1 Common Trace Format (CTF) Specification (pre-v1.8)
3 Mathieu Desnoyers, EfficiOS Inc.
5 The goal of the present document is to specify a trace format that suits the
6 needs of the embedded, telecom, high-performance and kernel communities. It is
7 based on the Common Trace Format Requirements (v1.4) document. It is designed to
8 allow traces to be natively generated by the Linux kernel, Linux user-space
9 applications written in C/C++, and hardware components. One major element of
10 CTF is the Trace Stream Description Language (TSDL) which flexibility
11 enables description of various binary trace stream layouts.
13 The latest version of this document can be found at:
15 git tree: git://git.efficios.com/ctf.git
16 gitweb: http://git.efficios.com/?p=ctf.git
18 A reference implementation of a library to read and write this trace format is
19 being implemented within the BabelTrace project, a converter between trace
20 formats. The development tree is available at:
22 git tree: git://git.efficios.com/babeltrace.git
23 gitweb: http://git.efficios.com/?p=babeltrace.git
25 The CE Workgroup of the Linux Foundation, Ericsson, and EfficiOS have
31 1. Preliminary definitions
32 2. High-level representation of a trace
36 4.1.1 Type inheritance
46 4.2.2 Variants (Discriminated/Tagged Unions)
50 5. Event Packet Header
51 5.1 Event Packet Header Description
52 5.2 Event Packet Context Description
55 6.1.1 Type 1 - Few event IDs
56 6.1.2 Type 2 - Many event IDs
61 7. Trace Stream Description Language (TSDL)
63 7.2 Declaration vs Definition
66 7.3.2 Static and Dynamic Scopes
70 1. Preliminary definitions
72 - Event Trace: An ordered sequence of events.
73 - Event Stream: An ordered sequence of events, containing a subset of the
75 - Event Packet: A sequence of physically contiguous events within an event
77 - Event: This is the basic entry in a trace. (aka: a trace record).
78 - An event identifier (ID) relates to the class (a type) of event within
80 e.g. event: irq_entry.
81 - An event (or event record) relates to a specific instance of an event
83 e.g. event: irq_entry, at time X, on CPU Y
84 - Source Architecture: Architecture writing the trace.
85 - Reader Architecture: Architecture reading the trace.
88 2. High-level representation of a trace
90 A trace is divided into multiple event streams. Each event stream contains a
91 subset of the trace event types.
93 The final output of the trace, after its generation and optional transport over
94 the network, is expected to be either on permanent or temporary storage in a
95 virtual file system. Because each event stream is appended to while a trace is
96 being recorded, each is associated with a distinct set of files for
97 output. Therefore, a stored trace can be represented as a directory
98 containing zero, one or more files per stream.
100 Meta-data description associated with the trace contains information on
101 trace event types expressed in the Trace Stream Description Language
102 (TSDL). This language describes:
106 - Per-trace event header description.
107 - Per-stream event header description.
108 - Per-stream event context description.
110 - Event type to stream mapping.
111 - Event type to name mapping.
112 - Event type to ID mapping.
113 - Event context description.
114 - Event fields description.
119 An event stream can be divided into contiguous event packets of variable
120 size. These subdivisions have a variable size. An event packet can
121 contain a certain amount of padding at the end. The stream header is
122 repeated at the beginning of each event packet. The rationale for the
123 event stream design choices is explained in Appendix B. Stream Header
126 The event stream header will therefore be referred to as the "event packet
127 header" throughout the rest of this document.
132 Types are organized as type classes. Each type class belong to either of two
133 kind of types: basic types or compound types.
137 A basic type is a scalar type, as described in this section. It includes
138 integers, GNU/C bitfields, enumerations, and floating point values.
140 4.1.1 Type inheritance
142 Type specifications can be inherited to allow deriving types from a
143 type class. For example, see the uint32_t named type derived from the "integer"
144 type class below ("Integers" section). Types have a precise binary
145 representation in the trace. A type class has methods to read and write these
146 types, but must be derived into a type to be usable in an event field.
150 We define "byte-packed" types as aligned on the byte size, namely 8-bit.
151 We define "bit-packed" types as following on the next bit, as defined by the
154 Each basic type must specify its alignment, in bits. Examples of
155 possible alignments are: bit-packed (align = 1), byte-packed (align =
156 8), or word-aligned (e.g. align = 32 or align = 64). The choice depends
157 on the architecture preference and compactness vs performance trade-offs
158 of the implementation. Architectures providing fast unaligned write
159 byte-packed basic types to save space, aligning each type on byte
160 boundaries (8-bit). Architectures with slow unaligned writes align types
161 on specific alignment values. If no specific alignment is declared for a
162 type, it is assumed to be bit-packed for integers with size not multiple
163 of 8 bits and for gcc bitfields. All other basic types are byte-packed
164 by default. It is however recommended to always specify the alignment
165 explicitly. Alignment values must be power of two. Compound types are
166 aligned as specified in their individual specification.
168 TSDL meta-data attribute representation of a specific alignment:
170 align = value; /* value in bits */
174 By default, the native endianness of the source architecture the trace is used.
175 Byte order can be overridden for a basic type by specifying a "byte_order"
176 attribute. Typical use-case is to specify the network byte order (big endian:
177 "be") to save data captured from the network into the trace without conversion.
178 If not specified, the byte order is native.
180 TSDL meta-data representation:
182 byte_order = native OR network OR be OR le; /* network and be are aliases */
186 Type size, in bits, for integers and floats is that returned by "sizeof()" in C
187 multiplied by CHAR_BIT.
188 We require the size of "char" and "unsigned char" types (CHAR_BIT) to be fixed
189 to 8 bits for cross-endianness compatibility.
191 TSDL meta-data representation:
193 size = value; (value is in bits)
197 Signed integers are represented in two-complement. Integer alignment,
198 size, signedness and byte ordering are defined in the TSDL meta-data.
199 Integers aligned on byte size (8-bit) and with length multiple of byte
200 size (8-bit) correspond to the C99 standard integers. In addition,
201 integers with alignment and/or size that are _not_ a multiple of the
202 byte size are permitted; these correspond to the C99 standard bitfields,
203 with the added specification that the CTF integer bitfields have a fixed
204 binary representation. A MIT-licensed reference implementation of the
205 CTF portable bitfields is available at:
207 http://git.efficios.com/?p=babeltrace.git;a=blob;f=include/babeltrace/bitfield.h
209 Binary representation of integers:
211 - On little and big endian:
212 - Within a byte, high bits correspond to an integer high bits, and low bits
213 correspond to low bits.
215 - Integer across multiple bytes are placed from the less significant to the
217 - Consecutive integers are placed from lower bits to higher bits (even within
220 - Integer across multiple bytes are placed from the most significant to the
222 - Consecutive integers are placed from higher bits to lower bits (even within
225 This binary representation is derived from the bitfield implementation in GCC
226 for little and big endian. However, contrary to what GCC does, integers can
227 cross units boundaries (no padding is required). Padding can be explicitly
228 added (see 4.1.6 GNU/C bitfields) to follow the GCC layout if needed.
230 TSDL meta-data representation:
233 signed = true OR false; /* default false */
234 byte_order = native OR network OR be OR le; /* default native */
235 size = value; /* value in bits, no default */
236 align = value; /* value in bits */
237 /* based used for pretty-printing output, default: decimal. */
238 base = decimal OR dec OR OR d OR i OR u OR 10 OR hexadecimal OR hex OR x OR X OR p OR 16
239 OR octal OR oct OR o OR 8 OR binary OR b OR 2;
240 /* character encoding, default: none */
241 encoding = none or UTF8 or ASCII;
244 Example of type inheritance (creation of a uint32_t named type):
252 Definition of a named 5-bit signed bitfield:
260 The character encoding field can be used to specify that the integer
261 must be printed as a text character when read. e.g.:
271 4.1.6 GNU/C bitfields
273 The GNU/C bitfields follow closely the integer representation, with a
274 particularity on alignment: if a bitfield cannot fit in the current unit, the
275 unit is padded and the bitfield starts at the following unit. The unit size is
276 defined by the size of the type "unit_type".
278 TSDL meta-data representation:
282 As an example, the following structure declared in C compiled by GCC:
289 The example structure is aligned on the largest element (short). The second
290 bitfield would be aligned on the next unit boundary, because it would not fit in
295 The floating point values byte ordering is defined in the TSDL meta-data.
297 Floating point values follow the IEEE 754-2008 standard interchange formats.
298 Description of the floating point values include the exponent and mantissa size
299 in bits. Some requirements are imposed on the floating point values:
301 - FLT_RADIX must be 2.
302 - mant_dig is the number of digits represented in the mantissa. It is specified
303 by the ISO C99 standard, section 5.2.4, as FLT_MANT_DIG, DBL_MANT_DIG and
304 LDBL_MANT_DIG as defined by <float.h>.
305 - exp_dig is the number of digits represented in the exponent. Given that
306 mant_dig is one bit more than its actual size in bits (leading 1 is not
307 needed) and also given that the sign bit always takes one bit, exp_dig can be
310 - sizeof(float) * CHAR_BIT - FLT_MANT_DIG
311 - sizeof(double) * CHAR_BIT - DBL_MANT_DIG
312 - sizeof(long double) * CHAR_BIT - LDBL_MANT_DIG
314 TSDL meta-data representation:
319 byte_order = native OR network OR be OR le;
323 Example of type inheritance:
325 typealias floating_point {
326 exp_dig = 8; /* sizeof(float) * CHAR_BIT - FLT_MANT_DIG */
327 mant_dig = 24; /* FLT_MANT_DIG */
332 TODO: define NaN, +inf, -inf behavior.
334 Bit-packed, byte-packed or larger alignments can be used for floating
335 point values, similarly to integers.
339 Enumerations are a mapping between an integer type and a table of strings. The
340 numerical representation of the enumeration follows the integer type specified
341 by the meta-data. The enumeration mapping table is detailed in the enumeration
342 description within the meta-data. The mapping table maps inclusive value
343 ranges (or single values) to strings. Instead of being limited to simple
344 "value -> string" mappings, these enumerations map
345 "[ start_value ... end_value ] -> string", which map inclusive ranges of
346 values to strings. An enumeration from the C language can be represented in
347 this format by having the same start_value and end_value for each element, which
348 is in fact a range of size 1. This single-value range is supported without
349 repeating the start and end values with the value = string declaration.
351 enum name : integer_type {
352 somestring = start_value1 ... end_value1,
353 "other string" = start_value2 ... end_value2,
354 yet_another_string, /* will be assigned to end_value2 + 1 */
355 "some other string" = value,
359 If the values are omitted, the enumeration starts at 0 and increment of 1 for
362 enum name : unsigned int {
370 Overlapping ranges within a single enumeration are implementation defined.
372 A nameless enumeration can be declared as a field type or as part of a typedef:
374 enum : integer_type {
378 Enumerations omitting the container type ": integer_type" use the "int"
379 type (for compatibility with C99). The "int" type must be previously
382 typealias integer { size = 32; align = 32; signed = true } := int;
391 Compound are aggregation of type declarations. Compound types include
392 structures, variant, arrays, sequences, and strings.
396 Structures are aligned on the largest alignment required by basic types
397 contained within the structure. (This follows the ISO/C standard for structures)
399 TSDL meta-data representation of a named structure:
402 field_type field_name;
403 field_type field_name;
410 integer { /* Nameless type */
415 uint64_t second_field_name; /* Named type declared in the meta-data */
418 The fields are placed in a sequence next to each other. They each possess a
419 field name, which is a unique identifier within the structure.
421 A nameless structure can be declared as a field type or as part of a typedef:
427 Alignment for a structure compound type can be forced to a minimum value
428 by adding an "align" specifier after the declaration of a structure
429 body. This attribute is read as: align(value). The value is specified in
430 bits. The structure will be aligned on the maximum value between this
431 attribute and the alignment required by the basic types contained within
438 4.2.2 Variants (Discriminated/Tagged Unions)
440 A CTF variant is a selection between different types. A CTF variant must
441 always be defined within the scope of a structure or within fields
442 contained within a structure (defined recursively). A "tag" enumeration
443 field must appear in either the same static scope, prior to the variant
444 field (in field declaration order), in an upper static scope , or in an
445 upper dynamic scope (see Section 7.3.2). The type selection is indicated
446 by the mapping from the enumeration value to the string used as variant
447 type selector. The field to use as tag is specified by the "tag_field",
448 specified between "< >" after the "variant" keyword for unnamed
449 variants, and after "variant name" for named variants.
451 The alignment of the variant is the alignment of the type as selected by the tag
452 value for the specific instance of the variant. The alignment of the type
453 containing the variant is independent of the variant alignment. The size of the
454 variant is the size as selected by the tag value for the specific instance of
457 A named variant declaration followed by its definition within a structure
468 enum : integer_type { sel1, sel2, sel3, ... } tag_field;
470 variant name <tag_field> v;
473 An unnamed variant definition within a structure is expressed by the following
477 enum : integer_type { sel1, sel2, sel3, ... } tag_field;
479 variant <tag_field> {
487 Example of a named variant within a sequence that refers to a single tag field:
496 enum : uint2_t { a, b, c } choice;
498 variant example <choice> v[seqlen];
501 Example of an unnamed variant:
504 enum : uint2_t { a, b, c, d } choice;
505 /* Unrelated fields can be added between the variant and its tag */
518 Example of an unnamed variant within an array:
521 enum : uint2_t { a, b, c } choice;
529 Example of a variant type definition within a structure, where the defined type
530 is then declared within an array of structures. This variant refers to a tag
531 located in an upper static scope. This example clearly shows that a variant
532 type definition referring to the tag "x" uses the closest preceding field from
533 the static scope of the type definition.
536 enum : uint2_t { a, b, c, d } x;
538 typedef variant <x> { /*
539 * "x" refers to the preceding "x" enumeration in the
540 * static scope of the type definition.
548 enum : int { x, y, z } x; /* This enumeration is not used by "v". */
549 example_variant v; /*
550 * "v" uses the "enum : uint2_t { a, b, c, d }"
558 Arrays are fixed-length. Their length is declared in the type
559 declaration within the meta-data. They contain an array of "inner type"
560 elements, which can refer to any type not containing the type of the
561 array being declared (no circular dependency). The length is the number
562 of elements in an array.
564 TSDL meta-data representation of a named array:
566 typedef elem_type name[length];
568 A nameless array can be declared as a field type within a structure, e.g.:
570 uint8_t field_name[10];
572 Arrays are always aligned on their element alignment requirement.
576 Sequences are dynamically-sized arrays. They refer to a a "length"
577 unsigned integer field, which must appear in either the same static scope,
578 prior to the sequence field (in field declaration order), in an upper
579 static scope, or in an upper dynamic scope (see Section 7.3.2). This
580 length field represents the number of elements in the sequence. The
581 sequence per se is an array of "inner type" elements.
583 TSDL meta-data representation for a sequence type definition:
586 unsigned int length_field;
587 typedef elem_type typename[length_field];
588 typename seq_field_name;
591 A sequence can also be declared as a field type, e.g.:
594 unsigned int length_field;
595 long seq_field_name[length_field];
598 Multiple sequences can refer to the same length field, and these length
599 fields can be in a different upper dynamic scope:
601 e.g., assuming the stream.event.header defines:
606 event.header := struct {
615 long seq_a[stream.event.header.seq_len];
616 char seq_b[stream.event.header.seq_len];
620 The sequence elements follow the "array" specifications.
624 Strings are an array of bytes of variable size and are terminated by a '\0'
625 "NULL" character. Their encoding is described in the TSDL meta-data. In
626 absence of encoding attribute information, the default encoding is
629 TSDL meta-data representation of a named string type:
632 encoding = UTF8 OR ASCII;
635 A nameless string type can be declared as a field type:
637 string field_name; /* Use default UTF8 encoding */
639 Strings are always aligned on byte size.
641 5. Event Packet Header
643 The event packet header consists of two parts: the "event packet header"
644 is the same for all streams of a trace. The second part, the "event
645 packet context", is described on a per-stream basis. Both are described
646 in the TSDL meta-data. The packets are aligned on architecture-page-sized
649 Event packet header (all fields are optional, specified by TSDL meta-data):
651 - Magic number (CTF magic number: 0xC1FC1FC1) specifies that this is a
652 CTF packet. This magic number is optional, but when present, it should
653 come at the very beginning of the packet.
654 - Trace UUID, used to ensure the event packet match the meta-data used.
655 (note: we cannot use a meta-data checksum in every cases instead of a
656 UUID because meta-data can be appended to while tracing is active)
657 This field is optional.
658 - Stream ID, used as reference to stream description in meta-data.
659 This field is optional if there is only one stream description in the
660 meta-data, but becomes required if there are more than one stream in
661 the TSDL meta-data description.
663 Event packet context (all fields are optional, specified by TSDL meta-data):
665 - Event packet content size (in bits).
666 - Event packet size (in bits, includes padding).
667 - Event packet content checksum. Checksum excludes the event packet
669 - Per-stream event packet sequence count (to deal with UDP packet loss). The
670 number of significant sequence counter bits should also be present, so
671 wrap-arounds are dealt with correctly.
672 - Time-stamp at the beginning and time-stamp at the end of the event packet.
673 Both timestamps are written in the packet header, but sampled respectively
674 while (or before) writing the first event and while (or after) writing the
675 last event in the packet. The inclusive range between these timestamps should
676 include all event timestamps assigned to events contained within the packet.
677 - Events discarded count
678 - Snapshot of a per-stream free-running counter, counting the number of
679 events discarded that were supposed to be written in the stream prior to
680 the first event in the event packet.
681 * Note: producer-consumer buffer full condition should fill the current
682 event packet with padding so we know exactly where events have been
684 - Lossless compression scheme used for the event packet content. Applied
685 directly to raw data. New types of compression can be added in following
686 versions of the format.
687 0: no compression scheme
691 - Cypher used for the event packet content. Applied after compression.
694 - Checksum scheme used for the event packet content. Applied after encryption.
700 5.1 Event Packet Header Description
702 The event packet header layout is indicated by the trace packet.header
703 field. Here is a recommended structure type for the packet header with
704 the fields typically expected (although these fields are each optional):
706 struct event_packet_header {
714 packet.header := struct event_packet_header;
717 If the magic number is not present, tools such as "file" will have no
718 mean to discover the file type.
720 If the uuid is not present, no validation that the meta-data actually
721 corresponds to the stream is performed.
723 If the stream_id packet header field is missing, the trace can only
724 contain a single stream. Its "id" field can be left out, and its events
725 don't need to declare a "stream_id" field.
728 5.2 Event Packet Context Description
730 Event packet context example. These are declared within the stream declaration
731 in the meta-data. All these fields are optional. If the packet size field is
732 missing, the whole stream only contains a single packet. If the content
733 size field is missing, the packet is filled (no padding). The content
734 and packet sizes include all headers.
736 An example event packet context type:
738 struct event_packet_context {
739 uint64_t timestamp_begin;
740 uint64_t timestamp_end;
742 uint32_t stream_packet_count;
743 uint32_t events_discarded;
745 uint32_t/uint16_t content_size;
746 uint32_t/uint16_t packet_size;
747 uint8_t stream_packet_count_bits; /* Significant counter bits */
748 uint8_t compression_scheme;
749 uint8_t encryption_scheme;
750 uint8_t checksum_scheme;
756 The overall structure of an event is:
758 1 - Stream Packet Context (as specified by the stream meta-data)
759 2 - Event Header (as specified by the stream meta-data)
760 3 - Stream Event Context (as specified by the stream meta-data)
761 4 - Event Context (as specified by the event meta-data)
762 5 - Event Payload (as specified by the event meta-data)
764 This structure defines an implicit dynamic scoping, where variants
765 located in inner structures (those with a higher number in the listing
766 above) can refer to the fields of outer structures (with lower number in
767 the listing above). See Section 7.3 TSDL Scopes for more detail.
771 Event headers can be described within the meta-data. We hereby propose, as an
772 example, two types of events headers. Type 1 accommodates streams with less than
773 31 event IDs. Type 2 accommodates streams with 31 or more event IDs.
775 One major factor can vary between streams: the number of event IDs assigned to
776 a stream. Luckily, this information tends to stay relatively constant (modulo
777 event registration while trace is being recorded), so we can specify different
778 representations for streams containing few event IDs and streams containing
779 many event IDs, so we end up representing the event ID and time-stamp as
780 densely as possible in each case.
782 The header is extended in the rare occasions where the information cannot be
783 represented in the ranges available in the standard event header. They are also
784 used in the rare occasions where the data required for a field could not be
785 collected: the flag corresponding to the missing field within the missing_fields
786 array is then set to 1.
788 Types uintX_t represent an X-bit unsigned integer, as declared with
791 typealias integer { size = X; align = X; signed = false } := uintX_t;
795 typealias integer { size = X; align = 1; signed = false } := uintX_t;
797 6.1.1 Type 1 - Few event IDs
799 - Aligned on 32-bit (or 8-bit if byte-packed, depending on the architecture
801 - Native architecture byte ordering.
802 - For "compact" selection
803 - Fixed size: 32 bits.
804 - For "extended" selection
805 - Size depends on the architecture and variant alignment.
807 struct event_header_1 {
810 * id 31 is reserved to indicate an extended header.
812 enum : uint5_t { compact = 0 ... 30, extended = 31 } id;
818 uint32_t id; /* 32-bit event IDs */
819 uint64_t timestamp; /* 64-bit timestamps */
822 } align(32); /* or align(8) */
825 6.1.2 Type 2 - Many event IDs
827 - Aligned on 16-bit (or 8-bit if byte-packed, depending on the architecture
829 - Native architecture byte ordering.
830 - For "compact" selection
831 - Size depends on the architecture and variant alignment.
832 - For "extended" selection
833 - Size depends on the architecture and variant alignment.
835 struct event_header_2 {
837 * id: range: 0 - 65534.
838 * id 65535 is reserved to indicate an extended header.
840 enum : uint16_t { compact = 0 ... 65534, extended = 65535 } id;
846 uint32_t id; /* 32-bit event IDs */
847 uint64_t timestamp; /* 64-bit timestamps */
850 } align(16); /* or align(8) */
855 The event context contains information relative to the current event.
856 The choice and meaning of this information is specified by the TSDL
857 stream and event meta-data descriptions. The stream context is applied
858 to all events within the stream. The stream context structure follows
859 the event header. The event context is applied to specific events. Its
860 structure follows the stream context structure.
862 An example of stream-level event context is to save the event payload size with
863 each event, or to save the current PID with each event. These are declared
864 within the stream declaration within the meta-data:
868 event.context := struct {
870 uint16_t payload_size;
874 An example of event-specific event context is to declare a bitmap of missing
875 fields, only appended after the stream event context if the extended event
876 header is selected. NR_FIELDS is the number of fields within the event (a
884 uint1_t missing_fields[NR_FIELDS]; /* missing event fields bitmap */
893 An event payload contains fields specific to a given event type. The fields
894 belonging to an event type are described in the event-specific meta-data
895 within a structure type.
899 No padding at the end of the event payload. This differs from the ISO/C standard
900 for structures, but follows the CTF standard for structures. In a trace, even
901 though it makes sense to align the beginning of a structure, it really makes no
902 sense to add padding at the end of the structure, because structures are usually
903 not followed by a structure of the same type.
905 This trick can be done by adding a zero-length "end" field at the end of the C
906 structures, and by using the offset of this field rather than using sizeof()
907 when calculating the size of a structure (see Appendix "A. Helper macros").
911 The event payload is aligned on the largest alignment required by types
912 contained within the payload. (This follows the ISO/C standard for structures)
915 7. Trace Stream Description Language (TSDL)
917 The Trace Stream Description Language (TSDL) allows expression of the
918 binary trace streams layout in a C99-like Domain Specific Language
924 The trace stream layout description is located in the trace meta-data.
925 The meta-data is itself located in a stream identified by its name:
928 The meta-data description can be expressed in two different formats:
929 text-only and packet-based. The text-only description facilitates
930 generation of meta-data and provides a convenient way to enter the
931 meta-data information by hand. The packet-based meta-data provides the
932 CTF stream packet facilities (checksumming, compression, encryption,
933 network-readiness) for meta-data stream generated and transported by a
936 The text-only meta-data file is a plain text TSDL description.
938 The packet-based meta-data is made of "meta-data packets", which each
939 start with a meta-data packet header. The packet-based meta-data
940 description is detected by reading the magic number "0x75D11D57" at the
941 beginning of the file. This magic number is also used to detect the
942 endianness of the architecture by trying to read the CTF magic number
943 and its counterpart in reversed endianness. The events within the
944 meta-data stream have no event header nor event context. Each event only
945 contains a "sequence" payload, which is a sequence of bits using the
946 "trace.packet.header.content_size" field as a placeholder for its length
947 (the packet header size should be substracted). The formatting of this
948 sequence of bits is a plain-text representation of the TSDL description.
949 Each meta-data packet start with a special packet header, specific to
950 the meta-data stream, which contains, exactly:
952 struct metadata_packet_header {
953 uint32_t magic; /* 0x75D11D57 */
954 uint8_t uuid[16]; /* Unique Universal Identifier */
955 uint32_t checksum; /* 0 if unused */
956 uint32_t content_size; /* in bits */
957 uint32_t packet_size; /* in bits */
958 uint8_t compression_scheme; /* 0 if unused */
959 uint8_t encryption_scheme; /* 0 if unused */
960 uint8_t checksum_scheme; /* 0 if unused */
963 The packet-based meta-data can be converted to a text-only meta-data by
964 concatenating all the strings in contains.
966 In the textual representation of the meta-data, the text contained
967 within "/*" and "*/", as well as within "//" and end of line, are
968 treated as comments. Boolean values can be represented as true, TRUE,
969 or 1 for true, and false, FALSE, or 0 for false. Within the string-based
970 meta-data description, the trace UUID is represented as a string of
971 hexadecimal digits and dashes "-". In the event packet header, the trace
972 UUID is represented as an array of bytes.
975 7.2 Declaration vs Definition
977 A declaration associates a layout to a type, without specifying where
978 this type is located in the event structure hierarchy (see Section 6).
979 This therefore includes typedef, typealias, as well as all type
980 specifiers. In certain circumstances (typedef, structure field and
981 variant field), a declaration is followed by a declarator, which specify
982 the newly defined type name (for typedef), or the field name (for
983 declarations located within structure and variants). Array and sequence,
984 declared with square brackets ("[" "]"), are part of the declarator,
985 similarly to C99. The enumeration base type is specified by
986 ": enum_base", which is part of the type specifier. The variant tag
987 name, specified between "<" ">", is also part of the type specifier.
989 A definition associates a type to a location in the event structure
990 hierarchy (see Section 6). This association is denoted by ":=", as shown
996 TSDL uses three different types of scoping: a lexical scope is used for
997 declarations and type definitions, and static and dynamic scopes are
998 used for variants references to tag fields (with relative and absolute
999 path lookups) and for sequence references to length fields.
1003 Each of "trace", "stream", "event", "struct" and "variant" have their own
1004 nestable declaration scope, within which types can be declared using "typedef"
1005 and "typealias". A root declaration scope also contains all declarations
1006 located outside of any of the aforementioned declarations. An inner
1007 declaration scope can refer to type declared within its container
1008 lexical scope prior to the inner declaration scope. Redefinition of a
1009 typedef or typealias is not valid, although hiding an upper scope
1010 typedef or typealias is allowed within a sub-scope.
1012 7.3.2 Static and Dynamic Scopes
1014 A local static scope consists in the scope generated by the declaration
1015 of fields within a compound type. A static scope is a local static scope
1016 augmented with the nested sub-static-scopes it contains.
1018 A dynamic scope consists in the static scope augmented with the
1019 implicit event structure definition hierarchy presented at Section 6.
1021 Multiple declarations of the same field name within a local static scope
1022 is not valid. It is however valid to re-use the same field name in
1023 different local scopes.
1025 Nested static and dynamic scopes form lookup paths. These are used for
1026 variant tag and sequence length references. They are used at the variant
1027 and sequence definition site to look up the location of the tag field
1028 associated with a variant, and to lookup up the location of the length
1029 field associated with a sequence.
1031 Variants and sequences can refer to a tag field either using a relative
1032 path or an absolute path. The relative path starts with "." to ensure
1033 there are no conflicts with dynamic scope names. It is relative to the
1034 scope in which the variant or sequence performing the lookup is located.
1035 Relative paths are only allowed to lookup within the same static scope,
1036 which includes its nested static scopes. Lookups targeting parent static
1037 scopes need to be performed with an absolute path.
1039 Absolute path lookups use the full path including the dynamic scope
1040 followed by a "." and then the static scope. Therefore, variants (or
1041 sequences) in lower levels in the dynamic scope (e.g. event context) can
1042 refer to a tag (or length) field located in upper levels (e.g. in the
1043 event header) by specifying, in this case, the associated tag with
1044 <stream.event.header.field_name>. This allows, for instance, the event
1045 context to define a variant referring to the "id" field of the event
1048 The dynamic scope prefixes are thus:
1050 - Trace Packet Header: <trace.packet.header. >,
1051 - Stream Packet Context: <stream.packet.context. >,
1052 - Event Header: <stream.event.header. >,
1053 - Stream Event Context: <stream.event.context. >,
1054 - Event Context: <event.context. >,
1055 - Event Payload: <event.fields. >.
1058 The target dynamic scope must be specified explicitly when referring to
1059 a field outside of the static scope (absolute scope reference).
1060 References to fields within the static scope (including local static
1061 scopes and nested static scopes) can be referenced by using a relative
1062 reference (starting with ".").
1064 As a matter of convenience, the leading "." in relative paths can be
1065 omitted. In case of conflict between relative and dynamic paths, the
1066 relative path is preferred. It is recommended to use the "." prefix for
1067 relative paths to ensure no path name conflict can occur.
1069 The information available in the dynamic scopes can be thought of as the
1070 current tracing context. At trace production, information about the
1071 current context is saved into the specified scope field levels. At trace
1072 consumption, for each event, the current trace context is therefore
1073 readable by accessing the upper dynamic scopes.
1078 The grammar representing the TSDL meta-data is presented in Appendix C.
1079 TSDL Grammar. This section presents a rather lighter reading that
1080 consists in examples of TSDL meta-data, with template values.
1082 The stream "id" can be left out if there is only one stream in the
1083 trace. The event "id" field can be left out if there is only one event
1087 major = value; /* Trace format version */
1089 uuid = "aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaaa"; /* Trace UUID */
1090 byte_order = be OR le; /* Endianness (required) */
1091 packet.header := struct {
1100 /* Type 1 - Few event IDs; Type 2 - Many event IDs. See section 6.1. */
1101 event.header := event_header_1 OR event_header_2;
1102 event.context := struct {
1105 packet.context := struct {
1112 id = value; /* Numeric identifier within the stream */
1113 stream_id = stream_id;
1122 /* More detail on types in section 4. Types */
1127 * Type declarations behave similarly to the C standard.
1130 typedef aliased_type_specifiers new_type_declarators;
1132 /* e.g.: typedef struct example new_type_name[10]; */
1137 * The "typealias" declaration can be used to give a name (including
1138 * pointer declarator specifier) to a type. It should also be used to
1139 * map basic C types (float, int, unsigned long, ...) to a CTF type.
1140 * Typealias is a superset of "typedef": it also allows assignment of a
1141 * simple variable identifier to a type.
1144 typealias type_class {
1146 } := type_specifiers type_declarator;
1150 * typealias integer {
1154 * } := struct page *;
1156 * typealias integer {
1171 enum name : integer_type {
1177 * Unnamed types, contained within compound type fields, typedef or typealias.
1192 enum : integer_type {
1196 typedef type new_type[length];
1199 type field_name[length];
1202 typedef type new_type[length_type];
1205 type field_name[length_type];
1217 integer_type field_name:size; /* GNU/C bitfield */
1227 The two following macros keep track of the size of a GNU/C structure without
1228 padding at the end by placing HEADER_END as the last field. A one byte end field
1229 is used for C90 compatibility (C99 flexible arrays could be used here). Note
1230 that this does not affect the effective structure size, which should always be
1231 calculated with the header_sizeof() helper.
1233 #define HEADER_END char end_field
1234 #define header_sizeof(type) offsetof(typeof(type), end_field)
1237 B. Stream Header Rationale
1239 An event stream is divided in contiguous event packets of variable size. These
1240 subdivisions allow the trace analyzer to perform a fast binary search by time
1241 within the stream (typically requiring to index only the event packet headers)
1242 without reading the whole stream. These subdivisions have a variable size to
1243 eliminate the need to transfer the event packet padding when partially filled
1244 event packets must be sent when streaming a trace for live viewing/analysis.
1245 An event packet can contain a certain amount of padding at the end. Dividing
1246 streams into event packets is also useful for network streaming over UDP and
1247 flight recorder mode tracing (a whole event packet can be swapped out of the
1248 buffer atomically for reading).
1250 The stream header is repeated at the beginning of each event packet to allow
1251 flexibility in terms of:
1253 - streaming support,
1254 - allowing arbitrary buffers to be discarded without making the trace
1256 - allow UDP packet loss handling by either dealing with missing event packet
1257 or asking for re-transmission.
1258 - transparently support flight recorder mode,
1259 - transparently support crash dump.
1265 * Common Trace Format (CTF) Trace Stream Description Language (TSDL) Grammar.
1267 * Inspired from the C99 grammar:
1268 * http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1124.pdf (Annex A)
1269 * and c++1x grammar (draft)
1270 * http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2011/n3291.pdf (Annex A)
1272 * Specialized for CTF needs by including only constant and declarations from
1273 * C99 (excluding function declarations), and by adding support for variants,
1274 * sequences and CTF-specific specifiers. Enumeration container types
1275 * semantic is inspired from c++1x enum-base.
1280 1.1) Lexical elements
1324 identifier identifier-nondigit
1327 identifier-nondigit:
1329 universal-character-name
1330 any other implementation-defined characters
1334 [a-zA-Z] /* regular expression */
1337 [0-9] /* regular expression */
1339 1.4) Universal character names
1341 universal-character-name:
1343 \U hex-quad hex-quad
1346 hexadecimal-digit hexadecimal-digit hexadecimal-digit hexadecimal-digit
1352 enumeration-constant
1356 decimal-constant integer-suffix-opt
1357 octal-constant integer-suffix-opt
1358 hexadecimal-constant integer-suffix-opt
1362 decimal-constant digit
1366 octal-constant octal-digit
1368 hexadecimal-constant:
1369 hexadecimal-prefix hexadecimal-digit
1370 hexadecimal-constant hexadecimal-digit
1380 unsigned-suffix long-suffix-opt
1381 unsigned-suffix long-long-suffix
1382 long-suffix unsigned-suffix-opt
1383 long-long-suffix unsigned-suffix-opt
1397 enumeration-constant:
1403 L' c-char-sequence '
1407 c-char-sequence c-char
1410 any member of source charset except single-quote ('), backslash
1411 (\), or new-line character.
1415 simple-escape-sequence
1416 octal-escape-sequence
1417 hexadecimal-escape-sequence
1418 universal-character-name
1420 simple-escape-sequence: one of
1421 \' \" \? \\ \a \b \f \n \r \t \v
1423 octal-escape-sequence:
1425 \ octal-digit octal-digit
1426 \ octal-digit octal-digit octal-digit
1428 hexadecimal-escape-sequence:
1429 \x hexadecimal-digit
1430 hexadecimal-escape-sequence hexadecimal-digit
1432 1.6) String literals
1435 " s-char-sequence-opt "
1436 L" s-char-sequence-opt "
1440 s-char-sequence s-char
1443 any member of source charset except double-quote ("), backslash
1444 (\), or new-line character.
1450 [ ] ( ) { } . -> * + - < > : ; ... = ,
1453 2) Phrase structure grammar
1459 ( unary-expression )
1463 postfix-expression [ unary-expression ]
1464 postfix-expression . identifier
1465 postfix-expressoin -> identifier
1469 unary-operator postfix-expression
1471 unary-operator: one of
1474 assignment-operator:
1477 type-assignment-operator:
1480 constant-expression-range:
1481 unary-expression ... unary-expression
1486 declaration-specifiers declarator-list-opt ;
1489 declaration-specifiers:
1490 storage-class-specifier declaration-specifiers-opt
1491 type-specifier declaration-specifiers-opt
1492 type-qualifier declaration-specifiers-opt
1496 declarator-list , declarator
1498 abstract-declarator-list:
1500 abstract-declarator-list , abstract-declarator
1502 storage-class-specifier:
1525 align ( unary-expression )
1528 struct identifier-opt { struct-or-variant-declaration-list-opt } align-attribute-opt
1529 struct identifier align-attribute-opt
1531 struct-or-variant-declaration-list:
1532 struct-or-variant-declaration
1533 struct-or-variant-declaration-list struct-or-variant-declaration
1535 struct-or-variant-declaration:
1536 specifier-qualifier-list struct-or-variant-declarator-list ;
1537 declaration-specifiers-opt storage-class-specifier declaration-specifiers-opt declarator-list ;
1538 typealias declaration-specifiers abstract-declarator-list type-assignment-operator declaration-specifiers abstract-declarator-list ;
1539 typealias declaration-specifiers abstract-declarator-list type-assignment-operator declarator-list ;
1541 specifier-qualifier-list:
1542 type-specifier specifier-qualifier-list-opt
1543 type-qualifier specifier-qualifier-list-opt
1545 struct-or-variant-declarator-list:
1546 struct-or-variant-declarator
1547 struct-or-variant-declarator-list , struct-or-variant-declarator
1549 struct-or-variant-declarator:
1551 declarator-opt : unary-expression
1554 variant identifier-opt variant-tag-opt { struct-or-variant-declaration-list }
1555 variant identifier variant-tag
1558 < unary-expression >
1561 enum identifier-opt { enumerator-list }
1562 enum identifier-opt { enumerator-list , }
1564 enum identifier-opt : declaration-specifiers { enumerator-list }
1565 enum identifier-opt : declaration-specifiers { enumerator-list , }
1569 enumerator-list , enumerator
1572 enumeration-constant
1573 enumeration-constant assignment-operator unary-expression
1574 enumeration-constant assignment-operator constant-expression-range
1580 pointer-opt direct-declarator
1585 direct-declarator [ unary-expression ]
1587 abstract-declarator:
1588 pointer-opt direct-abstract-declarator
1590 direct-abstract-declarator:
1592 ( abstract-declarator )
1593 direct-abstract-declarator [ unary-expression ]
1594 direct-abstract-declarator [ ]
1597 * type-qualifier-list-opt
1598 * type-qualifier-list-opt pointer
1600 type-qualifier-list:
1602 type-qualifier-list type-qualifier
1607 2.3) CTF-specific declarations
1610 event { ctf-assignment-expression-list-opt }
1611 stream { ctf-assignment-expression-list-opt }
1612 trace { ctf-assignment-expression-list-opt }
1613 typealias declaration-specifiers abstract-declarator-list type-assignment-operator declaration-specifiers abstract-declarator-list
1614 typealias declaration-specifiers abstract-declarator-list type-assignment-operator declarator-list
1617 floating_point { ctf-assignment-expression-list-opt }
1618 integer { ctf-assignment-expression-list-opt }
1619 string { ctf-assignment-expression-list-opt }
1622 ctf-assignment-expression-list:
1623 ctf-assignment-expression ;
1624 ctf-assignment-expression-list ctf-assignment-expression ;
1626 ctf-assignment-expression:
1627 unary-expression assignment-operator unary-expression
1628 unary-expression type-assignment-operator type-specifier
1629 declaration-specifiers-opt storage-class-specifier declaration-specifiers-opt declarator-list
1630 typealias declaration-specifiers abstract-declarator-list type-assignment-operator declaration-specifiers abstract-declarator-list
1631 typealias declaration-specifiers abstract-declarator-list type-assignment-operator declarator-list