed = true OR false; /* default false */
177 byte_order = native OR network OR be OR le; /* default native */
178 size = value; /* value in bits, no default */
179 align = value; /* value in bits */
2152348f 180 }
5ba9f198 181
80fd2569 182Example of type inheritance (creation of a uint32_t named type):
5ba9f198 183
359894ac 184typealias integer {
9e4e34e9 185 size = 32;
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186 signed = false;
187 align = 32;
359894ac 188} : uint32_t;
5ba9f198 189
80fd2569 190Definition of a named 5-bit signed bitfield:
5ba9f198 191
359894ac 192typealias integer {
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193 size = 5;
194 signed = true;
195 align = 1;
359894ac 196} : int5_t;
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197
1984.1.6 GNU/C bitfields
199
200The GNU/C bitfields follow closely the integer representation, with a
201particularity on alignment: if a bitfield cannot fit in the current unit, the
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202unit is padded and the bitfield starts at the following unit. The unit size is
203defined by the size of the type "unit_type".
5ba9f198 204
2152348f 205Metadata representation:
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206
207 unit_type name:size:
208
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209As an example, the following structure declared in C compiled by GCC:
210
211struct example {
212 short a:12;
213 short b:5;
214};
215
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216The example structure is aligned on the largest element (short). The second
217bitfield would be aligned on the next unit boundary, because it would not fit in
218the current unit.
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219
2204.1.7 Floating point
221
222The floating point values byte ordering is defined in the metadata.
223
224Floating point values follow the IEEE 754-2008 standard interchange formats.
225Description of the floating point values include the exponent and mantissa size
226in bits. Some requirements are imposed on the floating point values:
227
228- FLT_RADIX must be 2.
229- mant_dig is the number of digits represented in the mantissa. It is specified
230 by the ISO C99 standard, section 5.2.4, as FLT_MANT_DIG, DBL_MANT_DIG and
231 LDBL_MANT_DIG as defined by <float.h>.
232- exp_dig is the number of digits represented in the exponent. Given that
233 mant_dig is one bit more than its actual size in bits (leading 1 is not
234 needed) and also given that the sign bit always takes one bit, exp_dig can be
235 specified as:
236
237 - sizeof(float) * CHAR_BIT - FLT_MANT_DIG
238 - sizeof(double) * CHAR_BIT - DBL_MANT_DIG
239 - sizeof(long double) * CHAR_BIT - LDBL_MANT_DIG
240
241Metadata representation:
242
80fd2569 243floating_point {
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244 exp_dig = value;
245 mant_dig = value;
246 byte_order = native OR network OR be OR le;
2152348f 247}
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248
249Example of type inheritance:
250
359894ac 251typealias floating_point {
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252 exp_dig = 8; /* sizeof(float) * CHAR_BIT - FLT_MANT_DIG */
253 mant_dig = 24; /* FLT_MANT_DIG */
254 byte_order = native;
359894ac 255} : float;
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256
257TODO: define NaN, +inf, -inf behavior.
258
2594.1.8 Enumerations
260
261Enumerations are a mapping between an integer type and a table of strings. The
262numerical representation of the enumeration follows the integer type specified
263by the metadata. The enumeration mapping table is detailed in the enumeration
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264description within the metadata. The mapping table maps inclusive value ranges
265(or single values) to strings. Instead of being limited to simple
266"value -> string" mappings, these enumerations map
80fd2569 267"[ start_value ... end_value ] -> string", which map inclusive ranges of
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268values to strings. An enumeration from the C language can be represented in
269this format by having the same start_value and end_value for each element, which
270is in fact a range of size 1. This single-value range is supported without
4767a9e7 271repeating the start and end values with the value = string declaration.
80fd2569 272
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273If a numeric value is encountered between < >, it represents the integer type
274size used to hold the enumeration, in bits.
275
cfc73fdc 276enum name <integer_type OR size> {
359894ac 277 somestring = start_value1 ... end_value1,
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278 "other string" = start_value2 ... end_value2,
279 yet_another_string, /* will be assigned to end_value2 + 1 */
280 "some other string" = value,
281 ...
282};
283
284If the values are omitted, the enumeration starts at 0 and increment of 1 for
285each entry:
286
cfc73fdc 287enum name <32> {
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288 ZERO,
289 ONE,
290 TWO,
291 TEN = 10,
292 ELEVEN,
3bf79539 293};
5ba9f198 294
80fd2569 295Overlapping ranges within a single enumeration are implementation defined.
5ba9f198 296
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297A nameless enumeration can be declared as a field type or as part of a typedef:
298
299enum <integer_type> {
300 ...
301}
302
1fad7a85 303
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3044.2 Compound types
305
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306Compound are aggregation of type declarations. Compound types include
307structures, variant, arrays, sequences, and strings.
308
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3094.2.1 Structures
310
311Structures are aligned on the largest alignment required by basic types
312contained within the structure. (This follows the ISO/C standard for structures)
313
80fd2569 314Metadata representation of a named structure:
5ba9f198 315
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316struct name {
317 field_type field_name;
318 field_type field_name;
319 ...
320};
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321
322Example:
323
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324struct example {
325 integer { /* Nameless type */
326 size = 16;
327 signed = true;
328 align = 16;
329 } first_field_name;
330 uint64_t second_field_name; /* Named type declared in the metadata */
3bf79539 331};
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332
333The fields are placed in a sequence next to each other. They each possess a
334field name, which is a unique identifier within the structure.
335
2152348f 336A nameless structure can be declared as a field type or as part of a typedef:
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337
338struct {
339 ...
2152348f 340}
80fd2569 341
77a98c82 3424.2.2 Variants (Discriminated/Tagged Unions)
fcba70d4 343
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344A CTF variant is a selection between different types. A CTF variant must
345always be defined within the scope of a structure or within fields
346contained within a structure (defined recursively). A "tag" enumeration
347field must appear in either the same lexical scope, prior to the variant
348field (in field declaration order), in an uppermost lexical scope (see
349Section 7.2.1), or in an uppermost dynamic scope (see Section 7.2.2).
350The type selection is indicated by the mapping from the enumeration
351value to the string used as variant type selector. The field to use as
352tag is specified by the "tag_field", specified between "< >" after the
353"variant" keyword for unnamed variants, and after "variant name" for
354named variants.
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355
356The alignment of the variant is the alignment of the type as selected by the tag
357value for the specific instance of the variant. The alignment of the type
358containing the variant is independent of the variant alignment. The size of the
359variant is the size as selected by the tag value for the specific instance of
360the variant.
361
362A named variant declaration followed by its definition within a structure
363declaration:
364
365variant name {
366 field_type sel1;
367 field_type sel2;
368 field_type sel3;
369 ...
370};
371
372struct {
373 enum <integer_type or size> { sel1, sel2, sel3, ... } tag_field;
374 ...
375 variant name <tag_field> v;
376}
377
378An unnamed variant definition within a structure is expressed by the following
379metadata:
380
381struct {
382 enum <integer_type or size> { sel1, sel2, sel3, ... } tag_field;
383 ...
384 variant <tag_field> {
385 field_type sel1;
386 field_type sel2;
387 field_type sel3;
388 ...
389 } v;
390}
391
392Example of a named variant within a sequence that refers to a single tag field:
393
394variant example {
395 uint32_t a;
396 uint64_t b;
397 short c;
398};
399
400struct {
401 enum <uint2_t> { a, b, c } choice;
15850440 402 variant example <choice> v[unsigned int];
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403}
404
405Example of an unnamed variant:
406
407struct {
408 enum <uint2_t> { a, b, c, d } choice;
409 /* Unrelated fields can be added between the variant and its tag */
410 int32_t somevalue;
411 variant <choice> {
412 uint32_t a;
413 uint64_t b;
414 short c;
415 struct {
416 unsigned int field1;
417 uint64_t field2;
418 } d;
419 } s;
420}
421
422Example of an unnamed variant within an array:
423
424struct {
425 enum <uint2_t> { a, b, c } choice;
426 variant <choice> {
427 uint32_t a;
428 uint64_t b;
429 short c;
15850440 430 } v[10];
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431}
432
433Example of a variant type definition within a structure, where the defined type
434is then declared within an array of structures. This variant refers to a tag
435located in an upper lexical scope. This example clearly shows that a variant
436type definition referring to the tag "x" uses the closest preceding field from
437the lexical scope of the type definition.
438
439struct {
440 enum <uint2_t> { a, b, c, d } x;
441
442 typedef variant <x> { /*
443 * "x" refers to the preceding "x" enumeration in the
444 * lexical scope of the type definition.
445 */
446 uint32_t a;
447 uint64_t b;
448 short c;
449 } example_variant;
450
451 struct {
452 enum <int> { x, y, z } x; /* This enumeration is not used by "v". */
453 example_variant v; /*
454 * "v" uses the "enum <uint2_t> { a, b, c, d }"
455 * tag.
456 */
457 } a[10];
458}
459
4604.2.3 Arrays
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461
462Arrays are fixed-length. Their length is declared in the type declaration within
463the metadata. They contain an array of "inner type" elements, which can refer to
464any type not containing the type of the array being declared (no circular
3bf79539 465dependency). The length is the number of elements in an array.
5ba9f198 466
2152348f 467Metadata representation of a named array:
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468
469typedef elem_type name[length];
5ba9f198 470
2152348f 471A nameless array can be declared as a field type within a structure, e.g.:
5ba9f198 472
2152348f 473 uint8_t field_name[10];
80fd2569 474
5ba9f198 475
fcba70d4 4764.2.4 Sequences
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477
478Sequences are dynamically-sized arrays. They start with an integer that specify
479the length of the sequence, followed by an array of "inner type" elements.
3bf79539 480The length is the number of elements in the sequence.
5ba9f198 481
2152348f 482Metadata representation for a named sequence:
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483
484typedef elem_type name[length_type];
485
486A nameless sequence can be declared as a field type, e.g.:
487
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488long field_name[int];
489
490The length type follows the integer types specifications, and the sequence
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491elements follow the "array" specifications.
492
fcba70d4 4934.2.5 Strings
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494
495Strings are an array of bytes of variable size and are terminated by a '\0'
496"NULL" character. Their encoding is described in the metadata. In absence of
497encoding attribute information, the default encoding is UTF-8.
498
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499Metadata representation of a named string type:
500
359894ac 501typealias string {
5ba9f198 502 encoding = UTF8 OR ASCII;
359894ac 503} : name;
5ba9f198 504
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505A nameless string type can be declared as a field type:
506
507string field_name; /* Use default UTF8 encoding */
5ba9f198 508
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5095. Event Packet Header
510
511The event packet header consists of two part: one is mandatory and have a fixed
512layout. The second part, the "event packet context", has its layout described in
513the metadata.
5ba9f198 514
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515- Aligned on page size. Fixed size. Fields either aligned or packed (depending
516 on the architecture preference).
517 No padding at the end of the event packet header. Native architecture byte
5ba9f198 518 ordering.
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519
520Fixed layout (event packet header):
521
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522- Magic number (CTF magic numbers: 0xC1FC1FC1 and its reverse endianness
523 representation: 0xC11FFCC1) It needs to have a non-symmetric bytewise
524 representation. Used to distinguish between big and little endian traces (this
525 information is determined by knowing the endianness of the architecture
526 reading the trace and comparing the magic number against its value and the
527 reverse, 0xC11FFCC1). This magic number specifies that we use the CTF metadata
528 description language described in this document. Different magic numbers
529 should be used for other metadata description languages.
3bf79539 530- Trace UUID, used to ensure the event packet match the metadata used.
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531 (note: we cannot use a metadata checksum because metadata can be appended to
532 while tracing is active)
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533- Stream ID, used as reference to stream description in metadata.
534
535Metadata-defined layout (event packet context):
536
537- Event packet content size (in bytes).
538- Event packet size (in bytes, includes padding).
539- Event packet content checksum (optional). Checksum excludes the event packet
540 header.
541- Per-stream event packet sequence count (to deal with UDP packet loss). The
542 number of significant sequence counter bits should also be present, so
543 wrap-arounds are deal with correctly.
544- Timestamp at the beginning and timestamp at the end of the event packet.
545 Both timestamps are written in the packet header, but sampled respectively
546 while (or before) writing the first event and while (or after) writing the
547 last event in the packet. The inclusive range between these timestamps should
548 include all event timestamps assigned to events contained within the packet.
5ba9f198 549- Events discarded count
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550 - Snapshot of a per-stream free-running counter, counting the number of
551 events discarded that were supposed to be written in the stream prior to
552 the first event in the event packet.
5ba9f198 553 * Note: producer-consumer buffer full condition should fill the current
3bf79539 554 event packet with padding so we know exactly where events have been
5ba9f198 555 discarded.
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556- Lossless compression scheme used for the event packet content. Applied
557 directly to raw data. New types of compression can be added in following
558 versions of the format.
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559 0: no compression scheme
560 1: bzip2
561 2: gzip
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562 3: xz
563- Cypher used for the event packet content. Applied after compression.
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564 0: no encryption
565 1: AES
3bf79539 566- Checksum scheme used for the event packet content. Applied after encryption.
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567 0: no checksum
568 1: md5
569 2: sha1
570 3: crc32
571
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5725.1 Event Packet Header Fixed Layout Description
573
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574struct event_packet_header {
575 uint32_t magic;
576 uint8_t trace_uuid[16];
3bf79539 577 uint32_t stream_id;
80fd2569 578};
5ba9f198 579
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5805.2 Event Packet Context Description
581
582Event packet context example. These are declared within the stream declaration
583in the metadata. All these fields are optional except for "content_size" and
584"packet_size", which must be present in the context.
585
586An example event packet context type:
587
80fd2569 588struct event_packet_context {
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589 uint64_t timestamp_begin;
590 uint64_t timestamp_end;
591 uint32_t checksum;
592 uint32_t stream_packet_count;
593 uint32_t events_discarded;
594 uint32_t cpu_id;
595 uint32_t/uint16_t content_size;
596 uint32_t/uint16_t packet_size;
597 uint8_t stream_packet_count_bits; /* Significant counter bits */
598 uint8_t compression_scheme;
599 uint8_t encryption_scheme;
3b0f8e4d 600 uint8_t checksum_scheme;
3bf79539 601};
5ba9f198 602
fcba70d4 603
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6046. Event Structure
605
606The overall structure of an event is:
607
fcba70d4 6081 - Stream Packet Context (as specified by the stream metadata)
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609 2 - Event Header (as specified by the stream metadata)
610 3 - Stream Event Context (as specified by the stream metadata)
611 4 - Event Context (as specified by the event metadata)
612 5 - Event Payload (as specified by the event metadata)
5ba9f198 613
fdf2bb05 614This structure defines an implicit dynamic scoping, where variants
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615located in inner structures (those with a higher number in the listing
616above) can refer to the fields of outer structures (with lower number in
617the listing above). See Section 7.2 Metadata Scopes for more detail.
5ba9f198 618
fdf2bb05 6196.1 Event Header
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620
621Event headers can be described within the metadata. We hereby propose, as an
622example, two types of events headers. Type 1 accommodates streams with less than
62331 event IDs. Type 2 accommodates streams with 31 or more event IDs.
5ba9f198 624
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625One major factor can vary between streams: the number of event IDs assigned to
626a stream. Luckily, this information tends to stay relatively constant (modulo
5ba9f198 627event registration while trace is being recorded), so we can specify different
3bf79539 628representations for streams containing few event IDs and streams containing
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629many event IDs, so we end up representing the event ID and timestamp as densely
630as possible in each case.
631
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632The header is extended in the rare occasions where the information cannot be
633represented in the ranges available in the standard event header. They are also
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634used in the rare occasions where the data required for a field could not be
635collected: the flag corresponding to the missing field within the missing_fields
636array is then set to 1.
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637
638Types uintX_t represent an X-bit unsigned integer.
639
640
fdf2bb05 6416.1.1 Type 1 - Few event IDs
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642
643 - Aligned on 32-bit (or 8-bit if byte-packed, depending on the architecture
644 preference).
5ba9f198 645 - Native architecture byte ordering.
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646 - For "compact" selection
647 - Fixed size: 32 bits.
648 - For "extended" selection
649 - Size depends on the architecture and variant alignment.
5ba9f198 650
80fd2569 651struct event_header_1 {
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652 /*
653 * id: range: 0 - 30.
654 * id 31 is reserved to indicate an extended header.
655 */
656 enum <uint5_t> { compact = 0 ... 30, extended = 31 } id;
657 variant <id> {
658 struct {
659 uint27_t timestamp;
660 } compact;
661 struct {
662 uint32_t id; /* 32-bit event IDs */
663 uint64_t timestamp; /* 64-bit timestamps */
664 } extended;
665 } v;
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666};
667
5ba9f198 668
fdf2bb05 6696.1.2 Type 2 - Many event IDs
5ba9f198 670
fcba70d4 671 - Aligned on 16-bit (or 8-bit if byte-packed, depending on the architecture
5ba9f198 672 preference).
5ba9f198 673 - Native architecture byte ordering.
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674 - For "compact" selection
675 - Size depends on the architecture and variant alignment.
676 - For "extended" selection
677 - Size depends on the architecture and variant alignment.
5ba9f198 678
80fd2569 679struct event_header_2 {
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680 /*
681 * id: range: 0 - 65534.
682 * id 65535 is reserved to indicate an extended header.
683 */
684 enum <uint16_t> { compact = 0 ... 65534, extended = 65535 } id;
685 variant <id> {
686 struct {
687 uint32_t timestamp;
688 } compact;
689 struct {
690 uint32_t id; /* 32-bit event IDs */
691 uint64_t timestamp; /* 64-bit timestamps */
692 } extended;
693 } v;
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694};
695
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696
6976.2 Event Context
698
699The event context contains information relative to the current event. The choice
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700and meaning of this information is specified by the metadata "stream" and
701"event" information. The "stream" context is applied to all events within the
702stream. The "stream" context structure follows the event header. The "event"
703context is applied to specific events. Its structure follows the "stream"
704context stucture.
5ba9f198 705
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706An example of stream-level event context is to save the event payload size with
707each event, or to save the current PID with each event. These are declared
708within the stream declaration within the metadata:
5ba9f198 709
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710 stream {
711 ...
712 event {
713 ...
4fa992a5 714 context := struct {
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715 uint pid;
716 uint16_t payload_size;
3bf79539 717 };
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718 }
719 };
720
721An example of event-specific event context is to declare a bitmap of missing
722fields, only appended after the stream event context if the extended event
723header is selected. NR_FIELDS is the number of fields within the event (a
724numeric value).
5ba9f198 725
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726 event {
727 context = struct {
728 variant <id> {
729 struct { } compact;
730 struct {
731 uint1_t missing_fields[NR_FIELDS]; /* missing event fields bitmap */
732 } extended;
733 } v;
734 };
735 ...
736 }
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737
7386.3 Event Payload
739
740An event payload contains fields specific to a given event type. The fields
741belonging to an event type are described in the event-specific metadata
742within a structure type.
743
7446.3.1 Padding
745
746No padding at the end of the event payload. This differs from the ISO/C standard
747for structures, but follows the CTF standard for structures. In a trace, even
748though it makes sense to align the beginning of a structure, it really makes no
749sense to add padding at the end of the structure, because structures are usually
750not followed by a structure of the same type.
751
752This trick can be done by adding a zero-length "end" field at the end of the C
753structures, and by using the offset of this field rather than using sizeof()
3bf79539 754when calculating the size of a structure (see Appendix "A. Helper macros").
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755
7566.3.2 Alignment
757
758The event payload is aligned on the largest alignment required by types
759contained within the payload. (This follows the ISO/C standard for structures)
760
761
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7627. Metadata
763
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764The meta-data is located in a stream named "metadata". It is made of "event
765packets", which each start with an event packet header. The event type within
766the metadata stream have no event header nor event context. Each event only
5ba9f198 767contains a null-terminated "string" payload, which is a metadata description
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768entry. The events are packed one next to another. Each event packet start with
769an event packet header, which contains, amongst other fields, the magic number
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770and trace UUID. The trace UUID is represented as a string of hexadecimal digits
771and dashes "-".
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772
773The metadata can be parsed by reading through the metadata strings, skipping
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774newlines and null-characters. Type names are made of a single identifier, and
775can be surrounded by prefix/postfix. Text contained within "/*" and "*/", as
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776well as within "//" and end of line, are treated as comments. Boolean values can
777be represented as true, TRUE, or 1 for true, and false, FALSE, or 0 for false.
fcba70d4 778
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779
7807.1 Declaration vs Definition
781
782A declaration associates a layout to a type, without specifying where
783this type is located in the event structure hierarchy (see Section 6).
784This therefore includes typedef, typealias, as well as all type
785specifiers. In certain circumstances (typedef, structure field and
786variant field), a declaration is followed by a declarator, which specify
787the newly defined type name (for typedef), or the field name (for
788declarations located within structure and variants). Array and sequence,
789declared with square brackets ("[" "]"), are part of the declarator,
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790similarly to C99. The enumeration type specifier and variant tag name
791(both specified with "<" ">") are part of the type specifier.
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792
793A definition associates a type to a location in the event structure
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794hierarchy (see Section 6). This association is denoted by ":=", as shown
795in Section 7.3.
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796
797
7987.2 Metadata Scopes
799
800CTF metadata uses two different types of scoping: a lexical scope is
801used for declarations and type definitions, and a dynamic scope is used
802for variants references to tag fields.
803
8047.2.1 Lexical Scope
805
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806Each of "trace", "stream", "event", "struct" and "variant" have their own
807nestable declaration scope, within which types can be declared using "typedef"
fdf2bb05 808and "typealias". A root declaration scope also contains all declarations
7d9d7e92 809located outside of any of the aforementioned declarations. An inner
fdf2bb05 810declaration scope can refer to type declared within its container
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811lexical scope prior to the inner declaration scope. Redefinition of a
812typedef or typealias is not valid, although hiding an upper scope
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813typedef or typealias is allowed within a sub-scope.
814
8157.2.2 Dynamic Scope
816
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817A dynamic scope consists in the lexical scope augmented with the
818implicit event structure definition hierarchy presented at Section 6.
819The dynamic scope is only used for variant tag definitions. It is used
820at definition time to look up the location of the tag field associated
821with a variant.
822
823Therefore, variants in lower levels in the dynamic scope (e.g. event
824context) can refer to a tag field located in upper levels (e.g. in the
825event header) by specifying, in this case, the associated tag with
826<header.field_name>. This allows, for instance, the event context to
827define a variant referring to the "id" field of the event header as
828selector.
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829
830The target dynamic scope must be specified explicitly when referring to
831a field outside of the local static scope. The dynamic scope prefixes
832are thus:
833
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834 - Stream Packet Context: <stream.packet.context. >,
835 - Event Header: <stream.event.header. >,
836 - Stream Event Context: <stream.event.context. >,
837 - Event Context: <event.context. >,
838 - Event Payload: <event.fields. >.
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839
840Multiple declarations of the same field name within a single scope is
841not valid. It is however valid to re-use the same field name in
842different scopes. There is no possible conflict, because the dynamic
843scope must be specified when a variant refers to a tag field located in
844a different dynamic scope.
845
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846The information available in the dynamic scopes can be thought of as the
847current tracing context. At trace production, information about the
848current context is saved into the specified scope field levels. At trace
849consumption, for each event, the current trace context is therefore
850readable by accessing the upper dynamic scopes.
851
fdf2bb05 852
b9606a77 8537.3 Metadata Examples
d285084f 854
fcba70d4 855The grammar representing the CTF metadata is presented in
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856Appendix C. CTF Metadata Grammar. This section presents a rather ligher
857reading that consists in examples of CTF metadata, with template values:
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858
859trace {
fdf2bb05 860 major = value; /* Trace format version */
5ba9f198 861 minor = value;
fdf2bb05 862 uuid = "aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaaa"; /* Trace UUID */
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863 word_size = value;
864};
5ba9f198 865
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866stream {
867 id = stream_id;
fdf2bb05 868 /* Type 1 - Few event IDs; Type 2 - Many event IDs. See section 6.1. */
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869 event.header := event_header_1 OR event_header_2;
870 event.context := struct {
77a98c82 871 ...
3bf79539 872 };
4fa992a5 873 packet.context := struct {
77a98c82 874 ...
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875 };
876};
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877
878event {
3d13ef1a 879 name = event_name;
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880 id = value; /* Numeric identifier within the stream */
881 stream = stream_id;
4fa992a5 882 context := struct {
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883 ...
884 };
4fa992a5 885 fields := struct {
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886 ...
887 };
3bf79539 888};
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889
890/* More detail on types in section 4. Types */
891
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892/*
893 * Named types:
894 *
4fa992a5 895 * Type declarations behave similarly to the C standard.
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896 */
897
898typedef aliased_type_prefix aliased_type new_type aliased_type_postfix;
2152348f 899
3d13ef1a 900/* e.g.: typedef struct example new_type_name[10]; */
80fd2569 901
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902/*
903 * typealias
904 *
905 * The "typealias" declaration can be used to give a name (including
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906 * prefix/postfix) to a type. It should also be used to map basic C types
907 * (float, int, unsigned long, ...) to a CTF type. Typealias is a superset of
908 * "typedef": it also allows assignment of a simple variable identifier to a
909 * type.
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910 */
911
912typealias type_class {
80fd2569 913 ...
fcba70d4 914} : new_type_prefix new_type new_type_postfix;
2152348f 915
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916/*
917 * e.g.:
4fa992a5 918 * typealias integer {
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919 * size = 32;
920 * align = 32;
921 * signed = false;
fcba70d4 922 * } : struct page *;
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923 *
924 * typealias integer {
925 * size = 32;
926 * align = 32;
927 * signed = true;
928 * } : int;
3d13ef1a 929 */
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930
931struct name {
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932 ...
933};
5ba9f198 934
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935variant name {
936 ...
937};
938
cfc73fdc 939enum name <integer_type or size> {
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940 ...
941};
942
2152348f 943
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944/*
945 * Unnamed types, contained within compound type fields, typedef or typealias.
946 */
2152348f 947
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948struct {
949 ...
2152348f 950}
5ba9f198 951
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952variant {
953 ...
954}
955
4767a9e7 956enum <integer_type or size> {
80fd2569 957 ...
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MD
958}
959
960typedef type new_type[length];
3bf79539 961
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962struct {
963 type field_name[length];
964}
965
966typedef type new_type[length_type];
967
968struct {
969 type field_name[length_type];
970}
971
972integer {
80fd2569 973 ...
2152348f 974}
3bf79539 975
2152348f 976floating_point {
80fd2569 977 ...
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978}
979
980struct {
981 integer_type field_name:size; /* GNU/C bitfield */
982}
983
984struct {
985 string field_name;
986}
3bf79539 987
fcba70d4 988
3bf79539 989A. Helper macros
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990
991The two following macros keep track of the size of a GNU/C structure without
992padding at the end by placing HEADER_END as the last field. A one byte end field
993is used for C90 compatibility (C99 flexible arrays could be used here). Note
994that this does not affect the effective structure size, which should always be
995calculated with the header_sizeof() helper.
996
997#define HEADER_END char end_field
998#define header_sizeof(type) offsetof(typeof(type), end_field)
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999
1000
1001B. Stream Header Rationale
1002
1003An event stream is divided in contiguous event packets of variable size. These
1004subdivisions allow the trace analyzer to perform a fast binary search by time
1005within the stream (typically requiring to index only the event packet headers)
1006without reading the whole stream. These subdivisions have a variable size to
1007eliminate the need to transfer the event packet padding when partially filled
1008event packets must be sent when streaming a trace for live viewing/analysis.
1009An event packet can contain a certain amount of padding at the end. Dividing
1010streams into event packets is also useful for network streaming over UDP and
1011flight recorder mode tracing (a whole event packet can be swapped out of the
1012buffer atomically for reading).
1013
1014The stream header is repeated at the beginning of each event packet to allow
1015flexibility in terms of:
1016
1017 - streaming support,
1018 - allowing arbitrary buffers to be discarded without making the trace
1019 unreadable,
1020 - allow UDP packet loss handling by either dealing with missing event packet
1021 or asking for re-transmission.
1022 - transparently support flight recorder mode,
1023 - transparently support crash dump.
1024
1025The event stream header will therefore be referred to as the "event packet
1026header" throughout the rest of this document.
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1027
1028C. CTF Metadata Grammar
1029
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1030/*
1031 * Common Trace Format (CTF) Metadata Grammar.
1032 *
1033 * Inspired from the C99 grammar:
1034 * http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1124.pdf (Annex A)
1035 *
1036 * Specialized for CTF needs by including only constant and declarations from
1037 * C99 (excluding function declarations), and by adding support for variants,
1038 * sequences and CTF-specific specifiers.
1039 */
1040
10411) Lexical grammar
1042
10431.1) Lexical elements
1044
1045token:
1046 keyword
1047 identifier
1048 constant
1049 string-literal
1050 punctuator
1051
10521.2) Keywords
1053
1054keyword: is one of
1055
1056const
1057char
1058double
1059enum
1060event
1061floating_point
1062float
1063integer
1064int
1065long
1066short
1067signed
1068stream
1069string
1070struct
1071trace
3e1e1a78 1072typealias
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1073typedef
1074unsigned
1075variant
1076void
1077_Bool
1078_Complex
1079_Imaginary
1080
1081
10821.3) Identifiers
1083
1084identifier:
1085 identifier-nondigit
1086 identifier identifier-nondigit
1087 identifier digit
1088
1089identifier-nondigit:
1090 nondigit
1091 universal-character-name
1092 any other implementation-defined characters
1093
1094nondigit:
1095 _
1096 [a-zA-Z] /* regular expression */
1097
1098digit:
1099 [0-9] /* regular expression */
1100
11011.4) Universal character names
1102
1103universal-character-name:
1104 \u hex-quad
1105 \U hex-quad hex-quad
1106
1107hex-quad:
1108 hexadecimal-digit hexadecimal-digit hexadecimal-digit hexadecimal-digit
1109
11101.5) Constants
1111
1112constant:
1113 integer-constant
1114 enumeration-constant
1115 character-constant
1116
1117integer-constant:
1118 decimal-constant integer-suffix-opt
1119 octal-constant integer-suffix-opt
1120 hexadecimal-constant integer-suffix-opt
1121
1122decimal-constant:
1123 nonzero-digit
1124 decimal-constant digit
1125
1126octal-constant:
1127 0
1128 octal-constant octal-digit
1129
1130hexadecimal-constant:
1131 hexadecimal-prefix hexadecimal-digit
1132 hexadecimal-constant hexadecimal-digit
1133
1134hexadecimal-prefix:
1135 0x
1136 0X
1137
1138nonzero-digit:
1139 [1-9]
1140
1141integer-suffix:
1142 unsigned-suffix long-suffix-opt
1143 unsigned-suffix long-long-suffix
1144 long-suffix unsigned-suffix-opt
1145 long-long-suffix unsigned-suffix-opt
1146
1147unsigned-suffix:
1148 u
1149 U
1150
1151long-suffix:
1152 l
1153 L
1154
1155long-long-suffix:
1156 ll
1157 LL
1158
1159digit-sequence:
1160 digit
1161 digit-sequence digit
1162
1163hexadecimal-digit-sequence:
1164 hexadecimal-digit
1165 hexadecimal-digit-sequence hexadecimal-digit
1166
1167enumeration-constant:
1168 identifier
1169 string-literal
1170
1171character-constant:
1172 ' c-char-sequence '
1173 L' c-char-sequence '
1174
1175c-char-sequence:
1176 c-char
1177 c-char-sequence c-char
1178
1179c-char:
1180 any member of source charset except single-quote ('), backslash
1181 (\), or new-line character.
1182 escape-sequence
1183
1184escape-sequence:
1185 simple-escape-sequence
1186 octal-escape-sequence
1187 hexadecimal-escape-sequence
1188 universal-character-name
1189
1190simple-escape-sequence: one of
1191 \' \" \? \\ \a \b \f \n \r \t \v
1192
1193octal-escape-sequence:
1194 \ octal-digit
1195 \ octal-digit octal-digit
1196 \ octal-digit octal-digit octal-digit
1197
1198hexadecimal-escape-sequence:
1199 \x hexadecimal-digit
1200 hexadecimal-escape-sequence hexadecimal-digit
1201
12021.6) String literals
1203
1204string-literal:
1205 " s-char-sequence-opt "
1206 L" s-char-sequence-opt "
1207
1208s-char-sequence:
1209 s-char
1210 s-char-sequence s-char
1211
1212s-char:
1213 any member of source charset except double-quote ("), backslash
1214 (\), or new-line character.
1215 escape-sequence
1216
12171.7) Punctuators
1218
1219punctuator: one of
1220 [ ] ( ) { } . -> * + - < > : ; ... = ,
1221
1222
12232) Phrase structure grammar
1224
1225primary-expression:
1226 identifier
1227 constant
1228 string-literal
1229 ( unary-expression )
1230
1231postfix-expression:
1232 primary-expression
1233 postfix-expression [ unary-expression ]
1234 postfix-expression . identifier
1235 postfix-expressoin -> identifier
1236
1237unary-expression:
1238 postfix-expression
1239 unary-operator postfix-expression
1240
1241unary-operator: one of
1242 + -
1243
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1244assignment-operator:
1245 =
1246
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1247type-assignment-operator:
1248 :=
1249
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1250constant-expression:
1251 unary-expression
1252
1253constant-expression-range:
1254 constant-expression ... constant-expression
1255
12562.2) Declarations:
1257
1258declaration:
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1259 declaration-specifiers ;
1260 declaration-specifiers storage-class-specifier declaration-specifiers declarator-list ;
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1261 ctf-specifier ;
1262
1263declaration-specifiers:
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1264 type-specifier declaration-specifiers-opt
1265 type-qualifier declaration-specifiers-opt
1266
1267declarator-list:
1268 declarator
1269 declarator-list , declarator
1270
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1271abstract-declarator-list:
1272 abstract-declarator
1273 abstract-declarator-list , abstract-declarator
1274
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1275storage-class-specifier:
1276 typedef
1277
1278type-specifier:
1279 void
1280 char
1281 short
1282 int
1283 long
1284 float
1285 double
1286 signed
1287 unsigned
1288 _Bool
1289 _Complex
cfdd51ec 1290 _Imaginary
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1291 struct-specifier
1292 variant-specifier
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1293 enum-specifier
1294 typedef-name
1295 ctf-type-specifier
1296
1297struct-specifier:
3b0f8e4d 1298 struct identifier-opt { struct-or-variant-declaration-list-opt }
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1299 struct identifier
1300
1301struct-or-variant-declaration-list:
1302 struct-or-variant-declaration
1303 struct-or-variant-declaration-list struct-or-variant-declaration
1304
1305struct-or-variant-declaration:
1306 specifier-qualifier-list struct-or-variant-declarator-list ;
550aca33 1307 declaration-specifiers storage-class-specifier declaration-specifiers declarator-list ;
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1308 typealias declaration-specifiers abstract-declarator-list : declaration-specifiers abstract-declarator-list ;
1309 typealias declaration-specifiers abstract-declarator-list : declarator-list ;
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1310
1311specifier-qualifier-list:
1312 type-specifier specifier-qualifier-list-opt
1313 type-qualifier specifier-qualifier-list-opt
1314
1315struct-or-variant-declarator-list:
1316 struct-or-variant-declarator
1317 struct-or-variant-declarator-list , struct-or-variant-declarator
1318
1319struct-or-variant-declarator:
1320 declarator
1321 declarator-opt : constant-expression
1322
1323variant-specifier:
1324 variant identifier-opt variant-tag-opt { struct-or-variant-declaration-list }
1325 variant identifier variant-tag
1326
1327variant-tag:
1328 < identifier >
1329
1330enum-specifier:
1331 enum identifier-opt { enumerator-list }
1332 enum identifier-opt { enumerator-list , }
1333 enum identifier
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1334 enum identifier-opt < declaration-specifiers > { enumerator-list }
1335 enum identifier-opt < declaration-specifiers > { enumerator-list , }
1336 enum identifier < declaration-specifiers >
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1337 enum identifier-opt < integer-constant > { enumerator-list }
1338 enum identifier-opt < integer-constant > { enumerator-list , }
1339 enum identifier < integer-constant >
1340
1341enumerator-list:
1342 enumerator
1343 enumerator-list , enumerator
1344
1345enumerator:
1346 enumeration-constant
1347 enumeration-constant = constant-expression
1348 enumeration-constant = constant-expression-range
1349
1350type-qualifier:
1351 const
1352
1353declarator:
1354 pointer-opt direct-declarator
1355
1356direct-declarator:
1357 identifier
1358 ( declarator )
1359 direct-declarator [ type-specifier ]
1360 direct-declarator [ constant-expression ]
1361
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1362abstract-declarator:
1363 pointer-opt direct-abstract-declarator
1364
1365direct-abstract-declarator:
1366 identifier-opt
1367 ( abstract-declarator )
1368 direct-abstract-declarator [ type-specifier ]
1369 direct-abstract-declarator [ constant-expression ]
1370 direct-abstract-declarator [ ]
1371
4fa992a5 1372pointer:
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1373 * type-qualifier-list-opt
1374 * type-qualifier-list-opt pointer
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1375
1376type-qualifier-list:
1377 type-qualifier
1378 type-qualifier-list type-qualifier
1379
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1380typedef-name:
1381 identifier
1382
13832.3) CTF-specific declarations
1384
1385ctf-specifier:
1386 event { ctf-assignment-expression-list-opt }
1387 stream { ctf-assignment-expression-list-opt }
1388 trace { ctf-assignment-expression-list-opt }
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1389 typealias declaration-specifiers abstract-declarator-list : declaration-specifiers abstract-declarator-list ;
1390 typealias declaration-specifiers abstract-declarator-list : declarator-list ;
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1391
1392ctf-type-specifier:
1393 floating_point { ctf-assignment-expression-list-opt }
1394 integer { ctf-assignment-expression-list-opt }
1395 string { ctf-assignment-expression-list-opt }
1396
1397ctf-assignment-expression-list:
1398 ctf-assignment-expression
1399 ctf-assignment-expression-list ; ctf-assignment-expression
1400
1401ctf-assignment-expression:
1402 unary-expression assignment-operator unary-expression
1403 unary-expression type-assignment-operator type-specifier
550aca33 1404 declaration-specifiers storage-class-specifier declaration-specifiers declarator-list
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1405 typealias declaration-specifiers abstract-declarator-list : declaration-specifiers abstract-declarator-list
1406 typealias declaration-specifiers abstract-declarator-list : declarator-list
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