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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
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70An event stream is divided in contiguous event packets of variable size. These
71subdivisions have a variable size. An event packet can contain a certain amount
72of padding at the end. The rationale for the event stream design choices is
73explained in Appendix B. Stream Header Rationale.
5ba9f198 74
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75An event stream is divided in contiguous event packets of variable size. These
76subdivisions have a variable size. An event packet can contain a certain amount
77of padding at the end. The stream header is repeated at the beginning of each
78event packet.
5ba9f198 79
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80The event stream header will therefore be referred to as the "event packet
81header" throughout the rest of this document.
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82
83
844. Types
85
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86Types are organized as type classes. Each type class belong to either of two
87kind of types: basic types or compound types.
88
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894.1 Basic types
90
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91A basic type is a scalar type, as described in this section. It includes
92integers, GNU/C bitfields, enumerations, and floating point values.
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93
944.1.1 Type inheritance
95
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96Type specifications can be inherited to allow deriving types from a
97type class. For example, see the uint32_t named type derived from the "integer"
98type class below ("Integers" section). Types have a precise binary
99representation in the trace. A type class has methods to read and write these
100types, but must be derived into a type to be usable in an event field.
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101
1024.1.2 Alignment
103
104We define "byte-packed" types as aligned on the byte size, namely 8-bit.
105We define "bit-packed" types as following on the next bit, as defined by the
106"bitfields" section.
5ba9f198 107
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108All basic types, except bitfields, are either aligned on an architecture-defined
109specific alignment or byte-packed, depending on the architecture preference.
110Architectures providing fast unaligned write byte-packed basic types to save
5ba9f198 111space, aligning each type on byte boundaries (8-bit). Architectures with slow
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112unaligned writes align types on specific alignment values. If no specific
113alignment is declared for a type nor its parents, it is assumed to be bit-packed
114for bitfields and byte-packed for other types.
5ba9f198 115
3bf79539 116Metadata attribute representation of a specific alignment:
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117
118 align = value; /* value in bits */
119
1204.1.3 Byte order
121
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122By default, the native endianness of the source architecture the trace is used.
123Byte order can be overridden for a basic type by specifying a "byte_order"
124attribute. Typical use-case is to specify the network byte order (big endian:
125"be") to save data captured from the network into the trace without conversion.
126If not specified, the byte order is native.
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127
128Metadata representation:
129
130 byte_order = native OR network OR be OR le; /* network and be are aliases */
131
1324.1.4 Size
133
134Type size, in bits, for integers and floats is that returned by "sizeof()" in C
135multiplied by CHAR_BIT.
136We require the size of "char" and "unsigned char" types (CHAR_BIT) to be fixed
137to 8 bits for cross-endianness compatibility.
138
139Metadata representation:
140
141 size = value; (value is in bits)
142
1434.1.5 Integers
144
145Signed integers are represented in two-complement. Integer alignment, size,
146signedness and byte ordering are defined in the metadata. Integers aligned on
147byte size (8-bit) and with length multiple of byte size (8-bit) correspond to
148the C99 standard integers. In addition, integers with alignment and/or size that
149are _not_ a multiple of the byte size are permitted; these correspond to the C99
150standard bitfields, with the added specification that the CTF integer bitfields
151have a fixed binary representation. A MIT-licensed reference implementation of
152the CTF portable bitfields is available at:
153
154 http://git.efficios.com/?p=babeltrace.git;a=blob;f=include/babeltrace/bitfield.h
155
156Binary representation of integers:
157
158- On little and big endian:
159 - Within a byte, high bits correspond to an integer high bits, and low bits
160 correspond to low bits.
161- On little endian:
162 - Integer across multiple bytes are placed from the less significant to the
163 most significant.
164 - Consecutive integers are placed from lower bits to higher bits (even within
165 a byte).
166- On big endian:
167 - Integer across multiple bytes are placed from the most significant to the
168 less significant.
169 - Consecutive integers are placed from higher bits to lower bits (even within
170 a byte).
171
172This binary representation is derived from the bitfield implementation in GCC
173for little and big endian. However, contrary to what GCC does, integers can
174cross units boundaries (no padding is required). Padding can be explicitely
175added (see 4.1.6 GNU/C bitfields) to follow the GCC layout if needed.
176
177Metadata representation:
178
80fd2569 179 integer {
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180 signed = true OR false; /* default false */
181 byte_order = native OR network OR be OR le; /* default native */
182 size = value; /* value in bits, no default */
183 align = value; /* value in bits */
2152348f 184 }
5ba9f198 185
80fd2569 186Example of type inheritance (creation of a uint32_t named type):
5ba9f198 187
359894ac 188typealias integer {
9e4e34e9 189 size = 32;
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190 signed = false;
191 align = 32;
359894ac 192} : uint32_t;
5ba9f198 193
80fd2569 194Definition of a named 5-bit signed bitfield:
5ba9f198 195
359894ac 196typealias integer {
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197 size = 5;
198 signed = true;
199 align = 1;
359894ac 200} : int5_t;
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201
2024.1.6 GNU/C bitfields
203
204The GNU/C bitfields follow closely the integer representation, with a
205particularity on alignment: if a bitfield cannot fit in the current unit, the
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206unit is padded and the bitfield starts at the following unit. The unit size is
207defined by the size of the type "unit_type".
5ba9f198 208
2152348f 209Metadata representation:
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210
211 unit_type name:size:
212
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213As an example, the following structure declared in C compiled by GCC:
214
215struct example {
216 short a:12;
217 short b:5;
218};
219
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220The example structure is aligned on the largest element (short). The second
221bitfield would be aligned on the next unit boundary, because it would not fit in
222the current unit.
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223
2244.1.7 Floating point
225
226The floating point values byte ordering is defined in the metadata.
227
228Floating point values follow the IEEE 754-2008 standard interchange formats.
229Description of the floating point values include the exponent and mantissa size
230in bits. Some requirements are imposed on the floating point values:
231
232- FLT_RADIX must be 2.
233- mant_dig is the number of digits represented in the mantissa. It is specified
234 by the ISO C99 standard, section 5.2.4, as FLT_MANT_DIG, DBL_MANT_DIG and
235 LDBL_MANT_DIG as defined by <float.h>.
236- exp_dig is the number of digits represented in the exponent. Given that
237 mant_dig is one bit more than its actual size in bits (leading 1 is not
238 needed) and also given that the sign bit always takes one bit, exp_dig can be
239 specified as:
240
241 - sizeof(float) * CHAR_BIT - FLT_MANT_DIG
242 - sizeof(double) * CHAR_BIT - DBL_MANT_DIG
243 - sizeof(long double) * CHAR_BIT - LDBL_MANT_DIG
244
245Metadata representation:
246
80fd2569 247floating_point {
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248 exp_dig = value;
249 mant_dig = value;
250 byte_order = native OR network OR be OR le;
2152348f 251}
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252
253Example of type inheritance:
254
359894ac 255typealias floating_point {
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256 exp_dig = 8; /* sizeof(float) * CHAR_BIT - FLT_MANT_DIG */
257 mant_dig = 24; /* FLT_MANT_DIG */
258 byte_order = native;
359894ac 259} : float;
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260
261TODO: define NaN, +inf, -inf behavior.
262
2634.1.8 Enumerations
264
265Enumerations are a mapping between an integer type and a table of strings. The
266numerical representation of the enumeration follows the integer type specified
267by the metadata. The enumeration mapping table is detailed in the enumeration
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268description within the metadata. The mapping table maps inclusive value ranges
269(or single values) to strings. Instead of being limited to simple
270"value -> string" mappings, these enumerations map
80fd2569 271"[ start_value ... end_value ] -> string", which map inclusive ranges of
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272values to strings. An enumeration from the C language can be represented in
273this format by having the same start_value and end_value for each element, which
274is in fact a range of size 1. This single-value range is supported without
4767a9e7 275repeating the start and end values with the value = string declaration.
80fd2569 276
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277If a numeric value is encountered between < >, it represents the integer type
278size used to hold the enumeration, in bits.
279
cfc73fdc 280enum name <integer_type OR size> {
359894ac 281 somestring = start_value1 ... end_value1,
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282 "other string" = start_value2 ... end_value2,
283 yet_another_string, /* will be assigned to end_value2 + 1 */
284 "some other string" = value,
285 ...
286};
287
288If the values are omitted, the enumeration starts at 0 and increment of 1 for
289each entry:
290
cfc73fdc 291enum name <32> {
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292 ZERO,
293 ONE,
294 TWO,
295 TEN = 10,
296 ELEVEN,
3bf79539 297};
5ba9f198 298
80fd2569 299Overlapping ranges within a single enumeration are implementation defined.
5ba9f198 300
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301A nameless enumeration can be declared as a field type or as part of a typedef:
302
303enum <integer_type> {
304 ...
305}
306
1fad7a85 307
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3084.2 Compound types
309
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310Compound are aggregation of type declarations. Compound types include
311structures, variant, arrays, sequences, and strings.
312
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3134.2.1 Structures
314
315Structures are aligned on the largest alignment required by basic types
316contained within the structure. (This follows the ISO/C standard for structures)
317
80fd2569 318Metadata representation of a named structure:
5ba9f198 319
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320struct name {
321 field_type field_name;
322 field_type field_name;
323 ...
324};
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325
326Example:
327
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328struct example {
329 integer { /* Nameless type */
330 size = 16;
331 signed = true;
332 align = 16;
333 } first_field_name;
334 uint64_t second_field_name; /* Named type declared in the metadata */
3bf79539 335};
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336
337The fields are placed in a sequence next to each other. They each possess a
338field name, which is a unique identifier within the structure.
339
2152348f 340A nameless structure can be declared as a field type or as part of a typedef:
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341
342struct {
343 ...
2152348f 344}
80fd2569 345
77a98c82 3464.2.2 Variants (Discriminated/Tagged Unions)
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347
348A CTF variant is a selection between different types. A CTF variant must always
349be defined within the scope of a structure or within fields contained within a
350structure (defined recursively). A "tag" enumeration field must appear in either
351the same lexical scope or an uppermost scope, prior to the variant field (in
352field declaration order). The type selection is indicated by the mapping from
353the enumeration value to the string used as variant type selector. The field to
354use as tag is specified by the "tag_field", specified between "< >" after the
355"variant" keyword for unnamed variants, and after "variant name" for named
356variants.
357
358The alignment of the variant is the alignment of the type as selected by the tag
359value for the specific instance of the variant. The alignment of the type
360containing the variant is independent of the variant alignment. The size of the
361variant is the size as selected by the tag value for the specific instance of
362the variant.
363
364A named variant declaration followed by its definition within a structure
365declaration:
366
367variant name {
368 field_type sel1;
369 field_type sel2;
370 field_type sel3;
371 ...
372};
373
374struct {
375 enum <integer_type or size> { sel1, sel2, sel3, ... } tag_field;
376 ...
377 variant name <tag_field> v;
378}
379
380An unnamed variant definition within a structure is expressed by the following
381metadata:
382
383struct {
384 enum <integer_type or size> { sel1, sel2, sel3, ... } tag_field;
385 ...
386 variant <tag_field> {
387 field_type sel1;
388 field_type sel2;
389 field_type sel3;
390 ...
391 } v;
392}
393
394Example of a named variant within a sequence that refers to a single tag field:
395
396variant example {
397 uint32_t a;
398 uint64_t b;
399 short c;
400};
401
402struct {
403 enum <uint2_t> { a, b, c } choice;
15850440 404 variant example <choice> v[unsigned int];
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405}
406
407Example of an unnamed variant:
408
409struct {
410 enum <uint2_t> { a, b, c, d } choice;
411 /* Unrelated fields can be added between the variant and its tag */
412 int32_t somevalue;
413 variant <choice> {
414 uint32_t a;
415 uint64_t b;
416 short c;
417 struct {
418 unsigned int field1;
419 uint64_t field2;
420 } d;
421 } s;
422}
423
424Example of an unnamed variant within an array:
425
426struct {
427 enum <uint2_t> { a, b, c } choice;
428 variant <choice> {
429 uint32_t a;
430 uint64_t b;
431 short c;
15850440 432 } v[10];
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433}
434
435Example of a variant type definition within a structure, where the defined type
436is then declared within an array of structures. This variant refers to a tag
437located in an upper lexical scope. This example clearly shows that a variant
438type definition referring to the tag "x" uses the closest preceding field from
439the lexical scope of the type definition.
440
441struct {
442 enum <uint2_t> { a, b, c, d } x;
443
444 typedef variant <x> { /*
445 * "x" refers to the preceding "x" enumeration in the
446 * lexical scope of the type definition.
447 */
448 uint32_t a;
449 uint64_t b;
450 short c;
451 } example_variant;
452
453 struct {
454 enum <int> { x, y, z } x; /* This enumeration is not used by "v". */
455 example_variant v; /*
456 * "v" uses the "enum <uint2_t> { a, b, c, d }"
457 * tag.
458 */
459 } a[10];
460}
461
4624.2.3 Arrays
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463
464Arrays are fixed-length. Their length is declared in the type declaration within
465the metadata. They contain an array of "inner type" elements, which can refer to
466any type not containing the type of the array being declared (no circular
3bf79539 467dependency). The length is the number of elements in an array.
5ba9f198 468
2152348f 469Metadata representation of a named array:
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470
471typedef elem_type name[length];
5ba9f198 472
2152348f 473A nameless array can be declared as a field type within a structure, e.g.:
5ba9f198 474
2152348f 475 uint8_t field_name[10];
80fd2569 476
5ba9f198 477
fcba70d4 4784.2.4 Sequences
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479
480Sequences are dynamically-sized arrays. They start with an integer that specify
481the length of the sequence, followed by an array of "inner type" elements.
3bf79539 482The length is the number of elements in the sequence.
5ba9f198 483
2152348f 484Metadata representation for a named sequence:
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485
486typedef elem_type name[length_type];
487
488A nameless sequence can be declared as a field type, e.g.:
489
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490long field_name[int];
491
492The length type follows the integer types specifications, and the sequence
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493elements follow the "array" specifications.
494
fcba70d4 4954.2.5 Strings
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496
497Strings are an array of bytes of variable size and are terminated by a '\0'
498"NULL" character. Their encoding is described in the metadata. In absence of
499encoding attribute information, the default encoding is UTF-8.
500
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501Metadata representation of a named string type:
502
359894ac 503typealias string {
5ba9f198 504 encoding = UTF8 OR ASCII;
359894ac 505} : name;
5ba9f198 506
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507A nameless string type can be declared as a field type:
508
509string field_name; /* Use default UTF8 encoding */
5ba9f198 510
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5115. Event Packet Header
512
513The event packet header consists of two part: one is mandatory and have a fixed
514layout. The second part, the "event packet context", has its layout described in
515the metadata.
5ba9f198 516
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517- Aligned on page size. Fixed size. Fields either aligned or packed (depending
518 on the architecture preference).
519 No padding at the end of the event packet header. Native architecture byte
5ba9f198 520 ordering.
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521
522Fixed layout (event packet header):
523
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524- Magic number (CTF magic numbers: 0xC1FC1FC1 and its reverse endianness
525 representation: 0xC11FFCC1) It needs to have a non-symmetric bytewise
526 representation. Used to distinguish between big and little endian traces (this
527 information is determined by knowing the endianness of the architecture
528 reading the trace and comparing the magic number against its value and the
529 reverse, 0xC11FFCC1). This magic number specifies that we use the CTF metadata
530 description language described in this document. Different magic numbers
531 should be used for other metadata description languages.
3bf79539 532- Trace UUID, used to ensure the event packet match the metadata used.
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533 (note: we cannot use a metadata checksum because metadata can be appended to
534 while tracing is active)
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535- Stream ID, used as reference to stream description in metadata.
536
537Metadata-defined layout (event packet context):
538
539- Event packet content size (in bytes).
540- Event packet size (in bytes, includes padding).
541- Event packet content checksum (optional). Checksum excludes the event packet
542 header.
543- Per-stream event packet sequence count (to deal with UDP packet loss). The
544 number of significant sequence counter bits should also be present, so
545 wrap-arounds are deal with correctly.
546- Timestamp at the beginning and timestamp at the end of the event packet.
547 Both timestamps are written in the packet header, but sampled respectively
548 while (or before) writing the first event and while (or after) writing the
549 last event in the packet. The inclusive range between these timestamps should
550 include all event timestamps assigned to events contained within the packet.
5ba9f198 551- Events discarded count
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552 - Snapshot of a per-stream free-running counter, counting the number of
553 events discarded that were supposed to be written in the stream prior to
554 the first event in the event packet.
5ba9f198 555 * Note: producer-consumer buffer full condition should fill the current
3bf79539 556 event packet with padding so we know exactly where events have been
5ba9f198 557 discarded.
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558- Lossless compression scheme used for the event packet content. Applied
559 directly to raw data. New types of compression can be added in following
560 versions of the format.
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561 0: no compression scheme
562 1: bzip2
563 2: gzip
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564 3: xz
565- Cypher used for the event packet content. Applied after compression.
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566 0: no encryption
567 1: AES
3bf79539 568- Checksum scheme used for the event packet content. Applied after encryption.
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569 0: no checksum
570 1: md5
571 2: sha1
572 3: crc32
573
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5745.1 Event Packet Header Fixed Layout Description
575
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576struct event_packet_header {
577 uint32_t magic;
578 uint8_t trace_uuid[16];
3bf79539 579 uint32_t stream_id;
80fd2569 580};
5ba9f198 581
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5825.2 Event Packet Context Description
583
584Event packet context example. These are declared within the stream declaration
585in the metadata. All these fields are optional except for "content_size" and
586"packet_size", which must be present in the context.
587
588An example event packet context type:
589
80fd2569 590struct event_packet_context {
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591 uint64_t timestamp_begin;
592 uint64_t timestamp_end;
593 uint32_t checksum;
594 uint32_t stream_packet_count;
595 uint32_t events_discarded;
596 uint32_t cpu_id;
597 uint32_t/uint16_t content_size;
598 uint32_t/uint16_t packet_size;
599 uint8_t stream_packet_count_bits; /* Significant counter bits */
600 uint8_t compression_scheme;
601 uint8_t encryption_scheme;
3b0f8e4d 602 uint8_t checksum_scheme;
3bf79539 603};
5ba9f198 604
fcba70d4 605
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6066. Event Structure
607
608The overall structure of an event is:
609
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6101 - Stream Packet Context (as specified by the stream metadata)
6112 - Event Header (as specifed by the stream metadata)
6123 - Stream Event Context (as specified by the stream metadata)
6134 - Event Context (as specified by the event metadata)
6145 - Event Payload (as specified by the event metadata)
5ba9f198 615
fcba70d4 6166.1 Lexical Scope
5ba9f198 617
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618For variant tag definition only, the lexical scope of each structure (stream
619packet context, header, stream event context, event context and payload) is
620extended in the following way: lower levels (e.g. 3) can refer to fields defined
621in prior levels (e.g. 2 and 1). The field in the closest level has priority in
622case of field name conflict.
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623
624This allows, for instance, the event context to define a variant refering to the
625"id" field of the event header as selector.
626
6276.2 Event Header
628
629Event headers can be described within the metadata. We hereby propose, as an
630example, two types of events headers. Type 1 accommodates streams with less than
63131 event IDs. Type 2 accommodates streams with 31 or more event IDs.
5ba9f198 632
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633One major factor can vary between streams: the number of event IDs assigned to
634a stream. Luckily, this information tends to stay relatively constant (modulo
5ba9f198 635event registration while trace is being recorded), so we can specify different
3bf79539 636representations for streams containing few event IDs and streams containing
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637many event IDs, so we end up representing the event ID and timestamp as densely
638as possible in each case.
639
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640The header is extended in the rare occasions where the information cannot be
641represented in the ranges available in the standard event header. They are also
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642used in the rare occasions where the data required for a field could not be
643collected: the flag corresponding to the missing field within the missing_fields
644array is then set to 1.
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645
646Types uintX_t represent an X-bit unsigned integer.
647
648
fcba70d4 6496.2.1 Type 1 - Few event IDs
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650
651 - Aligned on 32-bit (or 8-bit if byte-packed, depending on the architecture
652 preference).
5ba9f198 653 - Native architecture byte ordering.
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654 - For "compact" selection
655 - Fixed size: 32 bits.
656 - For "extended" selection
657 - Size depends on the architecture and variant alignment.
5ba9f198 658
80fd2569 659struct event_header_1 {
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660 /*
661 * id: range: 0 - 30.
662 * id 31 is reserved to indicate an extended header.
663 */
664 enum <uint5_t> { compact = 0 ... 30, extended = 31 } id;
665 variant <id> {
666 struct {
667 uint27_t timestamp;
668 } compact;
669 struct {
670 uint32_t id; /* 32-bit event IDs */
671 uint64_t timestamp; /* 64-bit timestamps */
672 } extended;
673 } v;
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674};
675
5ba9f198 676
fcba70d4 6776.2.2 Type 2 - Many event IDs
5ba9f198 678
fcba70d4 679 - Aligned on 16-bit (or 8-bit if byte-packed, depending on the architecture
5ba9f198 680 preference).
5ba9f198 681 - Native architecture byte ordering.
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682 - For "compact" selection
683 - Size depends on the architecture and variant alignment.
684 - For "extended" selection
685 - Size depends on the architecture and variant alignment.
5ba9f198 686
80fd2569 687struct event_header_2 {
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688 /*
689 * id: range: 0 - 65534.
690 * id 65535 is reserved to indicate an extended header.
691 */
692 enum <uint16_t> { compact = 0 ... 65534, extended = 65535 } id;
693 variant <id> {
694 struct {
695 uint32_t timestamp;
696 } compact;
697 struct {
698 uint32_t id; /* 32-bit event IDs */
699 uint64_t timestamp; /* 64-bit timestamps */
700 } extended;
701 } v;
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702};
703
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704
7056.2 Event Context
706
707The event context contains information relative to the current event. The choice
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708and meaning of this information is specified by the metadata "stream" and
709"event" information. The "stream" context is applied to all events within the
710stream. The "stream" context structure follows the event header. The "event"
711context is applied to specific events. Its structure follows the "stream"
712context stucture.
5ba9f198 713
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714An example of stream-level event context is to save the event payload size with
715each event, or to save the current PID with each event. These are declared
716within the stream declaration within the metadata:
5ba9f198 717
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718 stream {
719 ...
720 event {
721 ...
4fa992a5 722 context := struct {
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723 uint pid;
724 uint16_t payload_size;
3bf79539 725 };
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726 }
727 };
728
729An example of event-specific event context is to declare a bitmap of missing
730fields, only appended after the stream event context if the extended event
731header is selected. NR_FIELDS is the number of fields within the event (a
732numeric value).
5ba9f198 733
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734 event {
735 context = struct {
736 variant <id> {
737 struct { } compact;
738 struct {
739 uint1_t missing_fields[NR_FIELDS]; /* missing event fields bitmap */
740 } extended;
741 } v;
742 };
743 ...
744 }
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745
7466.3 Event Payload
747
748An event payload contains fields specific to a given event type. The fields
749belonging to an event type are described in the event-specific metadata
750within a structure type.
751
7526.3.1 Padding
753
754No padding at the end of the event payload. This differs from the ISO/C standard
755for structures, but follows the CTF standard for structures. In a trace, even
756though it makes sense to align the beginning of a structure, it really makes no
757sense to add padding at the end of the structure, because structures are usually
758not followed by a structure of the same type.
759
760This trick can be done by adding a zero-length "end" field at the end of the C
761structures, and by using the offset of this field rather than using sizeof()
3bf79539 762when calculating the size of a structure (see Appendix "A. Helper macros").
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763
7646.3.2 Alignment
765
766The event payload is aligned on the largest alignment required by types
767contained within the payload. (This follows the ISO/C standard for structures)
768
769
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7707. Metadata
771
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772The meta-data is located in a stream named "metadata". It is made of "event
773packets", which each start with an event packet header. The event type within
774the metadata stream have no event header nor event context. Each event only
5ba9f198 775contains a null-terminated "string" payload, which is a metadata description
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776entry. The events are packed one next to another. Each event packet start with
777an event packet header, which contains, amongst other fields, the magic number
778and trace UUID.
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779
780The metadata can be parsed by reading through the metadata strings, skipping
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781newlines and null-characters. Type names are made of a single identifier, and
782can be surrounded by prefix/postfix. Text contained within "/*" and "*/", as
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783well as within "//" and end of line, are treated as comments. Boolean values can
784be represented as true, TRUE, or 1 for true, and false, FALSE, or 0 for false.
fcba70d4 785
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786Each of "trace", "stream", "event", "struct" and "variant" have their own
787nestable declaration scope, within which types can be declared using "typedef"
788and "typealias". An innermost declaration scope can refer to type declared
789within its container lexical scope prior to the innermost declaration scope.
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790Redefinition of a typedef or typealias, or hiding an uppermost definition, is
791not valid.
d285084f 792
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793The grammar representing the CTF metadata is presented in
794Appendix C. CTF Metadata Grammar.
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795
796trace {
797 major = value; /* Trace format version */
798 minor = value;
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799 uuid = value; /* Trace UUID */
800 word_size = value;
801};
5ba9f198 802
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803stream {
804 id = stream_id;
77a98c82 805 /* Type 1 - Few event IDs; Type 2 - Many event IDs. See section 6.2. */
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806 event.header := event_header_1 OR event_header_2;
807 event.context := struct {
77a98c82 808 ...
3bf79539 809 };
4fa992a5 810 packet.context := struct {
77a98c82 811 ...
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812 };
813};
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814
815event {
3d13ef1a 816 name = event_name;
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817 id = value; /* Numeric identifier within the stream */
818 stream = stream_id;
4fa992a5 819 context := struct {
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820 ...
821 };
4fa992a5 822 fields := struct {
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823 ...
824 };
3bf79539 825};
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826
827/* More detail on types in section 4. Types */
828
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829/*
830 * Named types:
831 *
4fa992a5 832 * Type declarations behave similarly to the C standard.
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833 */
834
835typedef aliased_type_prefix aliased_type new_type aliased_type_postfix;
2152348f 836
3d13ef1a 837/* e.g.: typedef struct example new_type_name[10]; */
80fd2569 838
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839/*
840 * typealias
841 *
842 * The "typealias" declaration can be used to give a name (including
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843 * prefix/postfix) to a type. It should also be used to map basic C types
844 * (float, int, unsigned long, ...) to a CTF type. Typealias is a superset of
845 * "typedef": it also allows assignment of a simple variable identifier to a
846 * type.
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847 */
848
849typealias type_class {
80fd2569 850 ...
fcba70d4 851} : new_type_prefix new_type new_type_postfix;
2152348f 852
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853/*
854 * e.g.:
4fa992a5 855 * typealias integer {
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856 * size = 32;
857 * align = 32;
858 * signed = false;
fcba70d4 859 * } : struct page *;
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860 *
861 * typealias integer {
862 * size = 32;
863 * align = 32;
864 * signed = true;
865 * } : int;
3d13ef1a 866 */
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867
868struct name {
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869 ...
870};
5ba9f198 871
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872variant name {
873 ...
874};
875
cfc73fdc 876enum name <integer_type or size> {
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877 ...
878};
879
2152348f 880
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881/*
882 * Unnamed types, contained within compound type fields, typedef or typealias.
883 */
2152348f 884
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885struct {
886 ...
2152348f 887}
5ba9f198 888
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889variant {
890 ...
891}
892
4767a9e7 893enum <integer_type or size> {
80fd2569 894 ...
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895}
896
897typedef type new_type[length];
3bf79539 898
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899struct {
900 type field_name[length];
901}
902
903typedef type new_type[length_type];
904
905struct {
906 type field_name[length_type];
907}
908
909integer {
80fd2569 910 ...
2152348f 911}
3bf79539 912
2152348f 913floating_point {
80fd2569 914 ...
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915}
916
917struct {
918 integer_type field_name:size; /* GNU/C bitfield */
919}
920
921struct {
922 string field_name;
923}
3bf79539 924
fcba70d4 925
3bf79539 926A. Helper macros
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927
928The two following macros keep track of the size of a GNU/C structure without
929padding at the end by placing HEADER_END as the last field. A one byte end field
930is used for C90 compatibility (C99 flexible arrays could be used here). Note
931that this does not affect the effective structure size, which should always be
932calculated with the header_sizeof() helper.
933
934#define HEADER_END char end_field
935#define header_sizeof(type) offsetof(typeof(type), end_field)
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936
937
938B. Stream Header Rationale
939
940An event stream is divided in contiguous event packets of variable size. These
941subdivisions allow the trace analyzer to perform a fast binary search by time
942within the stream (typically requiring to index only the event packet headers)
943without reading the whole stream. These subdivisions have a variable size to
944eliminate the need to transfer the event packet padding when partially filled
945event packets must be sent when streaming a trace for live viewing/analysis.
946An event packet can contain a certain amount of padding at the end. Dividing
947streams into event packets is also useful for network streaming over UDP and
948flight recorder mode tracing (a whole event packet can be swapped out of the
949buffer atomically for reading).
950
951The stream header is repeated at the beginning of each event packet to allow
952flexibility in terms of:
953
954 - streaming support,
955 - allowing arbitrary buffers to be discarded without making the trace
956 unreadable,
957 - allow UDP packet loss handling by either dealing with missing event packet
958 or asking for re-transmission.
959 - transparently support flight recorder mode,
960 - transparently support crash dump.
961
962The event stream header will therefore be referred to as the "event packet
963header" throughout the rest of this document.
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964
965C. CTF Metadata Grammar
966
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967/*
968 * Common Trace Format (CTF) Metadata Grammar.
969 *
970 * Inspired from the C99 grammar:
971 * http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1124.pdf (Annex A)
972 *
973 * Specialized for CTF needs by including only constant and declarations from
974 * C99 (excluding function declarations), and by adding support for variants,
975 * sequences and CTF-specific specifiers.
976 */
977
9781) Lexical grammar
979
9801.1) Lexical elements
981
982token:
983 keyword
984 identifier
985 constant
986 string-literal
987 punctuator
988
9891.2) Keywords
990
991keyword: is one of
992
993const
994char
995double
996enum
997event
998floating_point
999float
1000integer
1001int
1002long
1003short
1004signed
1005stream
1006string
1007struct
1008trace
3e1e1a78 1009typealias
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1010typedef
1011unsigned
1012variant
1013void
1014_Bool
1015_Complex
1016_Imaginary
1017
1018
10191.3) Identifiers
1020
1021identifier:
1022 identifier-nondigit
1023 identifier identifier-nondigit
1024 identifier digit
1025
1026identifier-nondigit:
1027 nondigit
1028 universal-character-name
1029 any other implementation-defined characters
1030
1031nondigit:
1032 _
1033 [a-zA-Z] /* regular expression */
1034
1035digit:
1036 [0-9] /* regular expression */
1037
10381.4) Universal character names
1039
1040universal-character-name:
1041 \u hex-quad
1042 \U hex-quad hex-quad
1043
1044hex-quad:
1045 hexadecimal-digit hexadecimal-digit hexadecimal-digit hexadecimal-digit
1046
10471.5) Constants
1048
1049constant:
1050 integer-constant
1051 enumeration-constant
1052 character-constant
1053
1054integer-constant:
1055 decimal-constant integer-suffix-opt
1056 octal-constant integer-suffix-opt
1057 hexadecimal-constant integer-suffix-opt
1058
1059decimal-constant:
1060 nonzero-digit
1061 decimal-constant digit
1062
1063octal-constant:
1064 0
1065 octal-constant octal-digit
1066
1067hexadecimal-constant:
1068 hexadecimal-prefix hexadecimal-digit
1069 hexadecimal-constant hexadecimal-digit
1070
1071hexadecimal-prefix:
1072 0x
1073 0X
1074
1075nonzero-digit:
1076 [1-9]
1077
1078integer-suffix:
1079 unsigned-suffix long-suffix-opt
1080 unsigned-suffix long-long-suffix
1081 long-suffix unsigned-suffix-opt
1082 long-long-suffix unsigned-suffix-opt
1083
1084unsigned-suffix:
1085 u
1086 U
1087
1088long-suffix:
1089 l
1090 L
1091
1092long-long-suffix:
1093 ll
1094 LL
1095
1096digit-sequence:
1097 digit
1098 digit-sequence digit
1099
1100hexadecimal-digit-sequence:
1101 hexadecimal-digit
1102 hexadecimal-digit-sequence hexadecimal-digit
1103
1104enumeration-constant:
1105 identifier
1106 string-literal
1107
1108character-constant:
1109 ' c-char-sequence '
1110 L' c-char-sequence '
1111
1112c-char-sequence:
1113 c-char
1114 c-char-sequence c-char
1115
1116c-char:
1117 any member of source charset except single-quote ('), backslash
1118 (\), or new-line character.
1119 escape-sequence
1120
1121escape-sequence:
1122 simple-escape-sequence
1123 octal-escape-sequence
1124 hexadecimal-escape-sequence
1125 universal-character-name
1126
1127simple-escape-sequence: one of
1128 \' \" \? \\ \a \b \f \n \r \t \v
1129
1130octal-escape-sequence:
1131 \ octal-digit
1132 \ octal-digit octal-digit
1133 \ octal-digit octal-digit octal-digit
1134
1135hexadecimal-escape-sequence:
1136 \x hexadecimal-digit
1137 hexadecimal-escape-sequence hexadecimal-digit
1138
11391.6) String literals
1140
1141string-literal:
1142 " s-char-sequence-opt "
1143 L" s-char-sequence-opt "
1144
1145s-char-sequence:
1146 s-char
1147 s-char-sequence s-char
1148
1149s-char:
1150 any member of source charset except double-quote ("), backslash
1151 (\), or new-line character.
1152 escape-sequence
1153
11541.7) Punctuators
1155
1156punctuator: one of
1157 [ ] ( ) { } . -> * + - < > : ; ... = ,
1158
1159
11602) Phrase structure grammar
1161
1162primary-expression:
1163 identifier
1164 constant
1165 string-literal
1166 ( unary-expression )
1167
1168postfix-expression:
1169 primary-expression
1170 postfix-expression [ unary-expression ]
1171 postfix-expression . identifier
1172 postfix-expressoin -> identifier
1173
1174unary-expression:
1175 postfix-expression
1176 unary-operator postfix-expression
1177
1178unary-operator: one of
1179 + -
1180
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1181assignment-operator:
1182 =
1183
1184constant-expression:
1185 unary-expression
1186
1187constant-expression-range:
1188 constant-expression ... constant-expression
1189
11902.2) Declarations:
1191
1192declaration:
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1193 declaration-specifiers ;
1194 declaration-specifiers storage-class-specifier declaration-specifiers declarator-list ;
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1195 ctf-specifier ;
1196
1197declaration-specifiers:
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1198 type-specifier declaration-specifiers-opt
1199 type-qualifier declaration-specifiers-opt
1200
1201declarator-list:
1202 declarator
1203 declarator-list , declarator
1204
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1205abstract-declarator-list:
1206 abstract-declarator
1207 abstract-declarator-list , abstract-declarator
1208
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1209storage-class-specifier:
1210 typedef
1211
1212type-specifier:
1213 void
1214 char
1215 short
1216 int
1217 long
1218 float
1219 double
1220 signed
1221 unsigned
1222 _Bool
1223 _Complex
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1224 struct-specifier
1225 variant-specifier
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1226 enum-specifier
1227 typedef-name
1228 ctf-type-specifier
1229
1230struct-specifier:
3b0f8e4d 1231 struct identifier-opt { struct-or-variant-declaration-list-opt }
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1232 struct identifier
1233
1234struct-or-variant-declaration-list:
1235 struct-or-variant-declaration
1236 struct-or-variant-declaration-list struct-or-variant-declaration
1237
1238struct-or-variant-declaration:
1239 specifier-qualifier-list struct-or-variant-declarator-list ;
550aca33 1240 declaration-specifiers storage-class-specifier declaration-specifiers declarator-list ;
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1241 typealias declaration-specifiers abstract-declarator-list : declaration-specifiers abstract-declarator-list ;
1242 typealias declaration-specifiers abstract-declarator-list : declarator-list ;
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1243
1244specifier-qualifier-list:
1245 type-specifier specifier-qualifier-list-opt
1246 type-qualifier specifier-qualifier-list-opt
1247
1248struct-or-variant-declarator-list:
1249 struct-or-variant-declarator
1250 struct-or-variant-declarator-list , struct-or-variant-declarator
1251
1252struct-or-variant-declarator:
1253 declarator
1254 declarator-opt : constant-expression
1255
1256variant-specifier:
1257 variant identifier-opt variant-tag-opt { struct-or-variant-declaration-list }
1258 variant identifier variant-tag
1259
1260variant-tag:
1261 < identifier >
1262
1263enum-specifier:
1264 enum identifier-opt { enumerator-list }
1265 enum identifier-opt { enumerator-list , }
1266 enum identifier
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1267 enum identifier-opt < declaration-specifiers > { enumerator-list }
1268 enum identifier-opt < declaration-specifiers > { enumerator-list , }
1269 enum identifier < declaration-specifiers >
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1270 enum identifier-opt < integer-constant > { enumerator-list }
1271 enum identifier-opt < integer-constant > { enumerator-list , }
1272 enum identifier < integer-constant >
1273
1274enumerator-list:
1275 enumerator
1276 enumerator-list , enumerator
1277
1278enumerator:
1279 enumeration-constant
1280 enumeration-constant = constant-expression
1281 enumeration-constant = constant-expression-range
1282
1283type-qualifier:
1284 const
1285
1286declarator:
1287 pointer-opt direct-declarator
1288
1289direct-declarator:
1290 identifier
1291 ( declarator )
1292 direct-declarator [ type-specifier ]
1293 direct-declarator [ constant-expression ]
1294
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1295abstract-declarator:
1296 pointer-opt direct-abstract-declarator
1297
1298direct-abstract-declarator:
1299 identifier-opt
1300 ( abstract-declarator )
1301 direct-abstract-declarator [ type-specifier ]
1302 direct-abstract-declarator [ constant-expression ]
1303 direct-abstract-declarator [ ]
1304
4fa992a5 1305pointer:
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1306 * type-qualifier-list-opt
1307 * type-qualifier-list-opt pointer
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1308
1309type-qualifier-list:
1310 type-qualifier
1311 type-qualifier-list type-qualifier
1312
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1313typedef-name:
1314 identifier
1315
13162.3) CTF-specific declarations
1317
1318ctf-specifier:
1319 event { ctf-assignment-expression-list-opt }
1320 stream { ctf-assignment-expression-list-opt }
1321 trace { ctf-assignment-expression-list-opt }
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1322 typealias declaration-specifiers abstract-declarator-list : declaration-specifiers abstract-declarator-list ;
1323 typealias declaration-specifiers abstract-declarator-list : declarator-list ;
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1324
1325ctf-type-specifier:
1326 floating_point { ctf-assignment-expression-list-opt }
1327 integer { ctf-assignment-expression-list-opt }
1328 string { ctf-assignment-expression-list-opt }
1329
1330ctf-assignment-expression-list:
1331 ctf-assignment-expression
1332 ctf-assignment-expression-list ; ctf-assignment-expression
1333
1334ctf-assignment-expression:
1335 unary-expression assignment-operator unary-expression
1336 unary-expression type-assignment-operator type-specifier
550aca33 1337 declaration-specifiers storage-class-specifier declaration-specifiers declarator-list
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1338 typealias declaration-specifiers abstract-declarator-list : declaration-specifiers abstract-declarator-list
1339 typealias declaration-specifiers abstract-declarator-list : declarator-list
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