enum : type is only allowed when body is provided
[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
370eae99 102"Integers" 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
3bf79539 108unaligned writes align types on specific alignment values. If no specific
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109alignment is declared for a type, it is assumed to be bit-packed for
110integers with size not multiple of 8 bits and for gcc bitfields. All
111other types are byte-packed.
5ba9f198 112
3bf79539 113Metadata attribute representation of a specific alignment:
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114
115 align = value; /* value in bits */
116
1174.1.3 Byte order
118
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119By default, the native endianness of the source architecture the trace is used.
120Byte order can be overridden for a basic type by specifying a "byte_order"
121attribute. Typical use-case is to specify the network byte order (big endian:
122"be") to save data captured from the network into the trace without conversion.
123If not specified, the byte order is native.
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124
125Metadata representation:
126
127 byte_order = native OR network OR be OR le; /* network and be are aliases */
128
1294.1.4 Size
130
131Type size, in bits, for integers and floats is that returned by "sizeof()" in C
132multiplied by CHAR_BIT.
133We require the size of "char" and "unsigned char" types (CHAR_BIT) to be fixed
134to 8 bits for cross-endianness compatibility.
135
136Metadata representation:
137
138 size = value; (value is in bits)
139
1404.1.5 Integers
141
142Signed integers are represented in two-complement. Integer alignment, size,
143signedness and byte ordering are defined in the metadata. Integers aligned on
144byte size (8-bit) and with length multiple of byte size (8-bit) correspond to
145the C99 standard integers. In addition, integers with alignment and/or size that
146are _not_ a multiple of the byte size are permitted; these correspond to the C99
147standard bitfields, with the added specification that the CTF integer bitfields
148have a fixed binary representation. A MIT-licensed reference implementation of
149the CTF portable bitfields is available at:
150
151 http://git.efficios.com/?p=babeltrace.git;a=blob;f=include/babeltrace/bitfield.h
152
153Binary representation of integers:
154
155- On little and big endian:
156 - Within a byte, high bits correspond to an integer high bits, and low bits
157 correspond to low bits.
158- On little endian:
159 - Integer across multiple bytes are placed from the less significant to the
160 most significant.
161 - Consecutive integers are placed from lower bits to higher bits (even within
162 a byte).
163- On big endian:
164 - Integer across multiple bytes are placed from the most significant to the
165 less significant.
166 - Consecutive integers are placed from higher bits to lower bits (even within
167 a byte).
168
169This binary representation is derived from the bitfield implementation in GCC
170for little and big endian. However, contrary to what GCC does, integers can
171cross units boundaries (no padding is required). Padding can be explicitely
172added (see 4.1.6 GNU/C bitfields) to follow the GCC layout if needed.
173
174Metadata representation:
175
80fd2569 176 integer {
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177 signed = true OR false; /* default false */
178 byte_order = native OR network OR be OR le; /* default native */
179 size = value; /* value in bits, no default */
180 align = value; /* value in bits */
2152348f 181 }
5ba9f198 182
80fd2569 183Example of type inheritance (creation of a uint32_t named type):
5ba9f198 184
359894ac 185typealias integer {
9e4e34e9 186 size = 32;
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187 signed = false;
188 align = 32;
38b8da21 189} := uint32_t;
5ba9f198 190
80fd2569 191Definition of a named 5-bit signed bitfield:
5ba9f198 192
359894ac 193typealias integer {
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194 size = 5;
195 signed = true;
196 align = 1;
38b8da21 197} := int5_t;
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198
1994.1.6 GNU/C bitfields
200
201The GNU/C bitfields follow closely the integer representation, with a
202particularity on alignment: if a bitfield cannot fit in the current unit, the
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203unit is padded and the bitfield starts at the following unit. The unit size is
204defined by the size of the type "unit_type".
5ba9f198 205
2152348f 206Metadata representation:
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207
208 unit_type name:size:
209
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210As an example, the following structure declared in C compiled by GCC:
211
212struct example {
213 short a:12;
214 short b:5;
215};
216
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217The example structure is aligned on the largest element (short). The second
218bitfield would be aligned on the next unit boundary, because it would not fit in
219the current unit.
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220
2214.1.7 Floating point
222
223The floating point values byte ordering is defined in the metadata.
224
225Floating point values follow the IEEE 754-2008 standard interchange formats.
226Description of the floating point values include the exponent and mantissa size
227in bits. Some requirements are imposed on the floating point values:
228
229- FLT_RADIX must be 2.
230- mant_dig is the number of digits represented in the mantissa. It is specified
231 by the ISO C99 standard, section 5.2.4, as FLT_MANT_DIG, DBL_MANT_DIG and
232 LDBL_MANT_DIG as defined by <float.h>.
233- exp_dig is the number of digits represented in the exponent. Given that
234 mant_dig is one bit more than its actual size in bits (leading 1 is not
235 needed) and also given that the sign bit always takes one bit, exp_dig can be
236 specified as:
237
238 - sizeof(float) * CHAR_BIT - FLT_MANT_DIG
239 - sizeof(double) * CHAR_BIT - DBL_MANT_DIG
240 - sizeof(long double) * CHAR_BIT - LDBL_MANT_DIG
241
242Metadata representation:
243
80fd2569 244floating_point {
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245 exp_dig = value;
246 mant_dig = value;
247 byte_order = native OR network OR be OR le;
2152348f 248}
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249
250Example of type inheritance:
251
359894ac 252typealias floating_point {
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253 exp_dig = 8; /* sizeof(float) * CHAR_BIT - FLT_MANT_DIG */
254 mant_dig = 24; /* FLT_MANT_DIG */
255 byte_order = native;
38b8da21 256} := float;
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257
258TODO: define NaN, +inf, -inf behavior.
259
2604.1.8 Enumerations
261
262Enumerations are a mapping between an integer type and a table of strings. The
263numerical representation of the enumeration follows the integer type specified
264by the metadata. The enumeration mapping table is detailed in the enumeration
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265description within the metadata. The mapping table maps inclusive value ranges
266(or single values) to strings. Instead of being limited to simple
267"value -> string" mappings, these enumerations map
80fd2569 268"[ start_value ... end_value ] -> string", which map inclusive ranges of
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269values to strings. An enumeration from the C language can be represented in
270this format by having the same start_value and end_value for each element, which
271is in fact a range of size 1. This single-value range is supported without
4767a9e7 272repeating the start and end values with the value = string declaration.
80fd2569 273
a9b83695 274enum name : integer_type {
359894ac 275 somestring = start_value1 ... end_value1,
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276 "other string" = start_value2 ... end_value2,
277 yet_another_string, /* will be assigned to end_value2 + 1 */
278 "some other string" = value,
279 ...
280};
281
282If the values are omitted, the enumeration starts at 0 and increment of 1 for
283each entry:
284
a9b83695 285enum name : unsigned int {
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286 ZERO,
287 ONE,
288 TWO,
289 TEN = 10,
290 ELEVEN,
3bf79539 291};
5ba9f198 292
80fd2569 293Overlapping ranges within a single enumeration are implementation defined.
5ba9f198 294
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295A nameless enumeration can be declared as a field type or as part of a typedef:
296
a9b83695 297enum : integer_type {
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298 ...
299}
300
1fad7a85 301
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3024.2 Compound types
303
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304Compound are aggregation of type declarations. Compound types include
305structures, variant, arrays, sequences, and strings.
306
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3074.2.1 Structures
308
309Structures are aligned on the largest alignment required by basic types
310contained within the structure. (This follows the ISO/C standard for structures)
311
80fd2569 312Metadata representation of a named structure:
5ba9f198 313
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314struct name {
315 field_type field_name;
316 field_type field_name;
317 ...
318};
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319
320Example:
321
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322struct example {
323 integer { /* Nameless type */
324 size = 16;
325 signed = true;
326 align = 16;
327 } first_field_name;
328 uint64_t second_field_name; /* Named type declared in the metadata */
3bf79539 329};
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330
331The fields are placed in a sequence next to each other. They each possess a
332field name, which is a unique identifier within the structure.
333
2152348f 334A nameless structure can be declared as a field type or as part of a typedef:
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335
336struct {
337 ...
2152348f 338}
80fd2569 339
77a98c82 3404.2.2 Variants (Discriminated/Tagged Unions)
fcba70d4 341
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342A CTF variant is a selection between different types. A CTF variant must
343always be defined within the scope of a structure or within fields
344contained within a structure (defined recursively). A "tag" enumeration
345field must appear in either the same lexical scope, prior to the variant
346field (in field declaration order), in an uppermost lexical scope (see
347Section 7.2.1), or in an uppermost dynamic scope (see Section 7.2.2).
348The type selection is indicated by the mapping from the enumeration
349value to the string used as variant type selector. The field to use as
350tag is specified by the "tag_field", specified between "< >" after the
351"variant" keyword for unnamed variants, and after "variant name" for
352named variants.
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353
354The alignment of the variant is the alignment of the type as selected by the tag
355value for the specific instance of the variant. The alignment of the type
356containing the variant is independent of the variant alignment. The size of the
357variant is the size as selected by the tag value for the specific instance of
358the variant.
359
360A named variant declaration followed by its definition within a structure
361declaration:
362
363variant name {
364 field_type sel1;
365 field_type sel2;
366 field_type sel3;
367 ...
368};
369
370struct {
a9b83695 371 enum : integer_type { sel1, sel2, sel3, ... } tag_field;
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372 ...
373 variant name <tag_field> v;
374}
375
376An unnamed variant definition within a structure is expressed by the following
377metadata:
378
379struct {
a9b83695 380 enum : integer_type { sel1, sel2, sel3, ... } tag_field;
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381 ...
382 variant <tag_field> {
383 field_type sel1;
384 field_type sel2;
385 field_type sel3;
386 ...
387 } v;
388}
389
390Example of a named variant within a sequence that refers to a single tag field:
391
392variant example {
393 uint32_t a;
394 uint64_t b;
395 short c;
396};
397
398struct {
a9b83695 399 enum : uint2_t { a, b, c } choice;
15850440 400 variant example <choice> v[unsigned int];
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401}
402
403Example of an unnamed variant:
404
405struct {
a9b83695 406 enum : uint2_t { a, b, c, d } choice;
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407 /* Unrelated fields can be added between the variant and its tag */
408 int32_t somevalue;
409 variant <choice> {
410 uint32_t a;
411 uint64_t b;
412 short c;
413 struct {
414 unsigned int field1;
415 uint64_t field2;
416 } d;
417 } s;
418}
419
420Example of an unnamed variant within an array:
421
422struct {
a9b83695 423 enum : uint2_t { a, b, c } choice;
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424 variant <choice> {
425 uint32_t a;
426 uint64_t b;
427 short c;
15850440 428 } v[10];
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429}
430
431Example of a variant type definition within a structure, where the defined type
432is then declared within an array of structures. This variant refers to a tag
433located in an upper lexical scope. This example clearly shows that a variant
434type definition referring to the tag "x" uses the closest preceding field from
435the lexical scope of the type definition.
436
437struct {
a9b83695 438 enum : uint2_t { a, b, c, d } x;
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439
440 typedef variant <x> { /*
441 * "x" refers to the preceding "x" enumeration in the
442 * lexical scope of the type definition.
443 */
444 uint32_t a;
445 uint64_t b;
446 short c;
447 } example_variant;
448
449 struct {
a9b83695 450 enum : int { x, y, z } x; /* This enumeration is not used by "v". */
fcba70d4 451 example_variant v; /*
a9b83695 452 * "v" uses the "enum : uint2_t { a, b, c, d }"
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453 * tag.
454 */
455 } a[10];
456}
457
4584.2.3 Arrays
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459
460Arrays are fixed-length. Their length is declared in the type declaration within
461the metadata. They contain an array of "inner type" elements, which can refer to
462any type not containing the type of the array being declared (no circular
3bf79539 463dependency). The length is the number of elements in an array.
5ba9f198 464
2152348f 465Metadata representation of a named array:
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466
467typedef elem_type name[length];
5ba9f198 468
2152348f 469A nameless array can be declared as a field type within a structure, e.g.:
5ba9f198 470
2152348f 471 uint8_t field_name[10];
80fd2569 472
5ba9f198 473
fcba70d4 4744.2.4 Sequences
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475
476Sequences are dynamically-sized arrays. They start with an integer that specify
477the length of the sequence, followed by an array of "inner type" elements.
3bf79539 478The length is the number of elements in the sequence.
5ba9f198 479
2152348f 480Metadata representation for a named sequence:
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481
482typedef elem_type name[length_type];
483
484A nameless sequence can be declared as a field type, e.g.:
485
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486long field_name[int];
487
488The length type follows the integer types specifications, and the sequence
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489elements follow the "array" specifications.
490
fcba70d4 4914.2.5 Strings
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492
493Strings are an array of bytes of variable size and are terminated by a '\0'
494"NULL" character. Their encoding is described in the metadata. In absence of
495encoding attribute information, the default encoding is UTF-8.
496
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497Metadata representation of a named string type:
498
359894ac 499typealias string {
5ba9f198 500 encoding = UTF8 OR ASCII;
38b8da21 501} := name;
5ba9f198 502
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503A nameless string type can be declared as a field type:
504
505string field_name; /* Use default UTF8 encoding */
5ba9f198 506
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5075. Event Packet Header
508
509The event packet header consists of two part: one is mandatory and have a fixed
510layout. The second part, the "event packet context", has its layout described in
511the metadata.
5ba9f198 512
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513- Aligned on page size. Fixed size. Fields either aligned or packed (depending
514 on the architecture preference).
515 No padding at the end of the event packet header. Native architecture byte
5ba9f198 516 ordering.
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517
518Fixed layout (event packet header):
519
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520- Magic number (CTF magic numbers: 0xC1FC1FC1 and its reverse endianness
521 representation: 0xC11FFCC1) It needs to have a non-symmetric bytewise
522 representation. Used to distinguish between big and little endian traces (this
523 information is determined by knowing the endianness of the architecture
524 reading the trace and comparing the magic number against its value and the
525 reverse, 0xC11FFCC1). This magic number specifies that we use the CTF metadata
526 description language described in this document. Different magic numbers
527 should be used for other metadata description languages.
3bf79539 528- Trace UUID, used to ensure the event packet match the metadata used.
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529 (note: we cannot use a metadata checksum because metadata can be appended to
530 while tracing is active)
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531- Stream ID, used as reference to stream description in metadata.
532
533Metadata-defined layout (event packet context):
534
535- Event packet content size (in bytes).
536- Event packet size (in bytes, includes padding).
537- Event packet content checksum (optional). Checksum excludes the event packet
538 header.
539- Per-stream event packet sequence count (to deal with UDP packet loss). The
540 number of significant sequence counter bits should also be present, so
541 wrap-arounds are deal with correctly.
542- Timestamp at the beginning and timestamp at the end of the event packet.
543 Both timestamps are written in the packet header, but sampled respectively
544 while (or before) writing the first event and while (or after) writing the
545 last event in the packet. The inclusive range between these timestamps should
546 include all event timestamps assigned to events contained within the packet.
5ba9f198 547- Events discarded count
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548 - Snapshot of a per-stream free-running counter, counting the number of
549 events discarded that were supposed to be written in the stream prior to
550 the first event in the event packet.
5ba9f198 551 * Note: producer-consumer buffer full condition should fill the current
3bf79539 552 event packet with padding so we know exactly where events have been
5ba9f198 553 discarded.
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554- Lossless compression scheme used for the event packet content. Applied
555 directly to raw data. New types of compression can be added in following
556 versions of the format.
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557 0: no compression scheme
558 1: bzip2
559 2: gzip
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560 3: xz
561- Cypher used for the event packet content. Applied after compression.
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562 0: no encryption
563 1: AES
3bf79539 564- Checksum scheme used for the event packet content. Applied after encryption.
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565 0: no checksum
566 1: md5
567 2: sha1
568 3: crc32
569
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5705.1 Event Packet Header Fixed Layout Description
571
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572struct event_packet_header {
573 uint32_t magic;
574 uint8_t trace_uuid[16];
3bf79539 575 uint32_t stream_id;
80fd2569 576};
5ba9f198 577
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5785.2 Event Packet Context Description
579
580Event packet context example. These are declared within the stream declaration
581in the metadata. All these fields are optional except for "content_size" and
582"packet_size", which must be present in the context.
583
584An example event packet context type:
585
80fd2569 586struct event_packet_context {
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587 uint64_t timestamp_begin;
588 uint64_t timestamp_end;
589 uint32_t checksum;
590 uint32_t stream_packet_count;
591 uint32_t events_discarded;
592 uint32_t cpu_id;
593 uint32_t/uint16_t content_size;
594 uint32_t/uint16_t packet_size;
595 uint8_t stream_packet_count_bits; /* Significant counter bits */
596 uint8_t compression_scheme;
597 uint8_t encryption_scheme;
3b0f8e4d 598 uint8_t checksum_scheme;
3bf79539 599};
5ba9f198 600
fcba70d4 601
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6026. Event Structure
603
604The overall structure of an event is:
605
fcba70d4 6061 - Stream Packet Context (as specified by the stream metadata)
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607 2 - Event Header (as specified by the stream metadata)
608 3 - Stream Event Context (as specified by the stream metadata)
609 4 - Event Context (as specified by the event metadata)
610 5 - Event Payload (as specified by the event metadata)
5ba9f198 611
fdf2bb05 612This structure defines an implicit dynamic scoping, where variants
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613located in inner structures (those with a higher number in the listing
614above) can refer to the fields of outer structures (with lower number in
615the listing above). See Section 7.2 Metadata Scopes for more detail.
5ba9f198 616
fdf2bb05 6176.1 Event Header
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618
619Event headers can be described within the metadata. We hereby propose, as an
620example, two types of events headers. Type 1 accommodates streams with less than
62131 event IDs. Type 2 accommodates streams with 31 or more event IDs.
5ba9f198 622
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623One major factor can vary between streams: the number of event IDs assigned to
624a stream. Luckily, this information tends to stay relatively constant (modulo
5ba9f198 625event registration while trace is being recorded), so we can specify different
3bf79539 626representations for streams containing few event IDs and streams containing
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627many event IDs, so we end up representing the event ID and timestamp as densely
628as possible in each case.
629
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630The header is extended in the rare occasions where the information cannot be
631represented in the ranges available in the standard event header. They are also
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632used in the rare occasions where the data required for a field could not be
633collected: the flag corresponding to the missing field within the missing_fields
634array is then set to 1.
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635
636Types uintX_t represent an X-bit unsigned integer.
637
638
fdf2bb05 6396.1.1 Type 1 - Few event IDs
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640
641 - Aligned on 32-bit (or 8-bit if byte-packed, depending on the architecture
642 preference).
5ba9f198 643 - Native architecture byte ordering.
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644 - For "compact" selection
645 - Fixed size: 32 bits.
646 - For "extended" selection
647 - Size depends on the architecture and variant alignment.
5ba9f198 648
80fd2569 649struct event_header_1 {
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650 /*
651 * id: range: 0 - 30.
652 * id 31 is reserved to indicate an extended header.
653 */
a9b83695 654 enum : uint5_t { compact = 0 ... 30, extended = 31 } id;
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655 variant <id> {
656 struct {
657 uint27_t timestamp;
658 } compact;
659 struct {
660 uint32_t id; /* 32-bit event IDs */
661 uint64_t timestamp; /* 64-bit timestamps */
662 } extended;
663 } v;
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664};
665
5ba9f198 666
fdf2bb05 6676.1.2 Type 2 - Many event IDs
5ba9f198 668
fcba70d4 669 - Aligned on 16-bit (or 8-bit if byte-packed, depending on the architecture
5ba9f198 670 preference).
5ba9f198 671 - Native architecture byte ordering.
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672 - For "compact" selection
673 - Size depends on the architecture and variant alignment.
674 - For "extended" selection
675 - Size depends on the architecture and variant alignment.
5ba9f198 676
80fd2569 677struct event_header_2 {
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678 /*
679 * id: range: 0 - 65534.
680 * id 65535 is reserved to indicate an extended header.
681 */
a9b83695 682 enum : uint16_t { compact = 0 ... 65534, extended = 65535 } id;
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683 variant <id> {
684 struct {
685 uint32_t timestamp;
686 } compact;
687 struct {
688 uint32_t id; /* 32-bit event IDs */
689 uint64_t timestamp; /* 64-bit timestamps */
690 } extended;
691 } v;
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692};
693
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694
6956.2 Event Context
696
697The event context contains information relative to the current event. The choice
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698and meaning of this information is specified by the metadata "stream" and
699"event" information. The "stream" context is applied to all events within the
700stream. The "stream" context structure follows the event header. The "event"
701context is applied to specific events. Its structure follows the "stream"
702context stucture.
5ba9f198 703
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704An example of stream-level event context is to save the event payload size with
705each event, or to save the current PID with each event. These are declared
706within the stream declaration within the metadata:
5ba9f198 707
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708 stream {
709 ...
710 event {
711 ...
4fa992a5 712 context := struct {
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713 uint pid;
714 uint16_t payload_size;
3bf79539 715 };
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716 }
717 };
718
719An example of event-specific event context is to declare a bitmap of missing
720fields, only appended after the stream event context if the extended event
721header is selected. NR_FIELDS is the number of fields within the event (a
722numeric value).
5ba9f198 723
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724 event {
725 context = struct {
726 variant <id> {
727 struct { } compact;
728 struct {
729 uint1_t missing_fields[NR_FIELDS]; /* missing event fields bitmap */
730 } extended;
731 } v;
732 };
733 ...
734 }
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735
7366.3 Event Payload
737
738An event payload contains fields specific to a given event type. The fields
739belonging to an event type are described in the event-specific metadata
740within a structure type.
741
7426.3.1 Padding
743
744No padding at the end of the event payload. This differs from the ISO/C standard
745for structures, but follows the CTF standard for structures. In a trace, even
746though it makes sense to align the beginning of a structure, it really makes no
747sense to add padding at the end of the structure, because structures are usually
748not followed by a structure of the same type.
749
750This trick can be done by adding a zero-length "end" field at the end of the C
751structures, and by using the offset of this field rather than using sizeof()
3bf79539 752when calculating the size of a structure (see Appendix "A. Helper macros").
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753
7546.3.2 Alignment
755
756The event payload is aligned on the largest alignment required by types
757contained within the payload. (This follows the ISO/C standard for structures)
758
759
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7607. Metadata
761
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762The meta-data is located in a stream identified by its name: "metadata".
763It is made of "event packets", which each start with an event packet
764header. The event type within the metadata stream have no event header
765nor event context. Each event only contains a null-terminated "string"
766payload, which is a metadata description entry. The events are packed
767one next to another. Each event packet start with an event packet
768header, which contains, amongst other fields, the magic number and trace
769UUID. In the event packet header, the trace UUID is represented as an
770array of bytes. Within the string-based metadata description, the trace
771UUID is represented as a string of hexadecimal digits and dashes "-".
772
773The metadata can be parsed by reading through the metadata strings,
774skipping null-characters. Type names are made of a single identifier,
775and can be surrounded by prefix/postfix. Text contained within "/*" and
776"*/", as well as within "//" and end of line, are treated as comments.
777Boolean values can be represented as true, TRUE, or 1 for true, and
778false, FALSE, or 0 for false.
fcba70d4 779
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780
7817.1 Declaration vs Definition
782
783A declaration associates a layout to a type, without specifying where
784this type is located in the event structure hierarchy (see Section 6).
785This therefore includes typedef, typealias, as well as all type
786specifiers. In certain circumstances (typedef, structure field and
787variant field), a declaration is followed by a declarator, which specify
788the newly defined type name (for typedef), or the field name (for
789declarations located within structure and variants). Array and sequence,
790declared with square brackets ("[" "]"), are part of the declarator,
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791similarly to C99. The enumeration base type is specified by
792": base_type", which is part of the type specifier. The variant tag
793name, specified between "<" ">", is also part of the type specifier.
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794
795A definition associates a type to a location in the event structure
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796hierarchy (see Section 6). This association is denoted by ":=", as shown
797in Section 7.3.
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798
799
8007.2 Metadata Scopes
801
802CTF metadata uses two different types of scoping: a lexical scope is
803used for declarations and type definitions, and a dynamic scope is used
804for variants references to tag fields.
805
8067.2.1 Lexical Scope
807
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808Each of "trace", "stream", "event", "struct" and "variant" have their own
809nestable declaration scope, within which types can be declared using "typedef"
fdf2bb05 810and "typealias". A root declaration scope also contains all declarations
7d9d7e92 811located outside of any of the aforementioned declarations. An inner
fdf2bb05 812declaration scope can refer to type declared within its container
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813lexical scope prior to the inner declaration scope. Redefinition of a
814typedef or typealias is not valid, although hiding an upper scope
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815typedef or typealias is allowed within a sub-scope.
816
8177.2.2 Dynamic Scope
818
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819A dynamic scope consists in the lexical scope augmented with the
820implicit event structure definition hierarchy presented at Section 6.
821The dynamic scope is only used for variant tag definitions. It is used
822at definition time to look up the location of the tag field associated
823with a variant.
824
825Therefore, variants in lower levels in the dynamic scope (e.g. event
826context) can refer to a tag field located in upper levels (e.g. in the
827event header) by specifying, in this case, the associated tag with
828<header.field_name>. This allows, for instance, the event context to
829define a variant referring to the "id" field of the event header as
830selector.
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831
832The target dynamic scope must be specified explicitly when referring to
833a field outside of the local static scope. The dynamic scope prefixes
834are thus:
835
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836 - Stream Packet Context: <stream.packet.context. >,
837 - Event Header: <stream.event.header. >,
838 - Stream Event Context: <stream.event.context. >,
839 - Event Context: <event.context. >,
840 - Event Payload: <event.fields. >.
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841
842Multiple declarations of the same field name within a single scope is
843not valid. It is however valid to re-use the same field name in
844different scopes. There is no possible conflict, because the dynamic
845scope must be specified when a variant refers to a tag field located in
846a different dynamic scope.
847
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848The information available in the dynamic scopes can be thought of as the
849current tracing context. At trace production, information about the
850current context is saved into the specified scope field levels. At trace
851consumption, for each event, the current trace context is therefore
852readable by accessing the upper dynamic scopes.
853
fdf2bb05 854
b9606a77 8557.3 Metadata Examples
d285084f 856
fcba70d4 857The grammar representing the CTF metadata is presented in
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858Appendix C. CTF Metadata Grammar. This section presents a rather ligher
859reading that consists in examples of CTF metadata, with template values:
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860
861trace {
fdf2bb05 862 major = value; /* Trace format version */
5ba9f198 863 minor = value;
fdf2bb05 864 uuid = "aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaaa"; /* Trace UUID */
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865 word_size = value;
866};
5ba9f198 867
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868stream {
869 id = stream_id;
fdf2bb05 870 /* Type 1 - Few event IDs; Type 2 - Many event IDs. See section 6.1. */
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871 event.header := event_header_1 OR event_header_2;
872 event.context := struct {
77a98c82 873 ...
3bf79539 874 };
4fa992a5 875 packet.context := struct {
77a98c82 876 ...
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877 };
878};
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879
880event {
3d13ef1a 881 name = event_name;
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882 id = value; /* Numeric identifier within the stream */
883 stream = stream_id;
4fa992a5 884 context := struct {
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885 ...
886 };
4fa992a5 887 fields := struct {
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888 ...
889 };
3bf79539 890};
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891
892/* More detail on types in section 4. Types */
893
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894/*
895 * Named types:
896 *
4fa992a5 897 * Type declarations behave similarly to the C standard.
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898 */
899
80af8ac6 900typedef aliased_type_specifiers new_type_declarators;
2152348f 901
3d13ef1a 902/* e.g.: typedef struct example new_type_name[10]; */
80fd2569 903
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904/*
905 * typealias
906 *
907 * The "typealias" declaration can be used to give a name (including
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908 * pointer declarator specifier) to a type. It should also be used to
909 * map basic C types (float, int, unsigned long, ...) to a CTF type.
910 * Typealias is a superset of "typedef": it also allows assignment of a
38b8da21 911 * simple variable identifier to a type.
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912 */
913
914typealias type_class {
80fd2569 915 ...
38b8da21 916} := type_specifiers type_declarator;
2152348f 917
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918/*
919 * e.g.:
4fa992a5 920 * typealias integer {
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921 * size = 32;
922 * align = 32;
923 * signed = false;
38b8da21 924 * } := struct page *;
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925 *
926 * typealias integer {
927 * size = 32;
928 * align = 32;
929 * signed = true;
38b8da21 930 * } := int;
3d13ef1a 931 */
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932
933struct name {
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934 ...
935};
5ba9f198 936
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937variant name {
938 ...
939};
940
a9b83695 941enum name : integer_type {
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942 ...
943};
944
2152348f 945
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946/*
947 * Unnamed types, contained within compound type fields, typedef or typealias.
948 */
2152348f 949
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950struct {
951 ...
2152348f 952}
5ba9f198 953
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954variant {
955 ...
956}
957
a9b83695 958enum : integer_type {
80fd2569 959 ...
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960}
961
962typedef type new_type[length];
3bf79539 963
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964struct {
965 type field_name[length];
966}
967
968typedef type new_type[length_type];
969
970struct {
971 type field_name[length_type];
972}
973
974integer {
80fd2569 975 ...
2152348f 976}
3bf79539 977
2152348f 978floating_point {
80fd2569 979 ...
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980}
981
982struct {
983 integer_type field_name:size; /* GNU/C bitfield */
984}
985
986struct {
987 string field_name;
988}
3bf79539 989
fcba70d4 990
3bf79539 991A. Helper macros
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992
993The two following macros keep track of the size of a GNU/C structure without
994padding at the end by placing HEADER_END as the last field. A one byte end field
995is used for C90 compatibility (C99 flexible arrays could be used here). Note
996that this does not affect the effective structure size, which should always be
997calculated with the header_sizeof() helper.
998
999#define HEADER_END char end_field
1000#define header_sizeof(type) offsetof(typeof(type), end_field)
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1001
1002
1003B. Stream Header Rationale
1004
1005An event stream is divided in contiguous event packets of variable size. These
1006subdivisions allow the trace analyzer to perform a fast binary search by time
1007within the stream (typically requiring to index only the event packet headers)
1008without reading the whole stream. These subdivisions have a variable size to
1009eliminate the need to transfer the event packet padding when partially filled
1010event packets must be sent when streaming a trace for live viewing/analysis.
1011An event packet can contain a certain amount of padding at the end. Dividing
1012streams into event packets is also useful for network streaming over UDP and
1013flight recorder mode tracing (a whole event packet can be swapped out of the
1014buffer atomically for reading).
1015
1016The stream header is repeated at the beginning of each event packet to allow
1017flexibility in terms of:
1018
1019 - streaming support,
1020 - allowing arbitrary buffers to be discarded without making the trace
1021 unreadable,
1022 - allow UDP packet loss handling by either dealing with missing event packet
1023 or asking for re-transmission.
1024 - transparently support flight recorder mode,
1025 - transparently support crash dump.
1026
1027The event stream header will therefore be referred to as the "event packet
1028header" throughout the rest of this document.
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1029
1030C. CTF Metadata Grammar
1031
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1032/*
1033 * Common Trace Format (CTF) Metadata Grammar.
1034 *
1035 * Inspired from the C99 grammar:
1036 * http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1124.pdf (Annex A)
1037 *
1038 * Specialized for CTF needs by including only constant and declarations from
1039 * C99 (excluding function declarations), and by adding support for variants,
1040 * sequences and CTF-specific specifiers.
1041 */
1042
10431) Lexical grammar
1044
10451.1) Lexical elements
1046
1047token:
1048 keyword
1049 identifier
1050 constant
1051 string-literal
1052 punctuator
1053
10541.2) Keywords
1055
1056keyword: is one of
1057
1058const
1059char
1060double
1061enum
1062event
1063floating_point
1064float
1065integer
1066int
1067long
1068short
1069signed
1070stream
1071string
1072struct
1073trace
3e1e1a78 1074typealias
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1075typedef
1076unsigned
1077variant
1078void
1079_Bool
1080_Complex
1081_Imaginary
1082
1083
10841.3) Identifiers
1085
1086identifier:
1087 identifier-nondigit
1088 identifier identifier-nondigit
1089 identifier digit
1090
1091identifier-nondigit:
1092 nondigit
1093 universal-character-name
1094 any other implementation-defined characters
1095
1096nondigit:
1097 _
1098 [a-zA-Z] /* regular expression */
1099
1100digit:
1101 [0-9] /* regular expression */
1102
11031.4) Universal character names
1104
1105universal-character-name:
1106 \u hex-quad
1107 \U hex-quad hex-quad
1108
1109hex-quad:
1110 hexadecimal-digit hexadecimal-digit hexadecimal-digit hexadecimal-digit
1111
11121.5) Constants
1113
1114constant:
1115 integer-constant
1116 enumeration-constant
1117 character-constant
1118
1119integer-constant:
1120 decimal-constant integer-suffix-opt
1121 octal-constant integer-suffix-opt
1122 hexadecimal-constant integer-suffix-opt
1123
1124decimal-constant:
1125 nonzero-digit
1126 decimal-constant digit
1127
1128octal-constant:
1129 0
1130 octal-constant octal-digit
1131
1132hexadecimal-constant:
1133 hexadecimal-prefix hexadecimal-digit
1134 hexadecimal-constant hexadecimal-digit
1135
1136hexadecimal-prefix:
1137 0x
1138 0X
1139
1140nonzero-digit:
1141 [1-9]
1142
1143integer-suffix:
1144 unsigned-suffix long-suffix-opt
1145 unsigned-suffix long-long-suffix
1146 long-suffix unsigned-suffix-opt
1147 long-long-suffix unsigned-suffix-opt
1148
1149unsigned-suffix:
1150 u
1151 U
1152
1153long-suffix:
1154 l
1155 L
1156
1157long-long-suffix:
1158 ll
1159 LL
1160
1161digit-sequence:
1162 digit
1163 digit-sequence digit
1164
1165hexadecimal-digit-sequence:
1166 hexadecimal-digit
1167 hexadecimal-digit-sequence hexadecimal-digit
1168
1169enumeration-constant:
1170 identifier
1171 string-literal
1172
1173character-constant:
1174 ' c-char-sequence '
1175 L' c-char-sequence '
1176
1177c-char-sequence:
1178 c-char
1179 c-char-sequence c-char
1180
1181c-char:
1182 any member of source charset except single-quote ('), backslash
1183 (\), or new-line character.
1184 escape-sequence
1185
1186escape-sequence:
1187 simple-escape-sequence
1188 octal-escape-sequence
1189 hexadecimal-escape-sequence
1190 universal-character-name
1191
1192simple-escape-sequence: one of
1193 \' \" \? \\ \a \b \f \n \r \t \v
1194
1195octal-escape-sequence:
1196 \ octal-digit
1197 \ octal-digit octal-digit
1198 \ octal-digit octal-digit octal-digit
1199
1200hexadecimal-escape-sequence:
1201 \x hexadecimal-digit
1202 hexadecimal-escape-sequence hexadecimal-digit
1203
12041.6) String literals
1205
1206string-literal:
1207 " s-char-sequence-opt "
1208 L" s-char-sequence-opt "
1209
1210s-char-sequence:
1211 s-char
1212 s-char-sequence s-char
1213
1214s-char:
1215 any member of source charset except double-quote ("), backslash
1216 (\), or new-line character.
1217 escape-sequence
1218
12191.7) Punctuators
1220
1221punctuator: one of
1222 [ ] ( ) { } . -> * + - < > : ; ... = ,
1223
1224
12252) Phrase structure grammar
1226
1227primary-expression:
1228 identifier
1229 constant
1230 string-literal
1231 ( unary-expression )
1232
1233postfix-expression:
1234 primary-expression
1235 postfix-expression [ unary-expression ]
1236 postfix-expression . identifier
1237 postfix-expressoin -> identifier
1238
1239unary-expression:
1240 postfix-expression
1241 unary-operator postfix-expression
1242
1243unary-operator: one of
1244 + -
1245
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1246assignment-operator:
1247 =
1248
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1249type-assignment-operator:
1250 :=
1251
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1252constant-expression:
1253 unary-expression
1254
1255constant-expression-range:
1256 constant-expression ... constant-expression
1257
12582.2) Declarations:
1259
1260declaration:
689e04b4 1261 declaration-specifiers declarator-list-opt ;
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1262 ctf-specifier ;
1263
1264declaration-specifiers:
689e04b4 1265 storage-class-specifier declaration-specifiers-opt
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1266 type-specifier declaration-specifiers-opt
1267 type-qualifier declaration-specifiers-opt
1268
1269declarator-list:
1270 declarator
1271 declarator-list , declarator
1272
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1273abstract-declarator-list:
1274 abstract-declarator
1275 abstract-declarator-list , abstract-declarator
1276
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1277storage-class-specifier:
1278 typedef
1279
1280type-specifier:
1281 void
1282 char
1283 short
1284 int
1285 long
1286 float
1287 double
1288 signed
1289 unsigned
1290 _Bool
1291 _Complex
cfdd51ec 1292 _Imaginary
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1293 struct-specifier
1294 variant-specifier
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1295 enum-specifier
1296 typedef-name
1297 ctf-type-specifier
1298
1299struct-specifier:
3b0f8e4d 1300 struct identifier-opt { struct-or-variant-declaration-list-opt }
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1301 struct identifier
1302
1303struct-or-variant-declaration-list:
1304 struct-or-variant-declaration
1305 struct-or-variant-declaration-list struct-or-variant-declaration
1306
1307struct-or-variant-declaration:
1308 specifier-qualifier-list struct-or-variant-declarator-list ;
550aca33 1309 declaration-specifiers storage-class-specifier declaration-specifiers declarator-list ;
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1310 typealias declaration-specifiers abstract-declarator-list := declaration-specifiers abstract-declarator-list ;
1311 typealias declaration-specifiers abstract-declarator-list := declarator-list ;
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1312
1313specifier-qualifier-list:
1314 type-specifier specifier-qualifier-list-opt
1315 type-qualifier specifier-qualifier-list-opt
1316
1317struct-or-variant-declarator-list:
1318 struct-or-variant-declarator
1319 struct-or-variant-declarator-list , struct-or-variant-declarator
1320
1321struct-or-variant-declarator:
1322 declarator
1323 declarator-opt : constant-expression
1324
1325variant-specifier:
1326 variant identifier-opt variant-tag-opt { struct-or-variant-declaration-list }
1327 variant identifier variant-tag
1328
1329variant-tag:
1330 < identifier >
1331
1332enum-specifier:
1333 enum identifier-opt { enumerator-list }
1334 enum identifier-opt { enumerator-list , }
1335 enum identifier
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1336 enum identifier-opt : declaration-specifiers { enumerator-list }
1337 enum identifier-opt : declaration-specifiers { enumerator-list , }
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1338
1339enumerator-list:
1340 enumerator
1341 enumerator-list , enumerator
1342
1343enumerator:
1344 enumeration-constant
1345 enumeration-constant = constant-expression
1346 enumeration-constant = constant-expression-range
1347
1348type-qualifier:
1349 const
1350
1351declarator:
1352 pointer-opt direct-declarator
1353
1354direct-declarator:
1355 identifier
1356 ( declarator )
1357 direct-declarator [ type-specifier ]
1358 direct-declarator [ constant-expression ]
1359
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1360abstract-declarator:
1361 pointer-opt direct-abstract-declarator
1362
1363direct-abstract-declarator:
1364 identifier-opt
1365 ( abstract-declarator )
1366 direct-abstract-declarator [ type-specifier ]
1367 direct-abstract-declarator [ constant-expression ]
1368 direct-abstract-declarator [ ]
1369
4fa992a5 1370pointer:
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1371 * type-qualifier-list-opt
1372 * type-qualifier-list-opt pointer
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1373
1374type-qualifier-list:
1375 type-qualifier
1376 type-qualifier-list type-qualifier
1377
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1378typedef-name:
1379 identifier
1380
13812.3) CTF-specific declarations
1382
1383ctf-specifier:
1384 event { ctf-assignment-expression-list-opt }
1385 stream { ctf-assignment-expression-list-opt }
1386 trace { ctf-assignment-expression-list-opt }
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1387 typealias declaration-specifiers abstract-declarator-list := declaration-specifiers abstract-declarator-list ;
1388 typealias declaration-specifiers abstract-declarator-list := declarator-list ;
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1389
1390ctf-type-specifier:
1391 floating_point { ctf-assignment-expression-list-opt }
1392 integer { ctf-assignment-expression-list-opt }
1393 string { ctf-assignment-expression-list-opt }
1394
1395ctf-assignment-expression-list:
1396 ctf-assignment-expression
1397 ctf-assignment-expression-list ; ctf-assignment-expression
1398
1399ctf-assignment-expression:
1400 unary-expression assignment-operator unary-expression
1401 unary-expression type-assignment-operator type-specifier
550aca33 1402 declaration-specifiers storage-class-specifier declaration-specifiers declarator-list
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1403 typealias declaration-specifiers abstract-declarator-list := declaration-specifiers abstract-declarator-list
1404 typealias declaration-specifiers abstract-declarator-list := declarator-list
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