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Common Trace Format (CTF) Specification (v1.8.1)Mathieu Desnoyers, EfficiOS Inc.The goal of the present document is to specify a trace format that suits the needs of the embedded, telecom, high-performance and kernel communities. It is based on the Common Trace Format Requirements (v1.4) document. It is designed to allow traces to be natively generated by the Linux kernel, Linux user-space applications written in C/C++, and hardware components. One major element of CTF is the Trace Stream Description Language (TSDL) which flexibility enables description of various binary trace stream layouts.The latest version of this document can be found at:git tree: git://git.efficios.com/ctf.gitgitweb: http://git.efficios.com/?p=ctf.gitA reference implementation of a library to read and write this trace format is being implemented within the BabelTrace project, a converter between trace formats. The development tree is available at:git tree: git://git.efficios.com/babeltrace.gitgitweb: http://git.efficios.com/?p=babeltrace.gitThe CE Workgroup of the Linux Foundation, Ericsson, and EfficiOS have sponsored this work.Table of Contents1. Preliminary definitions 2. High-level representation of a trace 3. Event stream 4. Types4.1 Basic types4.1.1 Type inheritance4.1.2 Alignment4.1.3 Byte order4.1.4 Size4.1.5 Integers4.1.6 GNU/C bitfields4.1.7 Floating point4.1.8 Enumerations 4.2 Compound types4.2.1 Structures4.2.2 Variants (Discriminated/Tagged Unions)4.2.3 Arrays4.2.4 Sequences4.2.5 Strings 5. Event Packet Header5.1 Event Packet Header Description5.2 Event Packet Context Description 6. Event Structure6.1 Event Header6.1.1 Type 1 - Few event IDs6.1.2 Type 2 - Many event IDs6.2 Event Context6.3 Event Payload6.3.1 Padding6.3.2 Alignment 7. Trace Stream Description Language (TSDL)7.1 Meta-data7.2 Declaration vs Definition7.3 TSDL Scopes7.3.1 Lexical Scope7.3.2 Static and Dynamic Scopes7.4 TSDL Examples 8. Clocks1. Preliminary definitions- Event Trace: An ordered sequence of events.- Event Stream: An ordered sequence of events, containing a subset of thetrace event types.- Event Packet: A sequence of physically contiguous events within an eventstream.- Event: This is the basic entry in a trace. (aka: a trace record).- An event identifier (ID) relates to the class (a type) of event withinan event stream.e.g. event: irq_entry.- An event (or event record) relates to a specific instance of an eventclass.e.g. event: irq_entry, at time X, on CPU Y- Source Architecture: Architecture writing the trace.- Reader Architecture: Architecture reading the trace.2. High-level representation of a traceA trace is divided into multiple event streams. Each event stream contains a subset of the trace event types.The final output of the trace, after its generation and optional transport over the network, is expected to be either on permanent or temporary storage in a virtual file system. Because each event stream is appended to while a trace is being recorded, each is associated with a distinct set of files for output. Therefore, a stored trace can be represented as a directory containing zero, one or more files per stream.Meta-data description associated with the trace contains information on trace event types expressed in the Trace Stream Description Language (TSDL). This language describes:- Trace version. - Types available. - Per-trace event header description. - Per-stream event header description. - Per-stream event context description. - Per-event- Event type to stream mapping.- Event type to name mapping.- Event type to ID mapping.- Event context description.- Event fields description.3. Event streamAn event stream can be divided into contiguous event packets of variable size. These subdivisions have a variable size. An event packet can contain a certain amount of padding at the end. The stream header is repeated at the beginning of each event packet. The rationale for the event stream design choices is explained in Appendix B. Stream Header Rationale.The event stream header will therefore be referred to as the "event packet header" throughout the rest of this document.4. TypesTypes are organized as type classes. Each type class belong to either of two kind of types: basic types or compound types.4.1 Basic typesA basic type is a scalar type, as described in this section. It includes integers, GNU/C bitfields, enumerations, and floating point values.4.1.1 Type inheritanceType specifications can be inherited to allow deriving types from a type class. For example, see the uint32_t named type derived from the "integer" type class below ("Integers" section). Types have a precise binary representation in the trace. A type class has methods to read and write these types, but must be derived into a type to be usable in an event field.4.1.2 AlignmentWe define "byte-packed" types as aligned on the byte size, namely 8-bit. We define "bit-packed" types as following on the next bit, as defined by the "Integers" section.Each basic type must specify its alignment, in bits. Examples of possible alignments are: bit-packed (align = 1), byte-packed (align = 8), or word-aligned (e.g. align = 32 or align = 64). The choice depends on the architecture preference and compactness vs performance trade-offs of the implementation. Architectures providing fast unaligned write byte-packed basic types to save space, aligning each type on byte boundaries (8-bit). Architectures with slow unaligned writes align types on specific alignment values. If no specific alignment is declared for a type, it is assumed to be bit-packed for integers with size not multiple of 8 bits and for gcc bitfields. All other basic types are byte-packed by default. It is however recommended to always specify the alignment explicitly. Alignment values must be power of two. Compound types are aligned as specified in their individual specification.TSDL meta-data attribute representation of a specific alignment:align = value; /* value in bits */4.1.3 Byte orderBy default, the native endianness of the source architecture the trace is used. Byte order can be overridden for a basic type by specifying a "byte_order" attribute. Typical use-case is to specify the network byte order (big endian: "be") to save data captured from the network into the trace without conversion. If not specified, the byte order is native.TSDL meta-data representation:byte_order = native OR network OR be OR le; /* network and be are aliases */4.1.4 SizeType size, in bits, for integers and floats is that returned by "sizeof()" in C multiplied by CHAR_BIT. We require the size of "char" and "unsigned char" types (CHAR_BIT) to be fixed to 8 bits for cross-endianness compatibility.TSDL meta-data representation:size = value; (value is in bits)4.1.5 IntegersSigned integers are represented in two-complement. Integer alignment, size, signedness and byte ordering are defined in the TSDL meta-data. Integers aligned on byte size (8-bit) and with length multiple of byte size (8-bit) correspond to the C99 standard integers. In addition, integers with alignment and/or size that are _not_ a multiple of the byte size are permitted; these correspond to the C99 standard bitfields, with the added specification that the CTF integer bitfields have a fixed binary representation. A MIT-licensed reference implementation of the CTF portable bitfields is available at:http://git.efficios.com/?p=babeltrace.git;a=blob;f=include/babeltrace/bitfield.hBinary representation of integers:- On little and big endian:- Within a byte, high bits correspond to an integer high bits, and low bitscorrespond to low bits. - On little endian:- Integer across multiple bytes are placed from the less significant to themost significant.- Consecutive integers are placed from lower bits to higher bits (even withina byte). - On big endian:- Integer across multiple bytes are placed from the most significant to theless significant.- Consecutive integers are placed from higher bits to lower bits (even withina byte).This binary representation is derived from the bitfield implementation in GCC for little and big endian. However, contrary to what GCC does, integers can cross units boundaries (no padding is required). Padding can be explicitly added (see 4.1.6 GNU/C bitfields) to follow the GCC layout if needed.TSDL meta-data representation:integer {signed = true OR false; /* default false */byte_order = native OR network OR be OR le; /* default native */size = value; /* value in bits, no default */align = value; /* value in bits *//* based used for pretty-printing output, default: decimal. */base = decimal OR dec OR OR d OR i OR u OR 10 OR hexadecimal OR hex OR x OR X OR p OR 16OR octal OR oct OR o OR 8 OR binary OR b OR 2;/* character encoding, default: none */encoding = none or UTF8 or ASCII;}Example of type inheritance (creation of a uint32_t named type):typealias integer {size = 32;signed = false;align = 32; } := uint32_t;Definition of a named 5-bit signed bitfield:typealias integer {size = 5;signed = true;align = 1; } := int5_t;The character encoding field can be used to specify that the integer must be printed as a text character when read. e.g.:typealias integer {size = 8;align = 8;signed = false;encoding = UTF8; } := utf_char;4.1.6 GNU/C bitfieldsThe GNU/C bitfields follow closely the integer representation, with a particularity on alignment: if a bitfield cannot fit in the current unit, the unit is padded and the bitfield starts at the following unit. The unit size is defined by the size of the type "unit_type".TSDL meta-data representation:unit_type name:size;As an example, the following structure declared in C compiled by GCC:struct example {short a:12;short b:5; };The example structure is aligned on the largest element (short). The second bitfield would be aligned on the next unit boundary, because it would not fit in the current unit.4.1.7 Floating pointThe floating point values byte ordering is defined in the TSDL meta-data.Floating point values follow the IEEE 754-2008 standard interchange formats. Description of the floating point values include the exponent and mantissa size in bits. Some requirements are imposed on the floating point values:- FLT_RADIX must be 2. - mant_dig is the number of digits represented in the mantissa. It is specifiedby the ISO C99 standard, section 5.2.4, as FLT_MANT_DIG, DBL_MANT_DIG andLDBL_MANT_DIG as defined by <float.h>. - exp_dig is the number of digits represented in the exponent. Given thatmant_dig is one bit more than its actual size in bits (leading 1 is notneeded) and also given that the sign bit always takes one bit, exp_dig can bespecified as:- sizeof(float) * CHAR_BIT - FLT_MANT_DIG- sizeof(double) * CHAR_BIT - DBL_MANT_DIG- sizeof(long double) * CHAR_BIT - LDBL_MANT_DIGTSDL meta-data representation:floating_point {exp_dig = value;mant_dig = value;byte_order = native OR network OR be OR le;align = value; }Example of type inheritance:typealias floating_point {exp_dig = 8; /* sizeof(float) * CHAR_BIT - FLT_MANT_DIG */mant_dig = 24; /* FLT_MANT_DIG */byte_order = native;align = 32; } := float;TODO: define NaN, +inf, -inf behavior.Bit-packed, byte-packed or larger alignments can be used for floating point values, similarly to integers.4.1.8 EnumerationsEnumerations are a mapping between an integer type and a table of strings. The numerical representation of the enumeration follows the integer type specified by the meta-data. The enumeration mapping table is detailed in the enumeration description within the meta-data. The mapping table maps inclusive value ranges (or single values) to strings. Instead of being limited to simple "value -> string" mappings, these enumerations map "[ start_value ... end_value ] -> string", which map inclusive ranges of values to strings. An enumeration from the C language can be represented in this format by having the same start_value and end_value for each element, which is in fact a range of size 1. This single-value range is supported without repeating the start and end values with the value = string declaration.enum name : integer_type {somestring = start_value1 ... end_value1,"other string" = start_value2 ... end_value2,yet_another_string, /* will be assigned to end_value2 + 1 */"some other string" = value,... };If the values are omitted, the enumeration starts at 0 and increment of 1 for each entry:enum name : unsigned int {ZERO,ONE,TWO,TEN = 10,ELEVEN, };Overlapping ranges within a single enumeration are implementation defined.A nameless enumeration can be declared as a field type or as part of a typedef:enum : integer_type {... }Enumerations omitting the container type ": integer_type" use the "int" type (for compatibility with C99). The "int" type must be previously declared. E.g.:typealias integer { size = 32; align = 32; signed = true } := int;enum {... }4.2 Compound typesCompound are aggregation of type declarations. Compound types include structures, variant, arrays, sequences, and strings.4.2.1 StructuresStructures are aligned on the largest alignment required by basic types contained within the structure. (This follows the ISO/C standard for structures)TSDL meta-data representation of a named structure:struct name {field_type field_name;field_type field_name;... }; Example:struct example {integer { /* Nameless type */size = 16;signed = true;align = 16;} first_field_name;uint64_t second_field_name; /* Named type declared in the meta-data */ };The fields are placed in a sequence next to each other. They each possess a field name, which is a unique identifier within the structure. The identifier is not allowed to use any reserved keyword (see Section C.1.2). Replacing reserved keywords with underscore-prefixed field names is recommended. Fields starting with an underscore should have their leading underscore removed by the CTF trace readers.A nameless structure can be declared as a field type or as part of a typedef:struct {... }Alignment for a structure compound type can be forced to a minimum value by adding an "align" specifier after the declaration of a structure body. This attribute is read as: align(value). The value is specified in bits. The structure will be aligned on the maximum value between this attribute and the alignment required by the basic types contained within the structure. e.g.struct {... } align(32)4.2.2 Variants (Discriminated/Tagged Unions)A CTF variant is a selection between different types. A CTF variant must always be defined within the scope of a structure or within fields contained within a structure (defined recursively). A "tag" enumeration field must appear in either the same static scope, prior to the variant field (in field declaration order), in an upper static scope , or in an upper dynamic scope (see Section 7.3.2). The type selection is indicated by the mapping from the enumeration value to the string used as variant type selector. The field to use as tag is specified by the "tag_field", specified between "< >" after the "variant" keyword for unnamed variants, and after "variant name" for named variants.The alignment of the variant is the alignment of the type as selected by the tag value for the specific instance of the variant. The alignment of the type containing the variant is independent of the variant alignment. The size of the variant is the size as selected by the tag value for the specific instance of the variant.Each variant type selector possess a field name, which is a unique identifier within the variant. The identifier is not allowed to use any reserved keyword (see Section C.1.2). Replacing reserved keywords with underscore-prefixed field names is recommended. Fields starting with an underscore should have their leading underscore removed by the CTF trace readers.A named variant declaration followed by its definition within a structure declaration:variant name {field_type sel1;field_type sel2;field_type sel3;... };struct {enum : integer_type { sel1, sel2, sel3, ... } tag_field;...variant name <tag_field> v; }An unnamed variant definition within a structure is expressed by the following TSDL meta-data:struct {enum : integer_type { sel1, sel2, sel3, ... } tag_field;...variant <tag_field> {field_type sel1;field_type sel2;field_type sel3;...} v; }Example of a named variant within a sequence that refers to a single tag field:variant example {uint32_t a;uint64_t b;short c; };struct {enum : uint2_t { a, b, c } choice;unsigned int seqlen;variant example <choice> v[seqlen]; }Example of an unnamed variant:struct {enum : uint2_t { a, b, c, d } choice;/* Unrelated fields can be added between the variant and its tag */int32_t somevalue;variant <choice> {uint32_t a;uint64_t b;short c;struct {unsigned int field1;uint64_t field2;} d;} s; }Example of an unnamed variant within an array:struct {enum : uint2_t { a, b, c } choice;variant <choice> {uint32_t a;uint64_t b;short c;} v[10]; }Example of a variant type definition within a structure, where the defined type is then declared within an array of structures. This variant refers to a tag located in an upper static scope. This example clearly shows that a variant type definition referring to the tag "x" uses the closest preceding field from the static scope of the type definition.struct {enum : uint2_t { a, b, c, d } x;typedef variant <x> { /** "x" refers to the preceding "x" enumeration in the* static scope of the type definition.*/uint32_t a;uint64_t b;short c;} example_variant;struct {enum : int { x, y, z } x; /* This enumeration is not used by "v". */example_variant v; /** "v" uses the "enum : uint2_t { a, b, c, d }"* tag.*/} a[10]; }4.2.3 ArraysArrays are fixed-length. Their length is declared in the type declaration within the meta-data. They contain an array of "inner type" elements, which can refer to any type not containing the type of the array being declared (no circular dependency). The length is the number of elements in an array.TSDL meta-data representation of a named array:typedef elem_type name[length];A nameless array can be declared as a field type within a structure, e.g.:uint8_t field_name[10];Arrays are always aligned on their element alignment requirement.4.2.4 SequencesSequences are dynamically-sized arrays. They refer to a a "length" unsigned integer field, which must appear in either the same static scope, prior to the sequence field (in field declaration order), in an upper static scope, or in an upper dynamic scope (see Section 7.3.2). This length field represents the number of elements in the sequence. The sequence per se is an array of "inner type" elements.TSDL meta-data representation for a sequence type definition:struct {unsigned int length_field;typedef elem_type typename[length_field];typename seq_field_name; }A sequence can also be declared as a field type, e.g.:struct {unsigned int length_field;long seq_field_name[length_field]; }Multiple sequences can refer to the same length field, and these length fields can be in a different upper dynamic scope:e.g., assuming the stream.event.header defines:stream {...id = 1;event.header := struct {uint16_t seq_len;}; };event {...stream_id = 1;fields := struct {long seq_a[stream.event.header.seq_len];char seq_b[stream.event.header.seq_len];}; };The sequence elements follow the "array" specifications.4.2.5 StringsStrings are an array of bytes of variable size and are terminated by a '\0' "NULL" character. Their encoding is described in the TSDL meta-data. In absence of encoding attribute information, the default encoding is UTF-8.TSDL meta-data representation of a named string type:typealias string {encoding = UTF8 OR ASCII; } := name;A nameless string type can be declared as a field type:string field_name; /* Use default UTF8 encoding */Strings are always aligned on byte size.5. Event Packet HeaderThe event packet header consists of two parts: the "event packet header" is the same for all streams of a trace. The second part, the "event packet context", is described on a per-stream basis. Both are described in the TSDL meta-data. The packets are aligned on architecture-page-sized addresses.Event packet header (all fields are optional, specified by TSDL meta-data):- Magic number (CTF magic number: 0xC1FC1FC1) specifies that this is aCTF packet. This magic number is optional, but when present, it shouldcome at the very beginning of the packet. - Trace UUID, used to ensure the event packet match the meta-data used.(note: we cannot use a meta-data checksum in every cases instead of aUUID because meta-data can be appended to while tracing is active)This field is optional. - Stream ID, used as reference to stream description in meta-data.This field is optional if there is only one stream description in themeta-data, but becomes required if there are more than one stream inthe TSDL meta-data description.Event packet context (all fields are optional, specified by TSDL meta-data):- Event packet content size (in bits). - Event packet size (in bits, includes padding). - Event packet content checksum. Checksum excludes the event packetheader. - Per-stream event packet sequence count (to deal with UDP packet loss). Thenumber of significant sequence counter bits should also be present, sowrap-arounds are dealt with correctly. - Time-stamp at the beginning and time-stamp at the end of the event packet.Both timestamps are written in the packet header, but sampled respectivelywhile (or before) writing the first event and while (or after) writing thelast event in the packet. The inclusive range between these timestamps shouldinclude all event timestamps assigned to events contained within the packet. - Events discarded count- Snapshot of a per-stream free-running counter, counting the number ofevents discarded that were supposed to be written in the stream prior tothe first event in the event packet.* Note: producer-consumer buffer full condition should fill the currentevent packet with padding so we know exactly where events have beendiscarded. - Lossless compression scheme used for the event packet content. Applieddirectly to raw data. New types of compression can be added in followingversions of the format.0: no compression scheme1: bzip22: gzip3: xz - Cypher used for the event packet content. Applied after compression.0: no encryption1: AES - Checksum scheme used for the event packet content. Applied after encryption.0: no checksum1: md52: sha13: crc325.1 Event Packet Header DescriptionThe event packet header layout is indicated by the trace packet.header field. Here is a recommended structure type for the packet header with the fields typically expected (although these fields are each optional):struct event_packet_header {uint32_t magic;uint8_t uuid[16];uint32_t stream_id; };trace {...packet.header := struct event_packet_header; };If the magic number is not present, tools such as "file" will have no mean to discover the file type.If the uuid is not present, no validation that the meta-data actually corresponds to the stream is performed.If the stream_id packet header field is missing, the trace can only contain a single stream. Its "id" field can be left out, and its events don't need to declare a "stream_id" field.5.2 Event Packet Context DescriptionEvent packet context example. These are declared within the stream declaration in the meta-data. All these fields are optional. If the packet size field is missing, the whole stream only contains a single packet. If the content size field is missing, the packet is filled (no padding). The content and packet sizes include all headers.An example event packet context type:struct event_packet_context {uint64_t timestamp_begin;uint64_t timestamp_end;uint32_t checksum;uint32_t stream_packet_count;uint32_t events_discarded;uint32_t cpu_id;uint32_t/uint16_t content_size;uint32_t/uint16_t packet_size;uint8_t compression_scheme;uint8_t encryption_scheme;uint8_t checksum_scheme; };6. Event StructureThe overall structure of an event is:1 - Stream Packet Context (as specified by the stream meta-data)2 - Event Header (as specified by the stream meta-data)3 - Stream Event Context (as specified by the stream meta-data)4 - Event Context (as specified by the event meta-data)5 - Event Payload (as specified by the event meta-data)This structure defines an implicit dynamic scoping, where variants located in inner structures (those with a higher number in the listing above) can refer to the fields of outer structures (with lower number in the listing above). See Section 7.3 TSDL Scopes for more detail.6.1 Event HeaderEvent headers can be described within the meta-data. We hereby propose, as an example, two types of events headers. Type 1 accommodates streams with less than 31 event IDs. Type 2 accommodates streams with 31 or more event IDs.One major factor can vary between streams: the number of event IDs assigned to a stream. Luckily, this information tends to stay relatively constant (modulo event registration while trace is being recorded), so we can specify different representations for streams containing few event IDs and streams containing many event IDs, so we end up representing the event ID and time-stamp as densely as possible in each case.The header is extended in the rare occasions where the information cannot be represented in the ranges available in the standard event header. They are also used in the rare occasions where the data required for a field could not be collected: the flag corresponding to the missing field within the missing_fields array is then set to 1.Types uintX_t represent an X-bit unsigned integer, as declared with either:typealias integer { size = X; align = X; signed = false } := uintX_t;ortypealias integer { size = X; align = 1; signed = false } := uintX_t;6.1.1 Type 1 - Few event IDs- Aligned on 32-bit (or 8-bit if byte-packed, depending on the architecturepreference).- Native architecture byte ordering.- For "compact" selection- Fixed size: 32 bits.- For "extended" selection- Size depends on the architecture and variant alignment.struct event_header_1 {/** id: range: 0 - 30.* id 31 is reserved to indicate an extended header.*/enum : uint5_t { compact = 0 ... 30, extended = 31 } id;variant <id> {struct {uint27_t timestamp;} compact;struct {uint32_t id; /* 32-bit event IDs */uint64_t timestamp; /* 64-bit timestamps */} extended;} v; } align(32); /* or align(8) */6.1.2 Type 2 - Many event IDs- Aligned on 16-bit (or 8-bit if byte-packed, depending on the architecturepreference).- Native architecture byte ordering.- For "compact" selection- Size depends on the architecture and variant alignment.- For "extended" selection- Size depends on the architecture and variant alignment.struct event_header_2 {/** id: range: 0 - 65534.* id 65535 is reserved to indicate an extended header.*/enum : uint16_t { compact = 0 ... 65534, extended = 65535 } id;variant <id> {struct {uint32_t timestamp;} compact;struct {uint32_t id; /* 32-bit event IDs */uint64_t timestamp; /* 64-bit timestamps */ } extended;} v; } align(16); /* or align(8) */6.2 Event ContextThe event context contains information relative to the current event. The choice and meaning of this information is specified by the TSDL stream and event meta-data descriptions. The stream context is applied to all events within the stream. The stream context structure follows the event header. The event context is applied to specific events. Its structure follows the stream context structure.An example of stream-level event context is to save the event payload size with each event, or to save the current PID with each event. These are declared within the stream declaration within the meta-data:stream {...event.context := struct {uint pid;uint16_t payload_size;};};An example of event-specific event context is to declare a bitmap of missing fields, only appended after the stream event context if the extended event header is selected. NR_FIELDS is the number of fields within the event (a numeric value).event {context = struct {variant <id> {struct { } compact;struct {uint1_t missing_fields[NR_FIELDS]; /* missing event fields bitmap */} extended;} v;};...}6.3 Event PayloadAn event payload contains fields specific to a given event type. The fields belonging to an event type are described in the event-specific meta-data within a structure type.6.3.1 PaddingNo padding at the end of the event payload. This differs from the ISO/C standard for structures, but follows the CTF standard for structures. In a trace, even though it makes sense to align the beginning of a structure, it really makes no sense to add padding at the end of the structure, because structures are usually not followed by a structure of the same type.This trick can be done by adding a zero-length "end" field at the end of the C structures, and by using the offset of this field rather than using sizeof() when calculating the size of a structure (see Appendix "A. Helper macros").6.3.2 AlignmentThe event payload is aligned on the largest alignment required by types contained within the payload. (This follows the ISO/C standard for structures)7. Trace Stream Description Language (TSDL)The Trace Stream Description Language (TSDL) allows expression of the binary trace streams layout in a C99-like Domain Specific Language (DSL).7.1 Meta-dataThe trace stream layout description is located in the trace meta-data. The meta-data is itself located in a stream identified by its name: "metadata".The meta-data description can be expressed in two different formats: text-only and packet-based. The text-only description facilitates generation of meta-data and provides a convenient way to enter the meta-data information by hand. The packet-based meta-data provides the CTF stream packet facilities (checksumming, compression, encryption, network-readiness) for meta-data stream generated and transported by a tracer.The text-only meta-data file is a plain-text TSDL description. This file must begin with the following characters to identify the file as a CTF TSDL text-based metadata file (without the double-quotes) :"/* CTF"It must be followed by a space, and the version of the specification followed by the CTF trace, e.g.:" 1.8"These characters allow automated discovery of file type and CTF specification version. They are interpreted as a the beginning of a comment by the TSDL metadata parser. The comment can be continued to contain extra commented characters before it is closed.The packet-based meta-data is made of "meta-data packets", which each start with a meta-data packet header. The packet-based meta-data description is detected by reading the magic number "0x75D11D57" at the beginning of the file. This magic number is also used to detect the endianness of the architecture by trying to read the CTF magic number and its counterpart in reversed endianness. The events within the meta-data stream have no event header nor event context. Each event only contains a "sequence" payload, which is a sequence of bits using the "trace.packet.header.content_size" field as a placeholder for its length (the packet header size should be substracted). The formatting of this sequence of bits is a plain-text representation of the TSDL description. Each meta-data packet start with a special packet header, specific to the meta-data stream, which contains, exactly:struct metadata_packet_header {uint32_t magic; /* 0x75D11D57 */uint8_t uuid[16]; /* Unique Universal Identifier */uint32_t checksum; /* 0 if unused */uint32_t content_size; /* in bits */uint32_t packet_size; /* in bits */uint8_t compression_scheme; /* 0 if unused */uint8_t encryption_scheme; /* 0 if unused */uint8_t checksum_scheme; /* 0 if unused */uint8_t major; /* CTF spec version major number */uint8_t minor; /* CTF spec version minor number */ };The packet-based meta-data can be converted to a text-only meta-data by concatenating all the strings in contains.In the textual representation of the meta-data, the text contained within "/*" and "*/", as well as within "//" and end of line, are treated as comments. Boolean values can be represented as true, TRUE, or 1 for true, and false, FALSE, or 0 for false. Within the string-based meta-data description, the trace UUID is represented as a string of hexadecimal digits and dashes "-". In the event packet header, the trace UUID is represented as an array of bytes.7.2 Declaration vs DefinitionA declaration associates a layout to a type, without specifying where this type is located in the event structure hierarchy (see Section 6). This therefore includes typedef, typealias, as well as all type specifiers. In certain circumstances (typedef, structure field and variant field), a declaration is followed by a declarator, which specify the newly defined type name (for typedef), or the field name (for declarations located within structure and variants). Array and sequence, declared with square brackets ("[" "]"), are part of the declarator, similarly to C99. The enumeration base type is specified by ": enum_base", which is part of the type specifier. The variant tag name, specified between "<" ">", is also part of the type specifier.A definition associates a type to a location in the event structure hierarchy (see Section 6). This association is denoted by ":=", as shown in Section 7.3.7.3 TSDL ScopesTSDL uses three different types of scoping: a lexical scope is used for declarations and type definitions, and static and dynamic scopes are used for variants references to tag fields (with relative and absolute path lookups) and for sequence references to length fields.7.3.1 Lexical ScopeEach of "trace", "env", "stream", "event", "struct" and "variant" have their own nestable declaration scope, within which types can be declared using "typedef" and "typealias". A root declaration scope also contains all declarations located outside of any of the aforementioned declarations. An inner declaration scope can refer to type declared within its container lexical scope prior to the inner declaration scope. Redefinition of a typedef or typealias is not valid, although hiding an upper scope typedef or typealias is allowed within a sub-scope.7.3.2 Static and Dynamic ScopesA local static scope consists in the scope generated by the declaration of fields within a compound type. A static scope is a local static scope augmented with the nested sub-static-scopes it contains.A dynamic scope consists in the static scope augmented with the implicit event structure definition hierarchy presented at Section 6.Multiple declarations of the same field name within a local static scope is not valid. It is however valid to re-use the same field name in different local scopes.Nested static and dynamic scopes form lookup paths. These are used for variant tag and sequence length references. They are used at the variant and sequence definition site to look up the location of the tag field associated with a variant, and to lookup up the location of the length field associated with a sequence.Variants and sequences can refer to a tag field either using a relative path or an absolute path. The relative path is relative to the scope in which the variant or sequence performing the lookup is located. Relative paths are only allowed to lookup within the same static scope, which includes its nested static scopes. Lookups targeting parent static scopes need to be performed with an absolute path.Absolute path lookups use the full path including the dynamic scope followed by a "." and then the static scope. Therefore, variants (or sequences) in lower levels in the dynamic scope (e.g. event context) can refer to a tag (or length) field located in upper levels (e.g. in the event header) by specifying, in this case, the associated tag with <stream.event.header.field_name>. This allows, for instance, the event context to define a variant referring to the "id" field of the event header as selector.The dynamic scope prefixes are thus:- Trace Environment: <env. >,- Trace Packet Header: <trace.packet.header. >,- Stream Packet Context: <stream.packet.context. >,- Event Header: <stream.event.header. >,- Stream Event Context: <stream.event.context. >,- Event Context: <event.context. >,- Event Payload: <event.fields. >.The target dynamic scope must be specified explicitly when referring to a field outside of the static scope (absolute scope reference). No conflict can occur between relative and dynamic paths, because the keywords "trace", "stream", and "event" are reserved, and thus not permitted as field names. It is recommended that field names clashing with CTF and C99 reserved keywords use an underscore prefix to eliminate the risk of generating a description containing an invalid field name. Consequently, fields starting with an underscore should have their leading underscore removed by the CTF trace readers.The information available in the dynamic scopes can be thought of as the current tracing context. At trace production, information about the current context is saved into the specified scope field levels. At trace consumption, for each event, the current trace context is therefore readable by accessing the upper dynamic scopes.7.4 TSDL ExamplesThe grammar representing the TSDL meta-data is presented in Appendix C. TSDL Grammar. This section presents a rather lighter reading that consists in examples of TSDL meta-data, with template values.The stream "id" can be left out if there is only one stream in the trace. The event "id" field can be left out if there is only one event in a stream.trace {major = value; /* CTF spec version major number */minor = value; /* CTF spec version minor number */uuid = "aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaaa"; /* Trace UUID */byte_order = be OR le; /* Endianness (required) */packet.header := struct {uint32_t magic;uint8_t uuid[16];uint32_t stream_id;}; };/** The "env" (environment) scope contains assignment expressions. The* field names and content are implementation-defined.*/ env {pid = value; /* example */proc_name = "name"; /* example */... };stream {id = stream_id;/* Type 1 - Few event IDs; Type 2 - Many event IDs. See section 6.1. */event.header := event_header_1 OR event_header_2;event.context := struct {...};packet.context := struct {...}; };event {name = "event_name";id = value; /* Numeric identifier within the stream */stream_id = stream_id;loglevel = value;context := struct {...};fields := struct {...}; };/* More detail on types in section 4. Types *//** Named types:** Type declarations behave similarly to the C standard.*/typedef aliased_type_specifiers new_type_declarators;/* e.g.: typedef struct example new_type_name[10]; *//** typealias** The "typealias" declaration can be used to give a name (including* pointer declarator specifier) to a type. It should also be used to* map basic C types (float, int, unsigned long, ...) to a CTF type.* Typealias is a superset of "typedef": it also allows assignment of a* simple variable identifier to a type.*/typealias type_class {... } := type_specifiers type_declarator;/** e.g.: * typealias integer {* size = 32;* align = 32;* signed = false;* } := struct page *;** typealias integer {* size = 32;* align = 32;* signed = true;* } := int;*/struct name {... };variant name {... };enum name : integer_type {... };/** Unnamed types, contained within compound type fields, typedef or typealias.*/struct {... }struct {... } align(value)variant {... }enum : integer_type {... }typedef type new_type[length];struct {type field_name[length]; }typedef type new_type[length_type];struct {type field_name[length_type]; }integer {... }floating_point {... }struct {integer_type field_name:size; /* GNU/C bitfield */ }struct {string field_name; }8. ClocksClock metadata allows to describe the clock topology of the system, as well as to detail each clock parameter. In absence of clock description, it is assumed that all fields named "timestamp" use the same clock source, which increments once per nanosecond.Describing a clock and how it is used by streams is threefold: first, the clock and clock topology should be described in a "clock" description block, e.g.:clock {name = cycle_counter_sync;uuid = "62189bee-96dc-11e0-91a8-cfa3d89f3923";description = "Cycle counter synchronized across CPUs";freq = 1000000000; /* frequency, in Hz *//* precision in seconds is: 1000 * (1/freq) */precision = 1000;/** clock value offset from Epoch is:* offset_s + (offset * (1/freq))*/offset_s = 1326476837;offset = 897235420;absolute = FALSE; };The mandatory "name" field specifies the name of the clock identifier, which can later be used as a reference. The optional field "uuid" is the unique identifier of the clock. It can be used to correlate different traces that use the same clock. An optional textual description string can be added with the "description" field. The "freq" field is the initial frequency of the clock, in Hz. If the "freq" field is not present, the frequency is assumed to be 1000000000 (providing clock increment of 1 ns). The optional "precision" field details the uncertainty on the clock measurements, in (1/freq) units. The "offset_s" and "offset" fields indicate the offset from POSIX.1 Epoch, 1970-01-01 00:00:00 +0000 (UTC), to the zero of value of the clock. The "offset_s" field is in seconds. The "offset" field is in (1/freq) units. If any of the "offset_s" or "offset" field is not present, it is assigned the 0 value. The field "absolute" is TRUE if the clock is a global reference across different clock uuid (e.g. NTP time). Otherwise, "absolute" is FALSE, and the clock can be considered as synchronized only with other clocks that have the same uuid.Secondly, a reference to this clock should be added within an integer type:typealias integer {size = 64; align = 1; signed = false;map = clock.cycle_counter_sync.value; } := uint64_ccnt_t;Thirdly, stream declarations can reference the clock they use as a time-stamp source:struct packet_context {uint64_ccnt_t ccnt_begin;uint64_ccnt_t ccnt_end;/* ... */ };stream {/* ... */event.header := struct {uint64_ccnt_t timestamp;/* ... */}packet.context := struct packet_context; };For a N-bit integer type referring to a clock, if the integer overflows compared to the N low order bits of the clock prior value, then it is assumed that one, and only one, overflow occurred. It is therefore important that events encoding time on a small number of bits happen frequently enough to detect when more than one N-bit overflow occurs.In a packet context, clock field names ending with "_begin" and "_end" have a special meaning: this refers to the time-stamps at, respectively, the beginning and the end of each packet.A. Helper macrosThe two following macros keep track of the size of a GNU/C structure without padding at the end by placing HEADER_END as the last field. A one byte end field is used for C90 compatibility (C99 flexible arrays could be used here). Note that this does not affect the effective structure size, which should always be calculated with the header_sizeof() helper.#define HEADER_END char end_field #define header_sizeof(type) offsetof(typeof(type), end_field)B. Stream Header RationaleAn event stream is divided in contiguous event packets of variable size. These subdivisions allow the trace analyzer to perform a fast binary search by time within the stream (typically requiring to index only the event packet headers) without reading the whole stream. These subdivisions have a variable size to eliminate the need to transfer the event packet padding when partially filled event packets must be sent when streaming a trace for live viewing/analysis. An event packet can contain a certain amount of padding at the end. Dividing streams into event packets is also useful for network streaming over UDP and flight recorder mode tracing (a whole event packet can be swapped out of the buffer atomically for reading).The stream header is repeated at the beginning of each event packet to allow flexibility in terms of:- streaming support,- allowing arbitrary buffers to be discarded without making the traceunreadable,- allow UDP packet loss handling by either dealing with missing event packetor asking for re-transmission.- transparently support flight recorder mode,- transparently support crash dump.C. TSDL Grammar/** Common Trace Format (CTF) Trace Stream Description Language (TSDL) Grammar.** Inspired from the C99 grammar:* http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1124.pdf (Annex A)* and c++1x grammar (draft)* http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2011/n3291.pdf (Annex A)** Specialized for CTF needs by including only constant and declarations from* C99 (excluding function declarations), and by adding support for variants,* sequences and CTF-specific specifiers. Enumeration container types* semantic is inspired from c++1x enum-base.*/1) Lexical grammar1.1) Lexical elementstoken:keywordidentifierconstantstring-literalpunctuator1.2) Keywordskeyword: is one ofalign const char clock double enum env event floating_point float integer int long short signed stream string struct trace typealias typedef unsigned variant void _Bool _Complex _Imaginary1.3) Identifiersidentifier:identifier-nondigitidentifier identifier-nondigitidentifier digitidentifier-nondigit:nondigituniversal-character-nameany other implementation-defined charactersnondigit:_[a-zA-Z] /* regular expression */digit:[0-9] /* regular expression */1.4) Universal character namesuniversal-character-name:\u hex-quad\U hex-quad hex-quadhex-quad:hexadecimal-digit hexadecimal-digit hexadecimal-digit hexadecimal-digit1.5) Constantsconstant:integer-constantenumeration-constantcharacter-constantinteger-constant:decimal-constant integer-suffix-optoctal-constant integer-suffix-opthexadecimal-constant integer-suffix-optdecimal-constant:nonzero-digitdecimal-constant digitoctal-constant:0octal-constant octal-digithexadecimal-constant:hexadecimal-prefix hexadecimal-digithexadecimal-constant hexadecimal-digithexadecimal-prefix:0x0Xnonzero-digit:[1-9]integer-suffix:unsigned-suffix long-suffix-optunsigned-suffix long-long-suffixlong-suffix unsigned-suffix-optlong-long-suffix unsigned-suffix-optunsigned-suffix:uUlong-suffix:lLlong-long-suffix:llLLenumeration-constant:identifierstring-literalcharacter-constant:' c-char-sequence 'L' c-char-sequence 'c-char-sequence:c-charc-char-sequence c-charc-char:any member of source charset except single-quote ('), backslash(\), or new-line character.escape-sequenceescape-sequence:simple-escape-sequenceoctal-escape-sequencehexadecimal-escape-sequenceuniversal-character-namesimple-escape-sequence: one of\' \" \? \\ \a \b \f \n \r \t \voctal-escape-sequence:\ octal-digit\ octal-digit octal-digit\ octal-digit octal-digit octal-digithexadecimal-escape-sequence:\x hexadecimal-digithexadecimal-escape-sequence hexadecimal-digit1.6) String literalsstring-literal:" s-char-sequence-opt "L" s-char-sequence-opt "s-char-sequence:s-chars-char-sequence s-chars-char:any member of source charset except double-quote ("), backslash(\), or new-line character.escape-sequence1.7) Punctuatorspunctuator: one of[ ] ( ) { } . -> * + - < > : ; ... = ,2) Phrase structure grammarprimary-expression:identifierconstantstring-literal( unary-expression )postfix-expression:primary-expressionpostfix-expression [ unary-expression ]postfix-expression . identifierpostfix-expressoin -> identifierunary-expression:postfix-expressionunary-operator postfix-expressionunary-operator: one of+ -assignment-operator:=type-assignment-operator::=constant-expression-range:unary-expression ... unary-expression2.2) Declarations:declaration:declaration-specifiers declarator-list-opt ;ctf-specifier ;declaration-specifiers:storage-class-specifier declaration-specifiers-opttype-specifier declaration-specifiers-opttype-qualifier declaration-specifiers-optdeclarator-list:declaratordeclarator-list , declaratorabstract-declarator-list:abstract-declaratorabstract-declarator-list , abstract-declaratorstorage-class-specifier:typedeftype-specifier:voidcharshortintlongfloatdoublesignedunsigned_Bool_Complex_Imaginarystruct-specifiervariant-specifierenum-specifiertypedef-namectf-type-specifieralign-attribute:align ( unary-expression )struct-specifier:struct identifier-opt { struct-or-variant-declaration-list-opt } align-attribute-optstruct identifier align-attribute-optstruct-or-variant-declaration-list:struct-or-variant-declarationstruct-or-variant-declaration-list struct-or-variant-declarationstruct-or-variant-declaration:specifier-qualifier-list struct-or-variant-declarator-list ;declaration-specifiers-opt storage-class-specifier declaration-specifiers-opt declarator-list ;typealias declaration-specifiers abstract-declarator-list type-assignment-operator declaration-specifiers abstract-declarator-list ;typealias declaration-specifiers abstract-declarator-list type-assignment-operator declarator-list ;specifier-qualifier-list:type-specifier specifier-qualifier-list-opttype-qualifier specifier-qualifier-list-optstruct-or-variant-declarator-list:struct-or-variant-declaratorstruct-or-variant-declarator-list , struct-or-variant-declaratorstruct-or-variant-declarator:declaratordeclarator-opt : unary-expressionvariant-specifier:variant identifier-opt variant-tag-opt { struct-or-variant-declaration-list }variant identifier variant-tagvariant-tag:< unary-expression >enum-specifier:enum identifier-opt { enumerator-list }enum identifier-opt { enumerator-list , }enum identifierenum identifier-opt : declaration-specifiers { enumerator-list }enum identifier-opt : declaration-specifiers { enumerator-list , }enumerator-list:enumeratorenumerator-list , enumeratorenumerator:enumeration-constantenumeration-constant assignment-operator unary-expressionenumeration-constant assignment-operator constant-expression-rangetype-qualifier:constdeclarator:pointer-opt direct-declaratordirect-declarator:identifier( declarator )direct-declarator [ unary-expression ]abstract-declarator:pointer-opt direct-abstract-declaratordirect-abstract-declarator:identifier-opt( abstract-declarator )direct-abstract-declarator [ unary-expression ]direct-abstract-declarator [ ]pointer:* type-qualifier-list-opt* type-qualifier-list-opt pointertype-qualifier-list:type-qualifiertype-qualifier-list type-qualifiertypedef-name:identifier2.3) CTF-specific declarationsctf-specifier:clock { ctf-assignment-expression-list-opt }event { ctf-assignment-expression-list-opt }stream { ctf-assignment-expression-list-opt }env { ctf-assignment-expression-list-opt }trace { ctf-assignment-expression-list-opt }typealias declaration-specifiers abstract-declarator-list type-assignment-operator declaration-specifiers abstract-declarator-listtypealias declaration-specifiers abstract-declarator-list type-assignment-operator declarator-listctf-type-specifier:floating_point { ctf-assignment-expression-list-opt }integer { ctf-assignment-expression-list-opt }string { ctf-assignment-expression-list-opt }stringctf-assignment-expression-list:ctf-assignment-expression ;ctf-assignment-expression-list ctf-assignment-expression ;ctf-assignment-expression:unary-expression assignment-operator unary-expressionunary-expression type-assignment-operator type-specifierdeclaration-specifiers-opt storage-class-specifier declaration-specifiers-opt declarator-listtypealias declaration-specifiers abstract-declarator-list type-assignment-operator declaration-specifiers abstract-declarator-listtypealias declaration-specifiers abstract-declarator-list type-assignment-operator declarator-list

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